ARS | Publication request: Interaction of calcium and phytate in broiler diets: 2. Effects on total and soluble phosphorus excretion

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 28, 2007
Publication Date: March 1, 2008
Citation: Leytem, A.B., Plumstead, P.W., Maguire, R.O., Kwanyuen, P., Brake, J. 2008. Interaction of calcium and phytate in broiler diets: 2. Effects on total and soluble phosphorus excretion. Poultry Science. 87:459-467.

Interpretive Summary: There are several factors that can alter the solubility of phosphorus (P) in broiler manure, two of which are dietary phytate concentrations and calcium (Ca) additions. To examine the impact of altering dietary phytate concentrations and Ca additions on P excretion, we fed 12 diets with varying levels of phytate P (0.07 to 0.30%) and Ca (0.47 to 1.16%) to broilers from 16 to 20 days of age. Fresh manure was collected at two separate times, once when diets were first introduced and a second collection after birds had been adapted to the diets for three days, manure was collected for 24 hours at each sampling time. Manure samples were analyzed for total P, water soluble P (WSP) and phytate P. There was a up to a 63% decrease in total P and 66% decrease in WSP by feeding the low-phytate soybean meal diet to broilers. When the Ca in the diets was increased, the WSP and ratio of WSP to total P both decreased. The effects of Ca were more pronounced after the birds had a three day dietary adaptation period. The concentration of phytate P in the diets influenced how much the WSP and ratio of WSP total P changed with increasing dietary Ca, with the greatest influence being in the diets having the greatest phytate P levels. The amount of phytate P excreted by the birds was linearly related to the manure WSP. This was important from an environmental perspective as WSP in manure is related to potential for off-site P losses following land application of manure.

Technical Abstract: Dietary calcium (Ca) can influence the amount of phytate excreted from broilers and therefore change the solubility of phosphorus (P) in manures. We investigate the effects of dietary Ca and phytate on P excretion in broilers by feeding 12 dietary treatments to broilers from 16 to 20 days of age. The treatments consisted of three levels of phytate P (0.07, 0.19, and 0.30%) and four levels of Ca (0.47, 0.70, 0.93 and 1.16%) in a randomized complete block design which was replicated four times. Fresh manure was collected from cages for two separate 24 h periods, once after the start of dietary treatments (16 d) and once following a 3 d adaptation period (20 d). Ileal samples were also collected at 20 d to determine the changes in phytate P from the broiler terminal ileum to final excretion. Manure samples were analyzed for total P (TP), water soluble P (WSP), and phytate P, while ileal samples were analyzed for total P and phytate P. Results indicated that TP could be reduced by up to 63% and WSP by up to 66% with the inclusion of low phytate soybean meal in the diets. There was a significant effect of dietary Ca on both the manure WSP and the ratio of WSP:TP. If dietary Ca levels are increased, manure WSP and WSP:TP decrease. It was also found that the impacts of dietary Ca levels on manure WSP and WSP:TP are more pronounced following a dietary adaptation period. There was a linear relationship between the slope of the response in manure WSP to dietary Ca and feed phytate content when birds were given a 3 day adaptation period. There was also a significant correlation between manure phytate concentration and manure WSP for both manure collections. This was important from an environmental perspective as WSP in manure is related to potential for off-site P losses following land application of manure.