Ruminal and Post-Ruminal Utilization of Starch in the Young Bovine

Abstract In the first of two experiments, ten calves, randomized into two groups, were fed a semi-purified diet containing 62% of either corn starch or lactose in the form of dry milk solids as the sole source of carbohydrate. At the end of 12 weeks, ration digestibility and blood glucose responses were determined, and the animals were switched to the opposite rations to test adaptive responses to carbohydrates. Calves in each group were then randomly assigned to five treatments to test digestibility and blood glucose responses. Treatments were 8.8 g/kg body weight of lactose or one of four amounts of starch (2.2, 4.4, 8.8, and 13.2g/kg body weight). Daily gains for the starch and lactose-fed calves averaged .12kg and .78kg for the 12 weeks. Blood sugar was two and one-half times greater during lactose ingestion than for starch. Digestibility of starch averaged 72.8% as compared to 92.5% for lactose. No adaptation to starch was evident. Blood sugar responses to different starch intakes were erratic. Starch digestion coefficients decreased linearly (P In the second experiment, 40 calves were randomly assigned to 10 rations containing five increasing per cents of straw (5 to 60%) and decreasing amounts of soluble carbohydrates (1 to 53%). Starch and cerelose were studied at ratios of 1:1 and 3:1. At 20 weeks of age, blood sugar response to test meals of starch and lactose were determined. After a readjustment period, calves were slaughtered and samples from various sites of the alimentary tract were analyzed for total carbohydrate content. Soluble carbohydrates, ratio of carbohydrates, and hour of sampling had no effect (P>.05) on blood sugar response to a ruminal bypass test meal of starch. Total carbohydrate recovery from the abomasum and fecal residue of calves receiving the different amounts of starch and cerelose increased with decreasing starch in the ration. Amylase activity determined on pancreatic tissue homogenate was not affected by dietary starch or cerelose.