Histo- and biochemical characteristics of the Longissimus dorsi muscle in pigs and their relationships to performance and meat quality.

Histo- and biochemical characteristics of the longissimus dorsi muscle at 65-70 kg body weight and their relationships to performance and meat quality at 100 kg were examined in Danish Landrace and Danish Large White female and castrated male pigs. Breed differences were observed for feed conversion rate, and a number of histochemical and biochemical traits. The organoleptic traits, flavour (13%), tenderness (15%) and overall acceptability (13%) were rated higher in Large White pigs. Significant correlations between histological and biochemical traits of the live muscle on the one side and performance, meat quality and organoleptic traits on the other side, could be demonstrated. However, these correlations were generally low (r < 0.35), and can thus only explain a small part of the variation in the measured quality traits. Consequently live muscle traits measured at 65-70 kg are poor predictors of meat quality characteristics after slaughter at 100 kg.

Comparison of Dehiding versus Scalding and Singeing: Effect on Temperature, pH and Meat Quality in Pigs.

The aim of this work was to investigate the temperature and pH changes taking place at the slaughter line and during the chilling process, and the subsequent effect on meat and eating quality in pig carcasses that had either been scalded and singed or dehided. Both processes were followed by fast chilling. 219 halothane-gene-free Duroc Sire and Landrace-Yorkshire pigs were delivered from three farms and slaughtered over 2 weeks at either a dehiding or a scalding singeing slaughterhouse. Temperature and pH were measured at intervals from exsanguination until 6 hours post mortem. Ultimate pH, internal reflection, drip loss and colour (Minolta) were measured the day after slaughter. Colour (JPCS scale) was evaluated after freezing and thawing, and eating quality was estimated on unaged and aged (4 days at 4°C) m. longissimus dorsi (LD), using a trained taste panel. At the slaughter line the dehided carcasses had an almost constant and lower temperature compared to the scalded and singed carcasses. During chilling there is a shift in temperature curves between treatments, where the scalded carcasses had the lowest muscle temperature in LD and m. biceps femoris (BF) from 2hr post mortem and throughout the measuring period. In spite of the shift in temperature, the dehided carcasses had the highest pH in LD and BF from exsanguination and throughout the measuring period. The rate of pH fall in LD and BF was slowest in the dehided carcasses from exsanguination until 3 and 2hr respectively, post mortem. Dehided carcasses showed a 40% lower drip loss, a darker meat colour and a lower internal reflection in LD and BF compared to scalded and singed carcasses, thus indicating less protein denaturation in dehided carcasses. Scalding and singeing, however, lead to increased tenderness compared to dehiding, and this difference persisted even after ageing for 4 days at 4°C. The differences in toughness may be caused by increased proteolysis by released lysosomal cathepsins.

Effect of early post-mortem cooling on temperature, pH fall and meat quality in pigs.

The aim of this study was to investigate how early cooling of carcasses after slaughter by showering with cold water affected the rate of the pH fall post mortem, protein denaturation and drip loss. Eighty pigs were selected in pairs at debleeding according to sex and farm of origin. All pigs were halothane genotyped and glycolytic potential in LD analysed. One of each pair was cooled 30 min post mortem by showering with 10-12 °C water for 12 min. The control pig was treated normally except for the same delay before batch chilling commenced. The initial pH fall in LD and BF did not depend on the glycolytic potential in LD but at 5 to 6 and 24 hr post mortem pigs with the lowest glycolytic potential had the highest pH. Weight and lean meat content did not affect the cooling curve, i.e. the temperature fall. The results showed that it was possible to reduce the temperature in BF and LD by cooling at slaughter. The maximum difference in temperature between control and cooled carcasses 2hr post mortem was 2 and 1 °C in LD and BF respectively. The lowering of the muscle temperature early post mortem resulted in a reduced rate of the pH fall and a higher pH from 2 to 6 hr in the cooled carcasses. The rate of the pH fall in LD and BF seemed to be independent of temperature at levels above approximately 37 °C, but decreased linearly as the temperature dropped below approximately 37 °C. The cooling procedure used here did not result in a significant reduction in protein denaturation or drip loss, although there was a tendency towards lower drip loss in LD and BF in cooled carcasses.

Electrical stimulation of pigs-effect on pH fall, meat quality and Cathepsin B+L activity.

This work was performed to evaluate the effect of electrical stimulation (ES) on pH fall and meat quality of LD and BF in Danish halothane free pigs stunned with CO(2). ES resulted in a significant drop in pH of 0.3 units in both LD and BF and 3 h lairage resulted in 0.1 units lower pH at 20 min post mortem. Lairage time did not affect and did not interact with the effect of ES on any of the measured meat quality parameters. ES did not affect the ultimate pH in LD, BF, SM and SC or internal reflection value in LD. However, ES caused higher internal reflection and drip loss in BF and increased the PSE frequency in LD (2 to 7%) and in BF (2 to 49%). The frequency of PSE areas in the centre of SM was 70% for ES pigs compared to 9% for control pigs. ES and ageing improved the tenderness and reduced the hardness in LD as well as shear force of unaged BF. The effect of ES on tenderness and hardness was approximately half the effect of ageing, but the effect of ES and ageing were additive. ES significantly increased the activities of cathepsin B+L in the myofibrillar fraction, but there were no differences in proteolytic activity in the other fractions. It is concluded that ES improves tenderness in LD and BF, but has a negative effect on the quality of BF and SM. Therefore ES is not an economically attractive alternative for improvement of tenderness in LD compared to ageing in Danish pigs. ©

Low stress pre-slaughter handling: effect of lairage time on the meat quality of pork.

