Genetic strategies towards robust animals
Several breeding strategies can be implemented to increase robustness: Global sensitivity to the environment is measured by techniques such as the reaction norm analysis by comparing animals with identical genotypes in different environments (Knap and Su, 2008). This is a difficult endeavour and heritability of the character is low. Sensitivity to the environment may also contribute to the environmental variance of a trait, which has been shown to be under genetic control (SanCristobal-Gaudy et al., 2001; Sorensen and Waagepetersen, 2003; Ros et al., 2004; Mulder et al., 2007 and 2008; Mulder et al., 2009). The reduction of trait variance by genetic selection is also known as canalizing selection or canalization (SanCristobal-Gaudy et al., 1998; Bolet et al., 2007; Garreau et al., 2008; Bodin et al., 2010).
Another strategy is direct selection for robustness-related traits. Genetic improvement in functional traits, such as leg soundness, mortality rates in various stages of the animal’s life and functional longevity is possible when these traits are properly included into breeding goals and selection criteria, and is being realized in existing breeding programmes (Knap, 2009). Disease resistance traits are more difficult to select for, except in specific cases such as the somatic cell count in milk that is a good indicator of sensitivity to mammary infections in dairy cattle (Colleau and Regaldo, 2001). Current efforts towards the discovery of molecular bases for genetic variation of these complex traits will possibly deliver DNA polymorphisms to be used for genomic selection.
The third strategy that will be developed in this paper focuses on the molecular genetics of neuroendocrine stress responses, more specifically the hypothalamic–pituitary–adrenocortical (HPA) axis.