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Tipping Point for the Friesian Horse?

Friesian Mare and Foal. Photo: Katya Druz /

The Friesian horse is beautiful. The shiny black coat, proud neck, flowing mane and impressive movements delight enthusiasts worldwide. An icon for Friesland and for the rest of the Netherlands. The Friesian horse is also an important export product, with enthusiastic buyers in the United States, Mexico, South Africa and China, among others. Still, many breeders and owners of Friesian horses are concerned about the future of the breed. This is mainly due to health problems resulting from inbreeding. In this long-read an investigation into those concerns, the backgrounds and possible solutions.

Supported by The Netherlands Support Fund for Freelance Journalists Original article in Dutch:

This English translation was largely carried out by translation software and checked for errors by Angie DePuydt and the author.

The Friesian horse has been on the verge of extinction a number of times in the course of history. The breed survived only thanks to a number of persistent breeders and studbook administrators. At the lowest point, there were about 500 broodmares and only three studbook stallions. These animals form the basis of the current Frisian population, which is estimated at about 75,000 horses, 50,000 of which are in the Netherlands. Because all these horses descend from a narrow base and because the population has not received any blood from outside for 44 years, the mutual kinship is high. This poses a risk of hereditary disorders and of a so-called ‘inbreeding depression’, in which the horses are less healthy, fertile and sustainable.


There have long been concerns about the genetic health of the Friesian horse. At the end of the twentieth century, those concerns became increasingly acute. Two highly visible hereditary conditions plagued breeding: dwarfism and hydrocephalus. Dwarf foals are born with too short limbs. Often these animals survive, but their lives are usually not long and healthy. A foal with hydrocephalus is not viable and also poses a serious threat to the mare.


When the science was ready, genetic testing of the DNA of dwarf and hydrocephalus foals pinpointed the genetic markers for these conditions within a few years. In both cases it turned out to be simple recessive abnormalities. That is to say: only if a foal receives the defective gene from both parents will it be sick.

The Inheritance of Dwarfism & Hydrocephalus. Source: KFPS

Tests have been available since 2014 to check hydrocephalus and dwarfism carriers so that breeders can avoid mating two carriers. This way, the risk of a hydrocephalus or dwarf foal can be excluded. All young star mares and studbook stallions are now tested and for other breeding animals the owner can easily arrange this through the studbook. The studbook explicitly chooses not to exclude carriers from breeding, because you also lose other favorable characteristics. The fewer breeding stock you use, the smaller the genetic diversity becomes. You don’t want to make that genetic diversity narrower than necessary. All breeders are asked to test their mares and to avoid ‘risky’ pairings. The responsibility is thus placed with the mare owner. Several breeders suspect that the genetic information for hydrocephalus lies in a gene that also brings a number of positive properties for the sport. Remarkably often, animals that carry the hydrocephalus gene carry favorable characteristics that are rewarded in sports and inspections. For that reason, they are often used as breeding animals. Some breeders even feel that for this reason there are more and more carriers of the hydrocephalus gene in the population. However, figures on the numbers of carriers are not public.

ARE DWARFS AND HYDROCEPHALUS FOALS STILL BEING BORN? Several foal buyers I spoke to over the past few months said they still occasionally encounter dwarf foals. The vets who contributed to this article say they see little or no abnormal foals. Marco de Bruijn, internist at the Wolvega veterinary clinic: “I have practically not seen dwarfs and hydrocephalus foals for a long time, since the genetic tests came into being, but actually before that.” Former veterinarian Siebren Boerma was very concerned in the past about the genetic abnormalities in Frisians: “Together with Professor Bak from Utrecht, I was first to collect genetic material from foals that were born with hydrocephalus or dwarfism. That was in the late 90s. The aim was to develop a reliable gene test so that these two disorders could be bred out of the population. The studbook and many keepers of Friesian horses wanted to know absolutely nothing about the large amount of likely hereditary defects within the Friesian breed. The problem did not exist, they thought. Or at least I was exaggerating. But it was at that time abundantly clear that hydrocephalus and dwarfism were much more common in Friesians than in other breeds and that this indicated a hereditary problem. Vets who were paying attention also knew, that there was much more going on. In 2007 a bill was passed to ban breeding with animals that have a genetic defect. After a lecture by me about the various genetic problems in the Friesian horse, the press translated this to me saying ‘we should stop breeding Friesian horses’. That’s not what I said, but it caused a lot of fuss and negativity at the time.” Boerma retired from his veterinary practice in April 2021. Lately he has observed a turnaround: “I think the number of deviations has fallen sharply in the last five or six years. The number of foals born with dwarfism and hydrocephalus has become very low since the tests started. If I may be optimistic, I think things are going in the right direction. But to be sure you would like to have numbers about how often something occurs. Dwarfs and hydrocephalus were covered up in the past, so we didn’t have good numbers on that.” Stories from the Friesian community on the internet seem to indicate that sufferers from one of these conditions still occasionally occur, but that this is in fact always the result of not testing the mare or of a ‘calculated risk’. The latter sometimes occurs when a mare does not become pregnant with the chosen stallion. Before the end of the breeding season another stallion from the same stud is then used. A gamble on things not getting out of hand too quickly, but with negative consequences in some cases.

THE RISKS OF INBREEDING The two best-known hereditary disorders in the Friesian horse, dwarfism and hydrocephalus, now appear to be reasonably under control. Unfortunately, that does not mean that all problems for the breed are over. The narrow genetic basis of the Friesian breed continues to have an impact. There is therefore a lot of scientific research into genetic disorders, with the complex of connective tissue disorders currently appearing to be the most urgent. Before we talk further about the risk of inbreeding in a breed, let’s talk a little more about the basic principles of inbreeding and how inbreeding and kinship are registered in the Friesian studbook.

MAKING INBREEDING AND KINSHIP VISIBLE Inbreeding is the result of mating between animals that are related to each other. Animals share genetic information when they have a common ancestor. How strong the inbreeding is, depends on the degree of kinship between the parents. This relationship is relatively high in the Friesian horse, because the breed has been on the verge of extinction a few times. Inbreeding and kinship are confusing terms that are not always used in the same way. This creates uncertainty, even among breeders. When KFPS members log in to the studbook website, they can see for their own horses what the inbreeding percentage of the animal itself is over five generations, the relatedness percentage compared to the entire population and they can calculate what those numbers will look like for their foals, when they breed their mares to specific studbook stallions. I asked Bart Ducro, university lecturer and geneticist at WUR, to provide interested readers with some more information about how these key figures are generated. If you find this information a bit ‘too much’, the main text continues below.

WHAT DOES THE INBREEDING PERCENTAGE SAY? Bart Ducro: “Whether an animal is inbred or not, has to do with the relationship between the parents. The inbreeding percentage indicates the chance that an offspring will receive the same information for a certain gene from the father as from the mother (is homozygous). For the Friesians, we actually use the level of inbreeding over all known generations as the kinship percentage. That number says something about what you can expect from inbreeding in the next generation. The Friesians are around 18.0% in the youngest generation of stallions. There is often confusion about these numbers because there are different definitions for the relationships between animals and how they are measured. Internationally, another measure is often used, the ‘average relatedness’. It is defined in a different way and that is why confusion sometimes arises. This international definition resembles a doubling, but should not be used to make a prediction for the next generation. For the Friesians, we opted for a practical explanation of the kinship percentage. You can use that number to make a statement about inbreeding in the next generations. It is your steering mechanism.”

HOW IS THE KINSHIP PERCENTAGE AMONG THE FRISIANS CALCULATED? Bart Ducro: “The relatedness percentage says to what extent there is overlap in the DNA of the horse in question with the future breeding population. We always calculate that number against the breeding population for the future. You can also choose to compare the relationship with the mares that are currently being used, for example the list of mares that are now producing foals. You then look at how much DNA they share. A common percentage is then derived from that analysis; the relatedness percentage. But not all mares in the population are used for breeding. Star and crown mares often produce more foals. You want to take that into account. That is why we have chosen a figure that points to the future to calculate the kinship percentage. We therefore use the last three years of foals as the reference population. This is because the next population of mares comes from those horses and we want to know what the relationship of that population is. By using the foals for the calculation, you also take into account popular mares more. It’s about that overlap in the DNA and it’s an estimate based on the family tree. When calculating the kinship percentage, we look at the last eight generations, as far as we know. In horses, a generation is about 10 years. If you were to read the DNA, you would get a more accurate picture, but the use of the family tree in itself is a suitable method. The registration is also quite good for the Friesian population. And if we notice that information is missing or incomplete, then the horse in question gets a little penalty, so that he doesn’t get a lower kinship based on incomplete information. Over time, you see that families that have more offspring become more and more closely related.”

