GENOTYPES AT THE LOCUS FOR HALOTHANE SENSITIVITY AND PERFORMANCE IN A PIETRAIN X LARGE WHITE F2

An F2 consisting of about 1 500 pigs was produced from a Pietrain x Large White cross. The experiment was designed so as to allow the identification of the 3 genotypes (NN, Nn and nn) at the locus for halothane sensitivity. The effects of these 3 genotypes on production traits were estimated as well as the contributions of this locus and ses to their total variation. The criteria considered were: growth conformation indices; carcass composition; and meat quality. The gene effect (difference between homozygotes) and the dominance deviation were also calculated. The most pronounced effects of this locus concern mainly those criteria related to conformation, such as lean percentage or carcass length, and the pH measurement (eye muscle). Their magnitude is approximately 1 standard deviation. The partial expression in the heterozygote of the effects on conformation explains why even a single copy of the gene was favoured by selection during the course of breed formation. Moreover, as an F2 individual of nn genotype cannot be mistaken for a pure Pietrain regarding carcass composition and conformation, it is concluded that the nn genotype is a necessary but not sufficient condition to make a Pietrain, other genes being involved whose action on carcass composition is similar to that of the n allele.