Breeding for robustness: the role of cortisol
Pierre Mormède1,2, Aline Foury1,2, Elena Terenina1,2 and Pieter W. Knap3
1 Université Victor Segalen Bordeaux 2, PsyNuGen, F-33076 Bordeaux, France
2 Institut National de la Recherche Agronomique, UMR 1286, F-33076 Bordeaux, France
3 PIC International Group, Ratsteich 31, D-24837 Schleswig, Germany
This paper was developed from the first author’s communication on the topic at the 2009 EAAP conference in Barcelona, which was triggered by Xavier Manteca (Universidad Autonoma de Barcelona, SP). Part of the results was obtained through the EC-funded FP6 Project “SABRE”.
Robustness in farm animals was defined by Knap as ‘the ability to combine a high production potential with resilience to stressors, allowing for unproblematic expression of a high production potential in a wide variety of environmental conditions’. The importance of robustness-related traits in breeding objectives is progressively increasing towards the production of animals with a high production level in a wide range of climatic conditions and production systems, together with a high level of animal welfare. Current strategies to increase robustness include selection for ‘functional traits’, such as skeletal and cardiovascular integrity, disease resistance and mortality in various stages. It is also possible to use global evaluation of sensitivity to the environment (e.g. reaction norm analysis or canalization), but these techniques are difficult to implement in practice. The hypothalamic–pituitary–adrenocortical (HPA) axis is the most important stress-responsive neuroendocrine system. Cortisol (or corticosterone) released by the adrenal cortices exerts a large range of effects on metabolism, the immune system, inflammatory processes and brain function, for example. Large individual variations have been described in the HPA axis activity with important physiopathological consequences. In terms of animal production, higher cortisol levels have negative effects on growth rate and feed efficiency and increase the fat/lean ratio of carcasses. On the contrary, cortisol has positive effects on traits related to robustness and adaptation. For instance, newborn survival was shown to be directly related to plasma cortisol levels at birth, resistance to bacteria and parasites are increased in animals selected for a higher HPA axis response to stress, and tolerance to heat stress is better in those animals that are able to mount a strong stress response. Intense selection for lean tissue growth during the last decades has concomitantly reduced cortisol production, which may be responsible for the negative effects of selection on piglet survival. One strategy to improve robustness is to select animals with higher HPA axis activity. Several sources of genetic polymorphism have been described in the HPA axis. Hormone production by the adrenal cortices under stimulation by adrenocorticotropin hormone is a major source of individual differences. Several candidate genes have been identified by genomic studies and are currently under investigation. Bioavailability of hormones as well as receptor and post-receptor mechanisms are also subject to individual variation. Integration of these different sources of genetic variability will allow the development of a model for marker-assisted selection to improve animal robustness without negative side effects on production traits.
Stress, robustness, cortisol, genetics, marker-assisted selection
Genetic and genomic studies, combined with a systems genetic approach, will deliver a model of the genetic architecture of the stress-responsive neuroendocrine hypothalamic–pituitary–adrenocortical axis as related to production and robustness traits. This model will generate molecular markers to be used in the selection of more robust animals and improved welfare with limited consequences on production traits.
Genetic selection in farm animals aims at optimizing the efficiency of production by increasing production level and product quality, and by reducing production costs (e.g. feed efficiency). However, the genetic potential of animals is usually not fully expressed in commercial conditions, due to the limiting influence of the environment. Robustness is the specific quality of an individual to express a high-production potential in a wide variety of environmental conditions and is now a specific breeding goal in the context of sustainable farm animal breeding. In this review paper, we explore the various strategies used to increase robustness, and more specifically the possible use of genetic variation in the hypothalamic–pituitary–adrenocortical axis, the main neuroendocrine system involved in adaptation to stress.