WHAT DOES THE NUMBER FOR INBREEDING RATE SAY? Bart Ducro: “The inbreeding rate indicates the increase in the average level of inbreeding in a population, from one generation to the next. The increase in inbreeding level is not linear and is expressed relatively, how much is left to complete inbreeding. Complete inbreeding means a percentage of 100%. That is a fictitious ceiling, in practice you will never achieve that. The figure we calculate for the inbreeding increase is the difference in increase for this generation and for the next generation, compared to the inbreeding level at that moment. So it is a relative number, a quotient.” Because the inbreeding rate is a relative number, this number also sometimes leads to some confusion. In the Genetics manual for BSc level it is summarized as follows: “The magnitude of the increase in inbreeding gives an indication of the risk of inbreeding depression and the decrease in genetic diversity. The more the animal is inbred, the more characteristics of the father and the mother will be equal. The two alleles in the DNA will then be the same, the animal is homozygous for that trait. The rate at which the remaining genes also become homozygous in the following generations decreases because there are fewer and fewer places where the animal is not yet homozygous. This means that the higher the inbreeding, the more the inbreeding increase will level off.” Bart Ducro: “That is why the increase in inbreeding is related to the remaining part of the population that has not yet been inbred. In the formula you divide by 1-F, where the F is the coefficient of inbreeding and indicates which part of the genome is homozygous if derived from descent. For example: Suppose the inbreeding in the parents is 0 and in the next generation is 0.008 (so in percentage is 0.8% inbreeding) then the inbreeding increase is equal to 0.008. That is below the limit of 1% inbreeding increase and therefore more or less safe. In another population in which the parents are 20% inbred (ie F=0.2) and the offspring 20.8% (=0.208), the difference is also 0.008. But since the parents are already inbred you have to divide this difference by 1-0.20 to calculate the inbreeding increase and then it is 1% and that is, the risk of inbreeding problems is equal to a population increasing from 0% to 1% inbreeding.”

STATE OF AFFAIRS: INCREASE IN INBREEDING A commonly used number to weigh whether the inbreeding of a population is getting worse, is the increase in inbreeding per generation. The United Nations Food & Agriculture Organization (FAO) uses this number to determine whether a variety is in danger of extinction. The FAO urges studbooks to keep the inbreeding rate well below 1% per generation and asks to aim for a growth rate of less than 0.25%. The organization finds a temporary increase to 0.5% acceptable. The textbooks state that an increase in inbreeding of more than 0.5% per generation poses a lot of risk: hereditary disorders manifest themselves and an accumulation of adverse effects on fertility, health and longevity can be expected. An inbreeding increase above 1% increases the chance that the population will not survive in the long term. Around the year 2000, the increase in inbreeding among Friesian horses was around 2% per generation, in 2012 that number fell below the critical 1% increase. At the moment, the increase in inbreeding within the Frisian studbook has been around 0.5% for several years and therefore within the FAO standards.

WHAT THE NUMBERS SAY Figures on inbreeding and kinship are one thing, but even if they were completely undisputed and crystal clear to everyone, the question remains: what do those numbers mean? The kinship percentage will probably soon rise above 20% among Friesian horses, but is that really bad? Hydrocephalus and dwarfism appear to have become a fringe problem within the breed, thanks to the testing. But what are the other risks of a related, closed population where only a limited part of the animals are used for breeding? Genetic diversity allows for flexibility in a population. If a bottleneck occurs, it results in a drastic decrease in population size, followed by a recovery. A bottleneck often has an enormous negative influence on genetic diversity and that effect is irreversible. Such bottlenecks have happened several times in the Friesian breed. Steven Janssens, geneticist at KU Leuven: “At one point there were very few approved stallions. Then you have a greater chance of certain health effects and hereditary diseases.” However, genes are not static, although change is slow. Bart Ducro: “Because the Friesians form a closed population, there will always be an increase in inbreeding. That’s not a problem, as long as it doesn’t go too fast. If the increase in inbreeding is not too great, the loss of genetic diversity through inbreeding is compensated by all kinds of other genetic processes, of which mutations are the most important. Those mutations bring new information to the population and therefore more diversity.”

GENES OPERATE IN A COMPLEX WAY Fighting genetic disorders and undesirable hereditary characteristics is difficult. Most hereditary diseases do not work as ‘simple’ as dwarfism and hydrocephalus. In fact, it is almost never a matter of one gene that only produces a sick animal if it is passed on to the offspring by both parents. Often several genes are involved and they also influence each other.

“Genes can be on or off, or a little on or off, or only on or off if another gene is at least a little off or a lot on… A handful of genes make an entire organism, just like eight notes are enough for all the symphonies of the world.” ~ Midas Dekkers

INBREEDING DEPRESSION OR NOT? In genetics, one speaks of the risk of an ‘inbreeding depression’ if animals are too closely related. With inbreeding depression, genetic abnormalities have arisen and the animals have become less durable and less fertile. A decreasing height can also be a signal. The problem with this is that you only really notice when it’s actually too late. Inbreeding depression is also described by geneticists as a kind of snowball effect, you do not know at the beginning that you are already in it. It is therefore very difficult to know whether there is currently an inbreeding depression in the Friesian horse. It is even very difficult to research that. Because the Frisian population has been very small on a number of occasions, the kinship among all Frisians is quite high. This limits the research possibilities, because truly unrelated animals simply do not exist. You cannot therefore make a scientific comparison between animals with very little and a lot of inbreeding. That makes it difficult to draw conclusions. The answer to the question of the real status of the Friesian breed can therefore only come from practice. Are the horses healthy, fertile and fit for the purpose people keep them for? However, there is no central registry of conditions and opinions about the general health of the breed are varied. This makes the evidence anecdotal and the impression you get about the status of the Friesian breed varies enormously with each person you ask. Known current problems in Friesian horses are: connective tissue disorders such as aortic rupture, dilatation of the esophagus and esophagus blockage (food plugs get stuck), gastric impaction (the stomach is not emptied into the intestines), fertility problems and retained placenta (the placenta does not detach on its own after birth).

CONNECTIVE TISSUE AND COLLAGEN: HOLDS EVERYTHING TOGETHER Connective tissue (fascia) has a supporting and caring function. It protects the organs and determines their shape and mobility. Connective tissue also leads the blood vessels and nerves to the organs. Connective tissue disorders are still under investigation, both in humans and in animals such as horses and dogs. Aortic rupture, esophageal dilatation (megaoesaphagus) and gastric impaction are examples of connective tissue problems in Friesian horses. Hypermobility is also related to the connective tissue. At the moment it seems that the connective tissue problems in Friesians are related to the incorrect production and breakdown of collagen. Collagen is a glue-forming protein and is a very important part of connective tissue. It seems that collagen formation in Friesian horses is often chaotic, which results in the connective tissue not obtaining the right structure. The Fenway Foundation reported in early February that there may be a common collagen problem in many of the genetic disorders that affect Friesian horses. These include aortic rupture, esophageal dilatation or paralysis, and gastric impaction and gastric rupture. Also with hydrocephalus and dwarfism there seems to be an error in the production of the collagen fibers. In addition, (often at a later age) the ‘bear-footedness’ of Friesian horses has a link with weak collagen production in both the superficial and the deep flexor tendon. The structure of the tendon tissue is different in these horses. A previous scientific study found that Frisians in general have more elastic tendons than English Thoroughbreds and ponies. Friezes with dwarfism were found to have extremely elastic tendons.

