Breeding for robustness: the role of cortisol

Abstract

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-pituitaryadrenocortical (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.

The cortisol response to ACTH in pigs, heritability and influence of corticosteroid-binding globulin

“…Several clinical studies have shown a relationship between CBG levels or CBG gene polymorphisms and metabolic parameters related to insulin resistance syndrome (e.g. Fernandez-Real et al, 2002;Barat et al, 2005;Richard et al, 2009), and the CBG locus has been shown to be linked with metabolic traits in several studies (see Moisan, 2010and Mormede et al, 2011aand 2011b for review), including in pigs (Desautes et al, 2002;Ousova et al, 2004), and we showed previously that CBG was a better predictor of carcass composition than cortisol levels (Ousova et al, 2004). In most cases, the physiological effects of CBG have been interpreted as resulting from the influence of CBG on the level and bioavailability of cortisol (Perogamvros et al, 2012;Moisan, 2013).…”

“…A hyperactive or hyper-reactive hypothalamic-pituitary-adrenocortical (HPA) axis has an unfavorable effect on production traits such as growth rate and feed efficiency (Hennessy and Jackson, 1987) or body composition with an increased lipids/proteins ratio (Foury et al, 2005 and. A few studies established a positive relationship between HPA axis activity and robustness traits such as newborn survival, heat tolerance and resistance to diseases (see Mormede et al, 2011b and Mormede and † E-mail: Pierre.Mormede@toulouse.inra.fr a These data have been presented in a preliminary form at the 9th World Congress on Genetics Applied to Livestock Production, Leipzig (GE), 2010, paper 0169. Terenina, 2012, for review).…”

“…The large individual variation in HPA axis activity and reactivity, and the importance of genetic factors are well documented (Kadarmideen and Janss, 2007;Mormede et al, 2011a). We have therefore hypothesized that genetic selection for a more active HPA axis activity could improve robustness (Mormede et al, 2011b;Mormede and Terenina, 2012).…”

The relationship between physiological stress and wildlife disease: consequences for health and conservation

“…The following question arises: what traits allow some individuals, populations or species to be more resilient to the synergistic effects of stress and infectious disease? Models have been developed in livestock for genetic selection and breeding for robustness based on the stress response (Mormède et al 2011) and, in the future, wildlife management too may employ similar strategies to build populations that are more resilient to the combined effects of stress and disease.…”

Genetics of behavioural adaptation of livestock to farming conditions

“…The strategies used to produce animals that are able to overcome the perturbations in their physical environment and return to homoeostasis are dependent on the type of stress the animals face. On the one hand, Mormè de et al (2011) suggest that animals that produce a strong physiological response to acute stress adapt better to the stressor. The parallel cannot be made for behavioural responses where a phase of inhibition of all behavioural patterns is followed by a phase of activity.…”