Horses are a risk of anticoagulant rodenticide poisoning. In over a hundred cases with follow up reported to the VPIS, most horses (>85%) remained well. Less than 10 horses had evidence of coagulopathy; none had significant haemorrhage and all the horses recovered.
Few cases of anticoagulant rodenticide poisoning in horses are reported in the literature. A recent report involved a pregnant Arabian mare who presented with bleeding from the mouth and nostrils after ingestion of rodenticide containing brodifacoum (0.005%). She had colic, haemarthrosis, venepuncture haemorrhage, severe normocytic and normochromic anaemia, Blood coagulation profile revealed prolongation of prothrombin time (PT) and activated partial thromboplastin time (aPTT).
The bait had been used on the farm 54 hours before presentation and it was thought that the rodenticide might have been accidentally mixed with feed and ingested. Three days after treatment with vitamin K1, all clinical signs resolved, however, abortion of the 7 month fetus occurred. Ten days after treatment, all haematological, biochemical and coagulation parameters were within the reference ranges and no sign of bleeding was noted; treatment with vitamin K continued for three weeks. Brodifacoum was confirmed in serum of the mare and liver tissue of the aborted fetus.
When assessing exposure in horses it is worth noting that unlike in dogs, there are reports of prolonged PTT with a normal PT in horses after ingestion of anticoagulant rodenticide. Therefore, both the PT and the aPTT should be checked. Vitamin K1 therapy should be started in any horse with prolonged PT and/or aPTT or evidence of bleeding. It should be given for at least 3 weeks, followed by rechecking of clotting parameters at 48-72 hours after cessation of therapy. If clotting parameters are abnormal vitamin K1 should be restarted.