Experimental models of endotoxaemia related to abortion in the mare

Three different routes of administering Salmonella typhimurium endotoxin to mimic naturally occurring endotoxaemia were tried in the mare. Bolus injection, repeated bolus injections and continuous low-dose infusion were compared with prostaglandin F2 alpha release, leucocyte count and clinical response. A biphasic prostaglandin release and a pronounced leucopenia of almost identical patterns were seen in all models. Repeated bolus injections showed that the second injection initiated only a small prostaglandin release indicating the development of refractoriness to the treatment. A similar refractoriness or desensitization occurred during the low-dose infusion. Flunixin meglumine, a potent inhibitor of prostaglandin biosynthesis, administered in different combinations in association with endotoxin demonstrated that this compound must be used at an early stage to prevent endotoxaemia and its deleterious effects on pregnancy. Taken together, the results show that horses are sensitive to endotoxins such that a short period of challenge (about 30 min) is enough to cause clinical signs and reproductive disorders.