AAEP Convention 2001: Kester News Hour
The Kester News Hour kicked off the scientific program of the AAEP convention. Named for the late veterinarian General Wayne O. "Sage" Kester, first president of the AAEP, the hour was designed to cover timely topics that were too brief and/or too new to be included in the scientific portion of the convention.
Larry Bramlage, DVM, MS, Dipl. ACVS, of Rood and Riddle Equine Hospital in Lexington, Ky., and John Madigan, DVM, MS, Dipl. ACVIM, of the University of California, Davis, took turns reviewing what they thought were some of the most newsworthy topics in 2001. Seasoning their upbeat presentation with periodic doses of humor, the two kept practitioners in the packed session interested and entertained.
Mare Reproductive Loss Syndrome
Bramlage began the news hour with discussion of mare reproductive loss syndrome (MRLS), which occurred in several states (including Kentucky) beginning in early May. Kentucky's horse industry lost as much as 5.6% of 2001 Thoroughbred foals due to stillbirth or abortion (and 9.1% of foals of all breeds, based on a survey). Also, that there will be an estimated 30.5% loss in the 2002 Thoroughbred foal crop due to losses of pregnancies this year (a 25.5% loss of foals of all breeds).
"There was a serious loss in stallion fees, lost production of horses to sell, and lost revenue. The most problematic (situation) was the early fetal losses," said Bramlage, adding that any mare bred between Feb. 15 and the first of April 2001 was in danger of losing her pregnancy.
"Initially, no one knew what to call it. There were no firm conclusions," said Bramlage.
Investigators believe that MRLS--and two other syndromes that affected hearts and eyes--most likely were not caused by an infectious or contagious entity, and probably were environmentally related. The first theory suggested that a mycotoxin or mold was released in pasture grasses that had grown quickly during warm weather, then were stressed by a hard freeze. Then cyanide was found during a few autopsies on foals which succumbed to MRLS.
The prime suspect then shifted to the large population of Eastern tent caterpillars when pasture samples yielded no conclusive results for mycotoxins. Scientists first thought that the caterpillars might have eaten wild cherry tree leaves with high levels of cyanide and passed the cyanide in pastures, but an entomologist pointed out that the caterpillars detoxify cyanide in their gut. A current theory suggests that mold on caterpillar "frass," or excrement, ingested by the grazing horses might have caused the syndromes.
The University of Kentucky has made recommendations to farm owners for preventing the possibility of the syndromes reappearing in 2002. These include minimizing the exposure of pregnant mares to Eastern tent caterpillars, keeping horses away from wild cherry trees, increasing the grass-to-clover ratio in pastures, and restricting time on pasture when a freeze follows warm weather and rapid grass growth.
Contrary to popular belief, the epicenter of the syndromes was not in Lexington, Ky., but nearer the Kentucky/Ohio border.
"This is a dollar and cents issue--we lost 516 (Thoroughbred foals) this year, and almost 3,000 pregnancies (Thoroughbreds which were to be born in 2002)," Bramlage said. This cost to the Kentucky Thoroughbred industry alone was estimated at over $300 million, and it cost an additional $14 million to the Quarter Horse and Paint horse industries of Kentucky. These figures don't even take into account lost stallion season fees, production of sale horses, or the revenue from foal/yearling care.
Also associated with the spring losses was an unusual amount of uveitis, epicarditis, and pericarditis cases. Bramlage pointed out that some cardiac symptoms resembled systemic fungal infections occasionally detected in dogs in the areas affected by MRLS.
For more on MRLS, see www.TheHorse.com/mrls.
Racetrack Surface and Catastrophic Injury
A study published in the Journal of the American Veterinary Medical Association found that in Florida, dirt tracks might be safer for horses than turf. The incidence of catastrophic injury was found to be 0.09% on dirt, compared to 0.23% on turf (0.12% overall).
Other factors associated with catastrophic injury were a delay of more than 33 days since the previous race and gelding horses. The point was made that severe injuries are more likely to result in euthanasia for geldings compared to mares or stallions, since geldings have no chance of a post-racing breeding career.
West Nile Virus Update
Madigan reported that since its appearance in the United States in 1999, West Nile virus (WNV) has progressed rapidly in its movement across North America. It was suggested that there are an estimated 150 undiagnosed, asymptomatic cases for every confirmed case in humans.
According to the United States Department of Agriculture on Nov. 20, 2001, there have been 416 confirmed equine cases of WNV, with the last case reported on Oct. 19. Nineteen states have been affected by equine WNV, with 33 Florida horses dying of the disease in Florida's first season of WNV. Approximately 24% of the confirmed cases died of the disease or were euthanized. (For more information on confirmed vs. unconfirmed cases, see article Quick Find #2879 at www.TheHorse.com.)
There is some hope of controlling equine infection with the recently released vaccine from Fort Dodge Animal Health. Since its conditional approval this summer, roughly one million doses have been distributed to equine veterinarians in high-risk areas (those with West Nile virus and large numbers of mosquitoes, such as Florida). Many practitioners and horse owners have asked about the safety and efficacy of the vaccine; a field study of 10 sites and nearly 650 horses indicates that the vaccine appears to be safe and the horses' antibody titers for WNV (a measure of immune system activity specific for WNV) are high following vaccination. It would seem that the vaccine should be partially or completely protective, and there are currently no restrictions on shipping of horses to the European Community following vaccination with the inactivated-virus vaccine.
An effective vaccine will be essential to minimizing the spread of WNV since it's estimated that the disease will make its way across the United States into California by late 2002 or early 2003. Some had expressed the hope that mosquito species native to California might vary from those able to carry WNV in the East, and thus California might be spared. Unfortunately, tests prove that six species of California mosquitoes can transmit WNV. Thus, it is entirely possible that the disease will spread quickly in that state.
