Blood group association with severity and speed of the halothane reaction.

The second generation (n = 227) of British Landrace pigs from selected halothane-positive parents (36 litters) were blood-typed for the S(A-O), H and Phi loci and subjected to four 5-minute halothane tests at 21, 35, 49 and 63 days of age. Cumulative scores based on severity and speed of reaction were analysed in relation to single-locus blood group genotypes and linkage group sequences at two and three loci. A highly significant negative correlation (r = -0.79) was found between severity and speed of reaction. Significant differences occurred between blood group genotypes and linkage groups in both severity and speed of reaction. Genotypes S s/s, H a/a or H a/- and Phi B/B and linkage groups involving these three types had the highest cumulative reaction score and the fastest reaction time, whereas genotypes Phi A/B, S S/S or S S/s and H a/cd and linkage groups with these types had the lowest and slowest reaction scores. Some differences between genotypes and linkage groups were attributed to phenotypically halothane-positive parents and offspring being genotypically Hal N/n. These effects could result from linkage with heterozygous types such as H a/cd and S S/s. The possible role of the H cd allele acting as a genetic marker for a suppressor gene to the halothane reaction is discussed.