Pre-slaughter sound levels and pre-slaughter handling from loading at the farm till slaughter influence pork quality.

This study investigates the relationship between sound levels, pre-slaughter handling during loading and pork quality. Pre-slaughter variables were investigated from loading till slaughter. A total of 3213 pigs were measured 30 min post-mortem for pH(30LT) (M. Longissimus thoracis). First, a sound level model for the risk to develop PSE meat was established. The difference in maximum and mean sound level during loading, mean sound level during lairage and mean sound level prior to stunning remained significant within the model. This indicated that sound levels during loading had a significant added value to former sound models. Moreover, this study completed the global classification checklist (Vermeulen et al., 2015a) by developing a linear mixed model for pH(30LT) and PSE prevalence, with the difference in maximum and mean sound level measured during loading, the feed withdrawal period and the difference in temperature during loading and lairage. Hence, this study provided new insights over previous research where loading procedures were not included.

Pre-slaughter rectal temperature as an indicator of pork meat quality.

This study investigates whether rectal temperature of pigs, prior to slaughter, can give an indication of the risk of developing pork with PSE characteristics. A total of 1203 pigs were examined, measuring the rectal temperature just before stunning, of which 794 rectal temperatures were measured immediately after stunning. pH30LT (M. Longissimus thoracis) and temperature of the ham (Temp30Ham) were collected from about 530 carcasses, 30 min after sticking. The results present a significant positive linear correlation between rectal temperature just before and after slaughter, and Temp30Ham. Moreover, pH30LT is negatively correlated with rectal temperature and Temp30Ham. Finally, a linear mixed model for pH30LT was established with the rectal temperature of the pigs just before stunning and the lairage time. This model defines that measuring rectal temperature of pigs just before slaughter allows discovery of pork with PSE traits, taking into account pre-slaughter conditions.

Pre-slaughter handling and pork quality.

Environmental variables, as sound levels, were collected during the pre-slaughter process in 18 different Belgian commercial slaughterhouses. Four pre-slaughter phases were determined: firstly after arrival of the truck at the slaughterhouse and just before unloading, secondly during unloading, thirdly at lairage and finally while moving to the stunner. A total of 8508 pigs was examined during the pre-slaughter process, of which the pH(LT) (M. longissimus thoracis), at 30 min post-mortem was measured. For each pre-slaughter phase, variables which might influence pork quality were determined. Moreover, this study made it possible to infer a checklist to represent and predict PSE traits of pork for all kind of pre-slaughter situations. The checklist shows also that the impact on pork quality is more decisive for the variables measured close to the stunning phase. Hence, this information is useful for the industry to optimize handling of pigs, reducing the risk for PSE traits.

Sound levels above 85 dB pre-slaughter influence pork quality.

This study investigates whether sound levels above 85 dB(A), determined in literature as a critical sound level to induce stress in pigs, has also an effect on the pH of pork. Sound levels were recorded during pre-slaughter phases. A measure was taken after the arrival of the truck at the slaughterhouse, during unloading, lairage and just before stunning. The pH of the Longissimus thoracis or lumborum, 30 min after sticking (pH(30LT)) was measured. 8508 pigs were examined and the pH was measured on the carcasses. The results show that the cut-off value of 85 dB(A) during the pre-slaughtering phase is not only a threshold to evaluate animal welfare but can also be associated with a slower drop of pH if sound levels are b85 dB(A). Finally a linear mixed model for pH(30LT) was built with the sound level during lairage and the sound level prior to stunning as independent variables, having statistically the highest impact on pH(30LT) of pork.

Effect of unloading, lairage, pig handling, stunning and season on pH of pork.

A total of 12,725 pigs originating from 90 transports were followed up at 17 Belgian commercial slaughterhouses. The effects of several pre-slaughter parameters concerning transport, unloading, lairage, pig handling, stunning and season on fresh meat quality based on pH measurements 30 minutes (min) after slaughter were investigated. Meat quality was measured on 4285 pigs. Ten pre-slaughter parameters had a significant effect on meat pH after separate introduction of the variable as a fixed effect in the model. Simultaneous analysis of these variables in the global model revealed that the pH was influenced by four main risk factors, namely the mean noise level produced during unloading, the percentage of panting pigs, the use of an electric prod and season. Meat quality in terms of the percentage of potentially PSE carcasses was better in summer than spring or autumn and could be explained by a lower observed pre-stunning stress in summer.

The prevalence of PSE characteristics in pork and cooked ham--effects of season and lairage time.

A total of 180 pigs was slaughtered in the same slaughterhouse, but divided in six different trials distributed over Winter (December-March) and Summer (April-September). Meat quality measurements (pH, electrical conductivity, color and/or water-holding capacity) were carried out 30 min, 24 and/or 35h after slaughter in three different muscles: M. gracilis, M. semimembranosus and M. longissimus dorsi. A tendency towards a higher proportion of PSE meat during Summer was found in the examined muscles. Moreover a higher protein, higher dry matter content, a lower water/protein ratio and a lower slicing yield were found for the cooked hams suggesting a higher PSE prevalence in the Summer. A lairage time between 2 and 4h during Summer and less than 2h during Winter was related to a lower proportion of PSE meat. The correlation coefficients between the individual meat quality variables were moderate, but showed the predictive power of the pH measured 24h post-mortem in the M. gracilis for meat quality.