| The protein requirement for poultry is actually a requirement for amino acids. Recently, there has been much interest in formulating diets on a digestible amino acid basis. The most accepted methods of determining amino acid digestibility are the precision-fed cecectomized rooster assay (PFR) and standardized ileal chick assay (SID). The PFR involves tube-feeding cecectomized adult roosters and excreta are then quantitatively collected for amino acids. For the SID, 3-week-old broiler chicks are ad libitum fed a semi-purified diet with the test ingredient added as a sole source of protein for a period of several days. The animals are then euthanized and ileal digesta are collected and analyzed for amino acids. When these two methods were compared for 15 feed ingredients, standardized amino acid digestibility was found to vary among feed ingredients and among samples of the same ingredient. There were generally no differences in amino acid digestibility for six corn and four distiller's dried grains with solubles (DDGS) samples between the two methods. The PFR did yield significantly (P<0.05) greater digestibilities for two other DDGS samples, a meat and bone meal sample, and a poultry by-product meal, whereas the SID yielded higher digestibility values for another meat and bone meal. A new method of determining amino acid digestibility was developed utilizing the precision-feeding of 3-week-old broiler chicks and collecting ileal digesta to measure amino acid digestibility. The new precision-fed ileal chick assay (PFC) involved fasting chicks for a period of at least eight hours, then precision-feeding 10 g of feed and subsequent collection of ileal digesta at four hours post-feeding. Amino acid digestibilities were standardized by precision-feeding a nitrogen-free diet and analyzing ileal digesta for amino acids. In order to determine the validity of the new PFC, several feedstuffs were obtained and standardized amino acid digestibility was determined using the PFR, PFC and SID methods. Differences in amino acid digestibility were not consistent among methods and ingredients. For corn, the PFC yielded significantly greater values than the PFR and SID. For corn gluten meal, the PFR yielded higher values than the PFC and SID for majority of the amino acids. The PFR yielded higher digestibilities than the PFC for three DDGS samples evaluated. Digestibility values for soybean meal and meat and bone meal were found to be in general agreement for the three methods. There were some differences among methods for fish meal; however, these differences were not consistent among methods or amino acids. The results of these studies validate that the PFR, SID, and the new PFC are all acceptable for determining amino acid digestibility in poultry. |
