Effects of lactose content in milk replacer on apparent digestibility, growth, liver messenger RNA expression, and blood parameters related to metabolism of dairy calves.

Even with the same energy supply, differences in energy sources may affect calf growth and metabolism. In this study, we evaluated the effects of feeding 3 different milk replacers (MR) with different lactose supplies under isoenergetic conditions on calf digestibility, growth, and metabolism-related markers. Fifteen Holstein bull calves were randomly assigned to one of 3 MR feeding treatments: low lactose (L: 38%), medium lactose (M: 41%), or high lactose (H: 46%). After birth, calves were provided colostrum, and treatment MR were fed from 1 d of age and gradually increased to a maximum feeding rate at 20 d of age (L: 1.16 kg/d, M: 1.21 kg/d, H: 1.26 kg/d DM) without feeding solid feeds during the experimental period. Blood samples were temporarily collected weekly to assess blood concentrations of metabolites and hormones. From 30 to 36 d of age, the calves were euthanized and liver samples were collected to determine growth-related mRNA expression. The L calves showed a greater body length than H calves and the highest growth hormone receptor (GHR) mRNA expression. Plasma concentrations of total cholesterol, urea nitrogen, total protein, albumin, insulin, and IGF-1 were not different, but plasma concentrations of triglycerides were greater in order H, M, and L. These results showed that the difference in lactose content in the MR affected calf metabolism, and the L-MR was suggested to be more likely to enhance growth into the peripheral tissues.