Diet Manipulation to Reduce Phosphorus Excretion by Poultry

Phosphorus is an essential dietary nutrient for growing birds and is also essential for egg production and eggshell quality of laying hens. Even though an adequate amount of phosphorus is needed to support growth and production, there is a great concern about the contamination of land and water sources due to the phosphorus content in poultry manure. Thus, there is a great need to reduce the amount of phosphorus excreted in poultry manure by lowering the dietary composition of phosphorus without compromising production performance.

In poultry diets, dietary phosphorus comes from plant and animal feedstuffs and from inorganic phosphorus supplements. The phosphorus that is present in plant sources is: 1) organically-bound phosphorus salts of phytic acid (phytate phosphorus); and 2) phosphorus in a nonphytate form. In general, poultry are unable to utilize the phytate-bound phosphorus, while the other phosphorus can be metabolized. Thus, phytate-bound phosphorus excreted in the feces produces increased phosphorus loading on land fertilized with poultry manure.

Many research institutions have experimented with adding or supplementing poultry diets with an exogenous phytase enzyme which helps poultry utilize the phytate-bound phosphorus in the feed, and thus reduces the fecal phosphorus content. This research has for the most part documented that dietary levels of phosphorus added to a diet can be decreased and phytase enzyme can be added with resulting production and growth being sustained.

At the University of Illinois, we have examined the effect of supplementing laying hen rations having adequate and deficient levels of supplemental phosphorus with phytase enzyme. The results of this work can be summarized in the following table.

Effect of Available Phosphorus and Phytase (300 U/kg) on Phosphorus Intake, Performance, and Phosphorus Excretion of Laying Hens from 20 to 70 Weeks of Age¹
AP	AP Intake	Egg Production	Egg Size	Excreta Phosphorus	Phosphorus Excreted
(%)	(mg/d)	(%)	(g)	(%)	(mg/bird/day)
.10²	100	82	58	.67	78
.10 + phytase	108	91	61	.63	77
.45	499	89	61	1.12	254
¹Data are means of six replications of twelve hens.
²The .10% treatment was terminated at 42 weeks of age due to poor performance and increased mortality.

In the above table, it is evident that having only .10% available phosphorus added to a laying hen diet resulted in decreased egg production. When that level of phosphorus was used, the addition of phytase enzyme to the diet substantially improved egg production and kept the level of excreta phosphorus to a minimum. Thus, this data shows that the addition of phytase enzyme to a laying hen diet can improve production performance while decreasing the amount of phosphorus excreted in the manure. Thus, this diet manipulation would substantially reduce the amount of phosphorus loading or contamination on land that is fertilized with laying hen manure. This technique of diet manipulation would also apply for other species of poultry as well.

References

Boling, S.D, M.W. Douglas, M.L. Johnson, X. Wang, C.M. Parsons, K.W. Koelkebeck, and R.A. Zimmerman, 1997. Supplemental phytase improves performance of laying hens consuming diets with low levels of available phosphorus. Poultry Sci. 76(Suppl. 1):5.

Waldroup, W., 1998. Nutritional approaches to reduce phosphorus excretion by poultry. Proceedings of Multi-State Poultry Feeding and Nutrition Conference and BASF Technical Symposium. Indianapolis, Indiana.