Comparative histomorphometry of seminiferous tubules in mature and immature cattle, yak, and cattle–yak

The hybrid of the yak and the yellow cattle is sterile, caused by disturbed spermatogenesis, resulting in the absence of mature spermatozoa. This study comparatively evaluated the histomorphology of the seminiferous tubules of the sexually mature and immature yak, cattle, and their crossbreed, the cattle–yak. No germ cells beyond the spermatocyte stage were seen in the mature and immature cattle–yak. Some of the primary spermatocytes had highly heteropycnotic nuclei typical of cells undergoing degeneration. In contrast, the cattle and yak tubules had all types of cells. The mature cattle–yak comprises 59% spermatogonia, 18% spermatocytes, and 29.9% Sertoli cells, whereas the immature cattle–yak had 56, 10, and 33.6% spermatogonia, spermatocytes, and Sertoli cells, respectively. Also, 97% and 93% of seminiferous tubules contained complete spermatogenesis in the observed tubules of mature cattle and yak, respectively. Morphological comparisons of the seminiferous tubules showed no significant difference in tubule diameter, cross-sectional area, and perimeter among the three groups. However, the lumen area and perimeter were noticeably widened, whereas the epithelial thickness was visibly decreased in the cattle–yak compared to the cattle and yak. No cells beyond the spermatocyte stage were found in the cattle-yak, and the lumen area was noticeably widened with a drastically decreased epithelial thickness compared to the domestic cattle and yak. In conclusion, aberrant spermatogenesis in the cattle–yak began at an early age and became pronounced with age.