Colostrum insulin supplementation to neonatal Holstein bulls affects small intestinal histomorphology, mRNA expression, and enzymatic activity with minor influences on peripheral metabolism

The objectives of this study were to evaluate how varying colostral insulin concentrations influenced small intestinal development and peripheral metabolism in neonatal Holstein bulls. Insulin was supplemented to approximately 5x (70.0 & mu;g/L; n = 16) or 10x (149.7 & mu;g/L; n = 16) the basal colostrum insulin (12.9 & mu;g/L; BI, n = 16) concentration to maintain equivalent mac-ronutrient intake (crude fat: 4.1 & PLUSMN; 0.06%; crude pro-tein: 11.7 & PLUSMN; 0.05%; and lactose: 1.9 & PLUSMN; 0.01%) among treatments. Colostrum was fed at 2, 14, and 26 h post-natal and blood metabolites and insulin concentration were measured at 0, 30, 60, 90, 120, 180, 240, 360, 480, and 600 min postprandial respective to the first and second colostrum meal. At 30 h postnatal, a subset of calves (n = 8/treatment) were killed to excise the gas-trointestinal and visceral tissues. Gastrointestinal and visceral gross morphology and dry matter and small intestinal histomorphology, gene expression, and carbo-hydrase activity were assessed. Insulin supplementation tended to linearly reduce the glucose clearance rate following the first meal, whereas after the second meal, supplementation linearly increased the rate of glucose absorption and nonesterified fatty acid clearance rate, decreased the time to maximum glucose concentrations, and decreased the time to reach minimum nonesterified fatty acid concentrations. Additionally, insulin clear-ance rate was linearly increased by insulin supplemen-tation following the second colostrum feeding. However, there were no overall differences between treatments in the concentrations of glucose, nonesterified fatty acids, or insulin in plasma or serum. With respect to macroscopic intestinal development, dry rumen tissue mass linearly decreased when insulin was supplemented in colostrum, and supplementation linearly increased duodenal dry tissue density (g dry matter/cm) while tending to increase duodenal dry tissue weight. Increas-ing the colostrum insulin concentration improved small intestinal histomorphological development in the distal small intestine, as ileal villi height and mucosal-serosal surface area index were increased by supplementing insulin. Lactase enzymatic activity linearly increased in the proximal jejunum while ileal isomaltase activ-ity linearly decreased with insulin supplementation. These data indicate that changes in colostrum insulin concentrations rapidly affect gastrointestinal growth prioritization and carbohydrase activity. The changes in gastrointestinal ontology result in minor changes in postprandial metabolite availability and clearance.

Automated summary

The study aimed to examine the effect of varying colostral insulin concentrations on small intestinal development and metabolism in neonatal Holstein bulls. Insulin supplementation at different levels was used to maintain equivalent macronutrient intake among treatments. Blood metabolites and insulin concentration were measured at different time points after colostrum feeding. Insulin supplementation affected glucose clearance rate, glucose absorption rate, and nonesterified fatty acid clearance rate. It also had an impact on small intestinal histomorphological development, carbohydrase activity, and gastrointestinal tissue mass. Overall, changes in colostrum insulin concentrations rapidly influenced gastrointestinal growth and carbohydrase activity, resulting in minor changes in postprandial metabolite availability and clearance.