Influence des hormones testiculaires sur le comportement et la physiologie des porcs – ANDROPIG

Most of the 250 millions of male piglets reared yearly in the EU are castrated by surgical means without pain prevention. Castration is performed primarily to improve meat quality and secondly to facilitate management. Indeed, pigs for meat production are usually slaughtered when testes are well developed and secrete sex steroids at the origin of boar taint, a specific taste of the meat rejected by consumers, and of behavioural problems linked to mounting and aggressive behaviours. Following the general trend of the society for a better recognition of animal sentience, there is an increasing pressure for banning surgical castration. In addition to avoiding suffering of piglets due to surgical castration, raising entire males may have positive effects on the environment since the food conversion of entire males is more efficient (about 10%). A positive influence of testicular hormones on health is also suspected. Another alternative to surgical castration would be to perform immuno-castration which consists of vaccinating the animals against reproductive hormones a few weeks before slaughter. Immuno-castrated animals benefit from the testicular hormones during most of their life and their feed conversion efficiency is intermediate between surgically castrated and entire males. The aim of the present project is to acquire more knowledge on the development of the behaviour, physiology and nutrient requirements of entire and immuno-castrated pigs to take advantage of their positive characteristics and to reduce the impact of their negative ones. The project will be divided into four tasks focusing on the influence of testicular hormones on behaviour (Task 1), on the hypothalamo-pituitary-adrenal (HPA) axis and sympathetic nervous system (Task 2), on the immune function and health (Task 3) and on the nutrient utilization (Task 4). Since the underlying physiological mechanisms of sexual development are connected, we will analyse the interactions between systems and functions. In each task, we will compare entire males, males surgically castrated early in life and males immuno-castrated during puberty (subjected to sex hormones for a large period of their life). Therefore, we will be able to determine short and long-term effects of testicular hormones. According to the present knowledge on the different aspects, we will follow the development of the pigs or focus on the actual slaughter age of fattening pigs. In addition, for Tasks 1-3, we will vary the housing as a possible solution for reducing the negative effects of sexual development since it may affect deeply the behaviour, HPA axis and immune system. For Task 1, animals will be observed either in their rearing environment, during controlled tests outside their home pen and at the slaughter house. Animals will be fitted with ear transponders to analyze feeding behaviour by telemetry. For Task 2, animals will be submitted either to single samplings (in blood, saliva and/or urine) at various ages or to serial blood samplings via a permanent catheter after a hormonal challenge or an acute stressor. Concentrations of hormones or their metabolites from the HPA axis and SNS will be measured. For Task 3, we will evaluate various dimensions of the immune system using blood cell numeration, in vitro tests of lymphocytes proliferation, analysis of lymphocytes subtypes by cytometry, IgG response to an immune challenge. Health of the animals will be evaluated by measurement of blood concentrations of proteins indicative of inflammatory reactions and by clinical examination of the viscera from slaughtered animals. In Task 4, we will measure circulating levels of hormones and nutrients with single samples collected at various ages or serial blood collected at one age in catheterized animals. In addition, we will evaluate energy and protein utilization by measurements in metabolic chamber. For Tasks 2-4, level of expression of receptors or enzymes from the HPA axis (in adrenals and liver), receptors to sex hormones (in liver, adrenals, muscle and lymphoid organs), receptors or hormones from the somatotropic axis (liver and muscle) will be measured in tissue samples collected in slaughtered animals. We expect that some of these results regarding the effects of testicular hormones on the behaviour and the physiology may apply to numerous mammalian species especially those characterized by a pubertal development similar to pigs. Some other results, for instance those regarding the handling easiness of pigs, the effect of housing or the nutrient requirements, will be more specific to pigs. These results will contribute to remove breaks to the production of entire and immuno-castrated pigs that may improve animal welfare and reduce environmental problems.