AAEP Wrap-Up: Kester News Hour
With researchers worldwide working on solutions to various horse health problems, there is a veritable mountain of information being published continuously. Much of this information is included in AAEP convention presentations, but some of this valuable research was either too new or brief to be included in the program. Thus, the Kester News Hour has new studies and information discussed by John Madigan, DVM, MS, Dipl. ACVIM, professor of medicine and epidemiology and section chief for equine medicine at the Veterinary Medical Teaching Hospital at the University of California, Davis, and Larry Bramlage, DVM, MS, Dipl. ACVS, president of the AAEP and a partner at Rood & Riddle Equine Hospital in Lexington, Ky. This conference kickoff session is always one of the best-attended due to its fun, fast-paced format. Following are reports on several of the topics discussed.
Hyaluronic Acid Efficacy
A study on the joint medication hyaluronic acid (HA) injected directly into the joint in addition to routine recommendations was published in The Joint Letter, said Bramlage. The report described several human studies that found a significant decrease in pain and increase in function with this medication in people. Although the effects generally didn't last more than two months in those studies, Bramlage noted that the high molecular weight of HA might be beneficial. These facts have been known in the horse for some time, he said.
Upward Fixation of the Patella
Upward fixation of the patella is a very distinct form of lameness. Bramlage presented a study published in the 2003 Proceedings of the British Equine Veterinary Association (BEVA) that examined the value of medial patellar ligament desmotomy (cutting the ligament) in relieving this problem. Forty-nine horses had the procedure; 45 (91.8%) achieved their intended use. Two remained lame, one had distal (lower) patellar fragmentation, and one had osteophyte (bone spur) formation.
"As long as you restrict their exercise for enough time afterward, they're okay," Bramlage said. The study recommended four to five weeks of reduced exercise, followed by a resumption of training at six weeks post-surgery.
Treating Navicular Disease
While many problems can cause clinical signs associated with navicular disease, navicular bone problems are some of the most devastating. However, one study published in the Equine Veterinary Journal (EVJ) found that tiludronate given intravenously for 10 days improved soundness to some degree in acute cases of navicular syndrome. Bramlage explained that tiludronate inhibits bone resorption and pathologic remodeling.
"This improvement provides evidence of navicular disease as a bone remodeling disease," he said, adding that this medication is experimental and not currently available for clinical use.
Racing and Sesamoid Pathology
Those in the racing industry hunger for any information that might help predict a horse's racing future before spending a lot of money and effort on him. A study published in EVJ cross-referenced racing performance of 487 Thoroughbreds with radiographic changes in the proximal sesamoid bones (the ones at the back of the horse's fetlocks). The researchers found that one or two abnormal canals in a proximal sesamoid (less dense lines of bone; 76 horses, 15.6%) resulted in fewer starts in the 2-year-old year if the canals were in either front or hind limbs. However, if canals were present in all four limbs, there was no effect on starts in the 2-year-old year.
If there were three or more abnormal canals in a proximal sesamoid bone (10 horses, 2.1%), those horses had less starts and earnings in all years. Contour or density changes alone had no effect, Bramlage noted.
Another EVJ study of more than 1,000 Thoroughbred yearlings found irregular vascular canals in the sesamoid bones in 79% of the horses, palmar hind fetlock chips in 5.9%, osteochondritis dissecans lesions of the intermediate ridge of the hock in 4.4%, dorsal (front surface) chips of the hind fetlock in 3.3%, dorsal chips of the front fetlock in 1.6%, and palmar (rear surface) front fetlock chips in 0.5%. In this group, 81% raced, and the following lesions decreased the number of starts:
- Supracondylar lysis of the fetlock (14 of 24 horses with the problem raced, 58%);
- Sesamoid enthesiophytes or bone spurs (8/14, 57%);
- Dorsal middle carpal joint inflammation (19/30, 63%); and
- First phalanx chips in the hind fetlocks (25/36, 69%); Bramlage noted that these chips are nearly always removed from front limbs, so they didn't cause a problem in these horses).
Other findings included decreased earnings with enthesiophytes of the hind sesamoids, and no effect with vascular canals of the sesamoids. The results of the previous study disagreed with this; the difference was in how an "abnormal canal" was defined, Bramlage said.
"Any time 79% of the population has a problem (in this case, irregular vascular canals of the sesamoids), you need to reassess how you define it," Bramlage commented.
