AAEP Convention 2006: Medicine
Uplifting Applications for UC Davis Large Animal Lift
John Madigan, DVM, MS, Dipl. ACVIM, professor of medicine and epidemiology and section chief of equine medicine at the University of California, Davis, developed the UC Davis Large Animal Lift (LAL) with colleagues over the last several years. He reported on the lift's applications and success stories in its first months of use, calling the lift "a necessary piece of equipment for every large animal practice."
After 20 months in service, the LAL has been used on 17 horses in the UC Davis clinic. These horses were recumbent (down) for a variety of reasons, including West Nile virus, hyperkalemic periodic paralysis (HYPP), myopathy (any muscle disorder), and spinal trauma. The time period from recumbency to lifting using the LAL was anywhere from four hours to 14 days. Of the horses lifted, 10 were discharged and seven were euthanatized, and Madigan referred to these outcomes as "way better than I would have thought."
Madigan explained that the lift was developed because of the difficulty of getting a down horse on her feet. In many instances veterinarians were left with no option but to euthanatize a horse that could have been treated if the veterinarian could get it standing. "The Anderson sling is great for upright horses, but is very hard to get on a down horse," Madigan said.
"I got tired of putting down horses who couldn't stand up, and wondering if they would do a lot better if they could stand up," Madigan said.
The UC Davis LAL can be put on a down horse by one person, working from the back of the horse (rather than having to work near the legs), making it safer for both horse and handler. The fitting and lifting is well-tolerated by most horses, which means that very little sedation, if any, is necessary, making the horse's own efforts to stand easier. Madigan also reported that it was easy to transition from the LAL to an Anderson sling for long-term care.
For more information on the UC Davis LAL see www.largeanimallift.com or www.TheHorse.com/emag.aspx?id=6517.
Flu: Interspecies Transmission
In 2004 researchers identified a highly contagious canine influenza virus strain (H3N8) that was closely related to an equine flu strain. Essentially that meant the virus had jumped from horses to dogs, and the scientists said it was "a very rare event of considerable scientific interest with regards to understanding influenza virus transmission across species barriers." It also illustrated the horse is not a dead-end host for the virus as once thought.
Gabriele A. Landolt, DVM, MS, PhD, Dipl. ACVIM, an assistant professor at Colorado State University, reviewed virus mutation and interspecies transmission of equine influenza viruses.
"In horses, influenza infection probably represents the most frequently diagnosed and economically important viral respiratory disease," Landolt explained. "However, equine herpesvirus-1 and -4 are quickly catching up. While experimentally horses of all age groups are susceptible to infection, the highest incidence of disease seems to be in the younger population (between two and three years old).
"Vaccination of horses with inactivated or modified-live virus vaccines has been (and remains) the cornerstone of the control of equine influenza," she said. "However, vaccine breaks (failures) do occur, and influenza virus infections still remain a serious health and economic problem in horses."
Why do we see vaccine failure?
According to Landolt, insufficient vaccination and maternal antibody interference in young horses (less than six months of age) present problems for vaccine protection against influenza.
She added, "Another important reason for vaccine failures is due to the fact that virus continues to evolve genetically."
There are two mechanisms by which influenza is transmitted from one species to another. One method is the exchange of genetic material (known as gene swapping or genetic reassortment) between flu viruses from different hosts that can result in the creation of a unique third virus that has the ability to infect and spread within a new host species. Examples of this are the viruses that caused the influenza pandemics (disease outbreaks impacting a large geographical area) of 1957 and 1968.
Another method is the transfer of a whole virus from one host species to another, and that virus has the ability to replicate in the new host. The best examples for this scenario are the pandemic of 1918, when an avian influenza strain was transmitted to humans and killed an estimated 675,000 people in the United States alone, as well as the recent infections of humans with the avian flu H5N1. However, in contrast to the 1918 strain, the H5N1 strain of influenza hasn't shown the ability to transfer efficiently from human to human.
"The transmission of influenza from horses to dogs is especially interesting in light of the fact that dogs were not commonly regarded as hosts for influenza A viruses," Landolt said. "Although circumstantial evidence from surveillance studies indicates that human-lineage influenza viruses occasionally cross the species barrier to dogs, none of these human viruses are known to have spread efficiently within the canine population. In contrast, the H3N8 equine-lineage virus that caused the recent canine influenza outbreak in the United States spread quickly among dogs."
