Use of the Relative Dose Response Assay to Determine the Vitamin A Status of Neonatal Calves: Effects of Season on Colostrum Quality and Immunological Parameters

Plasma vitamin A is not a reliable indicator of vitamin A status. Therefore, the feasibility of using the relative dose response (RDR) assay as a method for determining vitamin A status of calves was examined. In addition, effects of colostrum quality and season on vitamin A status and health of calves were determined. Blood was sampled from the jugular vein of 16 newborn calves to establish values over a 24 h period for immunoglobulin M (IgM) concentration, hematocrit, serum protein concentration, and leukocyte differentials. Liver biopsies were performed at birth, and successfully completed for 11 calves. Blood samples were obtained prior to feeding colostrum at 0, 12, and 24 h, with Oh being the first feeding of colostrum. Blood samples also were obtained at 5, 6, 7, 8, 17, 18, 19, 20, and 22 h after the first colostrum feeding. Blood plasma, liver, and colostrum samples were analyzed for vitamin A content using a spectrophotometric method. Based on peak vitamin A content, the RDR was calculated for 6, 8, and 20 h after the first feeding. Colostrum vitamin A was correlated with the 6 h RDR (R=.49, P \u3c .05) and 8 h RDR (R=.51, P\u3c .04). Liver vitamin A concentrations were not correlated with the RDA Assay at either time. Colostrum quality, as relates to both Ig and vitamin A concentration , is extremely important for newborn calves and may help to alleviate the effects of season