Influence of Dietary Protein Source on Muscle Structure and Myogenic Gene Expression in Broiler Chicken Pectoralis Major Muscle

Broiler breast muscle development is strongly affected by nutritional quality, particularly the source and biological value of dietary protein. Dietary protein source may influence muscle fiber growth, connective tissue organization, glycogen deposition and the transcriptional activity of myogenic regulatory genes. The aim of the present study was to evaluate the effect of dietary protein source on muscle structure, glycogen content and myogenic gene expression in the pectoralis major muscle of broiler chickens. A total of 9000 one-day-old broiler chicks were raised under field conditions and divided into two dietary groups: an animal protein-based diet containing fish meal and a plant protein-based diet based on corn-soybean meal. Samples of pectoralis major muscle were taken at 42 days of age and analyzed using morphological, histological, histochemical and molecular techniques. Birds fed the animal protein diet had significantly larger muscle fiber area and muscle bundle area than birds fed the plant protein diet (P < 0.05), whereas birds fed the plant protein diet exhibited thicker connective tissue layers. Periodic acid-Schiff staining showed greater glycogen deposition in the animal protein group. RT-qPCR analysis showed that MYF6 (MRF4) and MYOG were significantly more expressed in the animal protein group than in the plant protein group (P < 0.05). In conclusion, animal protein enhanced muscle hypertrophy, glycogen storage and myogenic gene expression in the pectoralis major muscle, indicating the importance of protein quality in improving broiler production and meat quality.