Methionine supplements in chicken diets. III. The biochemical difference in sulphur-amino acid metabolism between White Leghorns and Australorps

Abstract

The ability of White Leghorn and Australorp chickens to use supplements of methionine or cystine for growth has been studied. While chickens of both breeds responded to a cystine supplement, White Leghorns showed an increase in growth rate when methionine was added to the basal diet but Australorps showed a growth depression. The effect of intraperitoneal injection of DL-methionine on the liver cysteine content of chickens of both breeds was also studied. Injections of 10 or 20 mg DLmethionine produced significant (P < 0.05) and highly significant (P < 0.01) rises in the liver cysteine contents of White Leghorn chickens, but produced only small, non-significant rises in the liver cysteine contents of Australorp chickens. Providing methionine by either intraperitoneal injection or crop drenching did not alter the breed difference in response of liver cysteine content. This indicates no difference between breeds in ability to absorb methionine from the alimentary canal. When all data on the effect of an Injection of 20 mg DL-methionine were examined, there was a significant breed x methionine interaction. These results are interpreted as due to a blockage in the synthesis of cysteine from methionine in Australorps. Attention is drawn to the linkage of the gene (or genes) limiting this process in Australorps with a gene producing slow feathering and thus possibly conserving cysteine. Possible advantages of this linkage are discussed, and a model derived to show that genetic drift would be unlikely to separate the possible genotypes containing the balanced alleles of these genes provided the disadvantage of the unbalanced genotypes was sufficiently great.