Effect of Seminal Extenders on Equine Fertility

Abstract

Pregnancy rate, spermatozoan motility and spermatozoan agglutination were significantly lower in an extender containing .349% Tris than in an extender utilizing 2.4% Tris. First-cycle pregnancy rates of 22.2 and 11.1% were obtained with 500 and 100 × 106 motile spermatozoa in a 2.4% Tris extender, and a rate of 61.1% (P < .05) was obtained with 500 × 106 motile spermatozoa in raw semen. After four cycles there was no significant difference in fertility obtained with 2.4% Tris and the raw semen when 500 × 106 spermatozoa were utilized (72.2 vs 88.9%). First cycle pregnancy rates of 37.5, 75.0 and 75.0% were obtained in 1973 when mares were inseminated with 500 × 106 motile spermatozoa extended in 2.4% Tris, and cream-gel extenders and with raw semen, respectively. After three cycles, mares on the Tris-seminal treatment had a pregnancy rate of 75.0%, which was lower (P < .05) than the 95.8 and 91.7% for the cream-gel and raw-seminal treatments, respectively. The presence of glycerol in the Tris extenders may have been at least partially responsible for the depression of fertility. Pregnancy rates of 75.0 and 91.7% were obtained after one and three cycles, respectively, with a mean insemination volume of 1.5 ml of raw semen. Thus, a large insemination volume may not be necessary for maximum fertility in the mare.