Asymmetrical size and functionality of the pampas deer (Ozotoceros bezoarticus) testes: Right testis is bigger but left testis is more efficient in spermatogenesis.

Information about gonadal asymmetries in ruminants is very scarce. In this work, we performed three complementary studies to compare characteristics of both testes: (i) weight and size of offspring and adult dead males; (ii) the tissue:fluid relationship determined by ultrasound scanning; and (iii) the spermatogenic status using fine needle aspiration cytology. The right testis was heavier than the left one in both offspring and adult animals and had greater width and volume in adult males than the left one. The ultrasound pixel intensity was similar in both testes. The right testis tended to have more spermatogonia (p = .06) and had a greater percentage of early spermatids (p = .004) than the left testis. On the other hand, the left testis had a greater percentage of spermatozoa (p = .05). The left testis had a greater spermatozoa/spermatogonia ratio (p = .02) and tended to have more spermatozoa/Sertoli cells ratio (p = .07). The spermatogenic index tended to be greater in the left than in the right testis (p = .06). Overall, we concluded that the right testis of pampas deer males is bigger but according to the cytology, it seems to be less spermatogenically effective than the left one, but these differences are not explained by different tissue:fluid ratio in each testis. Although differences were greater in adults than in offspring, asymmetry was observed even in just born offspring.