Duration of the seminiferous epithelial cycle in hybrid Bos indicus x Bos taurus bulls.

The hybrids were carrying 50% (N = 4) or 75% (N = 4) zebu (Brahman) blood. The spermatogenic cells were labelled in vivo with [3H]thymidine. The relative frequencies of the seminiferous epithelial cycle stages, determined from examination of 6350 tubule cross-sections, did not differ between the 2 hybrid types examined, between regions of the testis or between testes within animals. Frequencies were generally similar to those for Bos taurus bulls except that the frequency of stage 4 tubules was lower and that of stage 8 tubules higher. The mean duration of the seminiferous epithelial cycle was 13.41 days and was similar for both types of hybrid. The durations of meiosis and spermiogenesis were calculated to be 20.7 and 17.4 days respectively, estimates which are similar to those for Bos taurus bulls. From the relative frequency of cell stages and estimates of the duration of the cycle, a time divisor of 5-11 days is suggested as being appropriate to determine daily sperm production from counts of spermatid reserves in testicular homogenates of these hybrid bulls.