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Reproductive Physiology of the Stallion. VII. Chemical Characteristics of Seminal Plasma and Spermatozoa¹

Colorado State University, Fort Collins 80523

Abstract

Chemical characteristics of spermatozoa and seminal plasma were measured in first and second ejaculates three times per month for 13 months. The means of the criteria measured in the seminal plasma from first and second ejaculates were: refractometer protein (mg/ml) 20.1, 9.8; non-protein sulfhydryl (µg/ml) 11.3, 6.2; glycerylphosphorylcholine (GPC, mg/ml) .95, .57; total carbohydrate (µ/ml) 387, 214; dry weight (mg/ml) 32.3, 21.8;ash weight (mg/ml) 9.1, 9.3; total nitrogen (mg/ml) 3.1, 1.7; and lactic acid (mg/ml) .25, .24; respectively. The means of the criteria measured in spermatozoa from first and second ejaculates were: dry weight (µg/10⁶ spermatozoa) 18.6, 20.5; ash weight (µg/10⁶) 1.8, 2.3; total nitrogen (µg/10⁶) 2.6, 2.7; and lactic acid (µg/10⁹) 46.2, 45.3, respectively. The difference between first and second 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 nitrogen between first and second 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 first and second ejaculates except non-protein sulfhydryl and ash weight. The effect of season on dry weight and ash weight of spermatozoa from first and second ejaculates was not significant, while significant effects were observed for total nitrogen and lactic acid in first ejaculates and lactic acid in second 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 = .50 or less) to permit prediction of seminal characteristics from individual testosterone values. Correlations based on the pooled monthly means for each stallion or calculated on a within-stallion basis were similar in magnitude to simple correlations.

¹ Animal Reproduction Laboratory, Department of Physiology and Biophysics. This investigation was supported in part by grants-in-aid from American Breeders Service, The Grayson Foundation and the National Association of Animal Breeders. Portions of these data were presented at the "First International Symposium Upon Equine Reproduction," Cambridge, England, 1974, and appeared in the J. Reprod. Fertil. (Suppl.) 23:25.

² Present address: Universal Semen Service Ltd., Box 910, Cardston, AB, Canada.

³ Statistics Department.