Phytate utilization and phosphorus excretion by broiler chickens fed diets containing cereal grains varying in phytate and phytase content

Authors: Leytem, April; WILLING, B - UNIV. OF SASKATCHEWAN; THACKER, P - UNIV. OF SASKATCHEWAN

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2007
Publication Date: 9/15/2008
Citation: Leytem, A.B., Willing, B.P., Thacker, P.A. 2008. Phytate utilization and phosphorus excretion by broiler chickens fed diets containing cereal grains varying in phytate and phytase content. Animal Feed Science and Technology. 146:160-168.

Interpretive Summary: Poor digestibility of phytate phosphorous by poultry leads to supplementation of poultry diets with inorganic phosphorus thereby increasing feed costs and also increasing the excretion of phosphorus by the birds which is an environmental concern. We investigated the ability of broiler chickens to utilize phytate in diets containing cereal grains with varying levels of phytate and intrinsic phytase and determined the amount and forms of phosphorus excreted by the birds. The diets were comprised of 97% corn, high fat-low lignin oat, normal barley or low phytate barley with the cereal grain supplying the sole source of dietary phosphorus. The diets were fed for a seven day acclimation period followed by a two day faecal collection while ileal digesta was collected at slaughter on day 21. The partial and total tract digestibilities were determined for dry matter, phosphorus, and phytate using chromic oxide as the indigestible marker. Ileal digesta and faecal phosphorus was characterized using solution state phosphorus nuclear magnetic resonance spectroscopy (31 P-NMR). The partial tract digestibilities for phosphorus and phytate ranged from 79% (normal barley) to 86% (corn and low phytate barley) and 71% (low phytate barley) to 86% (high fat-low lignin oat), respectively. Total tract digestibility coefficients (i.e. overall retention) for phosphorus and phytate ranged from 25% (corn) to 35% (low-phytate barley) and 90% (corn and low-phytate barley) to 96% (high fat-low lignin oat), respectively. There was very little phytate phosphorus excreted in the faeces regardless of the type of cereal grain fed (< 13% of total phosphorus), and phytate degradation was not related to the level of intrinsic phytase in the diet. In summary, our results indicate that regardless of the type of cereal grain fed, the dietary phytate is highly digestible when large amounts of Ca and P are not added into poultry diets and little phytate is excreted in the faeces.

Technical Abstract: Poor digestibility of phytate P by poultry leads to supplementation of poultry diets with inorganic P thereby increasing feed costs and also increasing the excretion of P by the birds. In order to quantify phytate utilization and P excretion by poultry, eighty, 12 day-old, male broiler chicks, weighing an average of 1578 plus or minus 161 g, were fed one of four diets to determine the effects of feeding diets containing cereal grains varying in phytate and phytase content on ileal and faecal P digestibility and composition. The diets contained approximately 970.7 g/kg corn, high fat-low lignin oat, normal barley or low phytate barley with the cereal grain supplying the sole source of dietary phosphorus. The diets were fed for a seven day acclimation period followed by a two day faecal collection while ileal digesta was collected at slaughter on day 21. Apparent ileal and total tract digestibility coefficients were determined for dry matter, phosphorus, and phytate using chromic oxide as the indigestible marker. Ileal digesta and faecal phosphorus was characterized using solution state phosphorus nuclear magnetic resonance spectroscopy (31 P-NMR). Apparent ileal digestibility coefficients for phosphorus and phytate ranged from 0.79 (normal barley) to 0.86 (corn and low phytate barley) and 0.71 (low phytate barley) to 0.86 (high fat-low lignin oat), respectively. Total tract digestibility coefficients (i.e. overall retention) for phosphorus and phytate ranged from 0.25 (corn) to 0.35 (low-phytate barley) and 0.90 (corn and low-phytate barley) to 0.96 (high fat-low lignin oat), respectively. There was very little phytate phosphorus excreted in the faeces regardless of the type of cereal grain fed (< 13% of total phosphorus), and phytate degradation was not related to the level of intrinsic phytase in the diet. In summary, our results indicate that regardless of the type of cereal grain fed, the dietary phytate is highly digestible when large amounts of Ca and P are not added into poultry diets and little phytate is excreted in the faeces.