Effects Of Dietary Carbohydrate Balance Index On Digestible Enzyme Activities In Gastrointestinal Tract And Rumen Nutrient Degradability Of Goats

Three experiments were taken to evaluate effects of Carbohydrate Balance Index (CBI), by altering dietary corn and silage content, on digestible enzyme activities in gastrointestinal tract and rumen nutrient degradability of goats. The objective was to investigate the mechanism, influence and recommendation of CBI in adult goats. The main results are as follows:1. Four goats surgically fitted with duodenal cannulas were used in 4×4 Latin square design to measure CBI of diets containing different concentrate and forage. Results have shown that dietary CBI was 0.42, 0.83, 1.42 and 2.48, respectively.2. Four goats surgically fitted with ruminal cannulas were used in 4×4 Latin square design and randomly fed diets having CBI of 0.42, 0.83, 1.42 and 2.48 to determine the effects of CBI on enzyme activities and rumen nutrient degradability. Results have shown that ruminal fiber degradability and cellulase activity in the rumen fluid increased linearly to a point between 0.83 and 1.42 of CBI, after which further increase was not observed with increasing CBI in goats. Increasing CBI results in a quadratic increase in ruminal degradability of starch and protein.3. Four goats surgically fitted with common bile duct catheter were used in 4×4 Latin square design to determine the effects of CBI on pancreatic exocrine secretion in goats. Periods consisted of 10 d of adaptation followed by 3 d of sample collection. Juice was collected in 1-h fractions continuously for 72 h. Total juice secreted was recorded, and 3% subsamples were retained to form a composite sample. The remaining fluid was returned to the duodenum. Juice composite samples were analyzed for activities ofα-amylase, trypsin, chymotrypsin and lipase. Total secretion of juice, trypsin and chymotrypin was not affected by CBI. Increasing CBI results in a quadratic increase in pancreaticα-amylase and lipase secretion. Maximum secretion ofα-amylase and lipase is reached when CBI is 0.83 in adult goats.These results indicate that the optimal CBI is 0.83 for goats regarding enzyme activities and nutrient degradability.