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

Open Access
Publisher Website
Google Scholar
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 di- gestibility 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 t3.2 g/kg body weight). Daily gains for the starch and lactose- fed calves averaged .12 kg and .78 kg 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 dif- ferent starch intakes were erratic. Starch digestion coefficients decreased linearly (P ~ .01) with increasing intake. Actual starch digested increased with starch intake. In the second experiment, 40 calves were randomly assigned to 10 rations contain- ing five increasing per cents of straw (5 to 60%) and decreasing amounts of soluble carbohydrates (1 to 53%). Starch and eerelose 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 sam-