The effect of wheat cultivar, growing environment, and enzyme supplementation on digestibility of amino acids by broilers

Fifty-four samples of wheat, representing duplicate samples of nine varieties grown in three environments, were included in chick bioassays using rapidly growing broilers, complete diets, and enzyme supplementation to remove the deleterious effects of non-starch polysaccharides. An insoluble ash marker was included in the diets, which allowed calculation of apparent digestibilities of CP and AA in the grain from analysis of the ileal contents obtained after sacrifice of the chicks at 17 d of age. The wheat cultivars contained from 13.5 to 16.8% CP and differed in the percentage of specific AA, with Pro, Glu and Phe making up proportionately larger parts of high CP samples than low CP samples. Without enzyme supplementation, the digestibility of CP varied from 83 to 88% and that of specific AA from 76 to 94%, determined in part by the class and variety of wheat. Xylanase enzyme supplementation improved the digestibility of protein by an average of 4 %, and reduced the differences in digestibility between wheat samples. These results suggest that variation between wheat samples should be taken into consideration when formulating broiler feed, especially when formulation is for specific AA. Enzyme supplementation may provide a partial alternative to using high-quality protein sources or supplementing with synthetic AA.