A group of 43 pigs from eight litters of purebred Pietrains were identified as malignant hyperthermia susceptible by halothane testing, and their reaction time (measured in seconds from the onset of halothane administration of the onset of skeletal muscle rigidity) was recorded. One week later, these pigs were treated with 0.02, 0.2, 0.5, 1.0 or 2.0 mg/kg of droperidol 1 hour prior to a second halothane test. Pigs with a post-droperidol reaction time of greater than 100.4 seconds (mean + 2.021 SD of initial reaction time) were considered to be protected from malignant hyperthermia. Droperidol afforded some degree of protection at all doses tested. The effective dose50 was determined to be 0.055 with 95% confidence limits of 0.017 to 0.183 mg/kg.
The defect causing malignant hyperthermia has been proposed to involve cardiac as well as skeletal muscle. We tested the hypothesis that histomorphometric parameters for ventricular wall from malignant hyperthermia-susceptible swine and dogs were abnormal. Hearts were obtained from: mature dogs, age- and weight-matched young swine (89 +/- 15 days, 30 +/- 3 kg); and market-weight swine (102 +/- 10 kg). Using light microscopy, estimates were made for muscle nuclear dimensions and the volume-fraction of nuclei, sarcoplasm, blood vessels, and interstitial space. Cardiac maturation in both MH and normal swine was accompanied by decreased myocyte volume-fraction due to decreased nuclear volume-fraction and increased interstitial space volume-fraction. Sarcoplasm and vasculature volume-fraction were unchanged after maturation. Nuclear volume-fraction was slightly greater (p less than 0.05) in the right ventricle than the left for malignant hyperthermia and normal swine. Myocyte nuclear dimensions were generally similar among animals. Dogs and the oldest group of swine were not significantly different. Myocytes of all swine contained multiple nuclei, closely spaced in rows of 2 to 12. In contrast, most myocytes of mature dogs apparently contained one or two nuclei. Histomorphometric values were not significantly different between normal and malignant hyperthermia young swine and dogs. However, within the market-weight swine, volume-fraction for malignant hyperthermia myocytes and myocyte nuclei was decreased and interstitial space was increased compared to normal.(ABSTRACT TRUNCATED AT 250 WORDS)
Data from 200 hogs, representing all possible two-breed and purebreed crosses of Minnesota No. 1 (M), Pietrain (P), and Yorkshire (Y) breeds and two sexes, barrows (1) and gilts (2), were recorded following slaughter at four developmental stages (22.5 kg, 45.0 kg, 67.5 kg, and 90.0 kg liveweight). The objectives were to examine: (a) breed and sex effects on allometric growth coefficients (AGC) and lean tissue growth rates (LTGR); (b) breed differences for feed efficiency on a live animal basis (GF) and lean tissue basis (LTGF); (c) heterosis and differences between reciprocal crosses for these traits; and (d) the relationship between live animal growth rate and LTGR. Breed differences were: P × P(2) < [M × M(1,2) = P × P(1) = Y × Y(1,2)] for AGC and (P = Y)> M for LTGR, GF, and LTGF. Differences (P < 0.05) between barrows and gilts were found in the P × P and Y × P crosses for AGC but none were found for LTGR. Heterosis estimates for LTGR increased in magnitude with stage of development, but were stable when expressed on a percent basis, and differences between reciprocal crosses remained constant. Heterosis estimates were found to be significant (P < 0.05) for AGC and GF but not for LTGR. Significant (P < 0.05) differences between reciprocal crosses were reported for GF and LTGF but not for AGC. Live animal growth rate was found to be a good predictor of LTGR with R 2 ranging from 0.65 to 0.84. Key words: Allometric growth coefficients, feed efficiency, breed differences, heterosis, reciprocal differences, swine
Abstract Six different breed groups (Yorkshire (Y), Pietrain (P), a Pietmin derivative breed Near Pietrain (NP), and crosses NP × P, P × NP and F 2 ) were tested for breed, skeltal muscle ryrl genotype (hal gene), and sex effects on growth, performance and carcass traits. Within the C/C (homozygous normal for the hal gene) or T/T (homozygous recessive for the hal gene) ryrl genotypes there were significant differences among breed groups in a number of performance and carcass quality traits. In contrast, the performance and carcass quality traits of the C/T (heterozygous for the hal gene) ryrl genotype-containing breed groups were similar. In the four breeds containing C/T and T/T ryrl genotypes, the additional copy of the ryrl T allele had a significantly positive effect on all measures of amount of lean meat with a negative effect on all meat quality scores ( P < 0·001). Notably, the C/C and T/T ryrl genotypes in the NP and F 2 breed groups differed significantly in all measures of amount of fat and lean; the C/T genotype was intermediate to the C/C and T/T genotypes in all traits with the C allele exhibiting partial dominance for these measures. It is concluded that within breed groups of similar genetic background, the ryrl genotype has positive effects on all measures of the amount of fat and lean, with associated negative effects on meat quality. The availability of the DNA-based test to identify the ryrl genotype allows pig breeders to take advantage of the beneficial traits or to eliminate the deleterious traits associated with this gene from their populations.
