GENOTYPE BY ENVIRONMENT INTERACTIONS IN LIVESTOCK BREEDING PROGRAMS: A REVIEW

In a simple genetic model for a quantitative trait, the phenotype is considered as the sum of independent genetic and environmental effects. Often, such a model is not satisfactory for the range of situations to which it is applied. If a genotype by environment interaction (GEI) exists, this independence is lost, and the simple model does not fit the data properly (Falconer, 1989). A possible remedy is to extend the model by including a term for GEI. Dickerson (1962) defined the GEI as "additional variation due to the joint effects of the genotype and environment, not predictable from their separate average effects" and added that "They are important to the extent that use of the best combination of genotype and environment would permit more efficient animal production." Genotype by environment interactions may affect the efficiency of selection programs by reducing the response in the performance traits (i.e., growth, milk production) in animals raised under environmental conditions different to that of the selected ones. These reductions may involve reproduction and survival rates in genotypes raised at particular locations. The effect of genotype x environment interactions resulting from the lack of adaptation of particular genotypes to specific conditions may reduce economic performance when the environmental conditions of the selected animals are different from those of the commercial population.