Kester News Hour Part Two

Probably the best-attended session at the American Association of Equine Practitioners (AAEP) Convention, the Kester News Hour features brief reports of new research that was too new or brief for inclusion in the scientific program. The information is presented in a fun, rapid-fire format by two of the country's top equine veterinary specialists--internal medicine guru John Madigan, DVM, MS, Dipl. ACVIM, professor of medicine and epidemiology and section chief of equine medicine at the Veterinary Medical Teaching Hospital of the University of California, Davis; and orthopedic surgery specialist Larry Bramlage, DVM, MS, Dipl. ACVS, a partner in Rood and Riddle Equine Hospital in Lexington, Ky., and the immediate past president of the AAEP. Following are brief reports of the research they found important for this popular session. Visit www.thehorse.com/ViewArticle.aspx?id=5574 to view part one of Kester that includes Bramlage's comments. Below are Madigan's portions of the session.

West Nile Virus
Madigan offered a retrospective look at West Nile virus (WNV). He said that scientists had expected WNV to affect horses in California in 2002, but the virus didn't actually hit until 2003. At least 496 equine cases were recorded as of October 8, 2004 (540 was the final count for 2004). Madigan said that many of the 210 horses that died or were euthanatized by Oct. 8 were unvaccinated animals--nine of the dead horses had been completely vaccinated. (The final California data showed 210 dead or euthanatized horses due to WNV, but data wasn't available on the vaccination status of the cases from Oct. 8-Dec.)  There was nearly a 50% mortality rate in all infected horses (higher than many areas of the country). He says this might be because of the aggressive mosquito species Culex tarsalis (a WNV vector) that is indigenous to California and because those who chose not to vaccinate might not pursue veterinary therapy for WNV infection, either.

Experts knew that at least 10 species of mosquitoes were vector competent for WNV in California before the disease hit. A multi-agency collaborative effort had established sentinel chicken flocks, and was testing for infected mosquitoes, dead birds, and horse and human cases.

Human cases numbers nationally dropped from 8,393 in 2003 to 2,282 in 2004 without a human immunization available, so presumably there has been exposure and subclinical infection.

The recombinant canarypox-vectored vaccine by Merial was tested recently—the rapidity of the antibody response to a single dose might be useful in an outbreak situation (see www.TheHorse.com/ViewArticle.aspx?id=5453). Another study of North Dakota WNV cases in 2002 showed that of WNV-affected horses, the odds of death in unvaccinated animals were three times higher than those getting one dose of either the Fort Dodge or Merial vaccine, and 16 times higher than in horses receiving two doses of vaccine. Vaccination clearly has benefits.

Madigan said it is difficult to predict the future epidemiology of equine WNV, and the virus is always going to be with us to some extent.

Equine Malignant Hyperthermia
This life-threatening disease can be triggered by a number of things, including halothane (an anesthetic) and succinylcholine (a relaxant). A mutation in the ryanodine receptor-1 gene was mapped out in 2004, and it was shown that in horses with these mutations, excess calcium is released in the body if triggered by the above substances, causing the appearance several clinical features: Muscle rigidity, elevated body temperature, profuse sweating, tachycardia (an excessively fast heartbeat), black urine, hypercapnia (excess carbon dioxide in the blood), creatine kinase (a muscle enzyme) increase, electrolyte disorders, tachypnea (rapid, shallow respiration), hypertension, acidosis (a drop in blood pH), and high mortality. The gene mutation can be detected in hair, whole blood, or muscle samples.

Glycogen-Branching Enzyme Disorder (GBED)
In 2004, the genetic mutation causing GBED, an autosomal recessive fatal fetal glycogen storage disease in American Quarter Horses, was discovered. Affected foals have a common ancestor, and their pedigrees could contain prolific stallions that are likely carriers of the gene. Veterinarians see abortion, still births, and diseased foals (from neonate to 18 weeks) as a result of the disease. Clinical signs are highly variable and can include weakness, inability to rise, respiratory or cardiac failure, seizures, low blood sugar, low white blood cell count, and sudden death. Hair samples can be submitted to the UC Davis Veterinary Genetics Laboratory for GBED genetic testing. Visit www.vgl.ucdavis.edu/service/horse/GBED.html .