Evaluating Lame Horses' Gaits
The first way most people detect lameness is by watching a horse move. However, one can misinterpret the gait--specifically the horse's head nod--with hind limb lameness. A treadmill study published in the American College of Veterinary Surgeons (ACVS) Proceedings found that horses with hind limb lameness also seemed lame in the forelimb on the same side if one only looked at the head nod. Also, he noted that you would see a false lameness in the hind limb on the opposite side from a true forelimb lameness if only looking at the head nod.
"If you look only at the head nod, you'll get confused," Bramlage said. "You have to look at the weight carriage."
Madigan reviewed the spread of West Nile virus (WNV) since 1999, when it first appeared in the Western Hemisphere. There were 8,393 human cases logged in the United States by Nov. 21, 2003. Colorado alone had nearly 2,500 human cases.
Migratory birds might contribute significantly to the spread of the virus even more than previously thought. The virus also can be spread from bird to bird without mosquitoes.
The impact of these migratory birds is evident if you compare seasonal flyways with where cases have been found. "Some bird species can develop very high viremia and are well suited as reservoirs, and maybe this is the key point to understanding the epidemiology," said Madigan. The viremia is high enough in these birds that mosquitoes can feed and become infected, but low enough that the bird isn't killed. Dead crow counts have been a benchmark for WNV since 1999, and Madigan pointed out that for every mosquito infected by a Canadian goose or three mallard ducks, there are 11,000 infected by house sparrows.
It's difficult to predict where the virus hot spots will be in horses. Although relatively fewer equine cases were detected in the Northeast (where the virus began its spread) than in the Midwestern states in 2003, "There is some clustering going on in the East. When you look by region (at a map of cases), many (horses) likely have developed natural immunity, although relatively fewer in the northeast region," he said. In Virginia, New Jersey, Maryland, and Pennsylvania combined, there were 29 equine cases in 2000, 49 in 2001, 201 in 2002, and 1,050 in 2003.
"There is some clear suggestion that the existing vaccine (Fort Dodge Animal Health's killed-virus vaccine, West Nile Innovator) has been helpful," said Madigan, adding that a recent study showed that the mortality rates were much lower in partially or fully vaccinated horses which were clinically infected with WNV than in horses which had never received the vaccine.
Madigan recalled the situation that sparked anxious phone calls in the summer of 2003 (see article #4440), when a group of horse owners expressed concern that the WNV killed-virus vaccine was causing adverse effects in their breeding animals. He simply summed up the story by saying, "The conclusions were that it does not appear that there's a relationship between WNV vaccination and reproductive problems or any other problems."
Madigan also relayed information about a new WNV canarypox-vectored vaccine (on which The Horse reported in the January and February issues; see article #4859 online to read more about how the technology works).
West Nile Virus Treatment
For the cases that weren't prevented, there's the important issue of treatment. There isn't a lot of hard data as to how much and what kind of medication to use in the treatment of WNV clinical signs.
"Be careful if you use dexamethasone-- use a low dose for a short period of time, and it may have an effect on viral clearance," Madigan said. "Some (veterinarians) are using lower doses than last year."
He mentioned that some veterinarians have used interferon alpha as a treatment with good results even in down horses.
Eastern Equine Encephalitis (EEE)
"EEE is alive and well," said Madigan, highlighting the epidemic that hit the Southeast in mid-2003. "There were over 300 cases in Florida (as of Nov. 21, 2003), and it's something to be aware of." (See article #4592 online.)
Focus: Bacterial Infections
Clostridium difficile--Diarrhea (caused by C. difficile) associated with antibiotics is a worldwide problem. A recent report in EVJ from Sweden showed that in horses which developed acute colitis during antibiotic treatment, 18 of 43 (42%) were positive to C. difficile culture. The researchers also isolated C. difficile from four of 72 horses (6%) which had diarrhea but had no history of antibiotic treatment. They did not find C. difficile in 273 healthy, mature horses which were examined or 65 with colic.
Additionally, C. difficile was isolated in one of three normal, healthy foals which were younger than 14 days old.
In another study, Gary Magdesian, DVM, Dipl. ACVIM, ACVECC, of UC Davis showed that 14% of healthy foals cultured positive for C. difficile, but did not have diarrhea, and 57% of intensive care unit foals cultured positive (only 14% of those had diarrhea).
These results and those of the EVJ study support the notion that foals commonly shed the organisms without diarrhea.
Also, for unknown reasons, some foals do develop clinical signs with C. difficile as the primary pathogen, but without antimicrobial use as a risk factor.
Methicillin-Resistant Staphylococcus aureus--Certain bacteria have developed resistance to penicillin and can present difficult situations in intensive care units. "Methicillin-resistant Staphylococcus aureus (MRSA) appears to be on the rise," said Madigan. "Be aware and be careful with antibiotics."
