Relative importance of adaptation and genotype3environment interactions in tropical beef breeding systems

Cattle grazed in (sub) tropical environments are subjected to numerous stressors such as parasites, seasonally poor nutrition, high heat and humidity and endemic diseases transmitted by parasites. The impact of each stressor on production and animal welfare is often multiplicative rather than additive, particularly when animals are already undergoing physiological stress (e.g. lactation). Under the extensive production systems common in the (sub) tropics, it is generally not possible to control the stressors through management strategies alone. The best method of reducing the impacts of these stressors so to improve productivity and animal welfare is to breed cattle that are productive in their presence, without the need for managerial interventions. Maximising beef production and profitability requires the genotype be matched to the specific production environment. Some genotypes are better suited to particular environments, with no one breed being ‘best’ in all environments. Genotype3environment (G3E) interactions may impact significantly on productivity across different environments. They are indicated by (i) re-ranking of breeds or sires within breeds for performance across different environments; or (ii) genetic correlations between environments that are antagonistic or, if positive, less than unity (e.g. ,0.80). Recently, interest has focused on possible changes in Single Nucleotide Polymorphism (SNP) associations with economically important traits across environments as a third indicator of G3E. This review examines the importance of adaptation and the extent of G3E in (sub) tropical beef production systems to identify opportunities to simultaneously improve productivity and cattle adaptation