Fertility of dairy heifers given a commercial diet free of β-carotene

Abstract

1. Dairy heifers given concentrates including vitamin A and wheat straw from 7 to 17 months of age had an average plasma β-carotene concentration of 20–60 μg/1. Control heifers given the same diet but supplemented with β-carotene had a β-carotene plasma concentration of 630–2190 μg/1.2. In contrast to previous findings no differences in duration of standing oestrus, length of oestrous cycle, plasma progresterone and luteinizing hormone (LH) concentrations and interval between LH peak and ovulation were observed between the groups. All the heifers conceived after one or two inseminations; conception rate being 69% for heifers given a diet free of β-carotene and 78% for the controls. 3. Average rate of growth of heifers not supplemented with β-carotene was 0.75±0.02 kg/d v. 0.81±0.02 kg/d for the controls ( P < 0.02). 4. The possible reasons for the discrepancy between present and previous findings are discussed.