A 1000-pig F2 intercross QTL detection experimental population was generated using two commercial sire lines. Independent carriers of HAL n and RN− mutations (10% and 14%, respectively) were included in this population as control genotypes. The effects of HAL n and RN− heterozygous genotypes on fresh and transformed loins and hams were estimated using a mixed model methodology. The results document the unfavorable effects of both mutations on meat quality. Smaller effects of HAL Nn genotype compared to HAL nn or RN−rn+ genotypes were estimated. Interestingly, effects of HAL Nn genotype on meat pH and loin color could be insignificant at 24-h postmortem, but translate into higher water losses on storage and cooking, and result in tougher cooked loin. Using the same methodology, significant effects of the PRKAG3 (RN) I199 allele on ultimate pH values but not on glycolytic potential were observed.

Two-dimensional electrophoresis was used to investigate sarcoplasmic protein expression in pig Semimembranosus muscles sampled 20 min after slaughter. Two groups (light and dark) of 12 animals were selected from 1000 pigs, based on meat L values measured 36 h postmortem. Twenty-two proteins or fragments (p < 0.05) were differentially expressed. Muscles leading to darker meat had a more oxidative metabolism, indicated by more abundant mitochondrial enzymes of the respiratory chain, hemoglobin, and chaperone or regulator proteins (HSP27, alphaB-crystallin, and glucose-regulated protein 58 kDa). Conversely, enzymes of glycolysis were overexpressed in the lighter group. Such samples were also characterized by higher levels of glutathione S-transferase omega, which can activate the RyR calcium channels, and higher levels of cyclophilin D. This protein pattern is likely to have severe implications on postmortem metabolism, namely, acceleration of ATP depletion and pH fall and subsequent enhanced protein denaturation, well-known to induce discoloration.

Heat shock protein ([Hsp70]) and ionized calcium ([Ca2+]) concentrations were examined in pigs’ blood at different times after heat stress (HS). Pigs were from different halothane genotypes (HAL) (NN, n=7; Nn, n=5; nn, n=6). [Hsp70] increased significantly from 1–2h after HS and [Ca2+] decreased significantly from HS-end in NN and Nn. No significant differences in [Hsp70] and [Ca2+] were detected among NN and Nn. [Hsp70] and [Ca2+] in nn did not vary significantly from baseline values. [Hsp70] was significantly higher in NN and Nn than in nn. Briefly, HAL affected [Hsp70] after HS in pigs probably via a disordered [Ca2+] regulation.

Pork quality depends on various genetic and environmental factors. Despite the improvement of slaughter conditions, the PSE type is still one of the main concerns in this field. This study was conducted on nonstressed animals to evaluate the tissue characteristics of some muscles usually involved during stress compared with a reference muscle, the M. triceps brachii, which is actually not subject to stress-caused damages. Samples of M. triceps brachii, M. longissimus dorsi, M. biceps femoris, and M. semimembranosus were taken from pigs exhibiting 1 of the 3 HAL genotypes (NN, Nn, or nn) and 2 of the 3 RN genotypes (rn+rn+ or rn+RN-). Histoenzymology and immunohistochemistry were used to compare the fiber typing and capillary network in these muscles within these different stress susceptibility genotypes. In comparison with the reference muscle, M. triceps brachii, the combination of a high value of the number of type IIb fibers and a low vascular network showed a primary effect on muscles usually involved during stress. This led to the definition of a PSE index. A dramatic increase (P < 0.001) in this PSE index was systematically found in muscles usually involved in the PSE-type condition. These results show that distinctive histological characteristics were associated with the vulnerability of some muscles independently of the genotypes. Moreover, this study highlights the distinctive histological features of each genotype and is likely to suggest some interactions between them.

Pigs of the same genetic type at the RN and HAL loci, i.e. rn(+)RN(-)/NN were reared in similar conditions of feeding and housing. They were slaughtered in two abattoirs (referred to as A1 and A2) using a mixture of air (30%) and CO(2) (70%), at a rate of 300 pigs per hour per slaughterline. One hundred and thirty-two pigs from 11 farms were slaughtered in A1 using a corusinga restrainer and 127 pigs from 5 farms were slaughtered in A2 with the backloading technique. pH at 40 min, 2.5 h and 24 h after slaughter and colour (L*, a*, b*) at 24 h after slaughter were measured in the semimembranosus muscle. Meat quality of the ham was scored as follows: 1, no PSE-zone; 2, doubtful; 3, PSE-zones in the semimembranosus and sometimes on the internal flexor muscles; 4, PSE-zones in all the flexor muscles. The muscle pH value was higher in A2 than in A1 at 40 min post mortem (P<0.01), but not at 2.5 and 24 h. L* (P<0.001) and b* (P<0.05) were higher in A1 than in A2. There was a remarkable difference in meat quality scores, with 50% of the hams scoring 3 or 4 in A1, vs 13% in A2. Lairage time before slaughter affected (P<0.01) the pH value at 2.5 h (5.69 vs 5.93). The values of pH1 and pH2.5 decreased with increasing the meat quality score. The values of L* and b* increased markedly with the score. The results of the present study indicate that the method of bringing the slaughter pigs to the stunning device affects the frequency and importance of PSE meat in the ham. The automated driving of groups of animals to the stunning machine combined with the backloading of a nacelle, compared to a traditional system driving pigs in single file using electrical goads and a restrainer was beneficial with respect to both meat quality and animal welfare.

