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Please use this identifier to cite or link to this item: http://hdl.handle.net/10225/89

Authors: Ao, Tuoying
Keywords: exogenous enzymes
organic acids
growth performance
Date Created: 2005
Publisher: University of Kentucky
Abstract: Studies were conducted to investigate the interactive effects of exogenous enzymes and organic acids on in vitro and in vivo nutrient digestion and growth performance of broiler chicks. In Study 1, five exogenous enzyme products including β-glucanase, xylanase, amylase, α- galactosidase and protease, were assayed in triplicate at their optimum pH levels and at pH levels of 3.0, 6.0, 6.5, 7.0 and 7.5, which were used to simulate pH levels found in the gizzard, the diet, the crop, and the proximal and distal parts of small intestine, respectively. The pH gradient was obtained by dissolving the enzymes in different buffers. Results suggested that the pH levels commonly found in the avian digestive tract were either too high or too low for maximum activity of the exogenous enzymes, such as α-galactosidase and protease. In Study 2, broiler chicks were fed corn basal, barley basal or wheat basal diets with different levels or different sources of organic acids. Dietary inclusion of graded levels of organic acids linearly reduced the pH of the diet and crop content, but not the pH of the digesta sampled in the gizzard and small intestine. The inclusion of 2% organic acids (citric acid or fumaric acid) in broiler diets had either no effect or negative effects on chick growth performance. In Study 3, an in vitro model was used to simulate the chicken’s digestive process in the crop, the gizzard and the small intestine. Soybean meal and raw whole soybean were used as substrates. Graded levels of either α-galactosidase (0 to 13,792 units/kg) or protease (0 to 888 units/kg) and 0 or 2% citric acid were added to the substrates in a factorial arrangement. Reducing sugars, α-amino nitrogen and trypsin inhibitor content were measured. The data indicated that increasing levels of α-galactosidase linearly increased the release of the reducing sugars from the soybean meal. Addition of citric acid further increased the activity of α- galactosidase, resulting in more reducing sugars were released. Increasing the supplementary levels of protease linearly increased the α-amino nitrogen release from the soybean meal and raw whole soybean. Trypsin inhibitor content in the raw whole soybean was not influenced by the application of the protease. In Study 4, broilers were fed low energy or normal energy basal diets with α-galactosidase, amylase and acidification of diet and water. Growth performance, AMEn and digestibility of DM, CP and NDF were observed. Alpha-galactosidase improved the AMEn of the diets and increased the weight gain and feed intake of broiler chicks. Citric acid decreased the crop pH and enhanced the activity of α-galactosidase in the crop. Citric acid decreased the AMEn of the diets and chick growth performance. These effects were corrected by supplementing α-galactosidase. The activity of α-galactosidase was enhanced by simultaneously using organic acid. The negative effects on chick growth performance by dietary inclusion of organic acids were corrected by simultaneously using α-galactosidase.
URI: http://hdl.handle.net/10225/89
Appears in Collections:Electronic Theses and Dissertations

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