Stress-resistant Pigs Research Articles

Lactobacillus johnsonii N5 from heat stress-resistant pigs improves gut mucosal immunity and barrier in dextran sodium sulfate-induced colitis

Developing effective strategies to prevent diarrhea and associated-gut disorders in mammals has gained great significance. Owing to the many health benefits provided by the commensal microbiota of the intestinal tract, such as against environmental perturbation, we explored the host phenotype-associated microbes and their probiotic potential. Based on the observations that the chronic heat stress-exposed weaned piglets present as heat stress-susceptible (HS-SUS) or heat stress-resistant (HS-RES) individuals, we confirmed the phenotypic difference between the two on growth performance (P < 0.05), diarrhea index (P < 0.001), intestinal heat shock protein 70 (HSP70) regulation (P < 0.01), and inflammatory responses (P < 0.01). By comparing the gut microbiome using 16S rRNA gene sequencing and KEGG functional analysis, we found that Lactobacillus johnsonii exhibited significantly higher relative abundance in the HS-RES piglets than in the HS-SUS ones (P < 0.05). Further experiments using a mouse model for chemical-induced inflammation and intestinal injury demonstrated that oral administration of a representative L. johnsonii N5 (isolated from the HS-RES piglets) ameliorated the clinical and histological signs of colitis while suppressing intestinal pro-inflammatory cytokines TNF-α and IL-6 production (P < 0.05). We found that N5 treatment enhanced tight junction proteins ZO-1 and occludin and cytoprotective HSP70 levels under physiological condition and restored their mucosal expressions in colitis (P < 0.05). In support of the high production of the anti-inflammatory cytokine IL-10, N5 promoted the intestinal Peyer's patches MHCII+ and CD103+ dendritic cell populations (P < 0.05), increased the regulatory T (Treg) cell numbers (P < 0.05), and decreased the Th17 population and its IL-17a production under physiological condition and during colitis (P < 0.01). Our results shed light on understanding the interaction between commensal Lactobacillus and the host health, and provide L. johnsonii N5 as an alternative to antibiotics for preventing diarrhea and intestinal diseases.

STRESS-RESISTANT OF PUREBRED AND CROSSBRED PIGS OF DIFFERENT BRED COMBINATIONS

The authors presented the results of experimental studies on the stress-resistant of pigs. The first group is a breed created in Sapphire Ltd. This breed is a breeding group (BG) in purebred breeding and their mixtures in two- and three-breed combinations with Landrace (L) and Duroc (D) boars under conditions of industrial farm technology in Siberia. Two methods assessed stress-resistant of piglets of different breed groups. The first method is “weaning crisis”. The second method is a com-parison of cortisol levels in the blood. Three-breed weanling piglets (SGxL)xD turned out to be the most stress-sensitive. Stress-resistant piglets had an effect on their growth during the rearing period. During this period, stress-resistant animals of all breed combinations had higher average daily gain than stress-sensitive animals (P &lt; 0.001). Stress-resistant animals of the breeding group (SG) showed an average daily growth of 547.5 g during the fattening period. Also, the stress-resistant animals of the breeding group reliably surpassed the stress-sensitive pigs by 461.4 g (P &lt; 0.01), the two-breed pigs by 455.9 g and 404.7 g and the three-breed pigs 451.8 g and 419.2 g, respectively. There was a statistically significant advantage in the indices of the average daily gain among the purebred young-sters of the breeding group (SG) (543 g) compared to the two-breed pigs (447g) and the three-breed pigs (402g), i. e., by 17.8 % and 26 % at P &lt; 0.001. The authors found that the EAAcr/- genotype in stress-sensitive pigs was more common than EAA-/(0.71 ± 0.07 vs 0.48 ± 0.09). Stress-resistant pigs of the breeding group (SG) with EAE edg/edf blood group genotypes were characterized by increased growth intensity and reliable superiority over stress-sensitive pigs. The authors believe that these genotypes can be accepted as preliminary candidates for genetic markers of stress resistant. Blood cortisol levels appeared to be unrelated to stress-resistant compared to the “weaning crisis” method. This relationship (blood cortisol level with stress-resistant) applies to all studied breed combinations, both individually and as a whole.

