Influence of Low Protein Rations on Growth and Semen Characteristics of Young Beef Bulls

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Abstract
Two experiments were conducted to study the effect of low protein rations on the growth and reproductive physiology of young beef bulls. Ten bulls were used in experiment I and 12 bulls in experiment II. The experimental periods were 365 days for experiment I and 182 days for experiment II. The low protein rations severely reduced feed intake and produced marked body weight losses in both studies. The protein-deficient bulls produced significantly smaller volumes of semen. The total number of sperm per ejaculate was significantly less for the protein-deficient bulls by the end of the experimental period in both studies. The percent of motile sperm was varied and not significantly affected by the treatments in either experiment. Semen depletion studies indicated that the total volume of semen produced in four collections on each of the two days was significantly less for the protein-deficient bulls in experiment I, but not in exjeriment II. The protein-deficient bulls in experiment II, however, produced significantly fewer sperm cells than did the control bulls in the depletion study. This difference was not apparent in experiment I. At the termination of the experiments or shortly before the time of death, motile sperm cells were collected from all of the protein-deficient bulls except one in each experiment. Four of the eight bulls on the low protein ration in experiment II either died or were slaughtered shortly before death appeared imminent. Average survival time for them was 151 days. Libido was adversely affected by the protein deficiency. The protein-deficient bulls became weak and failed to mate an estrogenized heifer during the latter part of the experiments. Some of the deficient bulls would not attempt to mount. Copyright © 1963. American Society of Animal Science . Copyright 1963 by American Society of Animal Science

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