Blood group association with severity and speed of the halothane reaction

Performance of British Landrace pigs selected for high and low incidence of halothane sensitivity

Halothane positive and negative selection lines were established to estimate the effects of the halothane gene on performance in British Landrace pigs. Incidences of positive reaction diverged from 0·12 in the foundation generation to 0·93 in the positive and to 0·02 in the negative line in generation 4. Differences in litter productivity as a trait of the dam were estimated from a total of 399 positive × positive and negative × negative parity 1 and 2 matings in generations 1 to 4.

Compared with negative contemporaries, positive females showed non-significant reductions in litter size at birth (−0·10, s.e. 0·26) and at 42 days (−0·28, s.e. 0·26), accompanied by significant reductions in average piglet weights at birth (−0·11, s.e. 0·02 kg) and 42 days (−0·4, s.e. 0·2 kg). There were no differences in conception rate or adult live weights. A subsample of 69 parity 2 and 3 sows slaughtered 30 days after mating showed no significant difference in ovulation rate or embryo survival, but for positive dams the length of embryos was significantly reduced (−3·1, s.e. 1·1 mm).

The study suggests that the principal effect of the halothane gene was in reducing foetal growth rather than litter size. However, the phenotypic difference is expected to under-estimate the genetic difference between homozygotes, and it was not possible to distinguish the effects of dam and offspring genotypes. The present economic loss of roughly £4·70 per positive litter would be unlikely to justify elimination of the gene from a purebred maternal Landrace herd.

Prediction of the halothane (Hal) genotypes of pigs by deducing Hal, Phi, Po2, Pgd haplotypes of parents and offspring: results from a large-scale practice in Swedish breeds

Results from a large-scale study, comprising 75 different breeding herds, are reported on predicting the halothane (Hal) genotypes of individual pigs by making use of the known close linkage between Hal and three electrophoretic blood marker loci (Phi, Po2, Pgd). The parents haplotypes (involving Hal and marker loci) were determined from the HAL phenotypes (halothane test results) and marker loci phenotypes of their offspring in the first one or two litters studied. In subsequent litters of the Hal-marker loci haplotyped parents, the offspring's expected Hal genotypes could be predicted on the basis of the marker loci haplotypes inherited by them. By comparing the expected and observed HAL phenotypes of offspring in subsequent litters, the predicted Hal genotype was found to be correct in 90-95% of the 4000 offspring (from Nn X Nn and Nn X nn matings) of Swedish Landrace and Yorkshire breeds studied. The order of the three marker loci was confirmed as Phi-Po2-Pgd but the position of Hal with regards to Phi could not be resolved. The recombination frequencies between the most distant loci in this region, viz. Hal-Pgd and Phi-Pgd, were estimated to be 3-4.5% and 4-6%, respectively. The easy and rapid electrophoretic techniques described in the study to phenotype PHI, PO2, PGD, also allowed phenotyping of six other polymorphic protein systems on the same gels. Thus Hal genotyping and effective parentage control can be conducted simultaneously.