Effects of the sex‐linked dwarf gene (dw) on skeletal muscle cellularity in broiler chickens

The number and size of muscle fibres and the DNA concentration in m. pectoralis superficialis of normal (Dw+/-) and dwarf (dw/-) White Plymouth Rock females were investigated at the ages of 9 and 52 weeks. 2. Live weight and total meat was reduced by 37.4 and 42.8% in dw/- as compared with Dw+/- females at the age of 9 weeks. The suppressive effect of the dwarf allele on the weight of m. pectoralis superficialis was 40.6% (67.8 v. 40.3 g in Dw+/- and dw/- genotypes). This reduction in weight was accompanied by a similar decrease of DNA content (28.8 v. 17.1 mg, i.e. 40.6%), a decrease in number of muscle fibres (829 x 10(3) v. 654 x 10(3), i.e. 21.2%) and fibre diameter (30.80 v. 28.95 microns, i.e. 6.0%). In mature hens, the differences between genotypes Dw+/- and dw/- were slightly smaller. 3. The different relationships between the muscle growth traits studied are discussed.