Evaluation of Testicular Volume and Correlation with Sperm Production in Martina Franca Donkeys: A Parameter to Consider When Approving Breeding Jacks

Abstract

Good sperm production is a notable requirement for subjects intended for reproduction, particularly in endangered species, and it has been demonstrated that in horse stallions, this is correlated to testicular volume. The present study, which involved Martina Franca jacks, aimed to determine whether, also in this endangered breed, there is a correlation between the total sperm number (TSN) and testicular volume. Testes were measured with both ultrasound and a caliper. Testicular volume was calculated using two different formulas: one representing the volume of an ellipsoid and one developed to describe round-shaped testicles. The average sperm concentration was 380.14 ± 254.58 × 106/mL, while the average TSN was 16.34 ± 7.76 × 109. Our findings evidenced a significant correlation (r > 0.75; p < 0.05) only between sperm production and the volume calculated with the formula V (cm3) = 33.57 × H − 56.57 for round-shaped testes. Moreover, significance was evidenced only for data obtained with ultrasound (VTs-us 315.03 ± 25.83 cm3) but not with caliper. In conclusion, testicular volume can be suggestive of good fertility in Martina Franca jacks; thus, this parameter could be considered when selecting breeding animals.