Abstract
The objectives of this study were to determine the effect of feeding various amounts of dietary vitamin A (0 or 110 IU/kg BW), protein (10% or 12%), and an ionophore (monensin at 0 or 400 mg/d per head) on performance measures, retinoid metabolism, immune function, and metabolic response. Multiparous cows (n = 80) were studied from day -35 to +21 post-parturition. Milk samples were obtained and processed for components, somatic cell count (SCC), retinol, α-tocopherol, and β-carotene. Serum samples were collected and processed for NEFA, BHBA, haptoglobin, and Thiobarbituric acid reactive species (TBARS) and retinol binding protein. Neutrophils, peripheral blood mononuclear cells (PBMC), hepatic, and adipose tissue were used to measure gene expression of selected products related to inflammation and energy metabolism. Overall, these observations show that dietary vitamin A, monensin and protein affect retinoid metabolism and have an effect on immune status without compromising performance measures.