Preweaning diet and stall weaning method influences on stress response in foals.

The stress response of foals during weaning was examined in terms of a behavioral protocol and the responses of plasma ascorbate, serum cortisol, and the serum cortisol response to an ACTH challenge. The experimental plan was a 2 x 2 factorial of two preweaning diets and two stall weaning methods. Dietary groups included foals raised on pasture supplemented with hay and a pelleted concentrate (PHC) and foals raised on pasture supplemented with hay only (PH). Stall weaning methods included foals placed in stalls singly or in pairs. Sex influences were also examined. The foals exhibited characteristic behavioral and physiological responses to weaning stress. Behavior scores indicated fewer outward signs of stress in single than in paired foals (P = .008) and tended to indicate fewer signs of stress in PHC than in PH foals (P = .15). No differences in plasma ascorbate concentrations were found among treatments. Responses of serum cortisol to an ACTH challenge were lower (representing adrenal depletion arising from stress) in PH than in PHC foals (P = .001) and in paired than in single foals (P = .058). Behavior scores were positively correlated with the response of serum cortisol to ACTH. Both behavioral data and the ACTH response indicated that foals may cope better with weaning when supplemented with concentrate before weaning or when placed singly in stalls rather than in pairs.