Kester News Hour
The Kester News Hour kicked off the scientific program of the AAEP Convention, held Nov. 24-28 in San Diego, Calif. Named for the late veterinarian General Wayne O. “Sage” Kester, the hour was designed to cover timely topics that are either too brief 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 the mare reproductive loss syndrome (MRLS) that occurred in several states (including Kentucky) beginning in early May. Kentucky’s horse industry lost as many as 5.6% of 2001 Thoroughbred foals due to stillbirth or abortion (and 9.1% of all breeds of horses, based on a survey), and it has been estimated that there will be a 30.5% loss in the 2002 Thoroughbred foal crop due to losses of pregnancies this year (25.5% loss of all breeds). “There was a serious loss in stallion fees, lost production of horses to sell, and lost revenue,” explained Bramlage. “The most problematic (situation) was the early fetal losses,” said Bramlage, adding that any mare bred between Feb. 15 and the first of April was in danger of losing her pregnancy.
“Initially, no one knew what to call it. There were no firm conclusions,” said Bramlage. Leading investigators believe that the MRLS--and two other syndromes that affected hearts and eyes were--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 blame 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 trees 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 out of proximity to 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 in an area closer to the Kentucky/Ohio border.
“This is a dollar and cents issue,” said Bramlage. “We lost 516 (Thoroughbred foals) this year, and almost 3000 foals (Thoroughbreds which were to be born) in the upcoming year.” The cost to the Kentucky Thoroughbred industry alone was estimated to over $300 million, and it cost an additional $14 million e 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 were 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 regions affected by MRLS. “Whether these complications were related to climatic factors or coincidence, or a part of the spring losses, is part of the puzzle now,” said Bramlage.
For more on the spring loss syndromes, visit http://www.thehorse.com/mrls.
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 is an estimated 150 undiagnosed asymptomatic cases for every confirmed case in humans.
So far in 2001, there have been 416 confirmed equine cases of WNV, with the last case reported on Oct. 17. Nineteen states have been affected, with 32 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 #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 that have been shown to carry WNV in the East, and thus California might not have mosquitoes capable of carrying the disease. Unfortunately, tests have proven this inaccurate—six species of California mosquitoes can transmit WNV. Thus, it is entirely possible that the disease will spread to that state.
Tongue Ties and Respiratory Performance
A study published in the American Journal of Veterinary Research (AVJR) suggests that tongue ties help racehorses perform that have problems with upper respiratory obstruction. These findings were based on assessment of airway flow rates. Tongue ties had no effect on normal horses.
“It may help horses that are having trouble,” said Bramlage.
Results from a study in Japan published in the Journal of the American Veterinary Medical Association (JAVMA) suggest that frequency of exercise-induced pulmonary hemorrhage epistaxis, or 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. Horses showed bleeding from the nostrils within 30 minutes of completing the race. 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 ones that were two years old, and more common in females rather than in sexually intact males.
A recent Michigan State University histopathology study published in AJVR confirmed the presence of myofibroblasts usually found around the edge of equine wounds also are found in tendons. Myofibroblasts are fibroblasts that have developed some of the functional and structural characteristics of smooth muscle cells, which contract once and cannot relax. Although this is good news for wounds in the skin (it pulls the skin together for healing), it could explain why tendon contraction is 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 the tendon stretched,” Bramlage explained. “You have to cut the check ligament.”
There have been good results relaxing contracted tendons in foals with tetracycline. “No one really understands why tetracycline works, but it might have some effect on the myofibroblasts,” said Bramlage.
Racetrack Surface and Catastrophic Injury
A study published in JAVMA found that at least 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.
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,
- Nasogastric intubation was abnormal (possibly a reflux situation),
- Leukopenia was present (a condition in which the number of white blood cells circulating in the blood is abnormally low),
- 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 it is readily inactivated by organic material. Therefore, areas to be disinfected should be first washed clean 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. The widespread use of antibiotics for non-therapeutic use 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 in 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 AJVR.
The Joint Letter recently featured a study in which researchers analyzed previously published papers looking at the use of therapeutic ultrasound in humans. Out of 35 total studies, 10 were chosen for examination, and overall in these studies, there was little evidence that therapeutic use of ultrasound is effective.
“Scintigraphy is very sensitive, but not very specific,” said Bramlage, about the take-home message from an abstract in the International Veterinary Radiology Association meeting proceedings. According to the study, 51.9% of Thoroughbreds in training were said to be lame. Of the racehorses that they examined with scintigraphy, 59% showed increased uptake sites. The combination of radiography and scintigraphy created a positive diagnosis in only 15% of the horses. If a clinical exam was added, 39% yielded a positive diagnosis. A certain unspecified percentage had soft tissue lameness and some were obviously undiagnosed. The point that researchers made was that scintigraphy is not a lameness meter, but is part of a lameness exam.
Surgical Prognosis for Medial Femoral Condyle Cysts is Good
Two-thirds of all the horses in a Japanese study were operated on for medial femoral condyle cysts, and raced post-surgery. Six out of 23 were related to other females with cysts (half-sisters or dams). The incidence of osteochondritis dissecans (OCD) is higher in males, but there might be a connection to the female’s genetics with the cysts.
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 a 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 in such rescues 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.
Heart Score and Racing Performance
An Irish study of 860 Thoroughbred yearlings over seven years looking at heart score measurements was presented. (The heart score is a numerical value that represents the magnitude of electrical events associated with ventricular contraction. The idea is that the larger the electrical events, the larger the heart and thus the more cardiovascular capacity.) While there might be some predictive value whether the horse will race, it had no value in predicting quality of race career. Bramlage said that the heart that predicts racing success, as all horse owners know, is not in the horse’s chest.
HA for Joints
A 2001 human study reported in Clinical Orthopedics and Related Research found that hyaluronan was better than a saline placebo, showing efficacy for hyaluronic acid (HA) use in joints. The research was done at 10 centers and involved 226 human patients receiving three injections. It was noted, however, that all injections--saline and HA--improved pain in humans. Bramlage said he would vote for use of HA.
Calcium and Colic
A Tufts University study published in the AJVR found that 86% of colics are hypocalcemic (showing a deficiency of calcium in the blood), perhaps suggesting that more attention should be paid to calcium management in the horse.
National Annual Incidence of Colic
When clients ask whether their farms have more colic cases than other farms, veterinarians now have some numbers on which to base a reply. In JAVMA in 2001, a Colorado State University study reported that the incidence of colic events was 4.2 per 100 horses per year. The fatality rate was 11% nationally.
Cation and Anion Balance
The AJVR in 2001 reported on a study that indicated that mares presented for colic had low levels of calcium and magnesium. A question arises with regard to the association of these low levels and gut motility and onset of the colic. Madigan stated that work done at UC Davis using total diet cation and anion levels may have an effect on calcium levels and activity similar to the situation in food animal medicine. In dairy cattle, a great deal of attention is focused on the cation and anion balance in the pregnant and lactating cows and disorders of calcium in that species (milk fever) have been prevented by adjusting the diet with regard to cation and anion balance. This suggests more work should be done to look at this in the diet of mares with colic.
POLL: Horses Living With Livestock