Impact of the halothane gene on muscle quality and pre-slaughter deaths inWestern Canadian pigs

The genotype with respect to the point mutation at position 1843 of the ryr -1 gene (halothane gene) and longissimus muscle quality of 1006 pigs in two Western Canadian packing plants was assessed to determine the frequency of this mutation within the commercial population and the relationship of gen otype to the frequency of PSE (pale, soft, exudative) pork. The frequencies of nn (homozygous carrier), Nn (heterozygous carrier) and NN (homozygous n ormal) pigs within the commercial population were 0.3, 9.4 and 90.3%, respe ctively. Based on the subjective pork quality standards of Agriculture and Agri-Food Canada, the frequencies of paler-than-normal (colour score <3) an d darker-than-normal pork (colour score >3) were 21.7 and 11.2%, respective ly. The frequencies of soft, exudative pork (structure score <3) and firm d ry pork (structure score >3) were 14.8 and 7.6%, respectively. The frequenc y of pale loin colour was 80 and 20% higher for Nn than for NN pigs in the two packing plants, whereas the frequency of dark pork was unaffected by ge notype. Nn pigs exhibited a twofold higher incidence of soft, exudative por k than did NN pigs, but because of their very low frequency in the commerci al kill, had a very small impact on the overall incidence of soft, exudativ e pork. Removing this mutation from the pig population would have very litt le impact on the frequency of pale or soft, exudative pork within the two p acking plants involved in this study. Determination of the halothane genoty pe of 401 pigs, arriving dead or dying at the packing plants, indicated tha t pigs of the nn, Nn and NN genotypes were responsible for 27.7, 25.2 and 4 7.1% of deaths. The frequency of deaths within the nn, Nn and NN genotypes was estimated to be 9.2, 0.27 and 0.05%, respectively. Approximately 90% of the PSE condition in Western Canada is caused by factors other than the ha lothane gene, but this gene has a major negative influence on the frequency of pre-slaughter deaths.