Effects of the naked neck (Na) gene on the sulfur-containing amino acid requirements of broilers
1996
Pesti, G.M. | Leclercq, B. | Chagneau, A.M. | Cochard, T.
Full-sibling normal (na/na) and naked neck (Na/na) chickens were fed from 28 to 42 d of age on one of five diets with different SAA contents (from 5.4 to 7.0 g/kg). The experimental diets were made by adding DL-methionine to a well-balanced corn, soybean, and cornstarch diet containing 5.4 g SAA/kg and 161 g crude protein/kg. Dietary SAA influenced the growth rate of both genotypes similarly. There were no significant differences (P > 0.125) in body weight gain due to genetics or a diet by genetics interaction. Body weight gains were maximized at 6.24 +/- 0.45 (R2 = 0.171) and 5.96 +/- 0.52 g/kg SAA (R2 = 0.107) for the na/na and Na/na stocks, respectively. There was a significant SAA by genotype interaction for feed efficiency: the na/na birds were more efficient at low SAA levels, but the Na/na birds were more efficient at high SAA levels. Feather weight gain increased in a linear manner with increasing dietary SAA and was greater in na/na than Na/na birds with high dietary SAA concentrations. Abdominal fat decreased with increasing dietary SAA; and although the Na/na birds had significantly more abdominal fat than their na/na siblings (P = 0.049), on average the difference was small and complicated by differences in body weight. Analysis of covariance showed (a significant interaction) that the relationship between abdominal fat and body weight was different for the na/na and Na/na chickens. Although the shape of the response curves of na/na and Na/na chickens to dietary SAA are different, the quantitative requirements are very similar during the growing period.
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