Genetic trends in different MHS genotypes of Piétrain boars in Lower Saxony

Genetic comparisons of homozygous negative (NN) and heterozygous negative (Nn) Piétrain boars in relation to the six economically important traits daily gain, loin eye area, ham proportion, lean meat content, pH1 loin and meat colour were made to describe effects on this traits in the case of eradicating the n-allele. Data of 11,422 female pigs tested in two test stations of Lower Saxony in the years 2000 to 2007 were analysed. Piétrain purebred and crossbred progenies were kept in two-pig pens, and crossbred progenies were also kept in groups of ten pigs. The crossbred progenies originated from hybrid sows (German Landrace * German Large White). For statistical analysis three animal groups were defined: purebreds in twopig pens, crossbreds in two-pig pens, and crossbreds in groups with ten pigs. Variance components were estimated simultaneously for all three animal groups with an animal model by REML. Statistical models considered the fixed effects month at the beginning of the fattening period within station (fattening), day of slaughtering within station (carcass and meat quality), regression on carcass weight and the random effects of test group and animal. Adjacent a breeding value estimation was conducted by using the same models and the estimated variance components. Between purebreds and crossbreds kept in two-pig pens the genetic correlations ranged from rg =0.67 to rg =0.99. Between purebreds and crossbreds kept in groups with ten pigs the genetic correlations resulted in rg =0.56 to rg = 0.77, and finally, between the two crossbred groups the genetic correlations are rg = 0.70 to rg = 0.99. Thus, genotype x environment interactions resulting in rank displacements are possible between purebreds and crossbreds kept in two-pig pens for the traits daily gain and pH1 loin and between purebreds and crossbreds kept in groups with ten pigs for all traits. Actually only few progeny tested boars have the genotype nn, but more than 50% of the boars are heterozygous gene carriers (Nn). Mean breeding values were calculated with respect to year of birth, MHS genotype, and animal group. In daily gain and in the two traits of meat quality homozygous negative sires (NN) have a genetic superiority compared to the heterozygous negative sires (Nn). In contrast the gene carriers (Nn) have somewhat higher breeding values in the three carcass traits, but over the years the differences between the two genotypes decreased clearly. Assuming that this trend will be continued an eradication of the n-allele will result in increasing daily gains and decreasing meat quality deficiencies combined with similar lean meat contents.

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