Growth, carcass composition and meat quality response to dietary concentrations in fast-, medium- and slow-growing commercial broilers

Growth, carcass composition and certain meat quality traits were studied in fast (F), medium (M) and slow (S) growing broilers fed with 3 regimes appropriate for each chicken type and differing on average by 418 kJkg -1 AMEn and 1% crude protein (P1 > P2 > P3). No significant interactions between chicken types and feed were measured before 3 weeks and after 6 weeks of age, indicating that the 3 genotypes had similar responses to the 3 diets during these periods. Before 3 weeks of age, body weight was 5% higher for P1 compared to P2 and P2 compared to P3 fed chickens for a comparable feed intake. After 6 weeks of age, a 10% reduction in feed intake occurred in P3 compared to P1 and P1 compared to P2 fed chickens for similar body weight gains. The differing responses after 6 weeks of age might be linked to high heat stress that occurred at 7 weeks of age. Between 3 and 6 weeks of age, interactions between chicken type and dietary concentration on feed intake, body weight gain characterised an "after 6 weeks of age" response for F-chickens whereas Mand S-chickens had a "before 3 weeks of age" response. These interactions might be explained by a higher sensitivity of fast-growing chickens to environmental conditions. For chickens slaughtered at market age (F = 6, M = 8 and S = 12 weeks of age), higher breast meat yield (Pectoralis major + minor) and lower abdominal fat content were observed in the F-chickens (17.2% and 2.64%, respectively) compared to the M-(15.7% and 2.86%, respectively) and S-chickens (14.4% and 3.44%, respectively; P < 0.05). Breast meat was more coloured in the S-chickens with lower L* and higher b* and a* 72 hours after slaughter than in the M-and F-chickens (P < 0.05). Dietary concentration had no significant effect on carcass composition, ultimate pH or drip loss of breast meat. Our results suggest that changes in dietary concentration alter growth performance but have little effect on carcass composition and meat quality traits. meat chicken / growth / dietary concentration / meat quality 65