Effect of Energy Intake on Reproductive Performance of Dairy Bulls. I. Growth, Reproductive Organs, and Puberty

Abstract

Two groups of Holstein bulls were fed from 8 wk to 46 months of age on 80 (underfed) or 100% (control) of the total digestible nutrient (TDN) intake recommended in Morrison's feeding standards. From 46 to 58 months of age the feeding regimen of the two groups was reversed. Underfeeding greatly impaired body, endocrine gland, and reproductive tract growth, especially during the early period of rapid growth. Puberty was delayed in the underfed group. Body weight and testis size in the underfed bulls closely followed the percentage difference in TDN intake until the rations were switched. Following the change in rations, the bulls originally underfed gained in body weight to near normal, but no appreciable recovery occurred in bone, endocrine, or testis growth. Reducing the rations of the normal-fed bulls to 60% of the recom- mended TDN intake caused slight reductions in body weight, but little or no change was observed in the other characteristics measured. The development of the bull from calfhood to serviceable age and size is highly dependent on the ration fed. In the past few years the effect of nutrient intake, especially total di- gestible nutrients (TDN), on reproductive per- formance of bulls has been under rather in- tensive investigation (1, 3-11, 13, 15, 16, 18). In general, these investigations have indicated the retardation of growth and the delay in reaching puberty that accompa.nies underfeed- ing and the stimulation of these by above- normal energy intake. These reports have also indicated that underfeeding results in little or no effect on fertility, tIowever, little emphasis has been put on investigating the effect of nutrient intake on the total reproductive ca- pacity of bulls. Also, the longer-term effects of underfeeding during early life on subsequent reproductive performance has been investigated only with underfeeding during the first two years of life, and rather complete recovery occurred after the restoration of full feeding (7). In several of the previously reported in- vestigations infrequent tests of semen-produc- ing ability were made. The investigations reported here were under- taken to determine the effects of two levels of energy intake on the growth and development of bulls from early life to near maturity (46 l~eceived for publication November 11, 1963.