Reproductive Capacity of Dairy Bulls. VIII. Direct and Indirect Measurement of Testicular Sperm Production1,2,3

Abstract

Summary It was desired to determine testicular daily sperm production (DSP) and compare it with daily sperm output (DSO). Two independent calculations of DSP for each testis from eight 2-yr-old and four mature Holstein bulls were based on counts of gonadal sperm reserves and on quantitative testicular histology. Limitations of the proposed methods and formulas were discussed. The duration of spermatogenesis in bulls was calculated to be 60 days. The average DSP values calculated from gonadal sperm reserves and histological data were 9.98 and 12.76 billion per bull. The differences between DSP values for the 24 testes by the two methods of calculation were highly significant, but the two 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 these methods has not been established, the two DSP values were averaged and ranged from 7.7 to 13.2 billion for eight bulls of similar age and body weight. The DSO during collection of six ejaculates weekly with intensive sexual preparation (6×) also was obtained for the 12 bulls. About five months elapsed between collection of DSO data and postslaughter determination of DSP. The DSO on 6× averaged 4.81 ± 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 on 6× (+0.87) suggests that DSP can be estimated in individual living bulls by collecting semen at a suitable high ejaculation frequency.