Advances in Equine Medicine Discussed at AAEP
What was the hottest news in equine veterinary medicine in 2009? During the popular Kester News Hour session at the annual American Association of Equine Practitioners (AAEP) Convention, three top veterinarians (who focus on equine reproduction, internal medicine, and lameness/surgery) summarized the top news topics and the most significant research reports of the year for a record crowd of equine veterinarians.
The presenters during the 2009 convention, held Dec. 5-9 in Las Vegas, Nev., were:
- Scott E. Palmer, VMD., Dipl. ABVP (Equine Practice), hospital director and a staff surgeon of the New Jersey Equine Clinic in Clarksburg, N.J., and past president of the AAEP and American Board of Veterinary Practitioners;
- Margo L. Macpherson, DVM, MS, Dipl. ACT, associate professor and section chief in Reproduction at the University of Florida, and past president of the American College of Theriogenologists; and
- Bonnie R. Rush, DVM, MS, Dipl. ACVIM, professor of equine internal medicine at Kansas State University, winner of the 1996 and 2003 Carl J. Norden Distinguished Teacher Award, and the 2002 Pfizer Award for Research Excellence, and the 2004 Outstanding Woman Veterinarian of the Year
Compounded medications The very public death of 21 polo ponies in April 2009 due to an incorrectly formulated compounded vitamin/mineral supplement (excessive levels of selenium) "was one of the biggest stories of 2009, drawing international attention to the sport of polo and the profession of medication preparation," said Palmer.
Macpherson noted that several factors contributed to the situation, not just a single mistake. "It's important for us to recognize what we need to learn from this situation," she commented, recommending the following:
- Take American Medicinal Drug Use Clarification Act guidelines very seriously. Rush described these as follows:
- A veterinary-client-patient-relationship must exist.
- The health of the animal must be threatened.
- The compounded medication must be made from FDA-approved, commercially available products.
- The amount of product compounded must be consistent with the needs of the animal identified in the prescription.
- Veterinarians should be very careful of the types of products they use.
- Write clear, legible prescriptions.
- Pharmacies must employ stringent quality control practices.
Rush weighed into the compounding discussion as well, adding a summary of a study published in the Journal of the American Veterinary Medical Association (JAVMA) on the compounding and storage of pergolide mesylate (used to treat equine Cushing's disease). Pergolide was withdrawn from the human medication market in 2007 due to concerns over its contribution to heart problems, but it's still widely used in horses as a compounded product. The study found that pergolide degrades to the point that it shouldn't be used after only 14 days in typical barn storage conditions, and after only 30 days when refrigerated in a dark container.
"If a color change occurs (from opaque white to brown), the drug should be discarded," advised Rush. "Remember, Day 1 for you with the product might not be Day 1 of the product; it might have already been one week old when it was shipped, or may have been exposed to heat during delivery."
She also made the following comments regarding compounding in general:
- Regulations are not permission to compound from bulk drug.
- Neither cost nor convenience is justification for using compounded preparations.
- The prescribing veterinarian assumes liability when using compounded preparations.
- Pharmacy Releases Statement on Polo Pony Test Results
- Vets Investigate Wellington Polo Pony Deaths
- Stability and Efficacy of Compounded Pergolide Examined
Davis, J.L.; Kirk, L.M.; Davidson, G.S.; Papich, M.G. Effects of compounding and storage conditions on stability of pergolide mesylate. Journal of the American Veterinary Medical Association 2009; 234:385-389.
Morgan, K. Compounding basics for the equine veterinarian. Equine Veterinary Education. Sept, 2009.
Exercise-induced pulmonary hemorrhage A study published in JAVMA and described by Rush as "one of the most logistically complicated studies of the decade" definitively answered the long-standing question of whether furosemide (Salix/Lasix) reduces the incidence of exercise-induced pulmonary hemorrhage (EIPH, airway bleeding). She said the researchers took over a South African track for four days and assigned 167 horses to race fields of nine to 16 animals. Half the horses were given furosemide in a randomized, placebo-controlled, blinded, crossover design, then they were raced by apprentice jockeys in nonrecorded races. After a seven-day washout period, the trial was repeated under the exact same conditions, but with the other half of the horses receiving furosemide.
"We knew bleeding impaired performance, and we knew furosemide improved performance, but we didn't know if furosemide really reduced bleeding," said Rush. "We now know. More than 80% of the horses in this study bled without furosemide, and less than 60% bled on the medication. No horses bled at Grade 3 or 4 levels on furosemide, and two-thirds of horses that bled without furosemide had a reduction of at least one grade of severity in their bleeding.
"This wasn't six horses running on a treadmill, these were real-world conditions," commented Rush. "They have answered a 30-year-old question."
Rush reported that more than 92% of Thoroughbreds running in North America race on furosemide, and that the drug's use costs more than $100 million annually in the United States.
More information: Study: Exercise-Induced Pulmonary Hemorrhage Prevented by Furosemide
Another EIPH study that Rush discussed focused on the mechanisms of EIPH within the lung, and it was published in the Equine Veterinary Journal. Researchers found EIPH resulted in thickened pulmonary (lung) vein walls and reduced inner diameter of the veins in the rearward portion of the lung.
