Succinylcholine and halothane as a field test for the heterozygote at the halothane locus in pigs

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Abstract
Reaction to the muscle relaxant succinylcholine was investigated as a possible method of distinguishing the heterozygote from the normal homozygote at the halothane locus. Totals of 54 assumed heterozygotes and 67 assumed homozygotes received intravenous succinylcholine during halothane anaesthesia at 6 to 10 weeks of age. Three separate measures of the duration and severity of the muscular reaction to succinylcholine were all significantly increased in heterozygotes compared with homozygotes. The genotypic difference for one of the three reaction traits was significantly influenced by the day of testing. Due to overlapping distributions for the two genotypes, succinylcholine reactions did not offer a precise method of identifying individual heterozygotes. Although test mating to recessive homozygotes would still be required to be certain of eliminating the halothane gene, the gene frequency among prosepective parents for test mating could be substantially reduced by succinylcholine screening. Due to the expertise and time required, succinylcholine testing would probably only be worthwhile for the production of specialized homozygous lines at nucleus level.