Get access to all handy features included in the IVIS website
- Get unlimited access to books, proceedings and journals.
- Get access to a global catalogue of meetings, on-site and online courses, webinars and educational videos.
- Bookmark your favorite articles in My Library for future reading.
- Save future meetings and courses in My Calendar and My e-Learning.
- Ask authors questions and read what others have to say.
Idiopathic Hemorrhage Associated With Anticoagulant Rodenticide Exposure in Exercising Horses
R.M. Arthur, F.R. Carvallo, R...
Get access to all handy features included in the IVIS website
- Get unlimited access to books, proceedings and journals.
- Get access to a global catalogue of meetings, on-site and online courses, webinars and educational videos.
- Bookmark your favorite articles in My Library for future reading.
- Save future meetings and courses in My Calendar and My e-Learning.
- Ask authors questions and read what others have to say.
Read
Anticoagulant rodenticide (AR) exposure has been associated with idiopathic hemorrhage in horses experiencing sudden death while exercising at four California racetracks. Strenuous exercise may alter the toxicity threshold for ARs in horses. AR use should be carefully restricted around exercising horses until further information is available.
1. Introduction
Six horses originating from four different racetracks in California were submitted for necropsy and diagnostic evaluation. The six horses had a history of collapse and sudden death during or immediately after exercise. All horses showed massive hemoperitoneum and/or hemorrhages in other cavities or organs. Traces of the ARs brodifacoum, diphacinone, or bromadiolone were detected in liver tissue from all six horses. The detected concentrations of ARs in the six horses were considerably less than what is typically thought to be associated with toxicity,1 although diagnostic liver concentrations have not been determined in most species. Other frequent causes of massive hemorrhages in horses were excluded in five of the six cases. One horse had a pelvic fracture that did not seem to be related to the abdominal hemorrhage. It is speculated that exercise-related physiological alterations or a combination of exercise and other unidentified factors present in a racetrack environment may reduce the toxicity threshold for ARs in strenuously exercising horses. The objective of this paper is to present the basis for the conclusion that ARs pose a potential and previously unrecognized risk to racehorses. Analysis of liver tissue for ARs should be performed whenever idiopathic hemorrhage is found in equine sudden deaths associated with exercise.
2. Materials and Methods
A full necropsy was performed on all six horses as previously described.2 All horses dying with California Horse Racing Board (CHRB) –regulated racing or training racetrack facilities are required to undergo a necropsy. Necropsies are conducted under standard protocols designed for racehorses from CHRB-regulated facilities by pathologists within the California Animal Health and Food Safety Laboratory System (CAHFS), which is managed through the University of California at Davis School of Veterinary Medicine. The necropsies in this study were conducted at the CAHFS laboratories at San Bernardino for southern California tracks and Davis for northern California tracks.
Between December 2012 and September 2014, six horses submitted for necropsy were diagnosed as having idiopathic hemorrhage, primarily in the abdomen. No obvious cause for the hemorrhage was identified and AR testing was performed on liver samples. Traces of ARs were identified through analysis of liver tissue. A total of 374 horses, including the six reported here, were submitted from CHRB racetracks for necropsy during the 22-month timeframe described. Three of the cases were Thoroughbreds dying during or immediately after racing, one was a Thoroughbred training at a gallop and the other two were pony horses working on the track. A pony horse in the racetrack setting refers to a full-sized working horse that accompanies competitive horses during the post-parade and pre-race warmup or during training workouts. One pony horse was a Quarter Horse taking a horse to the starting gate to race; the other pony horse was a Thoroughbred working in the morning. The Thoroughbred pony collapsed on the track, was removed to the stable area equine hospital, and died shortly thereafter. All other horses died on the track. The six fatalities occurred at four different racetracks. One horse had shipped from a fifth racetrack the morning of its fatal race.
