EFFECT OF SUPPLEMENTARY SEXUAL PREPARATION ON SEMEN CHARACTERISTICS OF STALLIONS

Sperm output from males of several species can be increased by supplementary sexual preparation (SSP). Since this has not been demonstrated for stallions, two experiments were conducted to a) evaluate the effect of SSP on semen characteristics of first and second ejaculates from depleted and sexually-rested stallions, and b) retrospectively evaluate semen characteristics of first and second ejaculates from sexually-rested stallions with semen volumes similar to those from stallions that received SSP (Experiment 1). In Experiment 1, when SSP was applied prior to collection of first ejaculates (SSP 1) from depleted stallions, gel-free and total semen volumes were higher (P < 0.05) in first vs second ejaculates, while SSP prior to collection of the second ejaculate (SSP 2) resulted in higher (P < 0.05) gel-free and total semen volumes, fewer mounts per ejaculate and lower sperm concentration in second vs first ejaculates. Higher (P < 0.05) gel, gel-free and total semen volumes in first vs second ejaculates were obtained when SSP 1 was applied to sexually-rested stallions while SSP 2 resulted in higher gel-free and total semen volumes, lower sperm concentration and higher pH in second vs first ejaculates. The number of spermatozoa was higher in first vs second ejaculates, regardless of SSP treatment, in depleted and sexually-rested stallions. Semen characteristics of stallions in Experiment 1 were compared with semen data from potential fertility evaluations of stallions with similar gel-free volumes (Experiment 2). Ratios of second to first ejaculate gel-free volume and sperm output were calculated for stallions from both experiments. Sexually-rested stallions in Experiment 1 that received SSP 1 had a gel-free volume ratio of 47% and a sperm output ratio of 47%; the SSP 2-treated stallions averaged 250 and 67%, respectively. Stallions in Experiment 2 with higher gel-free volumes in the first than second ejaculates (Group 1) had an average gel-free volume ratio of 66% and a sperm output ratio of 46%, while stallions with a higher gel-free volume in the second than in the first ejaculate (Group 2) averaged 144 and 62%, respectively.