Effects of amount of lactose in milk replacer on gastrointestinal function of dairy calves

Abstract

The objective of this study was to evaluate the effects of feeding milk replacer (MR) at different lactose amount while keeping osmolality constant on gastrointestinal function, blood parameters, and inflammation-related mRNA expression in the livers of dairy calves. Fifteen Holstein bull calves were assigned to one of three dietary treatments differing in MR lactose content (L: 38 %, M: 41 %, and H: 46 %). Feeding of the test diets was started at 1 day of age and gradually increased to a maximum feeding rate at 20 days of age (L: 1.16 kg/d, M: 1.21 kg/d, and H: 1.26 kg/d DM). Under these conditions, the lactose dosages for the treatments were 441 g/d, 496 g/d, and 580 g/d, respectively. The MR were prepared to ensure isocaloric and iso-osmotic (451 mOsm/kg) conditions. Fecal scores were recorded daily, and at 14 and 28 days of age, blood and breath samples were collected before and after MR feeding. In addition, feces and urine were collected for 2 consecutive days. Then, the calves were slaughtered to evaluate intestinal permeability and liver mRNA expression. The permeability in the duodenum and ileum was lower in H and M than in L; the permeability in the jejunum was also lower in H than in L. The hepatic mRNA expressions of toll-like receptor-2, IL-1β, and tumor-necrosis factor-α were lower in H and M than L. Nitrogen retention was higher in H than in L, and linear and quadratic increasing trends were observed in tissue ratio of gastrointestinal tract with the increase in lactose amount. Postprandial increase in plasma glucose concentration was smaller and postprandial increase in TG concentration was higher in H than in L. Fecal properties, digestibility, and breath hydrogen concentrations were not affected by treatment. These results indicate that feeding high-lactose MR may increase gastrointestinal weight and decrease permeability in the small intestine of calves.