Reproductive Capacity of Dairy Bulls. II. Gonadal and Extra-Gonadal Sperm Reserves as Determined by Direct Counts and Depletion Trials; Dimensions and Weight of Genitalia

Abstract

Summary Extra-gonadal sperm reserves (EGR) determined by direct counts averaged 69.4 billion for 15 sexually rested (SR) bulls, 73.5 billion for 15 sexually rested bulls depleted just before slaughter (SR-D), and 68.0 billion for five bulls ejaculated six or seven times per week for at least 6 wk. prior to slaughter (6–7 x). While total EGR, which included an average of 38.5 billion sperm collected on the day of slaughter from SR-D bulls and 10.5 billion from 6–7 × bulls, did not vary significantly among the three groups, sperm distribution was significantly different. Sperm counts of the caput, corpus, and cauda epididymis averaged 19.4, 4.7, and 37.6 billion for SR bulls, 16.2, 3.0, and 13.7 billion for SR-D bulls, and 22.6, 5.2, and 26.4 billion for 6–7 × bulls. Depletion removed 52.8 ± 2.3% of the total EGR of SR-D bulls; although the cauda epididymis was nearly emptied, partial replenishment with sperm from the caput and corpus occurred during the 60- to 90-min. interval between the end of depletion and slaughter. Daily sperm output for the 6–7 × bulls averaged 4.9 billion for 6 wk. The sperm content of the cauda epididymis was 25% lower than if they had been sexually rested. The ductus deferens and ampulla of SR bulls contained only 7.6 billion sperm. When corrected for preslaughter treatment, the EGR for the 35, 76 ± 5-mo.-old bulls averaged 72.6 billion sperm. Preslaughter treatment did not affect gonadal sperm reserves. Fifty testes, averaging 374 g., contained 20.2 billion sperm, or 54.8 ± 1.0 million per gram. Testis sperm numbers were highly significantly correlated (+ 0.62) with testis weight. The highly significant correlation (+ 0.87) between EGR and total sperm removed in a depletion should permit estimation of EGR in living animals by depletion trials of about 20 ejaculates. Gonadal sperm reserves were not significantly correlated to epididymal sperm reserves in SR bulls. The independence of testicular sperm production and storage of sperm in the excurrent duct system is stressed. Genitalia dimensions and weight for 55 bulls are presented by breeds and ages.