‘CONNECTIVE TISSUE PROBLEM IS UNDERESTIMATED’ Marco de Bruijn sees about 30% Friesian horses in his clinic. He is most concerned with the connective tissue problem in the Friesian horse. De Bruijn: “I have been collecting the cases of aortic rupture that I come across for years. I send blood samples from these horses to Ghent. Initially, the horses also went there for section. Cases of aortic rupture are also sent in from Utrecht. The same goes for esophageal dilatation. We work together with Ghent University, Utrecht University, WUR and the University of Kentucky on genetic research into Friesian horses. Since a few years I regularly see gastric emptying problems. The stomach stretches to the point where it can no longer empty itself. This leads to a blockage of the stomach, and sometimes even to a stomach rupture.” Breeder and former stallion selection jury member Bauke de Boer is also concerned about the disorders related to connective tissue and collagen. “The health problems are underestimated. I regularly meet people who have had to say goodbye to several young horses in quick succession. All with underlying conditions, which are mainly collagen-related. People are very sad about that, but there is also a lot of money involved. People often don’t choose a Friesian horse again, after such experiences.”

MEGAESOPHAGUS MOST URGENT Research into the connective tissue problem is currently taking place under the wings of the American Fenway Foundation. Former KFPS studbook director and geneticist Ids Hellinga is now scientific advisor there. Hellinga: “We are currently fully focusing on research into dilatation of the esophagus (megaoesophagus). We see that this is an increasing problem. It seems that aortic ruptures are somewhat less common. It is unclear why this is, but it could be because individual stallions have a lot of influence. The faculty in Utrecht has tried to find out the incidence, but in the Netherlands it has not been officially registered how many horses suffer from this. The Fenway Foundation has kept a reasonable record of that in the US. There you see that the esophagus problem happens more often than aortic rupture.”

FENWAY STUDY ON MEGAESOPHAGUS Ids Hellinga explains what the American research on esophageal dilatation entails: “In the US, they are very good at DNA technology and detecting the genetic mutations that cause conditions such as esophageal dilatation. We have already conducted research into this in the Netherlands and Belgium in the past, but it came to nothing. The phenotyping for this disease is more difficult, by which I mean that esophageal dilatation is much less recognizable than, for example, dwarfism or hydrocephalus. You do not always see that a horse suffers from this condition. Sometimes it only becomes apparent at a later age, for example we recently had an 18-year-old mare and she had already had twelve foals. That is also the dangerous thing about this condition: sufferers of megaesophagus could in an extreme case, be breeding stallions. Therefore, this problem may be even greater than previous genetic disorders in the Friesian horse.” This concerning suspicion of Hellinga seems to be confirmed by the many stories about esophageal dilation and paralysis that have appeared in recent years in, for example, Facebook groups of Friesian horse lovers. Many horses don’t show the first symptoms until later in life, although the problem certainly also affects foals and younger horses. Hellinga: “We now only have foals in the study and use the newer and more accurate technique of whole genome sequencing. Our starting point is that it comes down to one gene, but we are also expressly looking more broadly for more complex forms of inheritance. Fortunately, there is a good chance that it is a single recessive gene, which would make research easier. Thanks to the new techniques, we can limit the research to a smaller number of families. In America in particular, we have collected quite a few families, although we could add a few more. The research does not focus on individual horses, but on father, mother and some brothers and sisters, preferably young horses and foals.” Hellinga calls on owners of horses who have esophageal dilatation to participate: “If owners can provide us with data and hair samples from multiple family members, they are very much invited to come forward.” Hellinga continues: “I used to have the feeling that this was an unsolvable sudoku, but every time we add a family to the study, we observe that we are getting closer to a solution. When that will be, I can’t say. We will also have to validate the results and that takes time. But we’re doing everything we can, and the investigation is going well. I think we can develop a gene test for esophageal dilatation.”

“Megaesophagus may be an even bigger problem than previous genetic disorders in the Friesian horse.” ~ Ids Hellinga

TAIL AND MANE ECZEMA Bart Ducro: “Both aortic rupture and esophagus blockage are not pleasant at all for a horse owner, but we don’t really have an idea of what the biggest problems are with the breed. For example, tail and mane eczema will also not make an owner happy, but that disease is not life-threatening. It is an allergy and it is already clear that not one single gene plays a role, but several genes. This means that a gene test such as for dwarfism or hydrocephalus is simply not possible for tail and mane eczema. Research has contributed somewhat to the extent to which genetic predisposition plays a role, but without knowledge of the DNA behind it, breeding eczema-free is still very difficult.”

FERTILITY PROBLEMS AND SPERM QUALITY Fertility is an important characteristic by which you can tell if inbreeding is causing problems in a population. Steven Janssens of KU Leuven: “One way to investigate inbreeding depression is to plot a hereditary characteristic, such as height or fertility, against the degree to which the animals are inbred. The more inbred an animal is, the lower the height at the withers or fertility could be. This is quite difficult to do for fertility.” Bart Ducro of WUR: “Currently, about 75% of the matings with Friesian mares actually lead to a registered foal. That may not seem very good, but compared to other pedigree breeding farms it is not very bad. I don’t see a very big problem with mare fertility yet, the concerns are greater on the stallion side. A relatively large number of young Friesian stallions are removed from the stallion selection process, because their semen quality is insufficient in the tests. That percentage is much higher than in other breeds. That is a real shame and it diminishes the selection of stallions available. Years ago I myself investigated whether there is a relationship between sperm quality and inbreeding, but I could not prove any. Such research fails because all Friesian horses are inbred to some extent. For such a study you compare stallions with a higher and lower inbreeding, but that is not possible if there is not a big difference between much lower and much higher inbreeding percentages. You simply can’t see the difference. What struck me ten years ago in that study, is that the parameters of sperm quality, such as the number of cells and motility, were much worse in Frisians than in warmbloods and even Shetlanders. In my opinion, the fertility problem of the Frisians is more on the male side.”

IMMUNE SYSTEM AND DURABILITY In 2021, the breeding goal of the Friesian horse breed has been adjusted at the request of the KFPS Members’ Council. From now on, a healthy horse is the first goal, before racial type and sports aptitude. Health and sustainability go hand in hand. Obviously, many breeders and owners are concerned about the durability and longevity of their horses. Horses are sometimes unusable at a young age or have to be put down early. There is also no good overview of all this, because the registration of mortality is not (yet) in order. Many people do not hand in their horse passport after their horse has died and do not report the cause of death to the studbook. Other horses disappear abroad. This leads to a lack of really reliable figures about the average life expectancy of the Friesian horse. It means that we continue to rely on anecdotal ‘evidence’. Veterinarian Marco de Bruijn: “In our clinic I observe that the Friesian horse is less able to solve problems by itself these days, whether that is a respiratory infection, roundworm or a recovery after colic surgery; it is very difficult. To be honest, I am increasingly dreading operating on a Friesian with colic. Another breed often returns home within a week, but with Friesians you often first see diarrhea or an infection, if the intestines start up at all. The horse is just not that strong. I understand that people want a beautiful Friesian horse, but in my experience that comes at the expense of health and immunity. There are also problems that may be related to the immune system, such as poor uterine emptying and fluid in the uterus. I think it all comes down to immunity and little genetic diversity.” The afterbirth can also be related to inbreeding, explains De Bruijn. “A placenta is basically foreign tissue and is therefore rejected by the mare. But relatedness is high, the mare’s immune system may no longer recognize the placenta as foreign.” In 2004, M. Sevinga and colleagues from Utrecht University already investigated the influence of inbreeding on the mare’s retention on the afterbirth, after the number of cases increased spectacularly between 1980 and 2000. The researchers found a connection with the relatedness percentage of the foal. “A high incidence of afterbirth is at least partly due to inbreeding,” they concluded. Veterinarian Siebren Boerma says that the number of problems with retained placenta seems to be decreasing in recent years. “But that’s not necessarily because the hereditary factor has decreased,” says Boerma. “Today hygiene is better and people are also more aware of the problem than before, which means that interventions are carried out faster and fewer big problems arise.”

