Pork quality as related to halothane genotype and slaughter conditions in a belgian study

The objectives of this study were to evaluate technological and organoleptic properties of pork meat representative of different Belgian production systems and to determine the contribution of significant factors to meat quality variability, in particular the halothane genotype, fasting time, lairage time and slaughtering plant.
A total of 521 pigs were used in five Belgian commercial slaughtering plants over a 1 ½ year period. 79% of pigs belonged to four different quality production systems. The remaining 21% were randomly sampled in standard production. The lairage time (LT) was measured at slaughter. In the slaughterline, the entire intestinal tractus (OW) and the carcass (HCW) were weighed, the pH1 and electrical conductivity (PQM1) were measured 45 min post mortem in the longissimus dorsi muscle. One 2.5 cm thick cut of this muscle was removed 24h post mortem for further measurements in the lab : ultimate pH (pHu), ultimate electrical conductivity (PQMu), color (CIE L*a*b*), drip loss (DL), cooking loss (CL) and tenderness (WBPSF). The halothane genotype (CC, CT and TT for homozygote negative, heterozygote negative and homozygote positive for the RYR1 gene mutation respectively). The data were analyzed using SAS and the General Linear Model (GLM) SAS procedure was used in order to estimate the influence of halothane genotype, LT and slaughterhouse on the variability of pH1, PQM1, pHu, PQMu, drip loss, cooking loss, CIE Lab and WBPSF. The relative weight of OW on HCW was included in the models as covariate and used as inverse indicator of the fasting time. Least Squares Means (LSM) were computed for significant effect in the models and compared pairwise by the Student’s t-test.
A large variation was observed for the meat quality parameters, in particular for pH1 (from 5.30 to 6.85), DL (from 1.2 to 11.4%) and CIE L* (from 41.6 to 66.4%). The lowest values for pH1 and highest values for DL or CIE L* indicated the presence of pale, soft, exudative meat. For all parameters –except for the pHu, CL and WBPSF– a moderate to great part of variation was explained by the GLM models (R² = 0.22-0.56). The halothane genotype effect was highly significant (p<0.001) on most meat quality traits : pH1, PQM1, PQMu and color parameters (CIE Lab) but not significant on pHu and CL. The LT had a highly significant influence only on PQMu, CIE b and DL. There was a highly significant effect (p<0.01) of the slaughtering plant on pH1, PQM1, PQMu and color parameters (CIE Lab) and a significant influence (p<0.01) on the variability of DL and CL. By contrast, the fasting time had no effect on most meat quality parameters except on DL (p<0.01) and CL (p<0.001). As indicated by the regression coefficient, an increase of OW/hot HCW seems to be related to an increase of DL (p<0.01) or CL (p<0.001).
From the halothane genotype Least Squares Means and their standard errors, it appeared that meat quality was negatively affected by the presence of the RYR1 mutation. DL differed significantly (p<0.05) between genotypes with the TT pigs having the highest DL (6.8%) while that of the CC (5.5%) was the lowest and that of CT intermediate (6.1%). CL was also significantly higher (p<0.05) in TT pigs indicating lower water holding capacity. Significant differences between CC and TT genotypes (p< 0.05) were observed in terms of pH1 (6.12 vs 5.69), PQM1 (4.9 vs 6.4) and PQMu (9.7 vs 12.7). The CIE L and b values (56.9% and 16.6) were significantly higher (p<0.05) in the TT group comparatively to CC (55.0% and 15.8%) or CT pigs (54.6% and 15.4). The higher L value of the TT genotypes indicated paler meat. The WBPSF was the lowest for CT pigs with no significant difference observed between the CC and TT genotypes. A significant effect (p<0.05) of the abattoir was observed for all meat quality parameters. Although it would be necessary to determine the reasons for abattoirs differences, the small and old structure of one of the abattoirs and the lack of training of the staff could partially explain the results.
Further research is needed to evaluate the interaction terms and to identify slaughtering factors which could explain slaughterhouse differences in terms of meat quality.