Scientists believe H3N8 used the whole-virus transfer method to move between horses and dogs, except canines are able to transmit the virus to other canines, which is only rarely seen with this type of viral transfer.
"Because equine H3N8 viruses apparently have the ability to infect dogs, it raises the question if such an event has happened before or if it could happen again in the future," Landolt said. "Although it is unclear if the canine H3N8 viruses are still capable of infecting horses, they potentially represent a serious emerging disease threat to the American horse population."
What might be even more troubling, she said, is current vaccines might not protect horses from future flu strains because of the ability of the virus to mutate.
"The sustained antigenic drift (small, irreparable changes in the virus' makeup) of the equine H3N8 viruses continues to result in vaccine failures," Landolt explained. "Thus, inclusion of viral antigens representative of contemporary circulating viruses (in vaccines) has to remain a priority."
Are Mares a Source of R. Equi For Their Foals?
A study of one Lexington, Ky., Thoroughbred farm showed that on average, 30% of the farm's foals developed Rhodococcus equi pneumonia during the 2004 and 2005 foaling seasons. Researchers searching for a source of the disease questioned if R. equi in the mare's feces was a source of infection for her foal.
They found that all mares at some point post-foaling shed R. equi in their feces. This meant that screening mare feces for R. equi to help control the spread of the disease would be a waste of time.
Noah Cohen, VMD, PhD, MPH, Dipl. ACVIM, associate professor at Texas A&M University's College of Veterinary Medicine, said, "In either year, virulent R. equi was isolated from the feces of every mare in the study at one or more sampling times (there were four sample times)," Cohen explained. "One-third of the mares were shedding R. equi in all four of those samples." He added that 80% of the mares were positive in three or more samplings.
"Fecal concentrations of total or virulent R. equi were not higher in mares whose foals developed R. equi than in those whose foals were unaffected," Cohen said. "If this is true at other farms, screening mares for fecal concentrations cannot be used to help control R. equi pneumonia.
"Because all mares were culture- positive, they may be an important source of R. equi for their foals during the periparturient (immediately after foaling) periods," he explained.
The study was funded by the Grayson-Jockey Club Research Foundation with additional support from the Link Equine Research Endowment, College of Veterinary Medicine, Texas A & M University.
Gallium to Control R. equi Foal Pneumonia
In order to survive, R. equi requires iron from the foal's body to replicate and survive. Researchers at Texas A&M University's College of Veterinary Medicine recently examined the use of a semi-metal (gallium) that mimics iron as a means to disrupt R. equi's replication process. They concluded that gallium does interfere with R. equi's uptake of iron, which, in turn, inhibits the growth and development of the microorganism, thereby decreasing the number of bacteria in the body.
Ronald Martens, DVM, a professor at the university, said, "Iron is crucial for DNA synthesis of the bacteria. One of the body's innate immune mechanisms is that iron-transporting proteins in plasma bind iron and store it within macrophages (specialized white blood cells that fight infection). This is to prevent its uptake by bacteria, and most bacteria cannot survive in the absence of iron. However, R. equi has the ability to obtain and use protein-bound iron. So, it circumvents this innate immune mechanism.
"Gallium seems to have great potential for the prevention and control of disease in foals caused by R. equi," Martens said. "Short-term oral gallium therapy in newborn foals could provide protection against early infection with R. equi. This would provide additional time for maturation of requisite innate and adaptive immune functions and could substantially reduce the incidence of disease on R. equi-endemic farms. In addition, gallium used alone or in conjunction with standard antibiotic protocols may be valuable for the treatment of established R. equi infections."
Respiratory Viruses Detected at Shows, Sales
In a survey of horses arriving at several different show and sale facilities, researchers found that as many as 4% of the population were shedding equine herpesvirus-1 (EHV-1) from nasal passages, and as many as 2% were shedding equine herpesvirus-4 (EHV-4), based on a real-time polymerase chain reaction (PCR) tests. Josie Traub-Dargatz, DVM, MS, of Colorado State University's College of Veterinary Medicine and Biomedical Sciences, presented the study data on behalf of Paul Lunn, BVMS, MS, PhD, principal investigator on the study, and graduate student Jennifer Yactor.
