Effects of Vitamin A Supplementation on Plasma Retinol Concentrations, Fertility and Milk Yield of Dairy Cows

Abstract

Effects of vitamin A supplementation during the dry period and early lactation on vitamin A status, milk yield and reproductive performance of dairy cows were studied. Eleven primiparous and 10 multiparous Holstein Friesian cows were assigned into one of three groups: 1) control; 2)700, 000IU of vitamin A supplemented in diet at weekly intervals from 30 days before expected calving ; 3) 700, 000IU of vitamin A supplemented in diet at weekly intervals from 60 days before expected calving. The supplementation was done by mixing with concentrate weekly and lasted for 45 days after calving. Vitamin A supplementation slightly increased the plasma retinol concentrations of cows 1 day after calving. The supplementation had no significant effect on days to first service, days open and services per conception of cows. The supplementation 60 days before the expected calving significantly decreased milk yield 5 and 15 days after calving. The plasma retinol concentrations of multiparous cows were significantly lower than those of primiparous cows 45 and 90 days after calving. The plasma retinol concentrations of cows 90 days after calving were negatively correlated with milk yield of the same length period after calving. 700, 000IU of vitamin A supplemented in diet at weekly intervals from 60 days before calving might have an adverse effect on the milk yield at the beginning of lactation. The lower plasma retinol concentrations of multiparous cows at the peak of lactation were due to large transfer of vitamin A into milk.