Anticoagulant Use and Hemorrhage in Horses Back »

Written by Breanna Stoltenburg under the direction and review of Rebecca Bott and Sara Mastellar.


Article Summary: Cluster of cases of Massive hemorrhage associated with anticoagulant Detection in race horses

Anticoagulant rodenticides such as brodifacoum, diphacinone, bromadiolone, and chlorophacinone are used as pest control at various horse racing facilities. Targeted animals that ingest anticoagulant rodenticides generally develop hemorrhagic diathesis, which in most cases can result in death. The main effect of anticoagulant rodenticides on the body is the inhibition of vitamin K-dependent clotting factors. In 2014, a racehorse was submitted for diagnostic evaluation because of a sudden death during an exercise-related activity. An anticoagulant rodenticide screen was performed and traces of diphacinone were found in the liver. Whether the ingestion of the AR’s was accidental or intentional is under investigation. However, the pest control products used at two of the stables in California did not contain anticoagulant rodenticides. As a result, anticoagulant rodenticide screenings have become a routine test in cases of sudden death in horses that had or were partaking in exercise-related activities.

The California Animal Heath and Food Safety Laboratory received five dead geldings from four different racetracks within a 12-month period in 2014. The five horses, aged 3 to 16, were determined at necropsy to have hemoperitoneum, excessive blood within the peritoneal cavity. Liver samples were analyzed for anticoagulant rodenticides and found to be positive for brodifacoum in four of the five horses and diphacinone in the other. Liver samples from 27 racehorses that were euthanized because of catastrophic musculoskeletal injuries were also analyzed for anticoagulant rodenticides and used as a control group. No anticoagulant rodenticides were found in the livers from the horses in the control group. An association between anticoagulant rodenticides and internal hemorrhages can be made because of the trace amounts found in the five geldings, and the absence of anticoagulant rodenticides found in the control group. Although this association statistically holds true it is unlikely that anticoagulant rodenticides are solely responsible for the hemorrhages. Another common factor that all five of the geldings have is that they were involved in exercise-related activities upon death. Also, a number of drugs that are common to the horse racing business are known to increase the toxic effects of anticoagulant rodenticides. These drugs include anti-inflammatories such as phenylbutazone and oxyphenbutozone. It was reported that two of the geldings had been administered phenylbutazone 48 hours prior to their death. While there was no evidence that any of the other three geldings were administered an anti-inflammatory, it is a common practice in the racing industry to give these drugs to horses prior to racing. The results from this study suggest that there is an association between exercise, hemorrhages, anticoagulant rodenticides and possibly anti-inflammatory drugs. However, it is possible that other unknown factors may contribute to the hemorrhages and death of racehorses.

While this journal article is solely investigating traces of anticoagulant rodenticides in racehorses located in California, it may lead to further investigation of other racing stables. This could help increase the awareness of the toxic effects of anticoagulant rodenticides and how combinations of certain factors or drugs can have detrimental effects on horses. Horseracing is a large part of the horse industry and while this research only looks at one specific problem within the stables, it may uncover additional side effects of anticoagulant rodenticides on horses. The success of the horse racing industry is based on performance and production. This study has implied that anticoagulant rodenticides can directly affect the performance of racehorses in exercise situations that may put additional strain on their systems. It would be interesting to consider whether or not anticoagulant rodenticides could have similar effects on racehorses during the strain of labor or delivery, which could possibly result in hemorrhaging, anemia, and potentially death of the mare. This study indicates a need for additional research on the affects or anticoagulant rodenticides on non-targeted animals.


Reference: Carvallo, F. R., Poppenga, R., Kinde, H., Diab, S. S., Nyaoke, A. C., Hill, A. E., et al. (2015). Cluster of cases of massive hemorrage associated with anticoagulant detection in race horses. Journal of Veterinary Diagnostic Invesigation , 27, 112-116.

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