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

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Abstract
Two groups of Holstein bulls were fed from 8 weeks to 46 months of age on 60 (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 2 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 recommended TDN intake caused slight reductions in body weight, but little or no change was observed in the other characteristics measured.