HOW DID WE GET HERE? If you want to come up with solutions and make the future Friesian horse healthier and more sustainable, it is wise to be aware of how the breed ended up in its current situation. The history of the Friesian studbook and the development of the association culture provide insight into this.

‘FRIESIAN TYPE’ HORSES Stallion owner Erwin Spliethof likes to delve into the studbook history: “In the early days, the horses were registered in two registers: register A for the ‘Native breed’, which was the Friesian breed, and register B for the ‘Foreign and crossed breed’. Those were more typical of the Groningen type of horse as it occurred at the time. In the period between 1907 and 1915, the Friesian breed seemed doomed, after the then board decided to include all horses in one register. Stallions were limited to Friesian and Oldenburger or East Friesian breed and all possible crossing products could be registered in case of mares, as long as they met the breeding goal. That was: ‘a harness and agricultural horse with smooth and powerful gaits.’ In 1915, after persistent scrambling by the followers of the Friesian breed, the books were again split into ‘Friesian breed’ on the one hand and ‘Bovenlands or crossed breed’ on the other. Moreover, from 1918 onwards, horses could only be entered in register A or B if the pedigree was known. That is why the Support Book was opened for mares that were ‘Friesian type’ and met the breeding goal, but whose pedigree was unknown. In the first decades after the studbook was established, the association repeatedly went through ups and downs. It was difficult for the studbook to protect the breed. You can only have respect and admiration for the people who at the time worked hard to keep things going. But if you understand what that initial period looked like, you also understand that the term ‘racial purity’ is quite relative. ‘Friesian typical’ is a much better term. I think it’s important to realize that, especially with a view to future measures to curb inbreeding in Friesians.”

FROM PEDDLING FOR MEMBERS TO A CLOSED STUDBOOK Because of this history, for a long time the studbook did mention thoroughbred Friesians, but used the description: a ‘Friesian-typical’ horse. In the 1960s, racial purity wasn’t much of a concern. When a board member of the studbook saw a Friesian-looking horse standing in a meadow, he walked into the yard to convince the farmer to register the horse in the studbook and use it as a breeding animal for the endangered Friesian breed. Slowly the numbers of horses grew and by 1978 the situation had completely changed. The association believed that there were now enough Friesian horses and the studbook was closed. This means that since then no more animals from outside can be registered in the Friesian Horse Studbook (KFPS). From 1978 it is therefore no longer allowed to breed with animals with ‘foreign blood’. Foals with a sire or dam that are not registered with the KFPS no longer have the opportunity to enter the studbook. Not even if these ‘half’ Friesians are continued to be bred using registered breeding animals, and not even if this takes place over several generations. There is no more room in the statutes of the studbook for this kind of ‘lateral entrants’. This means that the gene pool – the total of hereditary characteristics within the breed – has not been supplemented since 1978. New combinations are always made, but from a limited stock of genetic material. This makes the Friesian studbook different from, for example, the largest sport horse studbook in the Netherlands, the Royal Warmblood Horse Studbook of the Netherlands (KWPN), but also from a studbook such as the Groninger Paard, which is an example of a registered rare breed.

‘FULL PAPER’ AS THE HOLY GRAIL When you read the advertisements for Friesian horses on the Dutch online ‘Market Place’ or the KFPS website these days, you immediately notice that people often talk about ‘full paper’. This is an important recommendation for a Friesian horse. ‘Full paper’ means that the horse comes from a maternal line of at least three generations of mares with a star predicate or higher (crown or model). Mares receive a star predicate when they receive a minimum average of 7 for conformation, walk and trot from the jury on a studbook inspection or breeding day. Horses born from a studbook mare (less than a 7 on average at the inspection) or a foalbook mare (never attended the inspection as an adult or underperformed there) do not have a ‘full paper’. These are still full Friesians, who are in the closed studbook or in the foal book, but they are often worth a lot less than the ‘full paper’ animals. Even for horses that are only used for sport and not for breeding, such as geldings, a ‘full paper’ has become a distinguishing feature that often makes thousands of euros difference in the resale value. As a result of this common obsession with a full paper, breeding is mainly done with star mares. That limits the breeding population. In recent years, only about 3,200 foals were registered per year. The studbook aims for 4,500. It is expected that several hundred more foals will be born this year.

REGISTRATION AND OPENNESS REQUIRED Vets, owners and geneticists observe a number of problems with the Friesian horse breed, but how often these occur and where they come from, remains unclear. Bauke de Boer is a big proponent of registration and openness: “You have to map out which lines are sustainable and which ones tumble. Of course there is luck involved in breeding, but I hear too much doom and gloom. There are breeders and stallion owners who want to keep everything under wraps, but I think that’s stupid. It has to be open and exposed, in order to get out of the misery. Breeding is foresight. We must all work together to ensure that you breed a healthy horse, which does retain the breed characteristics, but which you can do something with. It is a duty to breed a healthy horse.”

‘TAKING STRIDES’ Until now, there has been no systematic registration of genetic problems, disorders and longevity of the Friesian horse. This despite previous recommendations from scientists. For example, in 2011, Siem Korver argued for a completely closed (and mandatory) registration of matings, pregnancy and birth defects. Bart Ducro: “At the moment we lack a good overview of what exactly is going on and what the priorities should be. If it had been properly registered, I could now tell you: ‘These are the big problems’. It would be preferable to have some sort of database of the identified problems, with added DNA samples from blood or hair. This would allow us to take strides and move forward, because the techniques are getting better, cheaper and more reliable. You could even make such a database anonymous. Once you have the DNA profile, it doesn’t matter which horse it is. As long as you know what condition was seen in that horse. The DNA pattern is a kind of barcode, which we can then use to investigate which gene is behind which condition. But now we have little material or only material that has been selected very strongly.”

COVER-UPS AND CONSPIRACY THEORIES The old culture in the Frisian studbook, which veterinarian Boerma also encountered in the 1990s, meant that there was no registration and that data on the occurrence of genetic abnormalities was not shared. It remains unclear how often deviant foals are born. Some breeders and stallion owners still choose to keep problems under wraps as much as possible, because they fear openness would be bad for reputation and trade. A hotline on the internet that claims to register defects in the Friesian horse remains completely unreachable for comment, despite repeated attempts, and does not even want to anonymously indicate how many deviations they have registered in recent years. Over the years, the supposed cover-ups of hydrocephalus or dwarfism foals has led to suspicion among members of the association and sometimes even the spread of conspiracy theories among some of the breeders. For example, the theory regularly crops up that there are several types of dwarfism and that the existing test only detects one of those types of dwarfism. Geneticist Bart Ducro of Wageningen University earlier commented on this in De Paardenkrant: “Disproportionate dwarfism (chondrodysplasia) occurs in Friesian horses, that is the form we have always seen. This shape is specific to the Friesian breed.” This form of dwarfism is therefore tested. However, the lack of transparency and (public) registration of problems gives critics room to argue that the test is unreliable.

DEVELOP KNOWLEDGE AND IMPROVE REGISTRATION Veterinarians such as Marco Bruijn have been keeping their own lists for years and sometimes data has been collected for specific investigations, but the studbook does not have a numerical and structural overview of what is going on in terms of hereditary disorders in the population. Even the death rates are largely incomplete. In 2021, the studbook therefore started a campaign to encourage people to deregister their horses from the studbook if they die. In such a report, the cause of death can also be entered. Studbook director Marijke Akkerman: “The deregistration of deceased horses is still not done enough by our members. We hope to gain more insight thanks to the European law on the Identification and Registration of Horses that was implemented in 2021. The studbook can link to that data and thus gain a better insight into the mortality rates.” The studbook also wants to link the data on the causes of death to other data registered about the horses. Akkerman: “A working group from the Breeding Council is working on this. We want to compare certain linear scores for, for example, leg position and height with lifespan. This research into sustainability is still in its early stages. But of course everyone wants to enjoy their horse for a long time. In addition to sustainability and longevity, there is also a study into fertility, together with Utrecht University. That study focuses specifically on sperm quality.” Akkerman indicates that the studbook now also wants to keep better track of which studies are being conducted in different places in the world and how far along these studies are. “We also want to be more on top of this ourselves and in 2022 we will communicate more about this,” the director promises.

