Comparison of carcass and meat quality traits of fast-, medium - and slow-growing chicken genotypes fed diets with different protein-to-energy ratio

This study was conducted as part of a comprehensive project focused on the evaluation of novel slow-growing chicken genotypes as one of the several policies of the Better Chicken Commitment (BCC) that many companies have recently signed up. The main scope of this trial was to evaluate carcass cut yields and meat quality traits in chickens belonging to three genotypes differing in growth rate and fed either a control or low-protein diet. For this aim, a total of 1,800 one-d-old male chickens belonging to fast- (FG, Ross 308), medium- (MG, Ranger Gold) and slow-growing (SG, Gray Kabir Naked Neck) genotypes were housed in an environmentally controlled poultry facility and randomly allotted in 36 concrete floor pens (6 m2; 50 birds/pen), in compliance with BCC requirements. The birds received, throughout the trial, a multi-phase basal diet with two lysine-to-metabolizable energy ratios (CON: commercial standard; LOW: -10% lysine but the same metabolizable energy compared to CON). All birds were slaughtered in a commercial abattoir at the same body weight (~2.8 kg), which was reached at different ages (FG=34d, MG=50d, SG=77d). Fifteen carcasses per group were randomly selected and used to assess cut yields (breast, thighs, drumsticks, wings and back) and quality traits of breast meat (pHu, colour, cooking losses, shear force, TBARS and carbonyls). A two-way ANOVA was performed including genotype (FG, MG and SG), diet (CON and LOW) and their interaction in the model. As expected, total yield of high-value cuts (breast, legs and wings) was impaired in both SG and MG carcasses when compared with FG group (74.3 and 76.2 vs. 79.4%, P<0.001) basically as a consequence of dramatic decrease of breast percentage (29.9 vs. 35.9 vs. 39.6%, P<0.001). As for the dietary treatment, only FG and MG birds exhibited lower (P<0.001) percentage of breast meat when fed LOW diet, while SG chickens were unaffected. Likewise, meat quality traits strongly differed among genotypes. Breast meat from both MG and SG strains exhibited lower pHu, darker and yellower colour, higher cooking losses and shear force. In addition, SG evidenced higher TBARS values when compared with both MG and FG (0.86 vs. 0.50 and 0.50 mg/kg, P<0.001). Overall, the dietary treatment did not affect meat quality traits. These findings evidenced that the adoption of slow-growing genotypes strongly affects the profitability at slaughter and allows producers to obtain meat with peculiar quality properties (i.e. appearance, texture, etc.). Research supported by NextGenerationEU, National Grant PRIN2022 (Prot. 20228ANBKH)