The organism can also be carried in the nasal passages of people. "It's something we're just going to have to take a closer look at," he said.
"When it's resistant to penicillin, it's usually resistant to everything," said Bramlage.
The appropriate antibiotic treatment for strangles was revisited in a recent study completed at the University of Utrecht. "It convinced us that trimethoprim/sulfadiazine is not good for the treatment of strangles, especially bastard strangles (metastatic abscessation), when long-term antibiotics are required," said Madigan.
A recent report on bastard strangles showed that of horses experiencing a neurologic form, 20% had it in their brains on pathological examination.
Glucosamine and Cartilage
Glucosamine is a very popular ingredient in joint supplements, but does it really work? A report in the American Journal of Veterinary Research suggests that it might. Bramlage discussed this study in which chondrocytes (mature cartilage cells) cultured from fetlocks were exposed to glucosamine in a lab culture. The glucosamine appeared to regulate matrix metalloproteinase (an enzyme) activity, improving proteoglycan content (which creates stiffness to the cartilage and allows it to resist compression) in the chondrocytes.
"This is a potential mechanism of action for oral proteoglycan supplements slowing the progression of arthritis by decreasing degradation of proteoglycan in the cartilage of the joint," said Bramlage.
Pregnant Mare Urine (PMU) Farm Crisis
A recent study showed that the hormone replacement drug Premarin, which is made from pregnant mare urine, caused adverse effects in women at high doses. Because of recent federal approval of a lower-dose hormone replacement medication, about 7,500 PMU horses have become available for sale or adoption (see article #4763).
"Wyeth (the company that manufactures Premarin) has established an equine placement program trust," said Madigan, and pointed veterinarians toward the North American Equine Ranching Information Council web site for more information (www.naeric.org). "Maybe we should give a tip of the hat to Wyeth being responsible and getting horses adopted. Be aware and let potential owners know about (the situation)," said Bramlage.
Slaughter of horses is a hot topic in the United States, and Bramlage discussed the issue in some detail. "All slaughter plants are USDA-inspected and regulated during processing," he said. "The bill to ban horse slaughter in the U.S. pending in Congress has big holes in it. It contains provisions for confiscation of horses destined for slaughter, but no funding or provisions for long-term care of these horses. There's no mechanism for what to do with them.
"Also, the banning of slaughter eliminates our control of the shipment conditions for horses, a bill for which was recently passed by Congress," he added.
"The issue is unwanted horses; euthanasia at a slaughter facility is an acceptable option," he said. "The captive bolt method I think is more humane than barbiturate overload, and euthanasia is expensive compared to disposal. The expense is disposal."
In refuting an allegation by Blue Horse Charities, an anti-slaughter group, he said that nearly all AAEP members agree with the AAEP organization's opposition to the slaughter bill. "Eighty-eight percent of our members, in a survey, said they preferred to have slaughter as an option for these horses," he said.
"The AAEP is pro-horse, not pro-slaughter," he said. "We (the AAEP) support adoption facilities, and many of us volunteer our time at these. We have to find better ways to deal with unwanted horses than having them starving and ill-cared-for."
Madigan briefly reviewed a recent study that showed a dewormer containing ivermectin and praziquantel was safe for use in pregnant mares (see article #4714 online).
In addition, he mentioned that moxidectin has a new label recommending treatment in horses and ponies that are six months old and up. FDA records listed 111 reports of ataxia in horses younger than six months from 1997 to 2002 in horses dewormed with moxidectin, and 196 in all ages; and there's a correlation with overdose in horses lighter than 250 pounds and in older horses which are thin and debilitated.
Every day, veterinarians must make recommendations concerning individual patients. Ideally, they would base every decision on solid, published research data combined with their clinical experience. Unfortunately, there isn't a scientific paper with sufficient numbers and a control group for every veterinary procedure to help predict success. That is where practicing evidence-based medicine becomes difficult.
Madigan reported, "Evidence-based medicine is the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients." This best evidence could consist of studies that might not fit stringent research standards, but have a very useful take-home message or clinically sound, double-blinded studies that are based on technique. Sometimes the latter cannot be directly applied to clinical cases because of the variation between individual techniques and different aftercare.
Madigan presented an example of the difficulty in using evidence-based medicine in surgical decisions. "How do we score for different surgeries? Even with one surgeon, he modifies his technique with time," said Madigan. The conditions for the same procedure might vary, a surgeon might have an "off day," there might be different aftercare at different hospitals, and case selection for a specific procedure might have an effect on the outcome.
