How Low Can You Go? Broiler Breast Muscle Possesses a Mitochondrial Content of Just 2%

Abstract

Abstract In 1977 the pectoralis major (breast) muscle mitochondrial content of domestic broiler chickens, Gallus gallus domesticus, was estimated at 4.1%. This very low value is unsurprising in light of the bird’s unique muscle fibre composition, being exclusively composed of low aerobic capacity type IIB fibres. However, in the subsequent ~ 45 years broilers have been further modified by sustained intensive genetic selection on feed conversion efficiency and breast muscle mass. Objective With a view to understanding the metabolic implications of this historic selection – and also laying a foundation to better interpret current commercial performance - we quantitated the cellular bioenergetic structure of modern broilers. The breast muscle of 4 64 d old Ross308 broilers was subject to morphometric analysis based on transverse Transmission Electron Microscopy (TEM) images. Results This approach determined an average mitochondrial content, diameter and circularity ratio of 2.1%, 0.42 µm and 0.72, respectively. Broiler breast mitochondrial content has thus approximately halved in the last 45 years, and represents one of the lowest contents recorded for the muscle of any eukaryotic species. We have provided an updated benchmark for interpreting broiler muscle biochemistry and reinforce the view that domestic chickens are unique models of minimal aerobic capacity.