“WE KNOW TOO LITTLE” A growing group of breeders and enthusiasts has lately been pressing for transparency. The current board and the breeding council also seem to want to move in that direction. Tjitze Bouma, the new chairman of the KFPS breeding council, said in the online ‘College Tour’ of March 31, 2022: “You will have to collect more data about health and sustainability in breeding. In fact, we still know far too little about our horses. Few horses are deregistered when they are deceased. And if they have died, you would also like to know the reason. Not to denounce people in public, but because you want to be able to discern from the data which bloodlines have greater longevity, for example.” Bouma also said that they are also considering measuring older horses. At the moment, the young horses are assessed mostly, but that does not provide any information about durability. “One possibility is to ride and test the horses again sometime between the ages of 12 and 15, to see how they are doing.”

‘TACKLE PROBLEMS HEAD-ON’ Systematic registration of deviations would also be an important step. Marco de Bruijn: “I don’t think we have made any progress with the Friesian race in the past 20 years. In the context of preventive medicine, you have to see if you can do something up front, because management alone will not save you. So you have to find the solution in breeding. The question then is whether there is still enough genetic diversity in the breed to solve the problems. In my opinion, to be able to answer that question, you must first map out the connective tissue problem, after which you can examine whether the current diversity is still sufficient to get to a solution. And if the answer is no, then you have to think outside the box. That’s not something everyone wants to hear, I know. And will hurt some people. But the problem is: Now that pain is also there, but it is distributed among the individuals, among my customers. I stand against that.”

Systematic registration of abnormalities is an important step towards understanding the inbreeding problem and the prevention of genetic disorders

TRACKING HEALTH CHARACTERISTICS Stallion owner Erwin Spliethof would also like to see more attention being given to the health of the existing population: “I think it would be good to formulate more health characteristics, in addition to X-rays, cornage examination and the tests for dwarfism and hydrocephalus. Just as we once came up with the characteristics for the linear score, you can now start with a list of health characteristics. There are two major advantages to doing it this way. In the first place, health is universal and equally important to every owner or user of the horse. Whether you want to go for a ride in the forest, harnass your horse, or ride dressage at Grand Prix level, everyone benefits from a vital horse that can age healthily with little veterinary costs. A second important consideration with health, is that it provides hard data. Unlike jury judgments, which always contain a certain amount of subjectivity. I would therefore argue in favor of placing much more emphasis on health, especially in the stallion selection, and less on sports aptitude and exercise. Because however capable the jury corps may be, no one, absolutely no one, can tell from a three- or four-year-old horse what he has to offer by the time his talents reach their full maturity. Let alone estimate at such an early stage what his qualities could be as a breeding stallion. So it is also quite pointless to judge and test to the max, and prematurely knock a large number of stallions overboard in the process. You will probably miss a number of good breeding stallions that way. My advice: raise the lower limit for health traits considerably, leave the rest of the selection largely to the market and rely on the knowledge and skills of your breeders. Over the years, they have shown that they are capable of building successful mare lines, each following their own insight.”

HOW TO CURB INBREEDING In addition to collecting more information about the current population of Friesians, there is a lot of thought and discussion within and outside of the studbook about possible solutions to limit inbreeding in the next generations of horses. Some breeders have dropped out of the KFPS and will now breed their mares to stallions from other studbooks, but many involved think it is still too early for that, or warn of unwanted side effects. Over the years, scientists have provided several reports about inbreeding in the Friesian breed and how to control it. Although a number of recommendations from their reports have since been adopted by the studbook, such as publishing the kinship figures and assigning a breeding value to kinship, a lot still remains to be done.

STALLION SELECTION PROCESS Breeding decisions revolve around a mother’s or father’s genetic predisposition, which is what is passed on to the offspring. Breeding values and total indexes are frequently used in Friesian breeding when choosing a stallion. A breeding value is a substantiated estimate of the genetic predisposition. The number indicates to what extent a parent animal will pass on a particular trait. Breeding values are always calculated relative to the population average and are reassessed every year. The average breeding value is always 100, in practice this is a variation between 96 and 104. The more offspring an animal has, the more reliable the breeding value. For the Friesian breed, breeding values are calculated for breed appearance (race), build, legs, walk, trot and canter. In addition, a breeding value is calculated for each characteristic in the horse’s linear score. The information that is used to calculate breeding values comes from studbook inspections and talent tests, of the animal itself and its offspring. Unique to the Friesians is that since 2020 breeding values for character have also been published for the studbook stallions. This arose from the desire to maintain the gentle nature of the breed. In addition, a breeding value for relatedness is included in the rankings of active studbook stallions and of the 1,500 best mares. The more closely related the horse is, the lower the breeding value for that trait. In the so-called ’total index’, all breeding values are taken together in order to make a ranking of the most interesting broodmares. Unfortunately, the mare list also includes several animals that are no longer alive or have disappeared abroad. A problem with these rankings is that you are comparing very reliable breeding values of older animals with the much less reliable breeding values of young horses. As a result, breeders may sometimes place too much value on this index.

USE OF EXPECTED BREEDING VALUES In a special module on the studbook website, mare owners can see which stallions are expected to improve their mares for certain characteristics. For example, a better walk or a lighter head and neck connection. Breeders can also calculate the expected numbers for any foals, in a web module that specifies the breeding values for breed, build, legs, walk and trot. The expected inbreeding percentage over five or six generations and the relatedness percentage is stated here. A warning will also appear on the screen if the proposed mating poses a risk of breeding a dwarf or hydrocephalus foal. The expected breeding value of a foal is the average of the two parent animals. This means that the potential offspring of the highest scoring young stallions at inspections and in the performance tests, will show very high expected breeding values for their foals. The fact that these young stallions often do not have such reliable breeding values, is slightly underreported in this module. Low-related stallions are often at a disadvantage in these calculations because they do not protrude far above the masses in terms of breeding values for, for example, appearance and movement. All this influences the choices that breeders make. Sometimes there is even a self-reinforcing effect: when a young stallion has lower expectations, he gets fewer opportunities. Such a stallion is used less on the better mares and as a result the offspring are less good, which means the stallion’s breeding values do not increase over time. In the top 20 of studbook stallions with the highest breeding values there is only one lower related stallion: Omer 493. Looking mainly at high expected breeding values, for example because you breed for commerce or sport, therefore easily leads to lower genetic diversity in the population. Ultimately, the rider or trader also falls victim to this trap, because less diversity causes problems for the horses in the long term.

LOW-RELATED BREEDING The use of relatively low-related breeding stock is one of the ways to curb the increase in inbreeding. The family of Roelof Tjeerdsma (stable name fan ‘e Boppelannen) bred for years with the (very) low related mares from the Onyx line. From the mare Onyx (born 1988 Naen x Ewoud x Nuttert and 15.5% relatedness), Tjeerdsma’s father-in-law Marten van der Meer bred some even lower related horses between 2007 and 2010 using embryo transfer. “We did embryo transfer seven times, we were a bit ahead of our time. We chose Gjalt 426 and Fabe 348 because of their low relatedness. At the time, we hoped that the colts could have a role in breeding. But these descendants from Onyx were not real eye-catchers, not the most modern horses, nor outstanding in movement. Of course they would have been very suitable to the studbook breeding program for relatedness, but that insight was not really common ten years ago. They didn’t get a star certificate. There were also mares born, but all but one of them were sold abroad or died. At the time, there was no interest from the studbook in using such mares as potential stallion mothers and no advice to keep this type of mares for breeding. Nowadays, we might act differently. But at the same time, these were not necessarily ideal Friesian horses.”

FEW LOWER RELATED STALLIONS Of the newest batch of studbook stallions, approved at the end of 2021, only the two older stallions have a relatedness that’s somewhat below average. The four other stallions are all relatively highly related. We have to go back to 2019 for the approval of two young stallions that are significantly lower related, namely Wibout 511 and Wolter 513. The latter is the least related stallion in the studbook at 15.8, but is used relatively little. Omer 493, who is from the same dam as Wolter, currently has a 16.3% relatedness and is more popular.