Anticoagulant screens were performed on prepared liver samples by liquid chromatography– tandem mass spectrometrya using a previously published method modified for tissue analysis.3 Any sample testing positive for an anticoagulant was then quantitated by high-performance liquid chromatographyb using either ultraviolet diode array detectionc (diphacinone, chlorophacinone, and difethialone) or fluorescence detectiond (warfarin, coumachlor, bromadiolone, and brodifacoum). Limits of quantitation for these ARs vary according to their sensitivity to ultraviolet or fluorescence detection. The reporting limits in liver tissue are 0.01 ppm for brodifacoum; 0.05 ppm for bromadiolone, warfarin, and coumachlor; and 0.25 ppm for chlorophacinone, diphacinone, and difethialone.
Liver samples from 27 racehorses euthanized due to catastrophic musculoskeletal injuries were analyzed for ARs in the same manner as controls. The proportion of horses with idiopathic hemorrhage that had detectable AR in the liver was compared with the proportion of control horses that did not have detectable AR in the liver using Fisher’s exact test.
CHRB personnel conducted field investigations to determine AR use and identify possible exposure routes at California racetracks. The specific objective was to develop an understanding of all potential AR sources, types, distribution methods, and the associated risk of accessibility to the horses. On-site inspections of the stable areas were conducted at each track except one, Track A, which had closed. One horse had shipped into Track D in the morning from a fifth track, Track E. That track was similarly inspected. Interviews were conducted with stable managers, trainers, barn personnel, and either commercial pest control vendors and/or track personnel responsible for rodent control programs. Findings were recorded and evaluated relative to necropsy results.
3. Results
Case number, breed, age, sex, activity at time of death, pathological findings, AR identified at necropsy, track, and AR in use by track are listed in Table 1. The ARs identified at necropsy were brodifacoum, diphacinone, or bromadiolone. The most significant pathological finding in five of the six horses in the current series was severe hemoperitoneum, with a variable combination of hemothorax, hemopericardium, and mesenteric, muscular diaphragmatic, and/or pulmonary hemorrhages. One horse (Case 6) had multi-organ hemorrhagic diathesis but minimal hemoperitoneum. The hemorrhage into the abdomen, thorax, and pericardium was characterized by the presence of large quantities of mostly free unclotted blood within the corresponding cavity. The hemorrhage was characterized by approximately 8–20 liters of blood in the abdomen (Fig. 1) except for Case 6, in which there was a minimal hemoperitoneum; approximately 4 –10 liters in the thorax except for Case 6, in which there was a minimal hemothorax; and approximately 0.5 liters in the pericardial sac except for Case 6, in which there was an estimated 2 liters of free blood. Case 6 was unusual in that it was the only case that did not die immediately on the track and showed a general hemorrhagic diathesis in multiple organs and tissues. After careful gross examination and detailed dissection of the main thoracic, abdominal, and pelvic blood vessels, no tears or other vascular lesions could be identified. One horse (Case 4) had an acute pelvic fracture with evidence of a pre-existing stress fracture with extensive hemorrhaging into tissues surrounding the fracture, but after careful examination, the extra-peritoneal hemorrhage did not seem to communicate with the abdomen. [...]
Get access to all handy features included in the IVIS website
- Get unlimited access to books, proceedings and journals.
- Get access to a global catalogue of meetings, on-site and online courses, webinars and educational videos.
- Bookmark your favorite articles in My Library for future reading.
- Save future meetings and courses in My Calendar and My e-Learning.
- Ask authors questions and read what others have to say.
About
Affiliation of the authors at the time of publication
School of Veterinary Medicine, University of California, Davis, CA 95616 (Arthur); California Animal Health and Food Safety Laboratory System, University of California, Davis, CA – San Bernardino branch, Davis, CA 92408 (Carvallo, Kinde, Nyaoke, Uzal); Davis branch (Poppenga, Diab, Hill), Davis, CA 95616; and California Horse Racing Board, Sacramento, CA 95825 (Salmon)
Comments (0)
Ask the author
0 comments