The major component of skeletal muscle is the muscle fibers, which can be classified into different types based on metabolic characteristics, contractile properties, and myosin heavy chain polymorphism. The types and composition of muscle fiber are closely associated with pork quality. Therefore, the understanding of muscle fiber development regularity, fiber type differentiation and conversation, and their nutritional manipulation will help to improve efficiency of muscle growth and pork quality in animal production.［Chinese Journal of Animal Nutrition, ２００9，２1（6）:８０３-８０８］