Effect of nutrition on the onset of male sex hormone activity and sperm formation in monozygous bull-calves

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Abstract
The effect of a reduced food intake on the onset of androgenic activity and the appearance of spermatozoa was studied in maturing bull-calves. Three pairs of identical twin-calves were used. In each instance, one twin was reared on a ‘high plane’ of nutrition, consisting of normal feeding, and the other on a ‘low plane’ of reduced food intake. Semen was collected from the twin-calves by the electric stimulation method, and analyzed for sperm density, fructose and citric acid. The appearance of fructose and citric acid in semen was taken as an indicator of the onset of secretory function in the seminal vesicles, which depends on the presence of the male sex hormone. Fructose and citric acid appeared in electrically-discharged semen from the normally fed bull-calves several months before the first spermatozoa. This suggested that the male sex hormone began to act in the young animal several months before the appearance of the first spermatozoa. Restriction of food intake had a marked delaying influence on the onset of fructose and citric acid secretion, and a smaller delaying effect on the appearance of spermatozoa. The delaying effect of underfeeding on the secretory function of the bull seminal vesicles as reflected in the diminished output of fructose and citric acid, appeared to be the result of an inadequate stimulation of the gonads by the gonadotrophic hormone. Injections of gonadotrophin were found to elicit a prompt appearance of both fructose and citric acid in the semen. Alterations in the composition of semen caused by underfeeding were shown to run parallel to histological changes in the testes and male accessory organs. Low-plane feeding retarded the differentiation of the seminiferous tubules and of the interstitial tissue in the male gonads. The histological changes in the seminal vesicles induced by underfeeding corresponded closely to the diminished secretory output of fructose and citric acid in these glands.