COLLECTING DATA IS KEY Stallion owner Erwin Spliethof believes that time is of the essence: “The idea behind reducing inbreeding and encouraging lower kinship is ultimately to improve the health and sustainability of the population. The hope is that will diminish the typical Frisian ailments in the future. That is why it is important to collect good data in the coming years to see whether this policy is having an effect. Will the offspring of low-related stallions suffer less from ossified hoof cartilage, aortic ruptures and megaoesophagus? Will low-kinship mares show lower incidence of retained placenta? Do low-related horses score better on heart rate and lactate measurements during exercise? If this turns out not to be the case, it could mean that we took the wrong turn. And that we should start thinking about other instruments, such as more DNA tests, for example. But it can also mean that we are on the right track, but that using low kinship as a marker within our closed population, is only a drop in the ocean. If we can no longer make a difference using low kinship, then we may have to go one step further. At a certain point, foreign blood seems inevitable.”

SUFFICIENT BREEDING AND MAINTAINING THE MARE POPULATION Geneticists recommend keeping genetic diversity as high as possible in a closed population like the Friesian studbook. Using lower-related breeding animals is not enough. You have to breed a lot and also use as many animals as possible. That’s not happening now. Every year about 1,800 Friesian mares are born and 400 mares receive the star certificate. The generation interval of horses is 10 years. With the current birth rates, 18,000 mares are added every ten years, of which approximately 4,000 mares receive the star predicate or higher. That’s without taking mortality into account. But even with such a simple calculation it is obvious that breeding almost exclusively with the star mares, crown mares and model mares will mean that the population will continue to decline. It is therefore essential for the preservation of the breed and the preservation of diversity that many more mares are used. The studbook can actively encourage this, for example by placing less emphasis on full paper and inspection results. Or even by actively approaching the owners of mares who can contribute to the breed. The studbook has already started to do this by publishing a list of low-related mares, which also includes mares without a star predicate.

BETTER USE OF THE STALLION STOCK The Friesian studbook currently has about 80 active studbook stallions worldwide. The influence these animals have on the entire population varies enormously per stallion. About half of the studbook stallions service more than 50 mares per year, while a quarter only breed with less than 10 mares per year. There are families of stallions with great influence and there are bloodlines that are hardly used. In 2007, the KFPS already received a report from Wageningen University, which recommended, among other things, to designate more sires and fewer sons per sire. Since then, between two and six stallions were approved per year. Every year there are also stallions who ultimately have few offspring or who disappear from the breeding service through the back door. The WUR report: “More important than the number of sires is the extent to which they are used. Approving more sires will not lead to a more balanced use without additional measures such as a breeding restriction per stallion. (…) The increase in inbreeding can be considerably limited by standardizing the number of matings per stallion. Limiting the increase in inbreeding within the Friesian studbook is not possible without some form of breeding regulation.” In addition to the contributions of individual stallions, stallion families are also important. There is no official limit within the Frisian studbook on the number of sons that may be approved, although, according to the inspectors, stallions are judged more strictly if their sire already has several approved sons.

BREEDING LIMITS AND LIFE TOTALS There were always breeding limits in the Friesian studbook. At first, these grew along with the population, from 50 to 75 matings per year for example. Sometimes the limit was lower, based on reservations about the stallion in question. Such a stallion was only allowed to breed more widely after he had been approved for offspring. At the beginning of this century, the studbook experienced rapid growth. Since 2003, a young Friesian stallion, who has not yet been approved on the basis of his descendants, may service a maximum of 180 mares per year. After the stallion has been definitively approved, the number of breedings is free. There is no mention of a life total in the studbook, which population geneticists often advocate. According to scientists, applying breeding limits can result in a more equal contribution of all available sires to the next generation. They would restrict individual sires from gaining too much influence. However, the figure of 180 matings for the young stallions is controversial and was challenged a number of times. For instance in a 2011 lawsuit between stallion station De Nieuwe Heuvel and the KFPS. An independent report – by Siem Korver – in response to that case states that the current standard is only a very rough approximation. A life total per stallion may be more effective, if this total is based on population size.

“DISCUSSION HAS NOT ENSUED” Andries Zandee was a member of the members’ council of the KFPS when the discussion about stud limits took place in 2011/2012. The Siem Korver report recommended that life totals might work better. Zandee: “Korver made recommendations that were felt to be inconsistent with the vision that the KFPS was already working on with Ids Hellinga and the researchers in Wageningen. At the time, the focus was on research into hydrocephalus and dwarfism. I thought that was a good argument, that the board wanted to continue to follow their own course. But the only discussion that remained was unlimited breeding after approval on offspring. At that time, there was a lot of breeding, about 8,000 matings per year. But even then 180 was more than enough for young stallions for the first five years. At the time, as chairman of the stallion owners’ association, I suggested doing it the other way around. Our idea was to allow maybe a maximum of 1,000 mares in the first five years and then set a breeding limit of say 180 after that. We already noticed then that if a stallion gets 100 to 125 matings per year, this would be sufficient for the stallion owner to earn a living. That discussion never continued. But you might want to have that conversation again. The next question is whether you should also enter a life total and how high such a life total could or should be. Because such a measure would decrease the value of older stallions. Now that there are much fewer breedings within the studbook, the proportions have changed again. In a small population where there were around 4,000 matings per year for years, last year 5,000, we still see some older stallions breeding more than 200 mares. That is actually a bit crazy when you have 80 to 100 stallions at your disposal,” says Zandee.

BREEDING LIMITS IN A DECLINING POPULATION? As we have seen, the current breeding limit for young stallions was established at a time when the breed was booming, at the beginning of this century. For years there has been less breeding than the studbook would like, but it is difficult to entice breeders to produce more foals. The total number of Friesian horses is expected to decrease in the coming years. In the online autumn meeting of 2020, a KFPS member therefore asked whether it would not be better for genetic diversity to reduce the breeding limit for young stallions from 180 matings per year to 120. Ids Hellinga, studbook director at the time, replied: “The rule of thumb is that the contribution of an individual stallion should not exceed 5%. Even at the current level of numbers of matings, we comply with this rule with the breeding limit of 180 coverings per year.” That was almost true, but not quite. At that time there was one stallion – Alwin 469 – who had surpassed that 5% in each of the three previous years. But, more important than the influence of one stallion, is the breeding effect of stallion families.

THE INFLUENCE OF STALLION FAMILIES If you look past the individual studbook stallions, and instead at the stallion families, the proportions turn out to be quite skewed. For example, Tsjalle 454 and his sons Jehannes 484, Yme 507 and Tymen 503 and grandson Auwert 514 were jointly responsible for 15.9% of all breedings within the studbook in 2020. In 2021, Jehannes’ son Foeke 520 was added, but the breeding numbers for that year have not yet been made public. Norbert 444 now has six approved sons and five approved grandsons, including the much used Hessel 480, Menne 496 and Matthys 504. In the 2020 breeding season there were only two active grandsons but the Norbert stallion family was already responsible for 13.8% of all matings. That same year, Pier 448 and his sons accounted for 7.6% of the matings, Alwin 469 and his son for 6.5%. A grandson has also been added to the latter family. A rough estimate shows that about 23 studbook stallions, from these four ‘stallion families’, currently produce half of all Friesian foals.

An estimated 23 studbook stallions from four ‘stallion families’ currently produce half of all Friesian foals.

BREEDING LIMITS IN PERCENTAGES? Bart Ducro: “The existing breeding limits are set at a population of 8,000 foals per year. Currently, only about 3,000 foals are born each year. It would therefore perhaps be better not to express the breeding limits in absolute numbers, but in percentages. That way, they could fluctuate with the number of foals per year. It is difficult to say exactly how this will work out in practice. But with the current 3,000 foals, a breeding limit of 180 is probably too relaxed. Although at the same time, we notice that the kinship level has not risen too much in recent years, so maybe it’s not that bad. There may however be an aftereffect, whereby the effect on the kinship percentage is still to come. It is therefore wiser to switch to percentage coverage limits for the long term.”

