Effects of age and frequency of ejaculation on sperm production and extragonadal sperm reserves in stallions

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Extragonadal reserves totalled 89 x 109 spermatozoa for 5-16 year old sexually rested stallions and 60 x 109 for 2-4 year olds. Regardless of age, the cauda epididymidis contained 62% of the total reserves and the vas deferens, including the ampulla, contained 7% of the total reserves of spermatozoa. The caput plus corpus epididymidis from 5-16-year-old stallions (N=41) contained 14.9 x 109 spermatozoa per side as compared (P<0.01) to 8.5 x 109 for 2-4 year olds (N=30). Frequency of ejaculation did not influence the number of spermatozoa found in caput plus corpus epididymidis. Across all ages, the number of spermatozoa potentially available for ejaculation from the cauda epididymidis and vas deferens on each side totalled 54 x 109. Collection of 5 successive ejaculates from sexually rested stallions removed 40-60% of the available spermatoza while ejaculation every 2nd day reduced (P < 0.05) the number of spermatozoa potentially available for ejaculation by 27%. Nevertheless, sufficient spermatozoa are produced daily (6.4 and 4.2 x 109 for 5-16 and 2-4 year olds) to permit use of an average stallion once or twice daily, during spring and summer, providing sexual behaviour is adequate.

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Journal of Reproduction and Fertility

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