Abstract
Simple SummaryThe European Union imposes housing of pregnant sows in social groups since 2013 for animal welfare reasons. Nevertheless, the consequences of different housing conditions for the immune system of pregnant sows remain poorly investigated. We therefore analyzed important aspects of blood cellular immunity and cortisol concentrations of sows either housed in individual crates or in a group during gestation. The results show that individually housed sows had lower T cell numbers, but higher cortisol concentrations. Obviously, common housing conditions can differentially affect key elements of the adaptive immune system and hormonal indicators of stress in pregnant sows.In pig production, pregnant sows are either housed in individual crates or in groups, the latter being mandatory in the EU since 2013. The consequences of different housing conditions on the immune system are however poorly investigated, although immunological alterations may have severe consequences for the animal’s health, performance, and welfare. This study assessed measures of blood celluar immunity with special emphasis on T cells in pregnant German Landrace sows either housed in individual crates or in a social group. Blood samples were taken at four samplings pre partum to evaluate numbers of lymphocyte subpopulations, mitogen-induced lymphocyte proliferation and cytokine-producing T cells. Plasma cortisol concentrations were evaluated as an indicator of stress. We found lower blood lymphocyte numbers (p < 0.01) in individually housed as opposed to group-housed sows, an effect due to lower numbers of cytotoxic T cells, naive TH cells, and CD8+ γδ-T cells. Individually housed sows showed higher cortisol concentrations (p < 0.01), whereas lymphocyte functionality did not differ between sows of both housing systems. Possible implications and underlying mechanisms for the endocrine and immunological differences are discussed. We favor the hypothesis that differences in the stressfulness of the environment contributed to the effects, with crate-housing being a more stressful environment—at least under conditions of this study.
Highlights
In pig husbandry, pregnant sows are either housed individually or in social groups worldwide
(F(1,29.14) = 4.71, p < 0.05) than individually housed sows (Figure 1a). These differences were due to higher lymphocyte numbers (F(1,33.54) = 8.51, p < 0.01, Figure 1b) as numbers of granulocytes, monocytes, and DC did not differ between the housing systems (Figure 1c–e)
Subsequent analyses of lymphocyte subsets revealed that the effect in lymphocytes was caused by higher numbers of T cells (F(1,34.17) = 12.34, p < 0.01) in group-housed sows, whereas B cell and NK cell numbers did not differ between the housing systems (Figure 2a–c)
Summary
Pregnant sows are either housed individually (in gestation crates) or in social groups worldwide. In the European Union, group housing of pregnant sows is mandatory from four weeks after mating to one week before parturition since 2013 for animal welfare reasons 2001/88/EC), since confinement in individual crates is presumed to be a more stressful condition [1]. The inability to resolve conflict with neighboring sows by active avoiding behavior or direct physical interaction was presumed to cause frustration [4] and chronic stress [5,6]. Cortisol concentrations were found to be higher in crate-housed than in group-housed sows, at least under certain conditions [1,6,7]
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