THE GENETIC CHARACTERISTICS OF PIGS OF DIFFERENT BREED COMBINATIONS AND THEIR RELATIONSHIP TO STRESS

The genotypic characteristics of the Sapphire genotype (SG) pigs and their hybridization with the вoars Landras (L) and Duroc (D) of 2-breed (SGхL) and 3-breed [(SGxL) xD] hybrids by genes: FABR-H, FABR-D, Ms4r, LEP, ECR, RYR-1 was investigated. In SG animals, the frequency of the ECRGG genotype, which is increased in comparison with 2- and 3- breed hybrids, is 0.41-0.54. Two-breed hybrids are characterized by a higher frequency of the genotype FABP HH (by 0.22-0.27) and FABP dd (by 0.27-0.39) than SG and three-breed. The peculiarity of the 3-breed hybrids (SGxL) xD is the higher frequency of the homozygous genotype Ms4r AA (by 0.24-0.34), and the lower frequency of the heterozygous Mc4r AG (by 0.19-0.43) compared with pure SG and 2-breed hybrids. The polymorphism of the LEP and RYR-1 genes in the compared groups of pigs is mainly represented by the desired genotypes LEPTT (71-75 %) and RYR-1NN (71-86 %). The indices of genetic similarity between the SG and hybrids were determined. The most significant differences were found between 2-breed and 3-breed hybrids (0.7634 ± 0.0613), which can be explained by the presence of blood of the breed D. General homozygosity (GH ) in pigs SG was 24.89 %, in 3-breed hybrids - 14.6 %. The genotypic structure of stress-resistant and stress-sensitive animals and associative connection of genotypes with energy of growth are revealed. Piglets with genotype FABPHH, resistant to stress, during the growing period surpassed their peers with the FABPHh and FABPhh genotypes by an average daily gain of 81-139 g, sensitive to stress by 134 g. Animals with the FABPDD genotype, stress-resistant, had the highest energy of growth (593 g), which was higher than in peers with the homozygous genotype FABP Ddd by 91 g and heterozygous FABP DDd by 157 g. Among the piglets sensitive to stress, individuals with the LEPTT genotype had a higher growth energy of 87 g compared to heterozygous LEPTC. Stress-resistant pigs with the RYRNn genotype outperformed homozygous peers of RYRNN in this indicator by 95 g. Among the carriers of the Mc4r and ECR genotypes, no differences in growth energy of the pigs were detected.

Genetic variation at RYR1, IGF2, FUT1, MUC13, and KPL2 mutations affecting production traits in Chinese commercial pig breeds

The identification of causative mutations affecting economically important traits has benefited the worldwide pig industry. We investigated the genetic variation at five loci including RYR1, IGF2, FUT1, MUC13, and KPL2 affecting traits related to production, reproduction, and disease resistance in a sample of 8009 pigs representing 3 commercial breeds (Duroc, Landrace, and Large White) from 28 farms in China. We found that all breeds, especially Duroc pigs, have high frequencies of favourable alleles for lean production and stress resistance at the IGF2 and RYR1 loci. However, all breeds have low frequencies of the diarrhea-resistant allele of FUT1, indicating that multigenerational selection is required for E. coli F18&lt;sup&gt;+&lt;/sup&gt; resistant pigs. No linkage disequilibrium was found between the RYR1 and FUT1 loci on pig chromosome 6, supporting the possibility of combined selection for both F18 and stress-resistant pigs. Relatively high frequencies (&amp;gt; 0.5) of the MUC13 allele conferring resistance to E. coli F4ac were found in all three breeds with the highest frequency in Duroc pigs, suggesting that the breeders can establish F4ac diarrhea-resistant lines in a few generations. No defective allele at the KPL2 locus causing immotile short-tail sperms was found in Large White pigs of American, Canadian, Danish, English, and French origin, supporting the conclusion that the KPL2 defective allele is present exclusively in Finnish Large White pigs. These results provide useful information for pig breeding schemes in China.

Naloxone influences the morphine-induced enhancement of plasma β-endorphin in stress-resistant pigs

Naloxone influences the morphine-induced enhancement of plasma β-endorphin in stress-resistant pigs

The effect of interaction between genotype CAST/ RsaI (calpastatin) and MYOG/ MspI (myogenin) on carcass and meat quality in pigs free of RYR1T allele

