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Stop the surgical castration of pigs in 2018

Under the pressure of animal welfare NGOs and with the help of the European commission, pig producers have accepted the principle of stopping surgical castration of neonates by 2018. Two solutions are possible: rearing entire or immunocastrated (2 injections of a vaccine, Improvac®, directed against GnRH) pigs. Before generalizing these types of males, it is important to carry out their extensive characterization.

Characterization regarding behaviour of entire or immunocastrated male pigs

Comparison between males surgically castrated during the neonatal period and entire males showed that the total number of agonistic behaviours was higher around 3 months of age. The number of skin lesions, that is an indicator of the intensity of aggressions between pigs, was similar in entire and castrated males around 3, 4 and 5 months of age. However, observing in detail agonistic behaviours showed that the worst behaviours for animal welfare, fighting behaviours, were more frequent in entire than in castrated males around 4-5 months of age. Entire males were more attracted by human, suggesting that they have no fear of human, which is beneficial for their welfare. However, it could be dangerous during manipulations even though our results did not show a higher aggressiveness of entire than castrated male pigs towards human. Immunocastrated males had a similar behaviour towards human, before and after the second vaccination, suggesting an imprinting effect of testicular hormones prolonged during several weeks. However, the number of fighting was high in immunocastrated males before the 2nd injection and decreased thereafter to become similar to that observed in castrated males.

Characterization regarding physiology of entire or immunocastrated male pigs

• Regarding the adrenal axis, around 5 months of age, salivary concentrations of cortisol, the adrenal cortex (producing tissue of cortisol) development, the expression of enzymes controlling the first steps of steroidogenesis, the cortisol release in blood after a challenge (ACTH or LPS injections) were lower in entire than in castrated males. Results in immunocastrated males were close to those obtained in entire males or intermediate between entire and castrated males suggesting again an imprinting effect of testicular hormones.
• Regarding the sympathetic axis, differences between types of male pigs were less clear.
• Regarding the immune system, the number of circulating lymphocytes around 4 and 5 months of age and the thymus weight around 5 months of age were higher in entire than in castrated males suggesting a positive influence of testicular hormones on the thymic development before puberty. These changes were accompanied by an increase of one of the lymphocyte sub-populations, the Tγδ cells, in blood and thymus. Immunocastrated pigs had generally intermediate results between entire and castrated pigs. These effects could be mediated by a direct influence of testosterone and oestradiol or by an indirect influence of those hormones via cortisol and catecholamines. Indeed, we have observed the expression of the mRNA coding for the receptors of those four mediators in the lymphoid organs of pigs and demonstrated in vitro that cortisol and noradrenaline are able to modulate thymocyte proliferation. However, our data do not show repeatable differences between types of pigs on in vitro lymphocyte proliferation, neither on haptoglobin (inflammatory marker), nor on health indicators (for example lung score) around 5 months of age. Similarly, the inflammatory response to an injection of LPS characterized by the plasma release of cytokines and the variation in circulating leucocyte numbers were not modified by castration or immunocastration.

The characterisation of entire and immunocastrated male pigs is still under investigation with measures concerning nutrition and nutrient metabolism.

For further information

Merlot, E., Thomas, F., Prunier, A. (2013). Comparison of immune and health markers in intact and neonatally castrated male pigs. Veterinary Record, 173 (13). (DOI)

Prunier, A., Brillouët, A., Merlot, E., Meunier-Salaün, M.-C., Tallet, C. (2013). Influence of housing and season on pubertal development, boar taint compounds and skin lesions of male pigs. Animal, 7 (12), 2035-2043. (DOI)

Tallet, C., Brillouët, A., Meunier-Salaün, M.-C., Paulmier, V., Guerin, C., Prunier, A. (2013). Effects of neonatal castration on social behaviour, human–animal relationship and feeding activity in finishing pigs reared in a conventional or an enriched housing. Applied Animal Behaviour Science, 145 (3–4), 70-83. (DOI)

Prunier, A., Leclercq, C., Le Floc'h, N., Merlot, E. (2013). Response of blood hormones and nutrients to stress in male pigs differing by their gonadal status. In: Book of Abstracts of the 64th Annual Meeting of the European Federation of Animal Science (p. 559). EAAP Book Abstracts, 64. Presented at 64th Annual Meeting of the European Federation of Animal Science (EAAP), Nantes, FRA (2013-08-26 - 2013-08-30). Wageningen, NLD : Wageningen Academic Publishers. http://prodinra.inra.fr/record/254689

Tallet, C., Claude, S., Guerin, C., Meunier-Salaün, M.-C., Prunier, A. (2013). Conséquences de deux alternatives à la castration des porcs sur leur comportement en isolement et en présence d'un homme non familier. In: 45èmes Journées de la Recherche Porcine (p. 71-72). Journées de la Recherche Porcine, 45. Presented at 45. Journées de la Recherche Porcine, Paris, FRA (2013-02-05 - 2013-02-06). Paris, FRA : IFIP - Institut du Porc.
http://prodinra.inra.fr/record/183071

Leclercq, C., Prunier, A., Merlot, E. (2014). Effects of neonatal surgical castration and immunocastration in male pigs on blood T lymphocytes and health markers. Animal, 8 (5), 836-843. (DOI)

Leclercq, C., A. Prunier, F. Thomas, and E. Merlot. (2014). Neonatal surgical castration of male pigs reduces thymic growth but has moderate consequences on thymocytes. Journal of Animal science, 92, 2415-2421. (DOI)

Contact

Armelle Prunier, team Physiology of Adaptation, Animal Nutrition and Health (armelle.prunier[at]rennes.inra.fr)