Nutrient density and slaughter age have differential effects on carcase performance, muscle and meat quality in fast and slow growing broiler genotypes

1. A 2x2 factorial design was used to investigate the differences in carcase, muscle and meat characteristics between fast and slow growing genotypes fed on low nutrient (LND) or high nutrient diets (HND) at their respective slaughter ages. 2. The birds were randomly assigned to treatments with 5 replicates of 145 birds for Wens Yellow-Feathered Chicken (WYFC, 5 center dot 75 birds/m2) or 115 birds for White Recessive Rock Chicken (WRRC, 7 center dot 25 birds/m2), according to the commercial recommendations for the two breeds and were fed on HND or LND. Birds were slaughtered at 63d and 105d of age. 3. The results showed WRRC had higher carcase yield and meat yield than that of WYFC, lower fat content, higher moisture content and lower cooking loss. The meat from WRRC was less tender and contained lower levels of polyunsaturated fatty acids (PUFA). 4. Birds fed on HND had higher breast meat yield, myofiber area and protein content in the breast muscle and lower fat content than birds fed on LND. The thigh muscle of birds fed on HND had higher levels of PUFA. Age had a positive effect on carcase parameters, but a negative effect on pH, meat tenderness and cooking loss, and the two genotypes exhibited different responses to the influence of nutrient density and age. 5. Genotype and age had the largest effect on carcase performance and meat quality. LND benefited meat quality and WRRC had larger responses in meat yield and shear force when fed on HND.