Estimation of the Frequency of the Halothane Gene and Its Effects in Landrace and Yorkshire Pigs in Ontario

Data from 2554 Landrace and 2566 Yorkshire young boars submitted to the Record of Performance test station in Ontario between 1982 and 1986 were used to estimate frequency of reaction to halothane and frequency of the halothane gene. Approximately 1.4% of Landrace and 0.9% of Yorkshire boars had a positive reaction to halothane. The number of reactors detected at the test station declined with time, particularly in the Landrace. There was evidence of the presence of the halothane gene in 25 Landrace and 25 Yorkshire breeder herds and 5.8% of Landrace and 2.8% of Yorkshire sires had progeny which tested positive. Maximum likelihood estimates of frequency of the halothane gene were 0.10 ±.02 in Landrace and 0.09 ±.02 in Yorkshire. There was only weak selection against sire lines known to have had reactor progeny. Based on estimated breeding values, sires and dams that had reactor progeny were genetically leaner than contemporaries, but there was no consistent, or significant relationship with days to 90 kg.