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

The research investigated the influence of age and ejaculation frequency on sperm production and its reserves in stallions, finding that older stallions have more extragonadal sperm reserves than younger ones. Frequent ejaculation was found to significantly reduce the number of sperm, but daily sperm production is enough to allow for one or two uses of the stallion daily, given that they exhibit adequate sexual behaviour.

Age and sperm production

• The study revealed that extragonadal reserves, which refer to the total amount of sperm stored outside of the testicles, are significantly larger in 5-16-year-old stallions than in younger 2-4-year-old stallions.
• The researchers also noted that of the total sperm reserves, the cauda epididymidis (the another part of the reproductive system) held 62%, and the vas deferens (the duct responsible for transporting sperm from the testicle to the urethra), including the ampulla (an enlarged section of the vas deferens), contained about 7% of the total sperm reserves, regardless of the stallion’s age.

Sperm reserve location and counts

• The caput plus corpus epididymidis (a section of the epididymis, a tube where sperm is stored and matures) from 5-16-year-old stallions, contained about 14.9 X 10(9) spermatozoa per side.
• However, younger stallions (2-4 years old) had significantly fewer spermatozoa – only about 8.5 X 10(9) per side. This difference was statistically significant, with p less than 0.01.
• The frequency of ejaculation did not change the number of spermatozoa found in caput plus corpus epididymidis across these two age groups.

Effects of ejaculation frequency on sperm availability

• The researchers found that regardless of a stallion’s age, the total number of spermatozoa potentially available for ejaculation from the cauda epididymidis and vas deferens on each side totalled 54 X 10(9).
• After collecting five consecutive ejaculates from sexually-rested stallions, 40-60% of the available spermatozoa was depleted.
• Ejaculating every second day resulted in a statistically significant reduction (p less than 0.05) of 27% in the number of spermatozoa potentially available for ejaculation.

Daily sperm production

• Despite the reduction in available sperm due to frequent ejaculation, stallions produce sufficient amounts of sperm daily for practical use.
• 5-16-year-old stallions produce about 6.4 x 10(9) spermatozoa daily, while younger stallions produce about 4.2 x 10(9) daily.
• The result being that an average stallion could be used for ejaculatory purposes once or twice daily, during spring and summer, providing sexual behaviour is adequate.