Effect of dietary carotene on fertility of high-yielding dairy cows

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Abstract
Multiparous dairy cows were allotted at the beginning of the dry period to two groups, each of about 75 cows. In addition to a basal diet containing a very low concentration of carotene and a normal concentration of retinyl ester, the carotene group was given a daily supplement of 500 mg carotene during the dry period and 750 mg carotene during lactation, and the retinol group was given an equivalent amount of retinyl ester. Plasma carotene concentrations were much higher in the carotene group (ca. 4·2 mg/1v. ca.. 0·35 mg/1), but plasma retinol did not differ. Neither peripheral plasma progesterone concentration nor the interval between calving and first insemination were affected by carotene supplementation. Conception rate was greatly improved by carotene supplementation in the younger cows (second and third lactation) during the first part of the experiment (cows calving in September to December): conception rates at first insemination were 0·70v.0·33 (P < 0·05); for all inseminations, conception rates were 0·71v.0·38 (P < 0·01). However during the second part of the experiment (cows calving in January to April) no significant differences were found between the two groups.Plasma tocopherol concentration in cows given carotene was significantly higher during the dry period and the 1st weeks of lactation, but these differences disappeared in the later stages of lactation. Plasma cholesterol concentration in the carotene group was highly correlated with plasma carotene concentration (r = 0·52 to 0·59,P< 0·001); however even higher correlation coefficients were found between plasma cholesterol and plasma tocopherol in both the carotene and the retinol groups (r = 0·61 to 0·80,P< 0·001). Plasma concentrations of triglycerides, glucose, urea and aspartate aminotransferase were not affected by the treatment.A high plasma carotene concentration is not a prerequisite for conception; however, under certain conditions which need defining, the carotene concentration appears to be a limiting factor.