Alteration of dietary cysteine affects activities of genes of the transsulfuration and glutathione pathways, and development of skin tissues and feather follicles in chickens.

The dietary requirement for cysteine is not determined in poultry since it is not an essential amino acid. The cysteine need is expected to be met through the transsulfuration pathway where homocysteine, a precursor of methionine, is converted to cysteine. Cysteine is a major component of plumage, and the degree to which cysteine is involved in plumage and other keratized proteins are unknown. We randomly assigned chicks to control and treatment (deficient in cysteine) diets for 49 d. The thickness of the skin layers, feather follicle length, and thickness were measured at days 10, 24, 34, and 49. We also measured the hepatic mRNA expressions of cystathionine beta synthase (), cystathionine γ-lyase (), cysteine dioxygenase (), and glutathione synthetase (. Chickens fed the treatment diet had reduced epidermis thickness and shorter feather follicles compared with the controls. The chicken fed the treatment diet also had increased mRNA expression of and indicating a disruption of the transsulfuration pathway. The treatment chickens also had a decreased hepatic and increased mRNA expressions which are in concordance with the homeostatic regulation of cysteine. Compromised cysteine metabolism could affect thermoregulation and subsequently affect feed efficiency and welfare of the birds.