The purpose of the studies was to demonstrate to what degree genotypes of calpastatin ( CAST/RsaI) and myogenin ( MYOG) genes as well as the interaction between them may affect the carcass and meat quality of pigs. The investigations were conducted on 397 stress resistant pigs (free of RYR1 T allele). It was demonstrated that the favourable effect of the variants of CAST and MYOG genes on carcass quality traits depends on the cut. The gene variant favourably affecting the weight of ham simultaneously had a negative effect on the weight of the loin. It was also shown that the interaction between CAST and MYOG genotypes has a significant effect on backfat thickness. The effect of a given combination of CAST and MYOG genotypes on carcass traits is related to the weight of a substantial cut (ham, loin). Genotypes at loci CAST/ RsaI and MYOG have a significant effect on the value of certain traits and parameters of meat quality and its technological value (genotype CAST on pH at 35 min and 2, 3, 24, 48, 96, 144 h post-mortem (pH 35, pH 2, pH 3, pH 24, pH 48, pH 96, pH 144, respectively), R 1 (IMP/ATP), electrical conductivity at 3 and 4 h post-mortem (EC 3, EC 4), technological yield of meat in curing and thermal processing (TY) and protein content in the muscle tissue, while genotype MYOG on pH 48, EC 35, EC 3, EC 24 and dry matter content).

The possibility of positive selection for both F18 +Escherichia coli and stress resistant pigs opens new perspectives for pig breeding

F18 + Escherichia coli infections causing post-weaning diarrhoea and/or oedema disease are a major cause of economic losses in pig industry. To date, no preventive strategy can protect pigs from F18 + E. coli infections. One of the most attractive approaches to eliminate F18 + E. coli infections is the selection for pigs that are resistant to F18 + E. coli infections. However, this strategy was not believed to be favourable because of reports of genetic association with the stress-susceptibility gene in the Swiss Landrace. To investigate this potential association more thoroughly, 131 randomly selected Belgian hybrid pigs were genotyped for both the F18 + E. coli resistance alleles ( FUT1 A ) and the stress-susceptibility alleles ( RYR1 T ) and their association was investigated by determining the linkage disequilibrium. This linkage disequilibrium (LD = − 0.0149) is close to zero and does not differ significantly from 0 (likelihood ratio test χ 1 2 = 1.123 , P = 0.29), demonstrating no association between the FUT1 A and RYR1 T alleles. Furthermore, only a small fraction (4.6%) of the Belgian pigs was found to be resistant to F18 + E. coli infections. Our results suggest that selection for F18 + E. coli resistant pigs might be an attractive approach to prevent pigs from F18 + E. coli infections, unlike to what has previously been postulated.

Meat and carcass quality in two pig lines of different stress-susceptibility genotype and their crosses

AbstractIn order to investigate differences in carcass and meat quality between lines of different stress susceptibility, 150 pigs were slaughtered on 15 slaughter days, consisting of equal numbers of stress-susceptible (nn) pigs of a boar line, stress-resistant (NN) pigs of a sow line and stress-carrier (Nn) crosses of these two lines. Carcass quality was determined by a SKGII-device which combined four physical measurements into a carcass lean estimate and a conformation score, and meat quality traits were measured on the carcass and on a loin slice. Killing-out proportion was lower for the NN line compared with the Nn crosses and the nn line. Lean content increased and conformation score improved as the number of n alleles in the respective genotypes increased but the Nn genotype was closer to the nn genotype than to the NNgenotype. Similarly, a large difference in meat quality was found between the NN and the nn line, whereas the difference in meat quality between the Nn and the nn genotype was smaller than expected. This was probably due to the low-voltage stunning procedure. In addition, the method of transporting the pigs to the abattoir (by truck or by foot, for a distance 125 m) had a pronounced effect on meat quality in the loin.

Effect of halothane genotype, breed, feed withdrawal, and lairage on pork quality of belgian slaughter pigs.

A total of 434 Belgian Landrace (B) or Piétrain x B (PB) pigs, of known halothane genotype (NN, Nn, and nn), were slaughtered in a commercial abattoir. Pigs were either fed until loading or deprived of food overnight before delivery. Upon arrival at the abattoir, pigs were slaughtered after different lairage times (within 1 h after arrival, after 2 to 3 h lairage, or 4 to 5 h lairage). Meat quality traits were measured on the carcass, as well as on a piece of loin. Halothane genotype was the predominant factor determining meat quality traits related to the PSE condition (P < .001 for pH 40 min after death, internal reflectance, color L value; P < .01 for drip losses, transmission value). For these traits, nn pigs were always significantly different from Nn and NN pigs. Depending on the specific trait, Nn pigs were intermediate between NN and nn pigs, or close to NN pigs. For pH 40 min after death and drip losses, Nn and NN pigs were significantly different, whereas the difference between Nn and NN pigs was not significant for internal reflectance, color L value, and transmission value. Shear force and intramuscular fat content were apparently not related to the PSE condition and were not influenced by the halothane genotype (P > .05). Differences in meat quality between B and PB pigs and between gilts and barrows were rather unimportant compared with the effect of halothane genotype. Overnight feed withdrawal had no effect on meat quality (P > .05 for all PSE-related traits). On the other hand, holding pigs a few hours in lairage improved meat quality compared with immediate slaughtering (P < .05 for pH and temperature in the loin 40 min after death, internal reflectance, color L value, transmission value, drip losses). This effect was more pronounced in stress-susceptible pigs than in stress-resistant pigs.

