ARS | Publication request: Interaction of calcium and phytate in broiler diets: 1. Effects on apparent prececal digestibility and retention of phosphorus

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 23, 2007
Publication Date: March 1, 2008
Citation: Plumstead, P.W., Leytem, A.B., Spears, J.W., Maguire, R.O., Kwanyuen, P., Brake, J. 2008. Interaction of calcium and phytate in broiler diets: 1. Effects on apparent prececal digestibility and retention of phosphorus. Poultry Science. 87:449-458.

Interpretive Summary: Phosphorus utilization in feeds formulated with soybean meal (SBM) is dependent on both the level of phytate and calcium (Ca) in diets. It is not well known how changes in phytate content of SBM, for example low-phytate SBM, affect the absorption of Ca in broilers. Furthermore, the optimum dietary Ca:non-phytate P (NPP) ratio to maximize P retention in broilers fed diets with varying levels of phytate is not known. To determine how the phytate content of feeds affects Ca and P absorption in broilers, we fed broilers 12 diets with varying levels of Ca (from 0.47% to 1.16%) and phytate (from 0.10% to 0.30%) from 15 to 20d. Ileal digesta and manure were collected at the end of the 20 d feeding period and samples were analyzed for Ca, P, and phytate concentrations. Both partial tract and total tract digestibility coefficients were calculated for Ca, P and phytate. Partial tract P digestibility was greater in diets having lower both Ca concentrations and low-phytate SBM. The total amount of P in manures was reduced by between 42% and 62% when broilers were fed a low-phytate SBM diet. The Ca:NPP ratio that maximized P retention was dependent on the phytate concentration of the diets and was 2.53, 2.40, and 2.3 for the high-phytate, commercial and low-phytate diets respectively. Dietary Ca reduced the extent of phytate hydrolysis but the optimum Ca:NPP ratio where P retention was the greatest was not greatly affected by the phytate concentration of the diets.

Technical Abstract: Phytate phosphorus (P) utilization from soybean meal (SBM) included in broiler diets has been shown to be poor and highly dependent on dietary calcium (Ca) intake. Although low phytate varieties of SBM have been developed, it is not well known how reduced dietary phytate concentrations affect Ca absorption and the ratio of Ca:non phytate P (NPP) required for optimal P retention in broilers. To address this fed broilers diets with four levels of dietary Ca (from 0.47% to 1.16%) and three levels of phytate P (0.27%, 0.23%, and 0.10%) that were obtained by producing SBM from three varieties of soybeans with different phytic acid concentrations. Broiler chicks were fed one of the 12 diets from 15 to 20 d. Excreta was collected from 14-15d and from 18-19 d of age and ileal digesta was collected at 20 d of age. Samples of feed, excreta and ileal digesta were analyzed for Ca, P, and phytate concentrations and apparent ileal digestibility coefficients and retention of Ca and P and excretion of Ca, P, and phytate P calculated. Apparent prececal P digestibility decreased when dietary Ca concentration increased and was higher when diets contained low phytate SBM. The apparent absorption of Ca and percentage phytate P hydrolysis at the distal ileum was not reduced when dietary phytate concentration increased. Including low phytate SBM in diets reduced P in the excreta between 42% and 62% compared to a conventional or high phytate SBM, respectively. The optimum ratio of Ca:NPP that resulted in the highest P retention and lowest P excretion was 2.53:1, 2.40:1, and 2.34:1 for diets with 0.27%, 0.23%, and 0.10% phytate P. This suggested that while increased dietary Ca reduced the extent of phytate hydrolysis, the optimum Ca:NPP ratio at which P retention was maximized was not greatly altered when diets contained low phytate SBM.