Modified poultry diets : an approach to sustainable animal production

Environmental pollution from nitrogen (N) and phosphorus (P) in poultry wastes is becoming a serious problem in many areas of the world. Two broiler (each with 2400 birds) and one layer experiment (with 1350 birds) were conducted in which the crude protein (CP) content of practical diets was reduced by 3-4 percentage units in an attempt to reduce N excretion. The diets consisted of regular ingredients and the supplementary amino acids (AA) lysine, methionine, threonine and tryptophan, which were assessed to be the limiting A A . The results of Broiler Expt. 1 indicated that growth over the 3-6 week period was unaffected by reduction in the CP level of the diet from about 21 % to 18% and resulted in a more than 20% reduction in daily N output. In Broiler Expt.2 there were no significant differences in growth performance due to dietary CP level when limiting A A levels were maintained at 90, 100 or 110% of industry norms. Reduction in dietary CP content resulted in a 10 27% reduction in the total amount of N excreted. With layers, reduction in the dietary CP level had no significant effect on egg production or egg quality and resulted in a 30 35% reduction in daily N output. It was concluded that it is necessary to have accurate information on the amino acid composition of the dietary constituents and supplements such that the deficient A A can be added correctly. Successful reduction in dietary CP content is likely to have marked beneficial effects in terms of reducing the N output in waste from poultry operations. The effects of calcium and P levels on the potential of supplemental phytase to reduce P excretion by layers and broiler was studied (in two studies). The results indicated that it is possible to reduce the recommended total P (NRC 1994) content of layer diets by 10%, even without phytase supplementation, with no loss in performance. Daily P output of layers receiving the diet with reduced calcium and P and supplemented with phytase was 34.9% lower than in the iii controls. Results with broilers indicated that even without phytase supplementation, the level of dicalcium phosphate in the diet could be reduced to 75 % of the control level without a loss in performance. A further reduction in total P from 0.72% to 0.56% was possible with phytase supplementation at 50% of the recommended dosage. Broilers on such a diet excreted one third less P than those on the control diet. One broiler experiment and one layer experiment were conducted to evaluate the combined effect of enzyme supplementation and reduced CP diets on N and P excretion. The results indicated that reduced crude protein content diets supplemented with A A and phytase reduced N and P excretion of broilers and layers without a loss in performance. Broilers receiving the reduced protein diet (+ AA) supplemented with both phytase and pentosanase had the lowest daily output of N and P. However, broilers receiving this diet had the lowest final body weights and highest feed conversion ratios, although the differences were not statistically significant. Intestinal viscosity of the layers receiving the reduced CP diets was significantly decreased by supplementation with phytase and/or [3-glucanase. One broiler experiment was conducted to investigate 25hydroxy D 3 (Hy.D®) as a potential enhancer of natural phytase activity in the small intestine. The results indicated that the 25hydroxy D 3 (Hy.D®) significantly increased phytase activity in the duodenal tissues and contents and enhanced P utilization.