Prediction of meat quality in live pigs using stress-susceptible and stress-resistant animals

A new in-vivo procedure for predicting the potential meat quality in live pigs was devised using stress-susceptible (halothane positive) and stress-resistant (halothone negative) pigs. The potential meat quality in live pigs was determined using small biopsy samples of M. longissimus dorsi (LD). Meat quality was assessed by the combined measurements of pH and water-holding capacity (WHC) on the 12 000 g supernatant after incubation of 500 mg biopsy LD muscle with an equal volume of 150 m m KCl at 39°C for 45 min. With the LD muscles of halothane positive ( n = 37) and halothane negative (n = 55) pigs, high correlations (r = −0·854) were observed between the supernatant (i.e. fluid) pH and WHC of the biopsy samples, between fluid pH of the biopsy samples and 1-h post-mortem (pH 60) LD muscles (r = 0·951), and between pH 60 and WHC (r = −0·956). The experimental data show that our in-vivo test can differentiate halothane positive from halothane negative pigs and can also predict the potential meat quality in live pigs. The test could be applied to select pigs with differences in WHC to improve meat quality.

A comparison of some muscle metabolites in stress susceptible and resistant Landrace gilts after halothane exposure or exercise stress

Sixty-six South African Landrace gilts were used in the experiments. At the age of 21 weeks, 47 of the pigs were challenged with halothane exposure. As a result 17 of the pigs died, and were classified stress susceptible (SS), whereas the 30 survivors were classified stress resistant (SR). The other 19 pigs were subjected to treadmill exercise. Four of the exercised pigs died. The pigs that survived the treadmill exercise were later exposed to halothane. The pigs that died as a result of the halothane exposure ( n = 5) or the treadmill exercise ( n = 4), were classified SS ( n = 9) and the survivors as SR ( n = 10). A biopsy of the M. semitendinosus was used for measurement of difference in muscle lactate, ATP, glucose 6-phosphate, phosphocreatine, glucose and glycogen concentrations. The results show that in all pigs exercise resulted in the higher stimulation of glycogenolysis than did halothane exposure. However, SS pigs overall showed a greater stimulation of glycogenolysis and glycolysis and general anaerobic metabolism, compared to SR pigs. Under halothane exposure, glycogenolysis and anaerobic metabolism were stimulated in the SS pigs to a much greater extent than in SR pigs, with significant differences between all the muscle metabolites determined. However, treadmill exercise, although sufficient to cause death in some pigs, resulted only in significantly higher lactate and glucose 6-phosphate concentrations. SR pigs exposed to halothane had significantly higher ATP, phosphocreatine and glycogen concentrations, but a lower glucose concentration than exercised SR pigs, indicating less severe stimulation of glycogenolysis by halothane than exercise. No significant differences were found in the determined muscle metabolites in SS pigs exposed to halothane compared to exercised SS pigs. In conclusion, these differences suggest that different mechanisms of stimulation of metabolism on exposure to halothane and exercise may exist, although both types of stress cause stimulation of glycogenolysis.

β-adrenergic responsiveness in stress-sensitive and stress-resistant pigs

This study investigated whether enhanced metabolic responsiveness to beta-adrenergic stimulation might explain the liability of the stress-sensitive pig to develop an acidosis during stressful situations. Blood lactate, pH, PCO2 and heart rate response to an intravenous infusion of isoprenaline were examined in three lines of pentobarbitone anaesthetized, atropinized pigs. The lines were Pietrain X Hampshire which had been selected over eight generations for a positive reaction to the halothane test (stress-sensitive); Pietrain X Hampshire which had been selected over eight generations for no reaction to the halothane test (stress-resistant) and British Landrace which had been selected over four generations for a positive halothane reaction (stress-sensitive). The metabolic responses to isoprenaline were greater in the stress-sensitive Pietrain X Hampshire line than the stress-resistant line. The stress-sensitive Landrace pigs, however, had smaller changes in pH and PCO2 in response to isoprenaline than the stress-resistant Pietrain X Hampshire pigs. This inconsistent trend across the three lines led to the conclusion that enhanced beta-adrenergic responsiveness was not the likely cause of stress sensitivity.