"We can't eliminate the possibility of new technique in surgery because a control isn't possible (in a study)," said Bramlage.
An example of a study that wouldn't fit stringent study standards, but was very useful in application to veterinary practice, was a study on low-dose pergolide for Cushing's. The study showed that lower, more affordable doses were effective and revealed that the previous studies with high-dose pergolide might actually have been detrimental to horses. This was the "most significant paper leading to efficacious treatment for the most common problem in old horses," said Madigan.
There are problems in veterinary medicine where there are no published solutions, and many factors must be taken into consideration when veterinarians strive to use evidence-based medicine.
Madigan historically has shown video clips of his UC Davis rescue team performing equine rescues using slings and helicopters during the Kester News Hour. The situation he chose to highlight this year was the rescue of a pack mule which had fallen at an elevation of 9,500 feet into a canyon near Bishop, Calif. When the Pine Creek Pack Station reported the incident and veterinary help arrived, the mule was bright, alert, eating, and drinking, and his only injuries were "a good bit of granite burn on his butt." After sedation, a flawless rescue was performed using 150 feet of Kevlar line, a sling, a helicopter, and equipment that was packed in by the veterinary rescue team and the mule's owners.
Kester Tip of the Hat Awards
In a new segment of the Kester News Hour, Madigan recognized individuals who have made a difference in equine health.
- Claude Ragle, DVM, Dipl. ACVS, of Washington State University, began and maintains Equine Clinician's Network (ECN) as a forum for equine practitioners to share information related to equine medicine and surgery.
- Members of the Alta Loma Riding Club in Rancho Cucamunga, Calif., organized an emergency response team and practiced an evacuation plan that was used as the California wildfires raged in 2003. The group helped evacuate about 180 horses.
- Gregory Hass, DVM, and Rick Henninger, DVM, of the University of Findlay in Ohio, and Steve Reed, DVM, Dipl. ACVIM, head of equine medicine and surgery at The Ohio State University, treated an equine herpesvirus type-1 myeloencephalopathy outbreak at the University of Findlay (see article #4214 online).
Shock Wave Therapy's Effects
To investigate the effects of extracorporeal shock wave therapy (ESWT) on the nerves, one study published in the Proceedings of the Veterinary Orthopedic Society (VOS) tested nerve function in horses following 2000 impulses of non-focused ESWT applied to the mid-pastern, reported Bramlage. Researchers found a significant decrease in sensory nerve conduction velocity--a measure of nerve conduction--at three, seven, and in some horses 35 days after treatment. They also observed some axonal swelling and demyelination (loss of nerve cell sheaths), but no damage to axonal cytoplasm or Schwann cells. In other words, nerve effects are temporary and reversible. Another study published in the VOS Proceedings evaluated the effects of ESWT on bones (specifically, the metacarpus or forelimb cannon bone). This study found no effect on this bone as measured by quantitative ultrasonography.
Bramlage raised this question: "Does it not affect bone, or is it just that we can't measure it?"
Exercise and the Immune System
We often worry about the immune system function of horses which are heavily stressed with exercise, perhaps with good reason. A study from the EVJ found that horses which completed an 80-km endurance race had increased levels of cortisol, monocytes, and neutrophils in their bloodstreams. They also had decreased levels of lymphocytes (white blood cells, which are active immune system components) and plasma glucose. Thus,
Severe exercise leads to immune system suppression, which leads to an increased incidence of respiratory disease, he stated. Bramlage noticed that the white blood cell effects lasted more than three days.
Magnetic Resonance Imaging (MRI)
MRI (magnetic resonance imaging) is better than conventional means for evaluating penetrating foot wounds, said Bramlage in describing an article from the 2002 BEVA Proceedings. Another article in that publication found that it also can help practitioners find minor changes in small tarsal joints that aren't visible on radiographs. A third investigated the properties and symmetry of the deep digital flexor tendon in normal horses, and a fourth used MRI to examine the proximal suspensory ligament in more detail than with other methods.
For every FDA-approved and regulated drug, there are at least a few copycats with smaller price tags. But is use of these products ethical? Equine practitioners are put in a position of evaluating the integrity of the compounding pharmacies and their pharmaceuticals and are largely unaware of the legal and ethical issues, said Madigan. As an example, he said that malpractice insurance does not cover use of bulk product.
Lower price is not a legitimate rationale for using (compounded) drugs that mimic FDA-approved products.
Bramlage added, "Many pharmaceutical companies have little incentive to go through the approval process for new drugs, if practitioners don't support the FDA-approved products (see more on compounding on p. 17)."
By Stephanie L. Church and Christy West
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