EFFECTS OF THE SEX-LINKED DWARF GENE (DW) ON SKELETAL-MUSCLE CELLULARITY IN BROILER-CHICKENS

1. 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 mum, 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.