Level of Glycolyzable Substrates in Stallion Semen: Effect of Ejaculation Frequency on Sperm Survival after Cool Storage during the Nonbreeding Season

Abstract

Although seminal characteristics are routinely evaluated in the stallion, the effect of collection schedules and seminal plasma on semen quality during cool storage is not well understood, specifically during the nonbreeding season when cryopreservation of stallion semen is preferentially performed. To address these issues, behavioral characteristics, seminal parameters, and biochemical markers ( d-glucose, fructose, and citric acid) were measured in ejaculates (n = 60) obtained during the nonbreeding season. Semen was collected from three stallions, twice a day (1-hour gap between successive collections) and two times in a week. Differences between the means of first and second ejaculates were observed for erection latency ( P < .001), which was higher in second ejaculates and determined a higher total breeding time ( P < .1). Variations introduced by the stallion were significant for number of mounts ( P < .05, in first ejaculates), erection latency ( P < .001, in second ejaculates), and total breeding time ( P < .001, in second ejaculates). First and second ejaculates differed significantly for sperm motility and sperm concentration ( P < .001, higher in first ejaculates) and pH ( P < .01, higher in second ejaculates). d-glucose was present in seminal plasma at a much higher concentration than fructose ( P < .001) in both ejaculates. There were no significant stallion-associated differences in sperm vitality and pH in the first and second ejaculates as well as in sperm concentration for the second ejaculates. The effect of seminal plasma on equine sperm survival during cooled storage was analyzed by monitoring sperm motility and cell morphology after conservation in an extender medium with and without seminal plasma. When statistically considering seminal plasma and conservation time simultaneously, it was found that these variables affected acrosomal status and midpiece morphology.