Incorporation of tributyrin and tricaproin into milk replacer on intake, growth, and health of Holstein calves

Fat composition of milk replacers (MR) for calves differs from milk fat leading to low levels of butyric and caproic acids in MR. This study investigated how the incorporation of tributyrin (TB4) and tricaproin (TC6) in MR affects feed intake, growth, and health of newborn calves (Experiment 1) and 18-d-old calves (Experiment 2). In Experiment 1, 24 male calves (0.90 ± 0.35 d; 42.8 ± 4.43 kg BW; mean ± SD) were blocked by arrival sequence. Within each block, calves were randomly assigned to treatments consisting of a mixture of a control MR (CON) and an experimental MR containing TB4 and TC6 (TRI) at different mixing percentages being TRI0 (0 % TRI MR), TRI33, TRI67, and TRI100. The TRI100 MR contained 3.36 % C4:0 and 2.49 % C6:0 (as % total FA). All MR contained 237 g/kg of CP, 258 g/kg of fat, and 375 g/kg of lactose (DM basis). Calves were housed individually for 21 d. The daily MR allowance was 7.0 L/d (15 % solids) fed in 2 meals. Water and chopped straw were available ad libitum. Daily measurements included MR intake, fecal consistency scoring, and scoring of the need for drinking assistance. In Experiment 2, 60 calves (18.4 ± 2.4 d; 47.5 ± 1.46 kg) were blocked by BW at arrival and randomly assigned to treatments within a block, including 1) a control MR (CON) that did not include TB4 and TC6, 2) an MR containing TB4 with 3.36 % C4:0 of total FA, 3) an MR containing TC6 with 2.49 % C6:0, and 4) an MR with both TB4 and TC6 called TBTC with 2.41 % C4:0 and 2.10 % C6:0. All MR contained 292 g/kg of fat, 243 g/kg of CP, and 339 g/kg of lactose. Calves were individually housed for 28 d and then grouped in pairs or trios afterwards. The daily MR allowance was 7.0 L/d (13.5 % of solids) fed in 2 meals. Weaning was initiated on d 36 after arrival by feeding 4.0 L from d 36–49, and calves were completely weaned at d 50 and monitored until d 63. Calves had ad libitum access to starter feed, chopped wheat straw (3–7 cm), and water. Body weight was measured weekly. Daily measurements included feed intakes and fecal consistency (until d 28). In Experiment 1, the inclusion of TB4 and TC6 did not affect growth and MR refusals. Calves fed TRI0 and TRI33 tended to have higher abnormal fecal scores in wk 2 and 3 compared with other groups. In addition, higher TB4 and TC6 inclusion levels in MR reduced the need for drinking assistance in week 2. In Experiment 2, MR refusals were higher in calves fed TC6 and TBTC than in other treatments between wk 1 and 3 after arrival. Calves fed CON had a higher percentage of days with loose feces. In conclusion, higher levels of TB4 and TC6 reduced the need for drinking assistance in newborn calves, but TC6 inclusion increased MR refusals in older calves. Supplementing MR with TB4, TC6, or their combination improved the fecal consistency.