The effect of lairage time on meat quality was investigated when crossbred pigs were subjected to low stress pre-slaughter handling, where pigs were treated in mixed groups of 15 from the farm to group CO(2) stunning, and where electric goads were not used at any time. Two experiments were carried out, one in spring (n=270) using very standardised conditions and one producer, and one in summer (n=630) using a representative randomly chosen sample of producers. In the first experiment three lairage times were used, less than 30 min (average 26 min), 90 min (average 83 min) and more than 150 min (average 170 min) and no showering. The pH and temperature were measured in the m. longissimus dorsi at various times post mortem, and colour (L(*), a(*), b(*)), internal reflectance and drip loss the day after slaughter. Sensory evaluation was carried out on 16 randomly chosen samples from the shortest and longest lairage time groups. Drip loss, pH(ultimate) and internal reflectance were also measured in the m. biceps femoris and pH(ultimate) and internal reflectance in the m. semimembranosus. Finally, pH(ultimate) was measured in the m. semispinalis capitis. In the second experiment only two lairage times were used, less than 30 min (average 17 min) and more than 130 min (average 150 min) and with intermittent showering and only a subset of the meat quality measurements were made. Lairage time had no effect on any of the meat quality parameters measured in experiment 1. In experiment 2 the shortest lairage time led to a higher temperature in the m. longissimus dorsi at 2 min post mortem, a higher drip loss in the m. biceps femoris and higher internal reflectance values in both muscles the day after slaughter. The differences were, however, very small and may have been an effect of showering.

Effect of rearing system and mixing at loading on transport and lairage behaviour and meat quality: comparison of outdoor and conventionally raised pigs.

The effect of raising pigs outdoors or conventionally in a barren environment was investigated with respect to behaviour during a 3 to 4 h journey and a 2 h lairage, blood chemistry at slaughter and meat quality characteristics. Pigs were either kept in farm pen groups or were mixed at loading and kept in the groups, so formed, until slaughter. Non-mixed outdoor pigs settled more quickly during transport and lay down to a greater extent at the end of the journey and lairage period compared with conventionally raised pigs. Mixing led to fewer pigs sitting and lying during transport for conventionally raised pigs, where nearly 80% were still standing at the end of the journey. Mixing had no effect on pig posture in the lairage. Outdoor pigs were less aggressive than conventionally raised pigs especially during lairage and had a lower frequency of unacceptable skin damage in the rear and shoulder area. Aggressive interactions were almost exclusively confined to mixed groups and occurred mainly between pigs from different farm pens, i.e. between unfamiliar animals. Mixing at loading led therefore to higher levels of unacceptable skin damage. Cortisol concentrations in slaughter blood were not affected by rearing system or mixing, but mixed, conventionally raised pigs had higher plasma creatine kinase (CK) activities than non-mixed ones (1132 v. 761 U/l, respectively, P < 0.05). Outdoor pigs had similar CK activities, irrespective of mixing (682 and 771 U/l for mixed and non-mixed, respectively). Muscle pH early post mortem was highest in outdoor pigs and muscle temperature lower, but no pig showed pH values below 6.0. Ultimate pH values were both higher (Semimembranosus (S)) and lower (Semispinalis capitis (SC)) than in conventionally raised pigs, and outdoor pigs tended to have a lower frequency of higher than normal pH values. Internal reflectance (MQM) values in Biceps femoris (BF) were highest in outdoor pigs but the incidence of pale, soft and exudative (PSE) meat was low, varying between 0% and 1% for experimental groups. In general, the effects of rearing system and mixing on meat quality measurements taken early post mortem or the day after slaughter were slight, but the trends seen support the CK results, and show that conventionally raised pigs may have found mixing pre-slaughter to be more physically stressful than outdoor pigs did.

Effect of rearing system and mixing at loading on transport and lairage behaviour and meat quality: comparison of free range and conventionally raised pigs.

Free range pigs, born outdoors and reared after weaning in enriched indoor accommodation, were compared with conventionally raised pigs from a farm, matched for effects on meat quality, with respect to behaviour during transport and lairage, blood chemistry at slaughter and meat quality characteristics. Pigs were either kept in farm pen groups or were mixed at loading and kept in the groups, so formed, until slaughter. Free range pigs tended to settle faster during the 2½ h transport and 2 h lairage than conventionally raised pigs and were more likely to lie as resting posture during transport. Mixing at loading had no effect on posture during transport or during lairage for free range pigs but mixed conventionally raised pigs showed a greater variability in posture during lairage compared to non-mixed conventionally raised pigs, presumably as a result of disturbance from fighting conspecifics. Conventionally raised and free range pigs showed similar levels of aggression during transport but conventionally raised pigs were more aggressive during the lairage (average for mixed groups 12 v. 2 fights, P < 0.001). Aggressive interactions, such as one-way bites, were almost exclusively confined to mixed groups and all fights with mutual biting in mixed groups occurred solely between unfamiliar animals. The frequency of unacceptable skin damage in the middle and shoulder was highest in conventionally raised pigs and in mixed groups. Cortisol concentration and creatine kinase (CK) activity in slaughter blood were not affected by the rearing system. Mixing did not affect cortisol concentrations but led to higher CK activities compared to non-mixing (957 v. 588 U/l, respectively, P < 0.05). The rate of pH fall after slaughter was not affected by the rearing system but muscle temperatures early post mortem were highest in free range pigs. Mixing did not affect pH or temperature early post mortem. Neither rearing system nor mixing at loading affected ultimate pH or internal reflectance (meat quality marbling values).