Increased indices of lipid peroxidation in stress-susceptible pigs and effects of vitamin E

When stress-susceptible and stress-resistant pigs consumed diets containing 10 iu vitamin E kg-1, the stress-susceptible pigs had damaged cell membranes. This was indicated by increased plasma activities of creatine kinase and pyruvate kinase. Plasma concentrations of thiobarbituric acid reactive substances and conjugated dienes were also increased suggesting that the membrane damage was caused by free radicals. Susceptibility to free radicals was further demonstrated by an increased tendency for erythrocytes and tissue homogenates from stress-susceptible pigs to peroxidise when incubated with hydrogen peroxide and iron, respectively. Supplementation of the diets with approximately 20 times normal requirements of vitamin E decreased plasma creatine kinase and pyruvate kinase activities, and inhibited the formation of the indices of peroxidation in vivo and in vitro. It is concluded that the stress-susceptible pig has an abnormality in its antioxidant defence mechanisms. However, this abnormality was not due to a deficiency in selenium-dependent glutathione peroxidase, since activities were significantly increased in the longissimus dorsi of stress-susceptible pigs. Although the nature of the antioxidant defect is unclear, it is suggested that stress-susceptible pigs are under a sustained oxidant stress and that a decreased ability to accommodate even a normal free radical load may contribute to the rapid development of the fatal stress response.

Blood lactate kinetics in normal and stress-susceptible pigs.

In vitro rates of lactate metabolism were determined in stress-susceptible (SS) and stress-resistant (SR) pigs. Three SR and three SS pigs were given 20 muCi of [U-14C] L-lactate by a single injection method and resting blood lactate kinetics were measured. Seventeen blood samples were taken during the 60 min after injection. Lactate was separated from the deproteinized plasma by silicic acid column chromatography, and specific radioactivity was determined. Kinetic characteristics were calculated from plots of specific activity versus time. Pigs met steady-state requirements during the sampling period. There were no differences in kinetic characteristics of resting SS and SR pigs. Later, a second isotope injection was given after 5 min of electrical stress. Lactate pool sizes increased similarly in both types of pigs after stress; however, SS pigs had greater plasma lactate concentrations after stress. It is concluded that SS and SR pigs respond differently to stress but have similar capacities to metabolize lactate while resting.

Conversion of Alanine, Aspartate and Lactate to Glucose and CO2 in Liver from Stress-Susceptible and Stress-Resistant Pigs

Rates of conversion of lactate, alanine and aspartate to glucose and oxidation of each to CO2 were determined in incubated liver slices from nine stress-susceptible (SS) and seven stress-resistant (SR) Yorkshire pigs ranging in body weight from 24 to 54 kg. Pigs were screened for stress susceptibility by exposure to halothane at 7 weeks of age. Stress was minimized before slaughter, and liver samples were obtained immediately after death. Rates of lactate and aspartate conversion to glucose were not significantly different between pig types. Mean rates of lactate conversion to glucose in livers of SS and SR pigs were 637 and 413 nmoles/(100 mg X 2 hours), respectively. Mean rates of aspartate conversion to glucose were 441 and 540 nmoles/(100 mg X 2 hours) in SS and SR pigs, respectively. Alanine conversion to glucose in livers of SS pigs was slower than that in SR pigs [527 and 813 nmoles/(100 mg X 2 hours), respectively]. Rates of hepatic gluconeogenesis from lactate probably do not predispose SS pigs to the lactic acidosis observed during the porcine stress syndrome. Rates of lactate, alanine and aspartate oxidation to CO2 in livers of SS pigs were 61, 59 and 76%, respectively, of the rates observed in SR pigs. Decreased rates of substrate oxidation to CO2 may contribute to the development of the syndrome in SS pigs.

Effect of halothane on isometric contractile properties of muscle from stress-susceptible and stress-resistant pigs

The effect of clinical concentrations of halothane on the isometric contractile properties of muscle in stress-susceptible and stress-resistant pigs was studied. Exposure to halothane initially increased the percentage of peak twitch tension in the muscle of stress-susceptible pigs whereas the tension gradually decreased in the stress-resistant group of pigs. Halothane may act as a potentiator of muscle contraction in stress-susceptible animals, but this effect is transitory.

Response of stress-susceptible and stress-resistant Hampshire pigs to electrical stress. I. Physiological and biochemical effects.

