Monitoring Weaning Stress in Fillies and Colts on a Thoroughbred Breeding Farm by Cortisol and Blood Inflammatory Markers: The Benefits of Gradual Separation and Social Support

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Weaning represents a major developmental milestone for foals, especially when 4- to 7-month-old foals are abruptly separated from their dams. Studies have shown that the post-weaning period is associated with physiological and psychological stress, which may affect immune function. The present study aimed to describe and analyze the pattern of blood inflammatory biomarkers related to the innate immune system. A gradual foal–dam separation procedure was chosen, which included post-weaning social buffering by a familiar adult horse. Twelve Thoroughbred foals (six fillies, six colts) aged 4–6 months were enrolled and divided into a colt and a filly group, and after weaning, were kept as such. Blood samples were collected before and up to 7 days after weaning. Serum cortisol and cytokines (IL-2, IL-6, IL-10, TNF-α, IFN-γ) were quantified using equine-specific ELISA kits. Routine descriptive statistics were used to present the data, and inferences were drawn using a two-way repeated measures ANOVA. The level of significance was set at p < 0.05. Results showed significant differences in the concentrations of IL-10 (p < 0.001), IFN-γ (p < 0.01), and TNF-α (p < 0.01) on various days post-weaning. An apparent significant sex effect was not shown, but IL-10 peaked on day 3 in fillies. IFN-γ decreased significantly by day 5 in both sexes. Conversely, TNF-α levels increased significantly by day 5. No significant changes were observed for cortisol.