"With thickened walls, the vein can't expand when blood pressures increase from exercise," commented Rush. "This increases pressure at the level of alveolus and may contribute to stress failure of the capillaries."
Hinchcliff, K.W.; Morley, P.S.; Guthrie, A.J. Efficacy of furosemide for prevention of exercise-induced pulmonary hemorrhage in Thoroughbred racehorses. Journal of the American Veterinary Medical Association 2009; 235:76-82.
Derksen, F.J.; Williams, K.J.; Pannirselvam, R.R.; de Feijter-Rupp, H.; Steel, C.M.; Robinson, N.E. Regional distribution of collagen and haemosiderin in the lungs of horses with exercise-induced pulmonary haemorhage. Equine Veterinary Journal 2009; 41(6) 586-591.
Deafness in Paint horses "This paper confirms what many have thought for a long time--that there is a sub-population of Paint horses that is deaf," said Rush. Affected horses were mostly splashed white overos or a blend of frame and splashed white overo patterns, had extensive white on the head and limbs, and at least one heterochromatic (mixed color) eye or two blue eyes.
"Hearing and pigmentation of the skin are similar in that a small population of melanocytes (pigment-producing cells) within the inner ear is essential for hearing," Rush explained.
She noted that while more than 91% of known or suspected deaf horses have one copy of a mutated endothelin B receptor gene (two copies of this gene results in overo lethal white syndrome), not all horses with this mutation are deaf. About 21% of all Paints carry this gene, and about 94% of frame overos (the most common type of overo) carry it.
"These horses are difficult to train, more skittish, more likely to be injured by other horses, and don't like small spaces," Rush reported. "But once trainers figure out these horses are deaf and take that into account when working with them (i.e., eliminating verbal commands), they are able to achieve performance training."
Magdesian, K.G.; Williams, D.C.; Aleman, M.; LeCouteur, R.A.; Madigan, J.E. Evaluation of deafness in American Paint Horses by phenotype, brainstem-auditory-evoked responses, and endothelin receptor B genotype. Journal of the American Veterinary Medical Association 2009;235 (10):1204-1211.
Santschi, E.M.; Vrotsos, P.D.; Purdy, A.K.; Mickelson, J.R. Incidence of the endothelin receptor B mutation that causes lethal white foal syndrome in white-patterned horses. American Journal of Veterinary Research 2001; 62:97-103.
Prophylactic lidocaine to prevent ileus A lack of gastrointestinal motility is termed ileus, and it is a potentially lethal complication following colic surgery. In this retrospective study lidocaine was given prophylactically to horses having colic surgery in order to stimulate gut motility. Prophylactic lidocaine treatment was associated with reduced incidence of postoperative ileus and enhanced short-term survival.
"These findings are particularly important since a report published last year that evaluated lidocaine infusion on the motility of normal horses found that lidocaine treatment actually increased transit time in feces (slowed gut contents down) rather than having a pro-kinetic effect (helped them move faster)," Palmer commented.
Torfs, S.; Delesalle, C.; Dewulf, J.; Devisscher, L.; Deprez, P. Risk factors for equine postoperative ileus and effectiveness of prophylactic lidocaine. Journal of the American Veterinary Medical Association 2009;23:606-611.
Coo, V.L., et al. Anti-inflammatory effects of intravenously administered lidocaine hydrochloride on ischemia-injured jejunum in horses. American Journal of Veterinary Research 2009; 70:1259-1268.
Bacteremia in foals In another JAVMA study scientists evaluated the records of 423 foals presented to the University of Florida with bacteremia, or bacteria present in the bloodstream, over a 25-year period. Researchers reported that Escherichia coli was the most frequently identified pathogen and that surprisingly, susceptibility of the bacteria to common antibiotics did not decrease over time (except for rarely used enrofloxacin).
Factors that improved survival rate were the year (better treatment success rates as time went on), diarrhea, lower body temperature, higher neutrophil count (a type of immune cell), and higher arterial blood pH (lower acidity in the blood). Younger age, septic arthritis, higher band neutrophil count, and higher serum creatinine levels generally worsened the outcome.
Rush reported that surviving foals were just as likely to start--and to have the same number of starts--as unaffected maternal siblings. However, they had fewer wins and less total earnings ($3,967 vs. $12,931).
Sanchez, L.C.; Giguère, S.; Lester, G.D. Factors associated with survival of neonatal foals with bacteremia and racing performance of surviving Thoroughbreds: 423 cases (1982-2007). Journal of the American Veterinary Medical Association 2008; 233:1446-1452.
Rhodococcus equi transmission These bacteria, which can cause a virulent pneumonia in foals, has previously been thought to be spread by exposure to contaminated manure (possibly via inhaling contaminated manure dust). A study published in the Journal of Clinical Microbiology found that "the concentration of virulent R. equi organisms in exhaled air from foals was five to 12 times higher than that in environmental air," reported Rush. "Rhodococcal pneumonia has classically been categorized as an opportunitistic infection; this study indicates R. equi may be a contagious pathogen.
