Sreenivasulu Punna and David A. Roland, Sr.

Chickens need phosphorus in their diet; however their inability to break down phytate molecules results in the release of undigested phosphorus in chicken litter, which ultimately can cause pollution problems in waterways. A recent AAES study indicates that there is great variability among chickens in their ability to break down phosphorus. This research also substantiates the importance of phosphorus in poultry diets.

Phytate phosphorus under normal biological conditions exists in plants as a Ca-Mg-K salt of phytic acid. Approximately 70%, or two-thirds of the total phosphorus in plant material is in the phytate form. Chickens possess little intestinal phytase activity, the enzyme needed to break down the phytate molecule. Hence, most phosphorus, present as a part of phytate molecule, goes through a chicken's digestive system unutilized. This undigested phosphorus has been identified as one of the major pollutants of surface waters in many places in Europe and the United States. Phosphorus pollutes water by accelerating a natural process called eutrophication and has become a serious problem in water bodies of Alabama, Georgia, and other poultry-producing states.

One factor that influences the phosphorus requirements of chickens is the great variation among birds in utilizing phytate phosphorus. Previous observations indicated that individual birds in the same flock greatly differ in their ability to respond to phosphorus deficiency. Birds that were susceptible to phosphorus deficiency showed skeletal problems and severe reductions in overall performance. Hence, another study was conducted to determine the relationship between individual birds' abilities to use phytate phosphorus and response to phosphorus deficiency.

To determine individual phytate phosphorus retention, individually caged day-old chicks were fed diets containing 0.5% and 0.1% available phosphorus (Pa). At the end of the second week, birds fed the 0.1% Pa diet were separated into larger and smaller birds based on feed intake and growth rate. To measure phytate phosphorus retention, manure samples were collected from all birds at the end of the second and fourth weeks of the study. Dietary effects on bone quality were assessed after four weeks.

Birds fed diets containing 0.5% Pa showed higher growth rates (2.54 pounds vs 1.93 pounds) (see table) and lower mortality (0% vs 15%) than those fed deficient (0.1% Pa) phosphorus levels. Body growth and bone quality analysis revealed a large variation among broilers fed the phosphorus-deficient diet. The differences were evident by the time birds reached the age of 14 days. Manure analyses at the end of two and four weeks revealed significant variations among individual (larger vs smaller) birds in retaining phytate phosphorus (75.3% vs 60.4%). The efficient utilization of phytate phosphorus by larger birds was evident in terms of their higher feed consumption (3.23 pounds vs 2.90 pounds per bird), body growth (2.17 pounds vs 1.70 pounds), livability, and bone mineralization (0.12 grams per centimeter vs 0.08 grams per centimenter).

Effect of Available Phosphorus (Pa) on Feed Consumption, Body Weight, Phytate Phosphorus Retention, Total Phosphorus Retention, and Bone Mineral Content (BMC)

Dietary treatment	Feed consumption	Body weight	Phytate P retention	Total P retention	BMC
	Lbs./bird	Lbs.	Pct.	Pct.	g/cm
0.5% Pa	3.78	2.54	18.5	41.9	0.17
0.1%Pa-LB1	3.23	2.17	75.3	60.0	0.12
0.1%Pa-SB1	2.90	1.70	60.4	50.0	0.08
1LB=larger birds; SB=smaller birds

These results indicate that the ability to utilize phytate phosphorus is very important in responding to phosphorus deficient diets. Variability in utilizing phytate phosphorus results in variances in body growth, bone quality, and livability. In addition, data also indicate that phytate phosphorus is more efficiently used under phosphorus-deficient conditions compared to normal conditions (67.8% vs 18.3%).

The ability to utilize phytate phosphorus is related to a chicken's ability to survive phosphorus-deficient conditions. Based on the results, it is important to understand the nature of phytate phosphorus utilization in poultry to cut cost of production and phosphorus pollution. Further research is needed to explore the possibility of genetically selecting chickens on the basis of their ability to utilize phytate phosphorus without compromising other important traits, such as growth and bone quality.