Inclusion of a spray-dried fat concentrate containing tributyrin and tricaproin in milk replacer increased feed intake and growth and elicited metabolic and endocrine responses in calves fed ad libitum

The fat composition of milk replacer (MR) for calves differs from that of bovine milk fat, resulting in lower levels of butyric (C4:0) and caproic acid (C6:0). These fatty acids play a critical role in the gastrointestinal and metabolic development of calves by supporting rumen epithelial growth, enhancing energy metabolism, and promoting overall gut health. The objective of this study was to evaluate the effects of inclusion of a spray-dried fat concentrate containing tributyrin (TB) and tricaproin (TC) in a high-fat MR on the growth, feed intake, and metabolic profile of calves fed ad libitum. Forty-eight newborn Holstein calves were blocked based on arrival sequence. Within each block of 2 calves, calves were randomly assigned to a control MR (CON, n = 24) including vegetable fats from palm, coconut, and linseed or to an experimental MR including the same fat blend with the addition of TB and TC (TRI, n = 24) to the same levels found in bovine milk fat. Both MR contained 23.7% CP, 27.7% fat, and 35.6% lactose (DM basis) and were fed at 13.5% solids. Calves were group housed and fed MR ad libitum with automated feeders. Weaning was gradual and induced between d 43 and 70, after which calves were only fed solid feed until d 84. Starter feed, chopped straw, and water were offered ad libitum throughout the whole study period. Calves were weighed and blood was collected once weekly at 1300 h. Calves fed TRI showed a 73% reduction in therapeutic intervention days compared with calves fed CON. In addition, calves fed TRI consumed significantly more MR and starter feed, resulting in greater growth. Serum nonesterified fatty acid and plasma total cholesterol levels were lower, whereas the enzymatic activity of serum alkaline phosphatase was higher in calves fed TRI. In addition, calves fed TRI had lower serum ghrelin and higher IGF-I concentrations. Incorporating TB and TC is a suitable strategy to increase solid feed intake upon weaning, resulting in better growth performance in ad libitum systems, and to improve the health of dairy rearing calves.