Effects of Diet and Probiotic Supplementation on Stress during Weaning in Thoroughbred Foals

This study investigated effects of diet and probiotic supplement on stress in Thoroughbred foals at weaning. Twenty foals, whose dams were paired by age and breeding date, then randomly assigned to one of two diets prior to parturition, were used. Two groups were maintained on mixed grass pastures and fed supplements, one high in sugar and starch (SS) and one high in fat and fiber (FF) that met or exceeded NRC requirements. Half the foals on each diet were fed a commercial probiotic (Probios) containing lactic acid bacteria, while the rest were given a placebo. Plasma, fecal samples and behavioral ethograms were collected for four days pre- and post-weaning, and an ACTH response test was administered 48 h post-weaning. Cortisol, lactate, IgG, IgA and a-tocopherol were analyzed in plasma, volatile fatty acids and pH in feces. Foals fed FF had higher concentrations of IgA (P = 0.006), IgG (P = 0.012) and a-tocopherol (P = 0.005). Butyric and valeric acid concentrations were higher in feces of SS but not FF foals (P = 0.052), which may reflect better adaptation to forage in FF foals. Foals supplemented with probiotic had higher fecal lactate (P = 0.002) and lower fecal acetate (P = 0.0003) concentrations, suggesting that the lactic acid bacteria survived to the hindgut. Probiotic supplementation did not appear to benefit foals at weaning. Supplementation with FF may improve immune status and encourage a more diverse intestinal microbial population, enabling foals to better cope with the physiological stresses of weaning.