Effects of the sex-linked dwarf gene (dw) on the expression of the muscular dystrophy gene (am) in chicken.

The sex-linked dwarf gene (dw) was introduced into companion muscular dystrophic (am) and nondystrophic (Am+) New Hampshire chicken lines to investigate influences of the dwarf gene on breast muscle weights, muscle fiber area, and the histological expression of muscular dystrophy. Dystrophic and nondystrophic chickens within dwarf or nondwarf genotypes were similar in body and carcass weights. Pectoralis and supracoracoideus muscle weights (as a percentage of adjusted carcass weight) were similar in nondystrophic dwarf and nondwarf males and females. In addition, pectoralis weight was similar in dystrophic dwarf males and dystrophic nondwarf males and females. However, pectoralis weight was significantly smaller in dystrophic dwarf females than in dystrophic nondwarf females, whereas supracoracoideus weight was significantly larger in dystrophic dwarf males than in dystrophic nondwarf males. Supracoracoideus weight was similar in dystrophic dwarf males and females and dystrophic nondwarf females. Pectoralis muscle fiber area was influenced by sex and by dwarf and dystrophy genotype. Muscle fiber area was larger in females than in males, smaller in dwarfs than in nondwarfs, and smaller in dystrophic than in nondystrophic muscles. Muscle fiber degeneration and adipose infiltration was more extensive in dystrophic than in nondystrophic females and males, and it was more advanced in dwarfs than in nondwarfs. Excessive acetylcholinesterase staining patterns were characteristic of dystrophic muscle in both dwarf and nondwarf genotypes. Nondystrophic and dystrophic dwarf male and female chickens are comparable substitutes for nondwarfs as biomedical models with respect to pectoralis histology, acetylcholinesterase staining pattern, and pectoralis muscle hypertrophy.