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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #200690
Title: What aspect of dietary modification in broilers controls litter water soluble P: dietary phosphorus, phytase, or calcium?

Author
item Leytem, April
item PLUMSTEAD, P - N. CAROLINA STATE UNIV.
item MAGUIRE, R - VIRGINIA TECH
item Kwanyuen, Prachuab
item BRAKE, J - N. CAROLINA STATE UNIV.

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2006
Publication Date: 3/1/2007
Citation: Leytem, A.B., Plumstead, P.W., Maguire, R.O., Kwanyuen, P., Brake, J. 2007. What aspect of dietary modification in broilers controls litter water soluble P: Dietary phosphorus, phytase, or calcium? Journal of Environmental Quality. 36:453-463.

Interpretive Summary: Environmental concerns about phosphorus (P) losses from animal agriculture have led to interest in dietary strategies aimed at reducimg the total P concentration and solubility of P in manures. There has been some concern in the public that modifying broiler diets, in particular the use of phytase additions to feed, will increase the solubility of P in manures and make them more of an environmental risk once land applied. Past research has focused on manipulating dietary available phosphorus (AvP) with and without the addition of phytase. In these experiments the influence of other dietary factors were not considered in relation to effects on soluble P excretion. The addition of calcium (Ca) in broiler diets can have a large influence on soluble P excretion as it has an impact on both phytate hydrolysis and the formation of insoluble CaP precipitates in the gut, both of which can affect not only the total amount of P excreted but also how soluble the P in the resulting manure is. To address the effects of Ca on P excretion in broilers, we fed 18 treatments consisting of three levels of AvP (0.35%, 0.30%, and 0.25%) combined with three levels of Ca (0.80%, 0.69%, and 0.57%) and two levels of phytase (0 and 600 FTU). Phytase was added at the expense of 0.10% P from dicalcium phosphate. Fresh litter was collected from pens when the broilers were 41 d of age and analyzed for total P, soluble P, and phytate P as well as P composition by 31-phosphorus NMR. The inclusion of phytase in diets at the expense of inorganic P or reductions in AvP decreased litter total P by 28 to 43%. Litter water soluble P (WSP) decreased by up to 73% with an increasing dietary Ca:AvP ratio, irrespective of phytase addition. The ratio of WSP:total P in litter decreased as the dietary Ca:AvP ratio increased and was greater in the phytase amended diets. This study indicated that while feeding reduced AvP diets with phytase decreased litter total P, the ratio of Ca:AvP in the diet was primarily responsible for effects on WSP. Therefore previous dietary studies examining the influence of dietary P and phytase additions have not accounted for the effect that dietary Ca has on soluble P excretion. Most studies have formulated feeds that held the Ca level in diets constant while decreasing dietary AvP both with and without phytase additions, by doing so they have effectively increased the Ca:AvP ratio in the diets. Therefore, the results that they obtained were more likely due to the change in dietary Ca:AvP ratio rather than changes in dietary P level or phytase additions and therefore their interpretations are somewhat misleading. This is important from an environmental perspective as the amount of WSP in litter could be related to potential for off-site P losses following land application of manure.

Technical Abstract: Environmental concerns about phosphorus (P) losses from animal agriculture have led to interest in dietary strategies to reduce the concentration and solubility of P in manures. To address the effects of dietary modification in broilers, we fed 18 treatments consisting of three levels of AvP (0.35%, 0.30%, and 0.25%) combined with three levels of Ca (0.80%, 0.69%, and 0.57%) and two levels of phytase (0 and 600 FTU). Phytase was added at the expense of 0.10% P from dicalcium phosphate. Fresh litter was collected from pens when the broilers were 41 d of age and analyzed for total, soluble, and phytate P as well as P composition by 31-phosphorus NMR. Results indicated that the inclusion of phytase at the expense of inorganic P or reductions in AvP decreased litter total P by 28 to 43%. Litter water soluble P (WSP) decreased by up to 73% with an increasing dietary Ca:AvP ratio, irrespective of phytase addition. The ratio of WSP:total P in litter decreased as the dietary Ca:AvP ratio increased and was greater in the phytase amended diets. This study indicated that while feeding reduced AvP diets with phytase decreased litter total P, the ratio of Ca:AvP in the diet was primarily responsible for effects on WSP. This is important from an environmental perspective as the amount of WSP in litter could be related to potential for off-site P losses following land application of manure.