Production of monoclonal antibodies and enzyme immunoassay to bovine retinol-binding protein and determination of retinol-binding protein serum levels and retinol concentrations in serum and liver in dairy cows before and after parturition.

To study vitamin A transport in dairy cows and heifers around parturition, an enzyme immunoassay for bovine retinol binding protein (RBP) was developed and serum levels determined. Serum and liver concentrations of retinol were assayed by HPLC. Four weeks before expected calving the cows and heifers were divided into two groups each, and half of the animals received a protein supplementation during the dry period. The mean serum RBP concentration 4 weeks before calving was 42 mg l-1 for the cows and 44 mg l-1 for the heifers. The serum retinol concentrations were 0.53 mg l-1 for the cows and 0.42 mg l-1 for the heifers, and the liver retinol concentrations 0.30 mg l-1 and 0.13 mg g-1, respectively. In the groups without protein supplementation there was a significant decrease in serum RBP at sampling 1 week before parturition compared to initial values. The measurement of serum RBP may prove useful in assessment of amino acid availability in dairy cows.