Results from a study in Japan suggest that frequency of exercise-induced pulmonary hemorrhage (EIPH) epistaxis (nosebleeds) in racehorses is associated with the horse's age, sex, type of race, and the distance raced. Researchers obtained information on 247,564 Thoroughbred race starts and 4,045 Anglo-Arab race starts from 1992-97. Veterinarians endoscopically examined horses which bled from the nostrils within 30 minutes of completing the race. If they found blood in the trachea of a horse, it was diagnosed as an EIPH case. The researchers believe that higher-intensity exercise over a shorter period of time might increase the chance of EIPH, since the horses examined showed higher frequency of EIPH in shorter races. It was also found that epistaxis was more common in older horses than in two-year-olds, and more common in females than in sexually intact males.
Tongue Ties and Respiratory Performance
A study published in the American Journal of Veterinary Research suggests that tongue ties help racehorses that have problems with upper respiratory obstruction perform. These findings were based on assessment of time and performance. Tongue ties had no effect on normal horses.
"It may help horses that are having trouble," said Bramlage. "If it bothers them, there's a whole lot of horses being bothered all over the country," referring to the fact that more Thoroughbreds in the United States run with tongue ties than without.
A recent Michigan State University histopathology study published in the Journal of the American Veterinary Medical Association (JAVMA) confirmed that myofibroblasts usually found around the edge of equine wounds also are found in tendons. Fibroblasts are connective tissue cells that secrete proteins and molecular collagen from which the extracellular fibrillar matrix of connective tissue forms. Myofibroblasts are fibroblasts that have developed some of the functional and structural characteristics of smooth muscle cells, but they contract once and cannot relax. Although this is good news for wounds in the skin (myofibroblasts pull the skin together for healing), it could explain why tendon healing is so complicated, because the myofibroblasts appear to set the length of the tendon.
"Once the myofibroblasts set tension on the tendon, then you have no chance of getting it stretched," Bramlage explained. "You have to cut the check ligament."
Relaxing contracted tendons in foals with tetracycline has yielded good results. "No one really understands why tetracycline works, but it might have some effect on the myofibroblasts," said Bramlage.
Salmonellosis Spread and Antibiotic Resistance
Salmonella shedding is a concern in veterinary hospitals and on farms. One study found that out of 246 colic patients, 9% shed Salmonella at some point during their hospital stay. They were more likely to shed the bacterium if:
- They had diarrhea;
- The hospital stay was more than eight days long;
- Nasogastric intubation was abnormal (possibly a reflux situation);
- Leukopenia (a reduced number of circulating white blood cells) was present;
- The patient traveled more than one hour to reach the hospital (possibly causing transport stress).
Further study showed that environmental cultures were usually negative, leading the researchers to think that the sources of Salmonella in hospitals were usually the patients. Therefore, good hygiene practices and disinfection of stalls between patients become major concerns.
Bleach was found to be the most effective disinfectant against Salmonella when used in a 1:32 diluted solution. However, bleach in this concentration is very hard on equipment, and is readily inactivated by organic material. Therefore, areas to be disinfected should be cleaned of as much organic material as possible, and one might consider a more equipment-friendly disinfectant if disinfection will be done very often. Bleach could then be used on a less frequent basis for more powerful disinfection.
Not only is disinfection a concern, but antibiotic resistance has become a problem. Roughly 24.6 million pounds of antibiotics are given to animals for non-therapeutic use annually, compared with only two million pounds for therapy. Three million pounds go to human treatment each year. Widespread non-therapeutic use of antibiotics leads many to think that we are exposing too many pathogens to low levels of antibiotics that promote "tough" strains to survive. Thus, we might be inadvertently selecting for more resistant pathogens. For example, Salmonella type 104, which has been identified as a cause of salmonellosis in Ontario, Canada, has demonstrated resistance to 12 types of antibiotics.
Human food supplies are presenting the same problem. A survey of beef and chicken purchased from supermarkets showed that 20% contained Salmonella and 82.3% had Enterococcus. High percentages of both contained antibiotic-resistant bacteria, furthering the concern about genetically transmitted antibiotic-resistant genes becoming increasingly problematic.
Growth Hormone Not Beneficial in Tendon Healing
Researchers at the University of Sydney were unable to show any benefit of treating bowed tendons with a recombinant equine growth hormone. The data was analyzed through quantitative sonographic brightness healing. As the tendon healed, the sonograph was brighter. This study was published in the American Journal of Veterinary Research.
The Joint Letter recently featured a study in which researchers analyzed previously published papers on the therapeutic use of ultrasound in humans. Out of 35 studies, 10 were chosen for examination, and overall in these studies, there was little evidence that therapeutic use of ultrasound is effective.
Genetic Predisposition to Medial Femoral Condyle Cysts
Two-thirds of 23 horses in a study published in 2000 by the International Veterinary Radiology Association underwent surgery for medial femoral condyle cysts. Six of the 23 were related to one mare and had half-sisters or dams which also had cysts. The incidence of medial femoral condyle cysts seems to be higher in males, but the researchers feel there might be a connection to the female's genetics.
Madigan presented footage of several equine rescues involving helicopter lifts. The audience enjoyed seeing the creative ways in which the rescue teams managed to get horses out of tight spots, including the use of a human backboard to get one horse out of a narrow ravine.
Madigan emphasized the importance of good teamwork during an equine rescue, as well as the public attention that often accompanies the effort. He likened the supervising veterinarian's job to the American Association of Equine Practitioners' On Call program, in which veterinarians are present at races for the express purpose of evaluating any injury and accurately describing the situation in lay terms for the media.
"It's also important to remember that any down horse is a critical care patient," he added.
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