The Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) was contacted by a client who was concerned a group of horses had potentially consumed gopher bait containing an anticoagulant (diphacinone) as the toxic agent. Providing treatment for large animals with the antidote for anticoagulant intoxication can be challenging, therefore the suggestion was made to submit samples to determine which of the horses in the group actually consumed the bait product. TVMDL’s toxicology section offered the further suggestion that 24 hours should be allowed post-exposure to ensure that enough time had elapsed for the substance to be present in the serum.
Five of six horses had detectable diphacinone in the serum (detection limit 1 ng/mL).
No information is currently available regarding toxic serum diphacinone concentrations in equines, and the serum concentration does not necessarily directly reflect the ingested dose. Anticoagulants antagonize vitamin K to reduce production of clotting factors by the liver. The body usually has 3-5 days’ worth of clotting factors available, so the effects of an anticoagulant toxin would not be evident until 3-5 days after ingestion. Vitamin K1 is the antidote for anticoagulant poisonings and must be given long enough to ensure the toxin is no longer in the animal’s system to prevent a coagulopathy. According to Merck, the half-life of diphacinone in canine plasma is 5 days, with maximum effects estimated at 12-15 days post-ingestion.
It is suspected the group of horses in this particular case ingested gopher bait from containers that were too easily accessible. If the owner had not noticed the demolition of the gopher bait containers, these animals might not have been treated. TVMDL encourages clients to use this case as a reminder to be aware of where pesticides are stored and ensure they are not easily accessible to animals.
For more information about TVMDL’s test catalog, visit tvmdl.tamu.edu or call 1.888.646.5623.
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