Table 2.

Stages of the fetal and postnatal development of porcine skeletal muscle

Stage	Days of gestation	Major events
1	From conception to 25 d of gestation	Embryonic myogenesis from a common mesenchymal precursor
2	From 25 to 50 d of gestation	Formation of primary muscle fibers (rapid fusion of primary myoblasts)
3	From 50 to 90 d of gestation	Formation of secondary muscle fibers (formed on the surface of primary fibers)
4	From 90 to 95 d of gestation	Establishment of muscle fiber numbers
5	d 114 of gestation	Total numbers of muscle fibers are fixed at birth
6	After birth	Growth of skeletal muscle by increasing the size of its fibers (hypertrophy)a; and maturation of skeletal muscle

^aHypertrophy is defined as an increase in the size of the skeletal-muscle cell (also known as fiber), whereas hyperplasia refers to an increase in the number of cells or fibers

Adapted from Dwyer et al. [66], Handel and Stickland [65], Nissen et al. [61], and Oksbjerg et al. [42]