REPRODUCTIVE PHYSIOLOGY OF STALLION .7. CHEMICAL CHARACTERISTICS OF SEMINAL PLASMA AND SPERMATOZOA

Chemical characteristics of spermatozoa and seminal plasma were measured in 1st and 2nd ejaculates 3 times/mo. for 13 mo. The means of the criteria measured in the seminal plasma from 1st and 2nd ejaculates were refractometer protein (mg/ml) 20.1, 9.8; non-protein sulfhydryl (.mu.g/ml) 11.3, 6.2; glycerylphosphorylcholine (GPC, mg/ml) .95, .57; total carbohydrate (.mu.g/ml) 387, 214; dry weight (mg/ml 32.3, 21.8; ash weight (mg/ml) 9.1, 9.3; total N (mg/ml) 3.1, 1.7; and lactic acid (mg/ml) .25, .24, respectively. The means of the criteria measured in spermatozoa from 1st and 2nd ejaculates were dry weight (.mu.g/106 spermatozoa) 18.6, 20.5; ash weight (.mu.g/106) 1.8, 2.3; total N (.mu.g/106) 2.6, 2.7; and lactic acid (.mu.g/109) 46.2, 45.3, respectively. The difference between 1st and 2nd ejaculates was significant (P < .05) for all seminal plasma characteristics except lactic acid, while none of the differences between spermatozoal characteristics were significant. When the constituents in seminal plasma were analyzed on the basis of 106 spermatozoa, the difference in quantities of non-protein sulfhydryl, GPC, total carbohydrate, dry weight and total N between 1st and 2nd ejaculates changed from significant to nonsignificant. All seminal plasma characteristics except ash weight (P > .05) and all spermatozoal characteristics were influenced (P < .01) by stallion. Significant seasonal effects were found for all seminal plasma characteristics in both 1st and 2nd ejaculates except non-protein sulfhydryl and ash weight. The effect of season on dry weight and ash weight of spermatozoa from 1st and 2nd ejaculates was not significant, while significant effects were observed for total N and lactic acid in 1st ejaculates and lactic acid in 2nd ejaculates. The effects of season were highly variable but more pronounced among seminal plasma than spermatozoal characteristics. Although significant correlations were obtained among many of the seminal characteristics and plasma testosterone levels, the coefficients of correlation were too small (r = .05 or less) to permit prediction of seminal characteristics for individual testosterone values. Corelations based on the pooled monthly means for each stallion or calculated on a within-stallion basis were similar in magnitude to simple correlations.