Intravenous Dexamethasone
It was found that oral dexamethasone had a longer duration of action than dexamethasone administered intravenously (IV). If given before feeding, there is nearly double the absorption of dexamethasone compared to giving with feed in the stomach. Madigan said that orally administered dexamethasone that was intended for IV works just as well and maybe even better than when given IV.

Meconium Retention Therapy
A study showed that newborn foals with retained meconium (first feces) were more successfully treated using acetylcysteine enemas rather than surgery. The enemas decreased hospital time and made the foal's treatment less expensive. A few foals developed ruptured bladders, possibly from straining. The foal is restrained and sedated before the veterinarian uses a 30 French Foley catheter per rectum, and the 4% acetylcysteine enema is given as a retention solution for 45 minutes.

Gastric Ulcers and Zero Tolerance Drug Rules
Madigan reported on a study showing gastric ulcers in 67% of competing endurance horses and active bleeding in 27% at the end of a race. There has been disagreement over zero-tolerance medication rules at endurance competitions for this reason.
Madigan pushed for threshold levels of medication in competition horses. For example, if a colic case requires Banamine two weeks prior to a competition, it should not be denied relief because of drug rules.

Gut Flora
It's no secret that there are protective effects to normal flora in the stomach. Madigan said scientists have learned that normal flora activates toll receptors involved in protecting the sensitivity of the gut. When those receptors are disrupted by use of high-level antibiotics, there is a diminished capacity for repair of gut tissue. Gut flora might minimize colonization with pathogenic bacteria and might also be associated with mucosal defense.

In a study of recurrent Clostridium difficile colitis in humans, fecal transfaunation (transfer of bacterial flora from one host organism to another) via donor stool administration via nasogastric tube did not cause any adverse effects, resulted in a very high cure rate, and only one person experienced a single recurrence. This highlights how important it is that horses graze and take in bacteria needed in the gut.

Horse Rescue
Madigan told of two equine airlift rescue stories that occurred in 2004. Hank and his rider fell down 9,000 feet from the Tevis Cup trail in the Sierra Nevada mountains. The owner had a broken leg, but Hank was relatively uninjured. However, he could not move up the trail and had fallen three times and rolled back to the same spot and was stuck there for 48 hours. He would have to be euthanatized if he couldn't be airlifted.

Madigan and his team hiked in and put the horse in the Anderson sling that had been dropped from a helicopter. The helicopter came back in and lifted Hank out to safety.

Another horse, Smokey, a former feral mustang, got away from his rancher's herd and became lost in the mountains of Idaho's back country. Snowmobilers found him trapped in the snow after he had survived three months in an area with cougars and wolves. He was able to find a sheltered spot in the trees and had kept the snow trampled down in an area so that it wouldn't overwhelm him. He was lifted out by Blackhawk helicopters.

Headshaking Therapies in Competition
Another spin on what is allowed in competitions and what isn't was how horses with headshaking syndrome cope on the competition circuit. Madigan explained that horses that headshake can be light sensitive, sound sensitive, or sensitive to the slightest touch as with long-stem hay. Many owners are finding new freedoms with their headshaking horses with a "nose net,” which seems to normalize the horse, possibly by sending constant signals up to the trigeminal nerve, which keeps it from firing and causing the horses pain. Fifteen of 43 owners had a nose net working effectively on their horses. Some horses are ridden in masks or shields, and companies now make goggles for horses. Having results from evidence-based studies that support the use of these devices would be helpful in convincing show authorities to allow competitors to use them.

New Rescue Equipment
Veterinarians at the University of California, Davis, have developed a prototype rescue sling for short-term use in emergency situations and anesthesia recovery called the UC Davis Large Animal Lift (see www.largeanimallift.com for more information). It is comprised of a single bar with straps that lifts the horse by its skeletal system. It fits a pony or draft horse and is easy to put on a down horse. The patented device was developed by three members of the team that developed the Anderson Sling (Madigan, Charles Anderson, and Richard Morgan) and Gregory L. Ferraro, DVM, director of the Center for Equine Health at the UC Davis School of Veterinary Medicine.

About the Author

Multiple Authors

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More

Free Newsletters

Sign up for the latest in:

From our partners