Chicken meat quality: genetic variability and relationship with growth and muscle characteristics – BMC Genomic Data

For the first time in a commercial broiler line, this study evaluated both the contribution of genetics to variations in meat quality traits and the genetic correlations with muscle characteristics such as fiber size and glycogen content. Quite significant levels of heritability were evidenced for meat properties such as thawing-cooking loss that can affect the processability of meat, and color and toughness that can influence the sensorial quality of meat. These genetic results emphasized the importance of the decrease in muscle pH post-mortem for breast meat quality in poultry. They indicated that, as for pigs [1], the final pH has an extensive effect on the water-holding capacity, color and texture of raw and cooked meat, while the early decrease in pH mainly influences the drip loss and lightness (L*) of raw meat, at least in this genotype. Selection for a lower final pH would lead to a higher incidence of pale and exudative meat that is tough after cooking and not very appropriate for industrial processing. On the other hand, selection for a higher final pH could improve the processing yield but could also affect storage and sensorial quality because of negative influences on microbial development and juiciness of the meat [5]. Ultimate pH, lightness and drip loss of meat were introduced into the French national breeding program for pigs in the 1980s, forming a combined quality index. It has been maintained constant across the generations of selection.

The strong negative genetic correlation between glycogen content of breast muscle (estimated through the glycolytic potential) and ultimate pH represents a major result in the present study. The genetic control of glycolytic potential and its genetic relationships with meat quality have been more widely studied in pigs than in poultry. Genetic studies in pigs have focused on either post-mortem glycolytic potential (PMGP), as for the present study, or on in vivo glycolytic potential (IVGP) obtained from muscle biopsy on live animals (which is not yet available for the chicken). In pigs, fairly negative genetic correlations (ranging from -0.74 to -0.99) have been reported between PMGP and pHu measured on the same muscle or on different muscles with close metabolic characteristics [13]. Corresponding correlations were slightly lower when IVGP was considered [13]. Heritability values for IVGP were around 0.25 in a population of pigs without the RN- allele [13], while an average value of 0.21 was reported for pHu [1]. These genetic results together demonstrated that GP and pHu have close genetic control, and that in poultry, as in pigs, both traits can be modified by selection. In agreement with a previous genetic study in an experimental broiler line [10], the present study indicated that the rate and the extent of decrease in pH post-mortem are under the control of different genes. A similar conclusion was drawn from a selection experiment in pigs, in which a very low genetic correlation was found between IVGP and pH measured 30 min post-mortem [14]. In the chicken, the rate of decrease in pH was shown to be influenced by behavior at slaughter and hastened by struggle activity of the birds on the shackle line, especially wing flapping [15]. However, little is known to date about the influence of genetics on such behavioral traits and the implications for meat quality.

By estimating the genetic correlations, this study made it possible to correlate responses on muscle and meat quality traits with selection on growth and breast development applied in meat-type chicken. These results indicated that selection for increased breast muscle mass is expected to lead to greater fiber hypertrophy, since a strong positive genetic correlation was observed between both traits. This was in agreement with previous results obtained by comparing experimental chicken lines divergently selected for growth [16], or differing in breast yield [17]. Most studies in pigs have indicated that selection for lean growth is associated with increases in both fiber size and number [18]. The extent to which fiber number can be modified to increase breast muscle mass in the chicken has still to be investigated. Our original results also indicated that (at least in this meat-type strain) selection for increased growth and breast muscle mass can be expected to reduce glycogen storage and in turn to increase ultimate breast meat pH. Similar results have been reported at the phenotype level, when experimental and commercial chicken lines selected for increased body weight and breast yield were compared to their respective unselected control lines [19]. Inverse relationships have been reported in pigs, for which carcass leanness appeared to be moderately positively correlated with muscle GP and negatively with pHu [13, 1]. This suggests that physiological and genetic factors involved in the control of GP and pHu could be at least partly different between pigs and poultry.