Comparison of amino acid digestibility in broiler chickens, turkeys, and Pekin ducks

The objective of this study was to compare prececal amino acid (AA) digestibilities in broilers, turkeys, and Pekin ducks that were 3 wk old. Five diets were used: a basal diet and diets that contained either soybean meal (SBM) or rapeseed meal (RSM) at the expense of starch each at either 150 or 300 g/kg. The differences in dietary CP and AA concentrations resulted only from the inclusion of SBM or RSM. Titanium dioxide was used as an indigestible marker. Each diet was allocated to 6 pens of 12 birds from each species and provided ad libitum for 1 wk starting at 14 d of age. Digesta were sampled on a pen basis from the distal two-thirds of the section between Meckel's diverticulum and 2 cm anterior to the ileocecocolonic junction. Ingested and digested amounts of AA were determined for each pen. Digestibilities for the 2 meals were then determined by a multiple linear regression analysis, which makes a correction for basal endogenous AA losses unnecessary. Digestibilities for essential AA from the meals varied between 92% (Met, RSM, broilers) and 62% (Val, RSM, ducks). Digestibilities were not significantly different between SBM and RSM for broilers and turkeys, but the average digestibility across all AA was slightly higher for SBM and lower for RSM in turkeys than in broilers. Digestibilities were lower in ducks than in the 2 other species, and significant differences between SBM and RSM were detected for some AA in ducks. Amino acid digestibility ranking was very similar between broilers and turkeys but different for the 2 meals. It was concluded that differences among species cannot be explained by differences in basal endogenous AA losses among species. Amino acid digestibilities determined with broilers should not be used in formulating feed for ducks.