Abstract A possible relationship between muscle cell injury or deterioration and enhanced halothane sensitivity was studied by monitoring mechanical responses of skeletal muscles from normal pigs and pigs susceptible to malignant hyperthermia (MH). Increased time postbiopsy and decreased maximum control tetanic tension both correlated significently with enhanced sensitivity to halothane. In both normal and MHsusceptible (MHS) muscles, greater halothane sensitivity was observed in cut cell than in intact cell bundles and in low tetanic tension as compared to high tension preparations. Subsequent to halothane exposure, twitches of high tension (≥ 1.75 kg · cm −2 ) intact bundles of both normal and MHS muscles were potentiated. Tetani of normal intact bundles were not altered, whereas those of MHS bundles were depressed after halothane exposure. Control twitch‐to‐tetanus ratios (twitch ratios) were higher in MHS (0.23) than in normal (0.12) intact bundles. According to discriminant analysis, the best distinction between normal and MHS muscles, either cut or intact, was obtained by comparing halothane‐induced changes in tetanic tension and control twitch ratios.
Breed and sex effects on muscle properties and physiological parameters of stress-susceptibility were studied on purebred Pietrain (P× P), purebred Minnesota No. 1 (M× M) and F1 (P× M) cross-bred pigs. Four gilts and four barrows were used in each breed group. Blood samples were taken 10 min after heat stress (40.5 C) at approximately 60 kg live weight and analyzed for blood creatine kinase (CK) by the Rosalki method. Animals were sacrificed at 100 ± 4 kg live weight following a 10 min, 40.5 C heat stress. Lactate, glucose, cholesterol, lactate dehydrogenase (LDH) and CK (Rosalki, Sigma, Biodynamics) were determined on blood obtained from the carotid artery at exsanguination. Backfat thickness, longissimus muscle area, carcass length, percentage ham plus loin, longissimus muscle quality properties, adrenal weight and histology and heart weight were determined. P× P and M× M breeds displayed sharply contrasting traits: P× P pigs displayed the fastest longissimus muscle pH decline, the greatest longissimus muscle area and percentage ham plus loin of the three groups. M× M pigs exhibited the highest values for color, structure, marbling, adrenal weight, backfat thickness and carcass length. The P× M group exhibited means intermediate between the two purebred groups for the following: longissimus pH 45 min postmortem, structure, marbling, longissimus area, percentage ham plus loin and backfat thickness. The means for carcass length and adrenal weight in the P× M group were close to the means for M× M pigs. No significant differences were noted for heart weight unless it was expressed as grams per kilogram ham plus loin (an index of muscularity) in which case P× P pigs exhibited lower ratios than P× M and M× M pigs. No significant breed differences were noted for blood glucose or cholesterol. Lactate was significantly (P<.05) higher in P× P than M× M pigs. However, if expressed as milligrams lactate per kilogram ham plus loin, the statistical significance of the breed differences for lactate vanished. Serum levels of CK were higher (P<.05) in P× P pigs than in M× M and P× M pigs prior to and following heat stress at 60 kg live weight. Following heat stress, levels of CK and LDH were generally high in P× P, intermediate in P× M and low in M× M pigs at 100 kg live weight as determined by the Rosalki, Sigma and Biodynamic procedures. Significant sex differences were noted for blood CK (Sigma), backfat thickness, longissimus muscle area, carcass length and percentage ham plus loin which characterized gilts as more muscular than barrows (P<.01) and also exhibiting higher blood CK (P<.05). The same serum sample analyzed for CK (Rosalki) demonstrated that a significant (P<.05) breed × sex interaction existed in which for P× M pigs, barrows exhibited higher blood CK than gilts; for P× P pigs, gilts exhibited higher CK than barrows; and for M× M pigs, gilts and barrows were very similar in blood CK value.
Heritability of litter size was studied in three inbred lines of swine. An intra-group regression of the record of the daughter on the record of her dam was made to estimate heritability. A total of 1970 daughter-dam comparisons were made. Only data of the number born alive in the first litter were used. A heritability estimate for litter size for the Minnesota No. 1 was 0.05±0.13, for the Minnesota No. 2 it was −.04±0.10 and for the Minnesota No. 3 it was 0.17±0.14. An overall heritability estimate for all animals studied was found to be 0.03±0.07. None of the heritability estimates obtained were found to be significantly different from zero or significantly different from each other (P>.05). The values found in this study fall within the range of those reported elsewhere, but are considerably less than a major portion of those reported. From this study it was concluded that heritability for litter size is low and the response to mass selection for increased performance within a line or breed will be negligible.
The skeletal muscle ryanodine receptor of malignant hyperthermia‐susceptible (MHS) pigs contains a mutation at residue 615 that is highly correlated with various abnormalities in the regulation of sarcoplasmic reticulum (SR) Ca 2+ channel activity. In isolated SR membranes the Arg 615 to Cys 615 ryanodine receptor mutation is now shown to be directly responsible for an altered tryptic peptide map, due to the elimination of the Arg 615 cleavage site. Furthermore, trypsin treatment released 86–99 kDa ryanodine receptor fragments encompassing residue 615 from the SR membranes. We conclude that the 86–99 kDa domain containing residue 615 is near the cytoplasmic surface of the ryanodine receptor and likely near important Ca 2+ channel regulatory sites.
