Taking into account the genetic defects in selection: the case of cattle

Abstract

For years, genetic defects were discovered sporadically and this led breeders to eradicate drastically all the carriers in combination with the procreation of non carrier future reproducing animals. However there is a new paradigm with the setting up of genomic selection since genetic defects are now detected much faster and, consequently, in larger numbers. Therefore it is necessary to adapt the way genetic defects are taken into account in selection. A good overview of the genetic situation must be obtained by estimating the allelic frequency in the population and by assessing the status of most major reproducing animals with the available diagnosis tests, now often included in SNP chips. Noteworthy, this status may also be assessed indirectly through haplotypic prediction for older animals and does not always require to genotype them again. Then the selection plan must be set up in the light of the economic weight of the defects, which depends on the cost of affected cases and allelic frequency. The optimal method to gradually eradicate genetic defects relies on the use of a breeding objective combining genetic defects with the other traits, with their economic weights. The transition phase between the discovery of a genetic defect and its complete eradication is always delicate and is usually coped by orienting the matings to avoid cases. Finally, it is recalled that using a large number of breeding animals while restricting their number of offspring is a simple measure that efficiently limits the outbreaks of new genetic defects.