Influence of dietary vitamin A content on serum and liver vitamin A concentrations and health in preruminant Holstein calves fed milk replacer.

Evidence has suggested that the current requirement for vitamin A tabulated by the NRC [(approximately 3800 IU of vitamin A/kg of dry matter (DM)] for dairy calves fed liquid diets is too low. The objective of this study was to assess the effects of vitamin A content in milk replacers on serum and liver vitamin A concentrations, growth, and development of clinical signs of vitamin A deficiency in calves. Male Holstein calves were separated from their dams at birth and given standardized feedings of colostrum and milk replacer for 3 d. On d 4, calves were assigned to five groups and fed milk replacer containing 2300, 6200, 9000, 18,300, or 44,000 IU of vitamin A/kg of DM. Liver biopsies and serum samples were taken on d 4, 9, 15, 21, and 28 to monitor vitamin A concentrations. Weekly physical and neurological examinations were performed to monitor the development of deficiency signs. Fecal scores, body temperature, and the presence of nasal and ocular discharge were recorded daily. Liver vitamin A concentrations in calves allotted to diets with 2300 and 6200 IU of vitamin A/kg decreased from d 4 to 28. Calves fed 9000 IU of vitamin A/kg maintained liver stores, while those fed 18,300 and 44,000 IU of vitamin A/kg had significant increases in hepatic vitamin A. A strong negative association existed between incidence of hyperthermic temperatures and vitamin A concentration in the diet; calves fed 2300 IU of vitamin A/kg had approximately three times more hyperthermic readings than did calves fed other treatments. A strong negative association also existed between fecal score and concentration of vitamin A in the diet; calves fed diets containing low vitamin A concentration had a higher incidence of high fecal scores (more watery) than did calves fed diets with higher vitamin A concentrations. Although slight differences were detected in serum retinol concentration, growth performance and incidence of ocular and nasal discharges were not different among treatment groups. Our data indicate that vitamin A concentrations of less than 9000 IU/kg of DM in milk replacers result in declining liver vitamin A stores in preruminant calves. Using the human Dietary Reference Intakes as a model for calculating the requirement, we recommend that the vitamin A requirement for preruminant calves should be increased to 11,000 IU of vitamin A/kg of DM.