Stress susceptible (SS) and stress resistant (SR) purebred Hampshire swine, weighing approximately 100 kg, were utilized to study the effects of electrical stress on plasma creatine phosphokinase (CPK), blood pH, plasma lactic dehydrogenase (LDH), plasma glucocorticoids, rectal temperature, heart rate and respiration rate. Blood samples were obtained from jugular cannulas 15 min and 5 min pre-stress, and subsequently at 0, 5, 10, 15, 30, 60 and 120 min post-stress. The electrical stress (.05 amperes and 30 volts) was administered intermittantly (2 sec on and 1 sec off) directly on the skin at the point of the poll between the ears and on the medial side of the fore leg above the point of the elbow for a total stress time of 4 min over a 6-min period. Each pig was stressed three times with 3 days rest between stimulations. Post-stress responses (P<.01) were obtained over time for all the variables measured except respiration rate. Plasma CPK levels were greater (P<.01) for SS pigs at all the pre-stress and post-stress bleeding times. Thus, CPK may have value in differentiating between SS and SR pigs under standardized environmental (stress) conditions. The SS pigs had marked post-stress decrease (P<.01) in blood pH compared to SR pigs, although pre-stress blood pH was similar for both groups of pigs. Pre-stress plasma LDH levels were similar for the SS and SR pigs while several post-stress levels were greater for the SS pigs. Plasma glucocorticoid levels were similar for the SS and SR pigs at all the pre-and post-stress bleeding times. The SS pigs had a higher (P<.05) overall mean rectal temperature compared to the SR pigs. Both the SS and the SR pigs had elevated post-stress rectal temperatures. The heart rate of the SS pigs was higher at 0 min post-stress compared to the SR pigs while both groups were similar at the other times. Respiration rates were similar for both groups.

Energy phosphate turnover and glycolysis in skeletal muscle of the Piètrain pig: The effects of premedication with azaperone and pentobarbitone anaesthesia

The semitendinosus muscle of Piètrain pigs which were premedicated with azaperone and anaesthetized with pentobarbitone exhibited the slow rates of glycolysis and energy phosphate turnover that are characteristic of resting muscle from stress-resistant pigs and the rabbit. Curarization did not reduce further the rate at which such changes occurred. The results suggest that the high rate of energy phosphate hydrolysis usually associated with Piètrain muscle may have its origin within the nervous system rather than in the skeletal musculature itself. In the absence of neural stimulation, the rates at which such changes occur in resting muscle appear to be similar for both the Piètrain and stress-resistant breeds of pig.

The trigger for PSE condition in stress-susceptible pigs.

AbstractTightly coupled mitochondria from M. longissimus dorsi (LD) muscle of different breeds of pigs showed variations in the rate of Ca2+ efflux during anaerobiosis. The initial fast efflux rate of Ca2+ could be used to relate the stress‐susceptibility of the pigs used. Mitochondria from LD muscle of stress‐susceptible (SS) Pietrain and Poland China pigs showed an anaerobic rate of Ca2+ efflux twice that of stress‐resistant (SR) Large Whites. Mitochondria from crossbreds (Large White x Saddleback) showed a Ca2+ efflux rate intermediate between that of purebred SS and SR pigs. Halothane enhanced the rate of Ca2+ efflux only in SS pigs, and this effect could be eliminated by MgCl2. The marked difference in the rate of Ca2+ efflux between SS and SR pigs, and the enhancement in the rate of Ca2+ efflux by halothane only in SS pigs, offers an ultimate explanation for the formation of PSE (pale, soft and exudative) muscle and malignant hyperthermia in SS pigs. The excess Ca2+ liberated from mitochondria of SS pigs is postulated to be the trigger for PSE meat and also the case of malignant hyperthermia.

Some Biochemical Properties in the Excised Hearts of Stress Susceptible and Stress Resistant Pigs

No significant differences were found for cardiac muscle levels of G-6-P, ATP, CP or lactate in stress susceptible and stress resistant pigs. However, at exsanguination, hearts from stress susceptible pigs had higher levels of ATP and higher levels of lactate than hearts from stress resistant animals; but, the differences only approached statistical significance. Stresses prior to slaughter significantly lowered (P<.01) the ATP concentration and significantly decreased (P<.05) G-6-P concentration in the myocardium of the left ventricle. During heart incubation, cardiac muscle ATP levels significantly decreased (P<.01) whereas cardiac muscle lactate levels significantly increased (P<.01) for both stress susceptible and stress resistant pigs.