OPTIMAL CONTRIBUTION PER STALLION Another solution comes from Steven Janssens, geneticist in Leuven: “Theoretically, we need to determine a stallion’s contribution to the next generation. This contribution is not always proportional to the number of breedings. I would rather look at what a stallion could contribute to the population in his lifetime. For example, you can calculate what the contribution of each stallion should be, for each year. In Wageningen they have worked on the ‘optimum contribution theory’, which is the optimal contribution of each breeding animal. You calculate this on the basis of the average relationship to the population, possibly in combination with breeding value estimates for desired traits. This allows you to say: this stallion may contribute 10%, that one 7% and that one 5%. In practice, this is difficult, because the percentages need to be calculated yearly. That is not an easy message for stallion owners and breeders. This method could also run into logistical issues. But what you could do is look at the discrepancy between the ideal situation as calculated in a previous year and compare it with what has happened in practice. What foals were born and to what extent does the situation deviate from what the optimal distribution would have been?”

BREEDING WITH YOUNG STALLIONS The 80 studbook stallions are the only sires used in the Netherlands. Outside of the Netherlands, foal book stallions with a breeding license are used, but their descendants end up in the so-called ‘Support Book’. Many foreign horses even completely disappear from the radar of the KFPS: foreign owners find registration too complex or too expensive, or they start crossbreeding their Frisians. Bauke de Boer: “It is a shame that the route of the support book is closed. The current system with Additions I and II to the studbook, is not working. Between 1980 and 1985 young stallions were allowed to breed before the Central Examination. They were provisionally approved in February, after the third viewing and then they were allowed to service a maximum of 50 mares. Only then did they enter the CO, where stallions also dropped out. When certain stallions are low-related, but not approved after CO, it can still help a little if they have a few offspring. This can help genetic diversity by way of the damlines.”

“WE’RE RUNNING AGROUND” De Boer continues: “On the lists of the first viewing of 2021, I noticed that 70% of the registered young stallions descend from Beart, Norbert, Tsjalle, Alwin, Maurits and their sons. If that is a harbinger of those that will be approved, then the population will only become more narrow. The kinship of those young stallions is now usually over 18% and it won’t be long before that number rises to more than 20%. If we’re not careful, these stallions will only gain more influence. Actually, it should have been done sooner, but if you want to do something urgently, you can make some concessions for young low-related stallions with a good dam line. I think they can service 50 mares per stallion before they go through the CO. As far as I’m concerned, that has to be done right away, we can’t wait any longer. In such a small population you should not focus on index breeding. You can do that with cows, but not with Friesian horses. Breeders often want to go to the top right away and sometimes big money also plays a role. Breeding for high breeding values often produces better horses, but you ultimately do not help breeding itself. People often respond by saying: ‘We want progress!’, but this method in fact leads to regression. I myself experiment sometimes, putting an unusual stallion on a mare from a solid damline. The breeding value index is supposed to be a breeding tool, but many people use the index as a breeding target and you end up running aground. Just adding a breeding value for kinship is not enough in my opinion. You have be practical. Mares that are interesting in terms of kinship and, for example, free of Wessel blood, could be bred to a lower-related stallion. For example, there are still a few mares by stallions who have only bred in the Netherlands for a short time. You could encourage the owners of those mares with pairing advice. It is always about quality and kinship, it is very difficult to draw up a good policy on those issues. I also think we need to let go of certain fixed ideas. Line 50, for example, originated from two brown mares and it has become a very good line.”

COMPLICATION: FERTILITY OF THE STALLIONS When you study the birth rates of the Friesian horse closely, you will see that the fertility of the stallions varies enormously. For the 2018 breeding season (foals born in 2019), there were stallions with only about 30% of the matings leading to a birth and stallions where that percentage was above 80%. In the Friesian studbook, young stallions are used a lot. The newly appointed generation therefore has full dance cards almost every year: most new stallions breed with about 180 mares in their first season. But mare owners who don’t necessarily want to use the youngest generation and keep an eye on the birth numbers, will lean towards the fertile stallions, so as not to lose a season. In recent years, the stallions have been given more time during the inspection process to send in an acceptable semen sample. But a stallion that has lower quality sperm is not profitable at all for a stallion owner. Many of these animals will not enter the expensive stallion selection process at all, or will be withdrawn prematurely. And even if they are approved, the less fertile stallions quickly disappear into oblivion. Fertility problems in this way limit the range of stallions to choose from.

“IN FIVE YEARS WE WILL BE TOO LATE” Breeder Roelof Tjeerdsma spoke with the KFPS Breeding Council last winter. “I told them: Try to use the scarce low-related mares more widely, as long as they are around. I think it’s 12 o’clock now, in five years we’ll really be too late. Talking about these issues more openly, is absolutely necessary, there are many breeders with very good ideas. And perhaps it should also be financially encouraged. Also, the studbook should not want to be dependent on animal welfare regulations, but keep those issues under control. There are still stallions with a lower relatedness, although they must of course meet the basic requirements. If you have a stallion that is low related and has a good maternal line, you could compromise a little on conformation and movement. But you need to communicate about all this. I am not a proponent of outcross, that has to do with my love of the Friesian breed. It’s my personal opinion, I think the breed is too beautiful.”

ADVISE ON PAIRINGS AND BREEDER PREMIUMS Zandee: “In the Friesian breed we can manage without outcross just fine, limiting the increase in inbreeding has been successful lately. Stallions with a lower kinship also get their chance. It would be helpful to make a breeding plan and identify some really good bloodlines within the population. You could then ask the owners of those if they want to follow an advice on mating choices.” Zandee is not in favor of a bonus for low-related breeding, as the warmblood studbook KWPN is now providing for their harness horse breeders. “That can lead to excess. It is much better to look for a suitable part of your population and then look for a stallion that still fits in the line. We used to work with advice pairings for a while, then breeders received a few hundred guilders. You might as well do that again. You have to reward proper choices, and it is essential the studbook manages this well.” Siem Korver also argued in 2011 for the central selection of suitable stallion mothers. Several experts emphasize that in breeding it is important to think in terms of generations. This includes accepting that sometimes a lesser horse is born, that can still be valuable for breeding and keeping the population healthy. Andries Zandee: “For example, if you use the maternal lines of stallions that were rejected later in life, the kinship goes down. That is a risk from a breeding point of view, those stallions were rejected for a reason. But with strong dam lines you can achieve something. It’s not easy however, it is the art of breeding.”

IS OUTCROSS AN OPTION? The Friesian studbook has been closed for 44 years now. To keep such a population healthy, it is important to breed enough and use as much of the available genetic diversity as possible. New mutations will always add some diversity to the breed, but that is a slow process. The kinship rate will continue to increase in a closed population. It was around 13% in the early 1980s and was still below 16% in the year 2000. In 2021 it was 17.8% on average. As Rita Hoving, geneticist at WUR puts it: “Inbreeding always continues to grow in a closed studbook. That is why the growth rate is important and not the absolute rate. With very long family trees you always have a base number that you cannot change.” It is important to bear in mind that relatively low-related stallions also have ancestors. You never start from scratch. Hoving: “You have to ensure that the increase in inbreeding remains manageable. At some point, when you have too few animals or when fertility becomes problematic or you develop abnormalities, you should choose whether to bring in animals from outside.” The question that a number of breeders and experts are asking themselves is whether that point has now been reached for the Friesian horse. Some think it is already time for outcross, others reserve their judgment until more information is available about the current status of the hereditary disorders in the breed. ‘Outcross’ was a taboo in the studbook for a long time, but the discussion about the use of foreign blood has now tentatively started.

If you have too few animals, if fertility becomes problematic or if you develop abnormalities, you have to choose whether or not to include animals from outside.

