Broiler performance and mineral utilization of enzyme-supplemented defatted rice bran diet during heat stress

Defatted rice bran (DRB) is a by-product from the solvent-extraction of rice bran, which contains high amounts of phytate and non-starch polysaccharides. Two experiments were conducted to evaluate broiler performance and mineral utilization of DRB diets supplemented with phytase alone or a combination of phytase and xylanase under two different environmental temperatures (thermoneutral; 23.9°C or heat stress; 23.9--35°C, diurnal). In the first experiment, six replicate groups of day-old chicks were assigned to five dietary treatments comprised of a control corn-soybean meal diet with 25% corn starch and four diets containing two levels of DRB (10 and 25%) with or without phytase (500 units/kg diet) supplementation. In experiment 2, five replicate groups of chicks were assigned to dietary treatments similar to first experiment, but using both phytase (500 units/kg diet) and xylanase (1000 units/kg diet) plus an additional practical corn-soybean meal based diet.;Using up to 25% DRB in diets was not detrimental to broilers. Birds fed 25% DRB diet had the highest weight gain, which may due to the beneficial effect of high fat level in diets. Enzymes supplementation improved feed conversion ratio of 3-week-old chicks fed 10% DRB diet. No significant differences were found in weight percentage of most parts of the carcass, as well as the duodenal and jejunal villi height and crypt depth. Tibia phosphorus, zinc and manganese content of chicks fed 10% DRB diet were improved by supplemental phytase alone, while tibia calcium, phosphorus, and manganese were improved when both enzymes were added to 25% DRB diet. Only the improvement of tibia phosphorus of 7-week-old birds was detected when phytase was added to 25% DRB diet or when both enzymes were added to 10% DRB diet. Although enzymes supplementation decreased percent phosphorus in excreta of birds fed 25% DRB diets, phosphorus retention did not improve by using phytase alone. Use of 25% DRB diet lowered feed cost per weight gain of broilers. From the growth performance and feed cost per weight gain of birds, supplemental enzyme did not alleviate the adverse effects of heat stress.