Efficiency of selection strategies for halothane gene.

Use of a method to estimate the frequency of the halothane-negative allele in boars is illustrated for different sampling schemes for boar testing programs and for testing within closed breeding populations. This method uses information not only on the individual, but also on all mates and relatives including parents, siblings and offspring. Accuracy of the estimates of the allelic frequency in boars was measured through use of Monte Carlo simulation. The selection differential in real frequency of the halothane-negative allele when boars were selected on estimated allelic frequency was used as the criterion for accuracy. In the progeny testing situation, phenotypes of base boars and one generation of offspring were available. The average selection differentials with 90% selection (i.e., culling 10% of boars on estimated allelic frequency) when 2 and 10 litters of two boars each were tested were .017 and .044 in base boars and .013 and .025 in the offspring. The value of the boar's own phenotype was small. Higher selection differentials were found in the closed herd situation, where data on two generations were available. The selection differential in base boars when 10 litters were tested increased from .046 to .066 when the proportion of boars selected decreased from 90% to 50%. No improvement in selection differential with proportion selected was found in the progeny testing situation. Intense selection is most effective when the number of litters per boar is large and data over several generations are used. The estimation procedure for allelic frequencies in boars should improve current screening and selection programs to reduce halothane sensitivity in pigs.