Reproductive Capacity of Dairy Bulls. VIII. Direct and Indirect Measurement of Testicular Sperm Production

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Abstract
Two independent calculations of testicular daily sperm production (DSP) for each testis from 12 Holstein bulls were based on counts of gonadal sperm reserves and on quantitative testicular histology. Limitations of the proposed methods were discussed. The duration of spermatogenesis was calculated to be 60 days. . Average DSP values calculated from gonadal sperm reserves and histological data were 9.98 and 12.76 billion per bull. Differences between DSP values for the 24 testes by the 2 methods of calculation were highly significant, but the 2 values were correlated (0.81). However, testis weight accounted for most of the relationship, since the correlation was not significant when calculated on the basis of DSP per gram of testis (0.28). Since the validity and repeatability of the methods has not been established, the 2 DSP values were averaged and ranged from 7.7 to 13.2 billion for 8 bulls of similar age and body weight. Daily sperm output (DSO) during collection of 6 ejaculates weekly with intensive sexual preparation also was obtained. About 5 months elapsed between collection of DSO data and postslaughter determination of DSP. DSO averaged 4.8 1 + 0.35 billion or only 42% of the mean DSP of 11.49 + 0.64 billion. However, the highly significant correlation between DSP and DSO (0.87) suggests that DSP can be estimated in individual living bulls by collection of semen at a suitable high ejaculation frequency.