Abstract
This study aimed to evaluate the changes caused by the abrupt weaning of plasma total cortisol and the occurrence of cell immunosuppression, measured by the expression of tumour necrosis factor alpha (TNF-α). The abrupt weaning was performed in eight Mangalarga Marchador foals aged between 24 and 28 weeks. The animals were evaluated in four moments: seven days before weaning (DAD), and one day after weaning (DApD), seven DApD and 15 DApD. In these moments, blood samples were taken for determination of total plasma cortisol and the expression in vitro of TNF-α treated with lipopolysaccharide from E. coli (LPS) or dexamethasone (Dx). There was an increase of total plasma cortisol 24 hours after weaning (1 DAPD) (P <0.0001), time that the expression in vitro of TNF-α showed the lowest value in the LPS group, similar to the control group and the Dx group. After 15 DAPD, in vitro response of TNF-α was significantly higher in the LPS group (P = 0.0006). It was concluded that weaning stress provokes an acute condition in foals, which resulted in a decrease of cell-mediated immunity, expressed by lower TNF-α levels