BREAST MUSCLE DEVELOPMENT OF COMMERCIAL BROILERS FROM HATCHING TO 12 WEEKS OF AGE

The development of breast muscle (Pectoralis major) using male and female broilers from two commercial strain crosses (RR = Ross x Ross and PAA = Peterson x Arbor Acres) was evaluated from hatching to 12 wk of age by quantifying DNA, RNA, and total protein contents. All birds received diets satisfying the 1984 National Research Council requirements. Birds were selected from each pen at 2-wk intervals, and their breast muscles were excised. Body weight and cumulative feed conversion did not differ between strains. Breast muscle weight increased with age, and RR had greater (P < .001) total muscle mass than PAA following hatching. Concentrations (milligrams per gram of fresh tissue) of breast muscle DNA and RNA decreased rapidly from hatching (2 mg DNA and 3 mg RNA/g) to 6 wk (.29 mg DNA and 1.8 mg RNA/g), then remained unchanged thereafter. Total RNA and protein in the whole breast muscle were greater (P < .001) for RR than for PAA from 2 to 12 wk of age by virtue of differences in muscle weights. Total DNA content of the whole breast muscle was greater for RR than PAA at 8, 10, and 12 wk of age. The protein:DNA ratio, an indicator of cell size, was similar between strains. Males had more total muscle DNA, RNA, and protein than females because of greater body mass and breast weight.