Fertility of dairy heifers given a commercial diet free of beta-carotene.

1. Dairy heifers given concentrates including vitamin A and wheat straw from 7 to 17 months of age had an average plasma beta-carotene concentration of 20--60 micrograms/l. Control heifers given the same diet but supplemented with beta-carotene had a beta-carotene plasma concentration of 630--2190 micrograms/l. 2. In contrast to previous findings no differences in duration of standing oestrus, length of oestrous cycle, plasma progesterone 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 beta-carotene and 78% for the controls. 3. Average rate of growth of heifers not supplemented with beta-carotene was 0.75+/-0.02 kg/d v. 0.81+/-0.02 kg/d for the controls (P less than or equal to 0.02). 4. The possible reasons for the discrepancy between present and previous findings are discussed.