Pigs (n=186) of the same genetic strain at the RN and HAL loci, i.e. rn(+)rn(+) / NN, were slaughtered in two abattoirs (referred to as A1 et A2). All pigs were anaesthetised with CO2, using a mixture of air (30 %) and CO2 (70 %). One hundred and twenty-eight pigs were slaughtered in A1 (corusinga restrainer) and fifty-eight pigs were slaughtered in A2 (backloading) at a rate of 720 pigs per hour per slaughterline. In A1, the pigs were led in a single file to the restrainer which introduced them individually into the stunning machine. In A2, the pigs walked 5 or 6 abreast towards the stunning machine, being pushed by a sliding door from the piggery to the cradle of the machine without human intervention.The pH was measured at 40 min, 2h30 and 24h after slaughter in the semimembranosus muscle (SM). Colorimetric values (L*, a* and b*) were measured after deboning on the internal surface of the SM. The hams were graded as follows: 1, no PSE zone; 2, doubtful; 3, PSE zones in the SM and sometimes in the internal flexor muscle; 4, PSE zones in all the flexor muscles; each one of these grades being squared with pre-thresholded gaps of luminance.The muscle pH value was higher in A2 than in A1 at pH1 (40min). L* and a* value (P < 0.001) were higher in A1 than in A2. There was a remarkable difference between the two abattoirs in the proportion of hams graded 3-4, with 17,7% in A1,vs. 5 % in A2.Waiting-time before slaughter affected the pH value at 24h. The values of pH 1 and PH 2.5 decreased with the increase in the meat quality score in the two abattoirs.The result of the present study indicate that the method of handling the pigs to the stunning device affects the frequency and importance of PSE-zones in the ham. The stressless automated driving of groups of animals to the stunning machine, combined with the backloading of a nacelle, (compared to a traditional system driving pigs in single file, using electrical goads and a queue up restrainer) is beneficial with respect to both meat quality and animal welfare.

This article is aimed to review the research works carried out to date about structurless pig meat by three French organisations, i.e. ENVL and INRA in the Rhone Alpes region (South East), ITP and INRA in the West of France and Pen Ar Lan Company in Brittany. The results from the 3 groups are gathered and compared. It appears that the lesion is of a PSE type, however this syndrome recovers maybe various pathologies with different mechanisms but an identical expression. All genetic types together, the rate of structurless hams is of 10 to 20 % on average, with a strong variation according to slaughter series, season (more structurless meat in Summer); the heaviest and meatiest pigs show more defects, but this trend is not related to the growth rate. The HAL gene is a predisposing factor, but it is not the only one, as marked differences are observed among genetic types and among boars within-genetic type, although the latter observation should be confirmed. Regarding environmental factors, lairage conditions in the abattoir is noticeable, but other factors are probably involved. The biochemical mechanisms underlying the defect of structurless meat probably involve a deficiency in intracellular Ca++ as in PSE meat. Colour measurements appear as interesting indicators of the muscle destructuration. Moreover they have the interest to replace the subjective scoring by an objective and quantitative measure. Research is currently in progress to assess the possibility of using of video image analysis to quantify the intensity of the defect and to sort the hams in industrial conditions.

This article is aimed to review the research works carried out to dare about "structurless" pig meat by three French organisations, i.e. ENVL and INRA in the Rhone Alpes region (South East), ITP and INRA in the West of France and Pen At Lan Company in Brittany. The results from the 3 groups are gathered and compared. It appears that the lesion is of a PSE type, however this syndrome recovers maybe various pathologies with different mechanisms but an identical expression. All generic types together, the rate of "structurtess " hams is of 10 to 20 % on average, with a strong variation according to slaughter series, season (more,structurless" meat in Summer); the heaviest and meatiest pigs show more defects, but this trend is not related to the growth rate. The HAL gene is a predisposing factor, but it is not the only one, as marked differences are observed among genetic types and among boars within-genetic type, although the latter observation should be confirmed. Regarding environmental factors, lairage conditions in the abattoir is noticeable, but other factors are probably involved. The biochemical mechanisms underlying the defect of,structurless" meat probably involve a deficiency in intracellular Ca++ as in PSE meat. Colour measurements appear as interesting indicators of the muscle destructuration. Moreover they have the interest to replace the subjective scoring by an objective and quantitative measure. Research is currently in progress to assess the possibility of using of video image analysis to quantify the intensity of the defect and to sort the hams in industrial conditions.