Protein quality of chicken-based protein sources evaluated by precision-fed cecectomized rooster assay

Evaluating the protein quality of ingredients is essential for formulating nutritionally adequate canine and feline diets. This study aimed to determine and compare the standardized amino acid (AA) digestibility using the precision-fed cecectomized rooster assay. Four ingredients were tested: spray-dried chicken protein hydrolysate (CPH), spray-dried chicken meat (CC), spray-dried chicken broth (CB), and chicken meal (CM). Sixteen cecectomized roosters (4 roosters per substrate) were randomly assigned to the 4 test substrates. After 26 h of feed withdrawal, roosters were tube-fed 12 g of test substrates and 12 g of corn, and the AA digestibility of the test ingredient was calculated by difference. Following crop intubation, excreta were collected for 48 h. Endogenous corrections for AA were made using 5 additional fasted cecectomized roosters to calculate standardized AA digestibility values. All data were analyzed using the Mixed Models procedure of SAS. Generally, CC had the highest (P < 0.05) standardized digestibility for AA, followed by CPH. Methionine, phenylalanine, and valine had higher (P < 0.05) digestibility in CC and CPH than in CB and CM. Digestibility of isoleucine and leucine were higher (P < 0.05) in roosters fed CC, followed by CPH, CM, and CB. Higher lysine digestibility (P < 0.05) was observed in rooster-fed CC and CPH, followed by CM and CB. Histidine and threonine had the lowest digestibility (P < 0.05) in CB compared to all other ingredients. In contrast, the digestibility of tryptophan was highest (P < 0.05) in CC, followed by CPH and CB, while CM had similar (P > 0.05) digestibility to CC and CPH. Amino acid digestibility for most indispensable AA was above 80% for all ingredients, except for histidine, lysine, and threonine, which were exceptions only for CB (68%, 73%, and 74%, respectively). For selected dispensable AA, the digestibility was above 60% for all ingredients, except for aspartic acid in CB and CM, and serine in CB, which were exceptions (43%, 68%, and 66%, respectively). In general, the lowest digestible indispensable amino acid score values (DIAAS) were observed in roosters fed CB, followed by CPH, CM, and the highest in CC. Overall, CC and CPH have comparable indispensable AA digestibility. Based on DIAAS-like values, tryptophan and phenylalanine + tyrosine were identified as the first limiting AA for adult dogs and growing puppies, while phenylalanine + tyrosine was the first limiting AA for adult cats and growing kittens.