Reproductive Capacity of Dairy Bulls. V. Detection of Testicular Deficiencies and Requirements for Experimentally Evaluating Testis Function from Semen Characteristics1,2

Abstract

Summary Six ejaculates per week using intensive sexual preparation (6×) were collected from eight 2.5-yr.-old Holstein bulls for 5 wk. before unilateral vasectomy. Daily sperm output (DSO) averaged 4.58 billion and was correlated with paired testes weight at slaughter (+0.97). First ejaculates consistently contained a higher sperm concentration and more total sperm than second ejaculates. After unilateral vasectomy, two bulls were placed on sexual rest, three on two ejaculates per week (2×), and three on eight ejaculates per week (8×) for 20 wk. Even with the 50% decrease in potential sperm output resulting from unilateral vasectomy, sperm concentration (1.07 billion/ml) and total sperm per ejaculate (4.99 billion) for the 2× bulls were essentially normal. However, at the higher frequency (8×), these semen characteristics were clearly deficient (0.63 billion/ml and 1.90 billion). Four requirements suggested for detecting deficiencies in testicular function or for estimating daily sperm production on the basis of DSO under experimental conditions are: (a) high frequency of ejaculation with intensive sexual preparation, (b) short, uniform interval between collections, (c) pre-experimental stabilization of extra-gonadal sperm reserves and rate of sperm resorption, and (d) adequate duration of the experimental period. If sexual activity is adequate, these requirements are met best by collection of two ejaculates daily, preceded by intensive sexual preparation, for an eight- to ten-day pre-experimental period followed by ejaculation at the same frequency for a 2- to 8-wk. experimental period.