This study showed that horses attending events can shed these viruses from their nares (nasal passages). None of the horses attending these shows or sales demonstrated the neurologic form of EHV-1, and few of the EHV respiratory-positive horses showed signs of disease.
She said the study provided a snapshot of the important viral respiratory pathogens shed by horses at major competitive or sales events. The long-term goals of the study were to test three hypotheses:
1. Young horses attending a major equine competitive event will shed contagious viral pathogens that represent a disease threat to all horses in contact;
2. There is a difference between the rate of shedding at the time of entry to a competitive event and at two to four days after entry. This is caused by stress related to transporting the animal to the event and the mixing of animals; and
3. The shedding of pathogens is associated with risk factors that can be identified in individual horses.
The research was designed as a pilot study to assess the feasibility and likelihood of detecting viral shedding in the tested horses. For this reason, researchers selected horses at greatest risk of infection (such as juvenile horses).
Horses were sampled within 24 hours of arriving at facilities, and when possible, two to four days later. Traub-Dargatz said samples were collected from horses at four equine shows or sales (see Table 1 below): Barrett's Equine Sales in March 2004 in Pomona, Calif., the June 2004 National Appaloosa Horse Show and World Championship Appaloosa Youth Show in Oklahoma City, Okla., the October 2004 Fall Mixed Thoroughbred Sale held by the Ocala Breeder's Sales Company in Ocala, Fla., and the November 2004 American Quarter Horse Association World Championship Show in Oklahoma City.
The researchers also visited two farms in the Ocala area with suspected respiratory infections.
When possible, researchers completed questionnaires in order to collect information about risk factors associated with viral shedding, such as age, sex, vaccination history, travel history, total horse population at home, and if the home facilities were "open" or "closed" (no horses entering the premises within the last three months).
"This study demonstrated the utility of real-time PCR for the detection of EHV-1 and EHV-4 from nasal secretions from horses," Dargatz said. "Horses at equine events can shed EHV-1 and -4. The majority of horses detected to be shedding were less than two years of age, most had no history of recent illness, and there were positives at multiple events. There were no significant differences from initial and follow-up samples for EHV-1.
The study was funded by Intervet Inc. and grants from the university.
Researchers Test WNV Vaccines
In a recent study, University of Florida researchers evaluated the effectiveness of three commercially available equine West Nile virus (WNV) vaccines. While all vaccinated horses, irrespective of the vaccine administered, did not develop viremia and all survived a severe challenge model of WNV-induced encephalomyelitis (in this case, WNV was introduced directly into the spinal fluid), only the chimera-vaccinated horses did not develop any clinical signs of WNV-induced disease. Kathy Seino, DVM, MS, a PhD student at the university, presented the study's findings.
Pharmaceutical companies responded quickly to the invasion of WNV by developing vaccines to protect horses from this virus. To date, there are three types of vaccines on the U.S. market. These include a killed virus (or inactivated) vaccine, a modified-live canarypox-vectored virus vaccine, and the recently approved chimera vaccine (see www.TheHorse.com/emag.aspx?ID=7569).
Study design Researchers divided healthy horses that tested negative for WNV into three groups of eight receiving either the killed virus vaccine (produced by Fort Dodge), the modified-live canarypox-vectored virus vaccine (Merial), or the live-chimera vaccine (Intervet). Appropriate nonvaccinated controls were used.
Vaccines were administered in accordance with the manufacturers' labels, and horses were challenged after one month.
Horses were challenged with a model that reproduced clinical signs of WNV.
Within seven days of infection, all six of the control horses had increased rectal temperatures and clinical signs of WNV, and none survived to the end of the study period.
In horses vaccinated with the inactivated vaccine, mild or grade 1 signs of neurologic deficits were noted in four of the six horses (67%), and in the horses vaccinated with the modified-live vaccine, one of five horses (20%) had mild clinical signs.
No vaccinated horse had significant signs of encephalitis, and no vaccinated horse required humane destruction.
