Exertional myopathy in Finnish Landrace pigs a survey of the situation and evaluation of different control methods
Authors: Schulman Axel 
Published: July 2018

The exertional myopathy situation is surveyed for the top of the breeding pyramid of the Finnish Landrace breed by testing 2,003 pigs and from material on the Norwegian Landrace (86 pigs). The usefulness of the different methods as well as practical measures with regard to the breeding programme are discussed. The halothane sensitivity frequency in the Finnish Landrace breed was found to be 12.4%, indicating that about 58 % of all Finnish Landrace pigs at the top of breeding pyramid have the halothane sensitivity gene (Haln). In contrast, a frequency of only 3.2 % was found in the Norwegian material. Of the Finnish Landrace pigs 60.7 % had the H blood group factor a, 38.0 % factor c and 16.7 %none of these factors. In the Norwegian material 62.0 % had factor a and 55.6 % factor c. Of the Finnish hal+ pigs 91.1% had the H blood group factor a and 3.2 % factor c, while 6.1 % had none of these factors. About 96.6 % of the hal+ pigs had the Phi enzyme type BB and 3.4% the Phi-type AB. None of the Phi-type AA pigs were sensitive to halothane. Phi AA was found to be rare in the Finnish Landrace, with only 1.5 % of the animals having this Phi type. The water-holding capacity measurements from muscle biopsies taken from the pigs at the end of the halothane test did not show statistically significant differences between groups of hal+ and hal— pigs. It was concluded from the results of the present study that the measurement of CK serum activity in nonstressed pigs is not very useful for identification of the hetcrozygotic carriers of the Haln gene.The iterativeness of the CK test in non-stressed pigs was found tobe poor, but muscle tissue might have infected some of the serum samples taken from the vena cava and so caused false high serum CK activity. The halothane test is reliable for the identification of Haln gene homozygotes when conducted on pigs older than 50 days. The Phi AA type is so rare that Phi enzyme typing in Finland is of limited value at present for the breeding programme. A determination of the H blood group factors a and c of all pigs intended for breeding is advised. By increasing the number of pigs with the H blood group factor c it should be possible to reduce the exertional myopathy problem in the Finnish Landrace breed. Preferential use of the desirable genotype c of the H blood group system should be more attractive to breeders than selecting against the undesirable H blood group factor a, especially as many of the H a/a and H a/ pigs have a high K index and a high percentage of lean meat on the carcase. The best a/a and a/pigs may be kept as breeding animals but have to be mated only to H c/ pigs. Because some H c/ pigs are carriers of the Haln gene and a high K index and percentage of lean meat on the carcase favour carriers of the Haln gene, it is most probable that the existing low frequency of H c/ pigs sensitive to halothane will change in the future in an unfavourable direction. It is therefore advisable to stipulate a halothane test based on a progeny test for all H c/ boars with a high K index. Halothane-sensitive sows would be especially suitable for these test matings.