NO WHITE SPOTS The Friesian studbook is closed, but that does not apply to all horse studbooks in the Netherlands. The choice for ‘foreign blood’ depends, among other things, on the breeding goal. With Friesian horses, white hairs or blazes are a real no-go. That limits the possibilities. It’s a different story for the Groningen horses, they are allowed to have markings and this breed has a slightly less narrow race description than the Friesians. Lotte Merks, board member of Vereniging het Groninger Paard: “We have an open studbook, whereby the foals of stallions from recognized studbooks from a Groningen mother, or vice versa, can be fully included in the Groninger studbook. In addition, several stallions and mares have been brought in from abroad in the past for blood distribution. A few German stallions from a recognized studbook are also currently being used, and we are investigating the possibilities of bringing a stallion from abroad once every year or two years and having it approved according to the standards of the Groningen horse.” Vet Sybren Boerma: “I used to say that you might not avert using fresh blood in the population, but at the moment I no longer think it is absolutely necessary. You have to be careful: if you breed out one of the hereditary abnormalities, you run the risk that others may increase. Especially if you can’t test for them yet. If I’m optimistic, I still think things are going in the right direction. But I would really like to see numbers on how often certain abnormalities occur.” Andries Zandee doesn’t like breeding with stallions from other studbooks: “You would have to turn up a good black Andalusian somewhere who also breeds black, that is unthinkable. The Friesian horse is a cultural asset that we have to handle very carefully.”

‘PREMATURE’ Bart Ducro of WUR thinks outcross – using stallions from outside – is premature for the Friesian horse: “As far as I’m concerned, that’s a very last resort. It’s so easy to say, but you don’t know what you’re getting. The first generation often looks fantastic, because of the heterosis effect. You then have a 100% crossbreeding advantage. If you start crossbreeding again after that, you will never get all those benefits and that diversity again.” The fact that the first generation of offspring of a Friesian and a black dressage bred KWPN look fantastic is confirmed in conversations with three breeders who have experimented with this in recent years. But, says Ducro: “It is not obvious how you would successfully introduce foreign blood into the population. All kinds of methods and crossbreeding schemes are possible. You can only do it systematically, when you have control over all the steps in the process. It then needs to be supervised over several generations. That seems impossible in a studbook of individual private breeders such as the KFPS. And even if the studbook could regulate it, I still have my doubts. You don’t know what you get from pollution with other ailments, in which you don’t have any insight at the moment. The vast majority of the Friesians are very healthy in my opinion, so I don’t see a reason for outcross yet. It is important to balance your breeding. And to take all aspects into account and not just look for a beautiful mane.” Ducro says emphatically that stallions that are carriers of a recessive hereditary condition, such as dwarfism, should not be excluded. “You can still use the carriers in your breeding, as long as you make sure that you don’t mate with other carriers of the gene. And you should test the offspring. Don’t discard a stallion with very good qualities, which can contribute to the survival of the breed, based on one minus point. That’s a shame. Fortunately, I have the feeling that the Friesian breeders have a more down-to-earth approach to carrier status than breeders in some of the other studbooks.”

“USE ALL INSTRUMENTS” Former studbook director and geneticist Ids Hellinga does not want to make any firm statements about the use of foreign blood. Hellinga: “That is no longer my role. It will be quite a challenge to solve the problems within the current population. Getting unwanted traits out, while on the other hand you want to keep the population wide enough for sufficient blood distribution, that is really a diabolical dilemma. You certainly don’t solve all problems with blood from outside. You still have to keep developing DNA tests and you also bring in other problems. In any case, it remains important to keep inbreeding low. Introducing other blood could be part of the solution, but it will never be the whole solution. You will still have to track down the genetic defects and have a sound inbreeding policy. Different blood has been used in the harness horses and the baroque pintos, but in both this resulted in inbreeding on those stallions from outside. You will therefore have to use all other instruments against inbreeding, even when using a outside blood.”

‘KEEP AN EYE ON OFFSPRING’ Erwin Spliethof likes to leave decisions about outcross to the geneticists, but believes that good policy should underlie any crossbreeding. “In any case, you first have to know what such a crossbreeding does, what the risks are. It is probably difficult to maintain the black color, for example, but nobody wants a Frisian with three white socks and a blaze. Or a Friesian with a bad character. If you want to start using outcross, you have to regulate it very well and only use very good horses that you know the background of. That way, you know what you are bringing into the population. You also want to keep your eye on the crossbred offspring. It is important to inspect these horses, to have aptitude tests done and to observe how they compete in sports, for example. In order to do that, you will have to register them in some kind of support book or a separate register. If you keep them close and let them participate, you also know what kind of horses they are and what they can add to your population. If you then breed back the best horses with, for example, two or three generations of pure Friesians, that can add something, without losing the typical Friesian. So embrace this offspring of crossbreeding, but keep an eye on them and create a studbook policy.”

“NOT JUST FOR YOURSELF” Breeder Bauke de Boer fears that things will not work out without blood from outside: “In the end, I think you cannot avoid outcrossing with the Friesians. But, that has to be done very carefully, not everyone can participate and it should be coordinated with policy from the studbook. You then have to select the best mares for that, which are free of genetic disorders. And not just randomly use outside stallions, but select wisely. That could give a considerable boost to the quality of the breed, but only if it is done in the right way. Descendants must then be able to be included in the A-register. I do think that you can use warmbloods that inherit a good character and possibly PRE horses that can move well. I myself have a foal by the KWPN dressage stallion Toto’s Design US (v. Totilas) out of a Fabe mare. You cannot distinguish this foal from a pure-bred Friesian.” De Boer is cautiously optimistic: “My impression is that the Breeding Council is now seriously at work with inbreeding and kinship. And that they involve people who want to proceed in a proper way, for the breed and not just for themselves.”

CHANGE AND COMMUNICATION The conclusion of all this, could be that a lot of information is still missing, but also that there are more possibilities to limit inbreeding problems than have been used by the KFPS so far. Some options have been suggested by scientists to the studbook for 20 years now, but have so far encountered vested interests, bureaucracy or political machinations within the association. However, the winds are slowly changing. Although not everyone interviewed for this story wanted to be mentioned by name, many people were willing to do so. Messages about hereditary problems are now widely shared via social media, often including the confusion associated with those channels. Breeders’ premiums, designating stallion mothers and lowering breeding limits are likely to become part of renewed discussions. It is crucial that there is transparent and clear communication by both the studbook and the scientists involved.

PARTICIPATE IN REGIONAL MEETINGS That something is tilting in the communication and openness at the studbook, became apparent during the online breeders cafe at the end of March. In it, the new chairman of the Breeding Council, Tjitse Bouma, said, among other things: “We really need to address inbreeding and kinship. We have all kinds of instruments available to us, but we do have to make choices. That is why we, as members of the Breeding Council, will also attend the coming regional meetings. Not to present you with a ready-made plan, but we want to have a discussion. Perhaps there should be a ceiling on the number of matings of stallions that breed a lot or are closely related, or maybe we should approve more stallions. We all have to make choices about these things.” The Breeding Council will present several options in the regional meetings, but also says it would like to hear the ideas of members. Bouma: “I am not in favor of the Breeding Council only giving advice to the board and then having the Members’ Council agree immediately. We should all talk about it together.” Bouma stated that the studbook faces “a real challenge” with regard to health, durability and fertility of the horses. “On the other hand, it’s not hopeless either, we have to remain positive.” It is important for breeders, members and enthusiasts that they understand basic concepts such as inbreeding, kinship, genetic disorders and carrier status in order to be able to fully participate in the discussions to come. Hopefully this longread will contribute. SOURCES This longread is based on dozens of conversations I had during the past year with both named and unnamed breeders, experts, stallion owners, (former) jury members and (former) studbook directors.

Scientific article (2012) with an overview of genetic disorders in Frisians:

Clinical Commentary. The Friesian horse breed: A clinical challenge to the equine veterinarian? S. Boerma, W. Back and M. M. Sloet van Oldruitenborgh-Oosterbaan. Equine Veterinary Education. 2012. 24 (2) 66-71.

Scientific article (2004) on the relationship between inbreeding and standing on the afterbirth in Frisians: M. Sevinga, T. Vrijenhoek, J. W. Hesselink, H. W. Barkema, A. F. Groen, Effect of inbreeding on the incidence of retained placenta in Friesian horses, Journal of Animal Science, Volume 82, Issue 4, April 2004, Pages 982–986,

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