Seminal quality, spermatozoal outpost, and testicular changes in growing Holstein bulls

Nine Holstein bulls, initially between the ages of 17 and 22 mo, awaiting proofs in artificial breeding, were ejaculated each summer for 3 yr, and 8 and 7 survivors for 4 and 5 yr, respectively, to study changes in the same group of bulls and determine the predictive value of early measurements. Semen was collected twice a day, 2 days per wk, for 4 wk. Bulls differed in testicular size, consistency, ejaculate volume, total spermatozoal output, percentage of unstained spermatozoa and abnormal spermatozoa, and in several storage and freezing tests. The largest yearly effects were on testis size and consistency, ejaculate volume, and total output of spermatozoa. The latter increased per bull from 28.3 X 10(9) per wk at 17 to 22 mo of age to 40.9 X 10(9) per wk 4 yr later, representing a high output of spermatozoa with a total of only 20 min of intensive sexual preparation per wk. The correlation between testis size and spermatozoal output was .72. Testicular consistency was indicative of semen quality measured simultaneously as judged by correlations with spermatozoal characteristics ranging from .61 to .95. These characteristics are believed to be representative of those Holstein bulls in artificial breeding which are ejaculated frequently.