Effect of oral supplements of vitamin A on the plasma retinol levels in calves and their immunological unresponsiveness

Forty carves were used to evaluate the immune response effects induced by a wide range of dietary vitamin A intake levels. The immune response was not affected by the tested doses of vitamin A administered orally during a 56 day period. There was no change in plasma immunoglobulin concentrations and no difference in specific antibody titres following injection of keyhole limpet haemocyanin (KLH) at 10, 20 and 40 days of age. Some small and temporary variations were recorded in the plasma vitamin A concentration following daily oral administration of various doses up to 10 000 IU. Only oral supplementation of 20 000 IU of vitamin A daily over 50 days significantly increased the plasma level of vitamin A.