REDUCING DIETARY CRUDE PROTEIN FOR BROILERS WHILE SATISFYING AMINO-ACID-REQUIREMENTS BY LEAST-COST FORMULATION - LIVE PERFORMANCE, LITTER COMPOSITION, AND YIELD OF FAST-FOOD CARCASS CUTS AT 6 WEEKS

A dietary regimen employing the CP, ME, and essential amino acid (EAA) levels advocated by National Research Council in 1984 for broilers from 0 to 3 and 3 to 6 wk was compared with one in which only the CP was reduced from 23 to 20 and 20 to 17%, respectively. Com, soybean meal, com gluten meal, and fish meal analog were used together with the commercially available free EAA in least-cost formulation. Males and females from Peterson x Arbor Acres and Ross x Arbor Acres were grown in floor pens simulating commercial conditions. Live body weights were unaffected by dietary CP level throughout production; however, feed conversion was increased during the 3- to 6-wk interval when the CP was reduced. Reducing the dietary CP substantially decreased N content of the litter. Processing the birds revealed an increase of depot fat in the abdominal cavity when low CP had been fed. Removal of this fat depot led to a lower chilled carcass weight than when the 1984 National Research Council levels were employed. Cutting the carcass into fast-food portions indicated that reduced CP also decreased the proportion of split breast with back using an eight-piece cut and keel portion of the breast based on a nine-piece cut whereas thigh with split back increased. Both sexes and each strain responded similarly. Although reducing dietary CP reduces N content and, therefore, pollution potential of the resulting litter, adverse effects occur in live performance and the yield of breast pieces with two fast-food cutting procedures.