R E P R O D U C T I V E PHYSIOLOGY OF THE S T A L L I O N . V I I . C H E M I C A L C H A R A C T E R I S T I C S OF S E M I N A L P L A S M A AND SPERMATOZOA 1 M. R. Gebauer 2, B. W. Pickett, L. C. Faulkner, E. E. Remmenga 3 and W. E. Berndtson Colorado State University, Fort Collins 80523

SUMMARY 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 (/lg/ml) 11.3, 6.2; glycerylphosphorylcholine (GPC, mg/ml) .95, .57; total carbohydrate (/Jg/ml) 3 8 7 , 2 1 4 ; 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 (/~g/lO6 spermatozoa) 18.6, 20.5; ash weight (/ag/106) 1.8, 2.3; total nitrogen (/~g/106) 2.6, 2.7; and lactic acid (/Jg/109) 46.2, 45.3, respectively. The difference between first and second ejaculates was significant (P.05) and all spermatozoal characteristics were influenced (P