Effect of successive ejaculation on stallion seminal characteristics.

Five ejaculates were collected at hourly intervals from 32 sexually rested stallions. Gel volume, total seminal volume, sperm concentration and spermatozoa per ejaculate declined (P less than 0.01) from the first to the second or third ejaculate. Gel-free seminal volume or percentage of motile spermatozoa did not vary (P less than 0.05) among ejaculates. Ejaculates from 2- to 3-year-old stallions contained less volume and fewer spermatozoa than those from 9- to 16-year-old stallions. Regardless of the stallion's age the first, first 2, first 3 and first 4 ejaculates represented 50, 74, 86 and 93% of the total numbers of spermatozoa contained in the 5 ejaculates. In addition, the number of spermatozoa that might be obtained in 5 ejaculates can be predicted by multiplying the total number of spermatozoa in two successive ejaculates by 1.35 +/- 0.03. Although some fifth ejaculates contained as few as 0.02 X 10(9) motile spermatozoa, the mean number of motile spermatozoa in fifth ejaculates from sexually rested stallions was 0.52 X 10(9) spermatozoa; presumably enough to impregnate a mare during natural service.