Determination of halothane gene mutation associated with malignant hyperthermia in sows dead of cardiac failure.

Abstract

Significant losses due to sow mortality may be encountered in some swine breeding herds. Many conditions are responsible for death in sows; some, however, are more common Several investigations showed that cardiac failure is among the major causes of death in breeding females, accounting for up to 31% of the mortalities. 1,4,17,19,20 Parturition, heat stress, mating, fighting, and transport were identified as predisposing factors for cardiac failure in sows housed in total confinement. 1-6 Most of these events, which are demanding for the cardiovascular system, are also considered triggering factors for the development of malignant hyperthermia (MH) in pigs, a genetically transmitted disease. Differentiating a simple case of cardiac failure from MH might be difficult because these 2 conditions share many clinical and pathologic similarities. Recently, MH in swine, also called porcine stress syndrome (PSS), has been associated with a recessive mutation in the gene coding for porcine calcium release channel, also called the ryanodine receptor gene (ryr-1 locus) or halothane gene (Hal), which is located on chromosome 6. With molecular biology techniques, it is now possible to identify pigs that are MH susceptible, MH carrier, and norma1. The aim of this retrospective study was to determine if cases of cardiac failure in sows could be attributed to the defective gene responsible for MH. Formalin-fixed, paraffin-embedded tissues from 84 sows previously collected in a study on sow mortality in Canada were used in the present investigation. From these selected sows, 42 were identified to have died of cardiac failure and 42 died of various other causes (control group), such as torsions of abdominal organs, cystitis-pyelonephritis, gastric ulcers, and uterine prolapse. Paraffin-embedded tissue blocks from heart, skeletal muscle, liver, spleen, and kidney were used to determine the Hal genotype by a polymerase chain reaction (PCR) technique. 11,22 For each sow, a 10-μm-wide section was prepared from tissue blocks, and excess paraffin was trimmed. Sections were placed in 1.5-ml sterile microfuge tubes. The microtome blade, tweezers, and other equipment that could come into contact with the samples were carefully sterilized before processing each tissue block. Tissue sections were deparaffinized with toluene and washed twice with ethanol to remove the solvent. Ethanol was allowed to evaporate under vacuum for 10 minutes. To isolate genomic DNA, 100 μl of digestion buffer (50 mM Tris [pH