Reproductive Characteristics of Thawed Stallion Sperm

SIMPLE SUMMARY: It is very important to evaluate correctly the fertilizing capacity of frozen sperm before carrying out the artificial insemination of mares. It is not always possible to perform complex laboratory tests under the stud farm’s conditions. The purpose of our study was to determine the minimum set of relatively simple laboratory tests sufficient to confirm the feasibility of frozen/thawed sperm for insemination and to predict the pregnancy rate in mares. We found that sperm characteristics such as activity, survival at low temperature, and DNA damage are sufficient to determine the quality of frozen/thawed sperm. These characteristics can be determined by simple tests and assays that can be used for increasing the effectiveness of artificial insemination not only in horse breeding but also in other areas of livestock and even in reproductive medicine. ABSTRACT: The main goal of our study was to determine a set of thawed stallion sperm characteristics that have predictive value for the pregnancy rate (PR) of mares after artificial insemination (AI). DNA fragmentation and survival of sperm during hypothermic storage were studied in addition to routinely determined semen characteristics such as concentration, percentage of motile spermatozoa, and morphology. To estimate DNA fragmentation, a modified hallo assay was applied. Sperm survival was determined within hours as the ability of spermatozoa to maintain progressive motility (PM) during the storage of ejaculate diluted with lactose-chelate-citrate-yolk (LCCY) medium at +4 °C. Strong positive correlation between PR and thawed sperm motility (r = 0.90, p < 0.05) as well as between PR and sperm survival (r = 084, p < 0.05) was revealed. There was also a strong negative correlation between PR and DNA damages in spermatozoa (r = −0.94, p < 0.05). We found no dependence of PR on normal morphology spermatozoa percentage in thawed semen. We concluded that the sperm activity, survival, and DNA fragmentation should be considered as the sufficient reproductive characteristics of semen to evaluate the quality of frozen/thawed sperm and prediction of PR.