The optimal digestible valine, isoleucine and tryptophan intakes of broiler breeder hens for rate of lay

Abstract

Three concurrent assays were conducted with objective of to evaluate the response of broiler breeder hens to valine (Val), isoleucine (Ile), and tryptophan (Trp) intake, determine amino acid utilization efficiency (k), and develop a factorial model. One hundred ninety-two hens were used in each amino acid (AA) assay. A completely random design was used, which consisted of eight treatments, eight replicates, and one hen per cage. The diets were formulated by dilution technique using one summit diet and one nitrogen (N)-free diet, resulting in AA levels that ranged from 1.90 to 932, 1.75 to 8.75, and 0.52 to 2.59 g/kg of Val, Ile, and Trp, respectively. A validating diet was included for each amino acid studied to confirm that the response of the birds was a function of the limiting amino acid. Each experiment lasted nine weeks (five weeks of adaptation and four weeks for data collection). The data obtained were AA intake (AAI), body weight (BW), and egg output (EO). Broken line model was used to evaluate the responses. The model design used was AM = [AA(m) x (BW x 0.196)(0.73) + [(N-egg x EO x AA(egg))/k], where AA(m) is AA for maintenance (247, 134, or 37 mg/BPm0.73 for Val, Ile, and Trp respectively); BPm0.73 is mature body protein or (BW x 0.196)(0.73); k is 0.70 for Val, 0.66 for Ile, or 0.55 for Trp; Negg is the N content in the egg (1.89 g/100 g); and AA(egg) is the AA content in the egg (413, 338, or 108 mg/g for Val, Ile, and Trp respectively). The additional response seen with the supplementation of the crystalline amino acid confirmed that Val, Ile, and Trp were the first limiting amino acid. The values estimated by the model for utilization efficiency were: 70, 66, and 55% for Val, Ile, and Trp, respectively, The AAI estimated by the model at 30 weeks was 803, 708, and 232 mg/day for Val, Ile, and Trp, respectively. The prediction of the model was improved using the coefficients estimated here with physiologically relevant units.