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The effects of varying dietary energy and protein (E:P) ratios on the development of the gastrointestinal tract and biological performance of broiler chickens (10-24d) were evaluated. Changes in dietary protein level significantly (P<0.001) influenced feed intake, body weight gain and feed conversion efficiency, this being most profound at dietary energy levels of 11, 12 and 13 MJ/kg. Body eight was reduced (P<0.001) as dietary E:P ratios decreased at constant dietary energy level. The weights of some visceral organs were also affected by dietary treatment. These included a reduction (P<0.05) in the weight of the proventriculus/gizzard with an increase in dietary protein and energy contents. At a dietary energy level of 12 MJ/kg, the weight of the pancreas rose (P<0.001) with an increase in dietary protein content. The jejunal protein content was affected (P<0.01) by dietary protein level and interactions between dietary energy and protein. Mucosal protein was lowest at the highest dietary E:P ratios within the 11, 12 and 13 ME series. Maltase activity in the jejunum was influenced (P<0.05) by dietary energy, being lowest (P<0.05) in chicks that were fed diets containing 14 MJ ME/kg. An increase in dietary E:P ratio resulted in an increase in the activity of sucrase (P<0.001) and AP (P<0.05) for birds fed diets in the 11, 12 and 13 ME series. Overall, our findings suggest that the differences in biological performance of chicks fed diets varying in energy and protein contents may be traceable to a lack of energy for metabolic function. The higher the amount of mucosal protein the greater may be the bird's digestive function and absorptive capacity. Some of the effects of varying dietary E:P ratio also appear to be linked to changes in intestinal digestive function. |
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