"There were no significant differences in the median concentrations of virulent R. equi bacteria exhaled by clinically healthy or diseased foals; foals on endemic farms may be challenged and have subclinical infections," she went on. "The high concentrations of virulent R. equi bacteria in exhaled air suggested that aerosol transmission between foals is possible and may have a significant impact on the prevalence of R. equi pneumonia on farms. There may be less contact time required for a foal to get an infectious dose of R. equi from exhaled air compared to environmental contamination. Both sources may contribute to clinical disease."
Muscatello, G.; Gilkerson, J.R.; Browning, G.F. Detection of virulent Rhodococcus equi in exhaled air samples from naturally infected foals. Journal of Clinical Microbiology.2009 Mar; 47(3):734-7. Epub 2009 Jan 14.
Piroplasmosis Rush reported that in 2008 there were just over 20 cases of equine piroplasmosis in Florida, and the outbreak appeared to be spread by blood doping/contaminated needles. Previously the United States had been free of piroplasmosis since 1988.
"In June of this year (2009), there were seven cases in Kansas and Missouri, and it looked like blood doping was the transmission method again," she said. "But in October, a 7-year-old Quarter Horse got the disease, and now there are 334 cases in 12 states (most are in Texas). All of them have previously lived on the index (initially affected) premises, and now we're worried about other modes of transmission, such as natural spread of disease. The tick population may be contaminated; this will really be something to watch out for this (upcoming) year."
Unwanted Horse Survey
Rush spent a few minutes discussing the results of the Unwanted Horse Survey, which was conducted by the Unwanted Horse Coalition in late 2008 through early 2009. Selected results are as follows:
- 23,151 respondents (20,482 horse owners, 2,245 industry stakeholders, and 422 non-horse owners).
- All agree that the unwanted horse problem is escalating; 87% say that it is a "big problem."
- Rescue facilities are turning away about 38% of the horses brought to them because they are already full.
- Horse owners and industry stakeholders believe the public and media do not understand the challenges of maintaining horses.
- They also generally believe the top contributors to the problem are the closing of equine processing (slaughter) plants, the down economy, irresponsible breeding, and the high cost of euthanasia.
- Horse owners' and stakeholders' suggested solutions to the unwanted horse problem include reopening of processing plants, education of owners, and increased rescue funding.
- Rescues and nonowners believe the media and other public forums should be used to solve the problem, and that slaughter plants should never be reopened.
Rush reported several strategies have been used to address the problem in the past year, including low-cost euthanasia/disposal programs, discounted vouchers for castration with client education seminars, and free low-cost castration clinics (often done by vet students who gain experience during the clinics). Finally, she mentioned a nonpartisan agency is scheduled to study the impact of processing plant closures on the unwanted horse problem.
"It will be interesting to see what they find," she commented.
More information: Unwanted Horse Survey Results
Tips of the Hat
Each year, the Kester presenters offer up a few salutes, or "tips of the hat," to people or organizations that have done something special for equine veterinary medicine and/or horse welfare. This year, there were two tips of the hat:
- Veterinarians who volunteer for equitarian programs, providing veterinary help to some of the world's 100 million-plus working horses, donkeys, and mules.
- The Kentucky Horse Racing Commission, which modified its breeder incentive fund regulations to require a clean inspection of Tennessee Walking Horse breeders' winners (for soring) before the breeder can qualify for breeding incentive funds in Kentucky.
The Kester News Hour presenters always bring a few more studies than they can discuss. Following is a list of more papers they found worthy of mention, but were unable to discuss due to time constraints.
- Carter, R.A.; Treiber, K.H.; Geor, R.J.; Douglass, L.; Harris, P.A. Prediction of incipient pasture-associated laminitis from hyperinsulinaemia, hyperleptinaemia and generalised and localised obesity in a cohort of ponies. Equine Veterinary Journal 41, 171-178.
- Reuss, A.M.; Chaffin, M.K.; Cohen, N.D: Extrapulmonary disorders associated with Rhodococcus equi infection in foals: 150 cases (1987-2007). Journal of the American Veterinary Medical Association 2009; 235:855-863.
- Newquist, J.M.; Baxter, G.M. Evaluation of plasma fibrinogen concentration as an indicator of physeal or epiphyseal osteomyelitis in foals: 17 cases (2002-2007). Journal of the American Veterinary Medical Association 2009; 235:415-419.
- Anderson, M.E.D.; Lefebrvre, S.L.; Rankin, S.C.; Aceto, H.; Morley, P.S.; Caron, J.P.; Welsh, R.D.; Holbrook, T.C.; Moore, B.; Taylor, D.R.; Weese, J.S. Retrospective multicentre study of methicillin-resistant Staphylococcus aureus infections in 115 horses. Equine Veterinary Journal (2009)41(4)401-405.
- Boyle, A.G.; Sweeney, C.R.; Kristula, M.; Boston, R.; Smith, G. Factors associated with likelihood of horses having a high serum Streptococcus equi SeM-specific antibody titer. Journal of the American Veterinary Medical Association 2009; 235:973-977.
About the Author
Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.
POLL: Horse Height