A simple selection scheme to improve disease resistance and growth

A simple selection scheme is proposed that facilitates the selection for a growth trait (GROWTH) with heritability of 0.25 and one disease trait (SURVIVAL) with heritability of 0.1 or 0.4 using a two step selection procedure. First, the scheme applies phenotypic selection for SURVIVAL among all the 10,000 candidates per generation, assuming that Nsurvival = 2500, 5000 or 7500 survived a disease challenge test. Survivors were measured for GROWTH, and the (Ngenotyped = 1000 or 2000) highest ranked were DNA genotyped for parentage testing. Second, parents were selected for GROWTH on their BLUP breeding values using optimum contribution selection, which restricted the rates of inbreeding to 1% per generation. At this second selection step, no selection for SURVIVAL was possible, because all survivors had the same phenotype for this trait and the pedigree of the dead individuals were not known. Results show that selection for SURVIVAL was very efficient for schemes with high heritability of SURVIVAL (0.4) and positive genetic correlation between the traits (0.3), and more efficient with decreasing survival rate, because of the higher intensity of selection. However, for schemes with negative correlation between the traits (- 0.3), the heritability of 0.1 of SURVIVAL was too low to get positive genetic response for SURVIVAL. Genetic gain for GROWTH and SURVIVAL was not significantly improved by increasing Ngenotyped = 1000 to 2000 for the schemes used here, i.e. genotyping 1000 individuals allowed the best possible parents to be selected for breeding when using optimum contribution selection. In conclusion, this is an efficient and very simple selection scheme for aquaculture species which can be used for specific cases where a whole production system is limited by a disease that is not transmitted from parent to offspring. The scheme may be worth considering also for vertically transmitted diseases for which the breeding candidates or their gametes can be reliably disinfected and screened before being transferred to the nucleus and the industry.