Syed S. Sohail and David A. Roland, Sr.

Phosporus (P) is an essential ingredient in animal and plant production; however too much or too little P can be a problem both for animal production and the environment. AAES researchers are finding ways for poultry to better utilize P, thus increasing productive efficiency and protecting the environment.

The U.S. poultry industry, which contributes more than $12 billion annually to the economy, includes some 75,000 growers nationwide who produce more than 6.5 billion broilers, 270 million layers, 285 million turkeys, and 20 million ducks. These operations generate 20 million tons of manure annually, which must be disposed of in an environmentally safe manner. Generally the waste is applied to the land as a fertilizer. This waste contains phosphorus, which is used by a wide range of plants; however, excess P can run off land and enter lakes and streams causing severe environmental, health, and economic problems.

Phosphorus is an essential element for the growth and survival of poultry. In diets containing plant ingredients, such as corn and soybean meal, about 67% of the total P exists as phytate P that is P bound to phytic acid (Figure 1). Phytate P is not absorbed by the birds' bodies due to the absence of the enzyme phytase in their intestines. Inorganic or nonphytate P is therefore added in the feed to meet the demands. Unavailable phytate P is excreted in the manure, and may cause manure to contain more P than plants can use. Any excess P from the manure can be washed into waterways, where it causes rapid algal growth (Figure 2) and can affect the amount of oxygen in water, leading to fish kills (Figure 3). Phytase, an enzyme of microbial origin, can increase the availability of phytate P. An AAES study was conducted to determine if dietary P in broiler grower and finisher diets could be reduced by 0.1% by adding microbial phytase.	Figure 1. Structure of phytic acid showing six phosphorus molecules bound to a phytic acid molecule.
	Figure 2. Manure phosphorus promotes rapid algal growth in waterways.
	Figure 3. Excessive algal growth reduces dissolved oxygen in water resulting in fish kills.

A trial was conducted using 2,800 Ross x Hubbard male broiler chicks. Diets were formulated to contain two reduced levels of nonphytate P (0.225% and 0.325%) and three levels of phytase (0, 300, and 600 phytase units per kilogram feed). An additional diet with 0.425% nonphytate P was used as a positive control to represent diets typically used in the industry. Prior to assigning treatments, all chicks were fed a commercial starter mash adequate in all nutrients until three weeks of age.

Neither performance nor bone strength, which is important because stronger bones help birds withstand stress during growth and processing, was significantly influenced by a reduction of nonphytate P to 0.325% as compared to the positive control. However, when nonphytate P was reduced to 0.225%, a significant negative impact on body weight, feed consumption, feed efficiency, and bone strength was observed.

Phytase significantly increased body weight at the lower nonphytate P level, but not at the higher nonphytate P level. A significant nonphytate P-by-phytase interaction occurred in bone criteria and livability. The interaction indicates that phytase (300 units per kilogram feed) had a greater influence on bone mineral content, bone density, bone breaking strength, and livability in broilers fed 0.225% nonphytate P than in broilers fed 0.325% nonphytate P. This indicates that supplementing phytase in grower diets containing reduced levels of nonphytate P significantly improved performance and bone strength of broilers.

The negative impact on bone strength associated with the deficient level of 0.225% nonphytate P was completely reversed by the inclusion of 300 phytase units in diets containing marginal to deficient levels of nonphytate P (see table). The addition of microbial phytase at 300 and 600 phytase units per kilogram feed prevented P deficiency symptoms by allowing birds to utilize phytate P. However, increasing phytase levels from 300 to 600 phytase units per kilogram feed provided no additional benefit.

These results demonstrate that addition of 300 units of phytase per kilogram diet allows producers to reduce dietary P by 0.1% in grower and finisher diets with no adverse effect on broiler performance. Use of phytase in poultry diets will significantly reduce environmental phosphorus pollution.