Physiological Effects of Feeding High vs Low Levels of Milk Replacer and Starch to Holstein Dairy Calves During the Weaning Transition

Abstract

Current calf nutrition programs revolve around two central themes: liquid feed, to provide early nutritional needs for the calf, and calf starter, to provide the stimuli for rumen development to prepare the calf for weaning. It is currently unclear how milk provision and calf starter starch content affect gastrointestinal physiology and development in the young calf. The aim of this study was to assess how milk provision and dietary starch concentration impact the morphological and physiological development of the gastrointestinal tract. Forty-eight male Holstein calves were blocked by body weight and assigned to one of four treatments with a 2 x 2 factorial arrangement of milk replacer and calf starter starch content: low milk replacer (600 g/d; 4L) and low starch (12% starch, DM; LL), low MR and high starch (35.6% starch, DM; LH), high MR (1,200 g/d; 8L) and low starch (HL), and high MR and high starch (HH). Calves were weaned starting on day 42 and ending on day 49, and calves were harvested one week later. Gut permeability was measured on days 28 and 56. Gastrointestinal tissue samples were analyzed for tissue histology, gene expression of metabolic enzymes and nutrient transporter protein abundance. High milk diets resulted in increased intestinal permeability and jejunal sodium-glucose cotransporter 1 abundance. High starch diets resulted in increased monocarboxylate transporter 1 and tended to result in increased anion exchanger 1 abundance as well as decreased papillae sloughing in the rumen. In the lower gut, higher starch diets resulted in increased jejunum villous blunting, and ileal epithelial separation. Higher milk provision likely increased glucose absorption in the jejunum. Increased starch conferred a protective effect on the rumen through increased SCFA absorption capacity and decreased sloughing, but low rumen pH may negatively impact the lower gut.