Researchers at Texas A & M University, recognizing that equine veterinarians are limited by a lack of information, undertook a study to describe sperm quality following cooled storage and its relationship to embryo recovery rate (a method to measure fertility).
488 ejaculates were collected from QH and Paint stallions and shipped to an ET facility for AI. Samples were evaluated for total sperm motility, morphology, viability, semen concentration and volume, and DNA quality. A total of 204 mares were bred on 492 estrus cycles, and fertility was measured using embryo recovery rates. Cutoff values were determined that separated “average and high fertility groups” and identified as follows:
Total sperm motility > 65%
Progressive sperm motility > 45%
Extended semen concentration > 31.8 million sperm/ml
Total sperm number in the inseminate (dose) > 1.14 billion sperm
Viable sperm > 71%
Sperm with abnormal DNA < 26.8%
Morphologically normal sperm > 47%.
The researchers concluded, “these guidelines will allow the clinician to more critically interpret the results of sperm quality analysis form cooled-shipped semen.”
When breeding with cooled-shipped semen, the success is directly dependent on not just the correct timing and breeding of the mare but also the contribution made by the stallion. With the use of semen analyzers that can provide us with the “numbers” on a semen sample, these general guidelines can help to predict the probability and possibility of success better.
Scientific article: Love, CC, et al. “Relationship Between Sperm Quality and the Embryo
Recovery Rate of Cooled-Shipped Stallion Sperm”. AAEP proceedings vol. 60, 2014,
Companion Article: Beckstett, Alexandra “Cooled-Shipped Sperm Quality’s Effect on
Fertility”, the Horse, May 1, 2015, Article # 35720.