Composition and phosphorus bioavailability of a solid by-product from anaerobically digested waste from caged layer hens.

A poultry waste digester was constructed at the North Carolina State University Poultry Research Farm to produce methane from the waste of caged layer hens. A solid by-product (SBP) from the digester was recovered and dried for chemical and biological analysis as a feed supplement. Dried SBP was chemically analyzed for minerals, trace elements, and certain vitamins. The SBP was evaluated as a phosphorus (P) supplement in broiler diets. Biological availability of P in the SBP was determined by a slope ratio assay with femur bone ash as the criterion of P availability. Dietary treatments consisted of graded levels of standard available P (AP) supplemented as to provide .2, .3, .4, and .6% AP and graded levels of SBP added to provide 1.5, 2.5, 3.5, and 4.5% SBP to a corn-soy basal diet. Two treatments, containing 1.5% and 2.5% SBP added to an adequate diet (.4% AP) were used to determine if other factors in SBP were contributing to femur bone ash. The P in SBP was determined to be 90% available to the growing broiler chick. Femur bone ash did not respond to SBP in the diets already adequate in AP. Body weight gain, feed consumption, and feed conversion were not significantly different (P less than .05) among treatments with similar AP levels. The study concluded that SBP is a safe, effective feed supplement that supplies P, Ca, and total minerals.