Meat quality (pH, color, and drip loss) and muscle characteristics (composition and metabolic pattern) were compared among four broiler lines: an experimental line, a commercial line selected for increased body weight and breast yield, and the respective unselected control lines. By comparison to their controls, the commercially selected birds exhibited higher body weight and breast yield (127 and 61%, respectively), whereas only breast yield was increased (21%) in the experimental selected line. Commercial selection resulted in higher protein content and lower moisture in the breast muscle. Experimental and commercial selection decreased the heme pigment content, which could explain why breast meat of the selected birds was more pale and less red. This change in the color did not correspond to a pale, soft, and exudative (PSE) defect, as the selected birds did not exhibit excessive drip loss. By comparison with their controls, both selected lines showed a lower rate and extent of pH decline postmortem, which was consistent with the lower glycolytic potential they also exhibited. However, no significant changes in the metabolic pathways of breast muscle, as measured by enzyme activities, could be found to explain differences in rates of pH decline among lines. This study did not support the idea that selection had a negative impact on meat quality, despite evidence of modified breast metabolism.
Genetic parameters of breast meat characteristics [pH 15 min postmortem (pH15min), ultimate pH (pHu), CIELAB color parameters (L*, lightness; a*, redness; b*, yellowness) and drip loss (DL)] as well as their genetic correlations with BW and body composition [breast yield (BRY) and abdominal fat percentage (AFP)] were estimated in an experimental meat-type chicken line. Heritability of the pH of meat was high for pHu (0.35 +/- 0.03) and even more so for pH15min (0.49 +/- 0.01). Color parameters appeared to be the most heritable traits, with heritability values ranging from 0.50 to 0.57. Drip loss heritability was estimated at 0.39 +/- 0.04. The rate and the extent of pH decline seemed to be controlled by different genes, as shown by the extremely low estimated genetic correlation (0.02 +/- 0.04) between pH15min and pHu. The ultimate pH of the meat was genetically very strongly related to its lightness (-0.91 +/- 0.02) and water-holding capacity (-0.83 +/- 0.04). These results suggest that selection for pHu could be exploited to prevent increased incidence of pale and exudative meat. The pH15min was poorly correlated with the other meat characteristics, with estimated correlations of 0.13, -0.23, 0.05, and -0.29 for L*, a*, b*, and DL, respectively. These results may be explained by the fact that, in our experimental conditions, pH15min remained high (between 6.01 and 6.75). Body weight and BRY exhibited poor genetic correlations (ranging from -0.06 to 0.13) with the pH of the meat at 15 min and 24 h postmortem. Both of the former traits were moderately negatively correlated with a* and b* values. A significant negative genetic correlation was observed between abdominal fatness and pHu. These results do not support the idea that selection for growth and breast development has a detrimental effect on breast meat quality even if, in the long term, the color intensity could be decreased.
Ultimate pH (pHu), color measurements, and water holding capacity of the chicken Pectoralis major muscle were compared between birds of an experimental line selected for 13 generations for increased BW and breast meat yield and reduced abdominal fat percentage and its control line. Ultimate pH differed slightly between lines after selection, with values of 5.78 +/- 0.10 and 5.68 +/- 0.12 in the selected and control birds, respectively. Drip loss was significantly lower in the selected birds. Although selection did not modify lightness L*, it led to paler meat, as redness a* and yellowness b* were significantly lower in the selected line than in the control line. Ultimate pH of the meat was related to lightness and drip loss (with mean correlations over both lines of -0.59 and -0.40, respectively). Storage of the meat resulted in similar color variation in both lines, with a significant increase in a* and b* until 3 d postslaughter and in L* after 6 d postslaughter. Estimates of the genetic parameters of the criteria of meat quality were calculated in the selected line. The estimates suggested that there is a predominant role of genetics in the control of these traits, with heritability estimates of 0.49 +/- 0.11 for pHu, 0.75 +/- 0.08 for L*, 0.81 +/- 0.04 for a*, and 0.64 +/- 0.06 for b*. A significant negative genetic correlation (-0.65) was found between pHu and L*. The genetic correlation between a* and b* measurements was estimated at 0.72.
The genetic parameters of digestibilities for a wheat-based diet were estimated on 864 broilers. Two divergent lines (D+ and D-) were developed based on AMEn. The Rialto wheat variety was used as it is known to result in low digestibility values. Digestibility of lipids (DL), starch (DS), and proteins (DP) were measured individually using Near Infrared (NIR) analysis of freeze-dried excreta. Body weight, feed consumption (FC), feed conversion ratio (FCR) and residual feed consumption (RES) were recorded to evaluate their correlation with AMEn. The mean AMEn value was 3,093 kcal/kg DM (CV = 9.0%), with a range of 1,001 to 4,022 kcal/kg DM, and was highly heritable (0.36 to 0.38) based on the Restricted Maximum Likelihood method. Genetic correlations with BW were low (-0.10 to -0.15). Selection for AMEn can thus be performed without modifying BW. In contrast, the estimated genetic correlations between AMEn and the other traits were highly negative (-0.53 to -0.60 for FC, -0.77 to -0.80 for RES, and -0.77 to -0.84 for FCR). Finally, digestibilities of feed components were moderately to highly heritable (0.33 to 0.47) and highly correlated with AMEn (0.91 for DL, 0.83 for DS, and 0.86 for DP). Selecting for improved AMEn should thus improve digestibility of proteins, starch, and lipids. The first generation of divergent selection on AMEn confirmed these results, D+ and D- lines showing a 13% difference in AMEn (P < 0.0001) and similar BW.
1. Genetic parameters of body weight (BW), breast meat weight or yield (BRW, BRY) and abdominal fat weight or yield (FTW, FTY) were estimated in males and females originated from an experimental line selected for improving broiler carcase quality and its control line. 2. Mean heritabilities over both sexes of BW, FTW and FTY were 0.43, 0.56 and 0.63 respectively. Those of BRW and BRY were 0.53 and 0.65 respectively. 3. BW was unfavourably correlated with FTW (rg of 0.40) and to a lesser extent with FTY (rg of 0.12). BW was, as expected, highly correlated with BRW (rg 0.77), but a poor correlation was obtained with BRY (rg of 0.15). Selection for more breast yield should not reduce the leanness of the birds, with a genetic correlation between BRY and FTY of -0.15. 4. The variance explained by the maternal effects accounted for a rather small part of the total phenotypic variance (from 3% to 8% according to the trait), but ignoring these effects led to a significant overestimation of the heritabilities (by 11% to 19%). 5. Except for BRY, the heritability estimates differed between sexes, only moderately for BW but more for BRW, FTW and FTY. However, estimated genetic correlations between sexes were high (between 0.94 and 0.99) and in turn heritabilities of sexual dimorphism of the various traits very low (between 0.02 and 0.07). 6. A significant improvement of the genetic level for growth and carcase composition had been obtained in the selected line, with a mean genetic gain per generation of 0.12 sigma g, 0.13 sigma g and -0.30 sigma g for BW, BRY and FTY respectively.
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