A group of researchers in Austria looked at the effect that a long-day light program would have on the hair coat, semen, and a series of metabolic measurements in a group of Shetland pony stallions.
18 Shetland pony stallions were assigned to one of two groups: a control group, which was kept under natural lighting conditions, and a treatment group that was exposed to an artificially lengthened period of daylight from December 15th to the following March 20th. The two groups were housed the same and were evaluated over an 8-month period. Rectal temperature, heart rate, heart rate variability, hematology (blood work), coat changes, semen parameters, and plasma testosterone concentration were measured.
During the 8-month study, rectal temperature, heart rate, and heart rate variability did not differ between the two groups. The length of the guard hair (the longer hairs seen on the horse’s hair coat) decreased over time, and this decrease occurred earlier in the group under artificial light than in the control group. Total sperm count increased from January to April in both groups and did not differ between groups. Sperm motility and the number of intact sperm cells “showed no clear seasonal changes, and semen parameters did not differ between groups.” The researchers concluded that the Shetland stallions showed “seasonal variations in hair coat and total sperm count, but only changes in hair coat but not semen parameters were advanced by a long-day light program.”
In climates where the breeding season begins long before spring arrives, there has been much interest in management techniques that will help to increase semen quality early in the breeding season (many breeders start shipping semen as early as February 1st). The idea that artificial lighting will help to improve semen quality has been put forth as a management option. This study suggests that the seasonal changes that we see naturally as we move into the more “normal breeding season” cannot be artificially reproduced with the lighting protocols that are used so successfully with mares.
Scientific Article: Schrammel N, Deichsel K, Aurich J, Aurich C. A long-day light program accelerates seasonal coat changes but is without effect on semen and metabolic parameters in Shetland pony stallions. Theriogenology 2015
Nov 12. pii: S0093-691X(15)00623-8. doi: 10.1016/j.theriogenology.2015.11.003. [Epub ahead of print]