Effects of a methionine deficiency on chicken tissue protein turnover: comparative analysis of methionine source.

Methionine (Met) supply is critical for optimum growth rate, muscle development, antioxidant activity, one-carbon metabolism in liver, and feather production in birds. Met is the first limiting amino acid (AA) in chicken diets, yet little is known about how different Met levels and sources influence tissue protein metabolism. Growth performance and tissue protein metabolism were compared in broilers fed either deficient or sufficient in Met, supplemented with either DL-Met or DL-HMTBA (a Met analogue). Protein synthesis rates were quantified in vivo in the liver, in 2 muscle types, and in the jejunum of 3-week-old chickens using a flooding dose of [13C]-Valine. Additionally, tissue proteolytic activities and the expression of genes involved in proteolysis and autophagy were measured. The deficient Met supply reduced chicken weight, Pectoralis major (PM) muscle weight and protein synthesis (P<0.05), though liver weight and protein synthesis remained unaffected. When expressed as fractional synthesis rates (FSR, %/d), protein synthesis was never depressed by Met deficiency irrespective of the tissue studied, whereas the proteasome proteolytic activity was consistently greater (P<0.01) in the Met-deficient birds. These results were supported by the expression of proteolysis-related genes in the PM. For most parameters, including FSR and proteolytic activities (with the exception of the liver), there were minimal differences between birds receiving DL-Met and DL-HMTBA, indicating that DL-HMTBA effectively supports muscle protein synthesis when adequately supplied, similar to DL-Met. In conclusion, Met deficiency profoundly impacts chicken growth, PM development, and tissue protein turnover, while the two Met sources exhibit similar effects.