Adverse effect of beta-carotene in diet on fertility of dairy cows.

A total of 155 high yielding dairy cows were used to study the effect of dietary beta-carotene (carotene) on fertility. The diet of group 1 was supplemented with 69 mg retinyl acetate per cow daily before calving and 96 mg retinyl acetate after calving: diet of group 2 was supplemented with 500 mg carotene per cow before calving and 96 mg retinyl acetate after calving; and that of group 3 with 500 mg carotene before and 700 mg after calving. Conception rates were 53.9, 42.2, and 27.9% for cows of groups 1, 2, and 3. Days open were 110 and 112 for young (second and third lactation) and old (fourth and later lactations) cows of the group 1; 130 and 129 for young and old cows of group 2; and 133 and 166 for young and old cows of group 3. Number of inseminations per conception was 1.8 and 1.8, 2.2 and 2.2, and 2.5 and 3.4 for the same groups, respectively. Within group 3 the percent of cows pregnant 120 d after calving was 57 and 20 for the young and old cows. Correlation coefficients between plasma carotene of 53 old cows of all groups 4 and 8 wk after calving, and the number of open days and the number of inseminations per conception were significant. The intake of high carotene may have adverse effects on the fertility of dairy cows.