Effect of Cooling, Storage, Glycerolization and Spermatozoal Numbers on Equine Fertility1

Abstract

The effects of cooling, storage, glycerolization and spermatozoal numbers on fertility were investigated utilizing three stallions and 72 mares. Semen was extended in a cream-gel extender and inseminated: a) within 1 hr (fresh) at 38 C, b) after cooling for 2 hr to 5 C, c) after cooling for 2 hr plus the addition of 7% (v/v) glycerol, and d) after cooling for 24 hours. One-half of the mares were inseminated with 100 and one-half with 500 × 106 progressively motile spermatozoa per insemination. First-cycle pregnancy rates of 55.6, 38.9, 5.6 and 27.8% were obtained with the fresh, cooled 2 hr, cooled 2 hr plus glycerol and the cooled 24-hr seminal treatments, respectively; after three cycles, the pregnancy rates were 94.4, 83.3, 44.4 and 55.6%. The fertility of freshly extended semen was superior (P<.05) to that of semen cooled for 2 hr plus glycerol and to semen cooled and stored for 24 hours. Semen cooled for 2 hr was superior (P<.05) to semen cooled for 2 hr plus glycerol. The 63.9% pregnancy rate for mares inseminated with 100 × 106 did not differ (P>.05) from the 75.0% for mares receiving 500 × 106 spermatozoa. There was no difference in fertility among the three stallions.