Take-home message The study reported that all vaccines protected the study horses and all of the vaccinated horses survived the challenge. However, some horses vaccinated with modified-live and killed vaccines did show mild clinical signs of WNV after challenge.
Horses achieved protective immunity with only one injection of the chimera vaccine.
Avoid Mayflies to Minimize PHF Risk
Minimizing your horse's risk of contracting Potomac horse fever (PHF) might be as simple as shutting off the lights. Mayflies--swarms of which are common in Southeast Minnesota and adjacent areas of Wisconsin--were incriminated as a vector of PHF during a 2005 outbreak in Wisconsin and Minnesota.
Julia Wilson, DVM, Dipl. ACVIM, an associate professor of Veterinary Population Medicine at the University of Minnesota, investigated the 2005 outbreak when six horses got PHF after attending the same show. The horses' owners reported a swarm of mayflies at the show--inches of the dead insects covered the ground and some blew into the barn and trailers.
Wilson visited the show grounds nearly a month later and found desiccated (dried out) samples of mayflies, which were found to be positive for PHF.
Wilson sent a questionnaire to members of the Minnesota Quarter Horse Association and found five more cases had developed in horses that did not attend the show. In all but one of those cases, the horses' owners reported seeing aquatic insects swarming around lights at night.
Wilson suggested horse owners keep barn lights off at night during summer months to keep from attracting the clusters of mayflies.
Wilson said she has suggested this to several other veterinarians experiencing high numbers of PHF cases, and they have reported good results.
Influenza Canarypox Vaccine
Researchers found that clinical signs of influenza and virus shedding were significantly reduced in horses vaccinated with a recombinant canarypox-vectored influenza vaccine and experimentally exposed to influenza compared to unvaccinated horses, explained Jules Minke, DVM, PhD, project leader of Biologicals at Merial, who completed the study with the help scientist at the Animal Health Trust in Newmarket, England.
A vectored vaccine uses a specific piece of DNA from the pathogen against which you want immunity. It is carried into the animal's cells by a carrier or vector that does not cause disease itself. Merial introduced the vaccine in the European market in 2003 and has received USDA approval to market the vaccine in the United States.
Canarypox platform Minke said, "These viruses (canarypox) can't replicate in horses, reversion is not possible (it doesn't mutate into an influenza virus), and horses previously vaccinated with the killed vaccine and subsequently vaccinated with the canarypox vaccine mount a very strong anamnestic response (where the body recognizes an invading antigen and produces antibodies against it)."
A strong feature of this vaccine platform is that vaccination does not induce a neutralizing response against the vector (a common problem with most other vector vaccines), meaning that the vaccine can be used to booster horses over and over again without the body becoming unresponsive to the vectors.
Study Researchers challenged 12 control horses and 12 horses vaccinated with the canarypox vaccine. Vaccinated horses received two injections at Day 0 and Day 36. They were challenged two weeks after the second vaccination with a common strain (related to the Ky/02 virus) of the flu virus They scored horses on the severity and duration of coughing, nasal discharge, anorexia, dyspnea (difficulty breathing), and depression.
"All of the controls developed coughing, and it was very pronounced and prolonged," he said. "Of the vaccinates, there were only two horses that showed coughing for one day."
The most predominant clinical sign in the vaccinated group was nasal discharge. However, compared to the control group, clinical signs were minimal.
"When you look at the nasal discharge in the controls, it was very prolonged and severe," Minke explained. "The duration of the discharge was significantly different (greater) in the controls than in the vaccinated horses."
Minke said dyspnea is a very important and severe sign of influenza. It is indicative of lower airway disease. Dyspnea was only found in the control group (five of 12 horses were positive).
Viral shedding Protection against viral shedding is an important characteristic of any influenza vaccine. Each of the control horses shed virus for about 41/2 days. No virus was recovered from any of the vaccinated horses on any occasion during the post-vaccination period.
Humoral vs. cell-mediated Researchers also found that horses vaccinated with the recombinant vaccine had humoral (in the serum) and cell-mediated (in the cells) immunity. Humoral immunity involves antibodies--specific proteins made by B-cells (B-lymphocytes, a type of white blood cell) that physically attach to foreign material and help the body do its job of removing the foreign material. This is the type of immunity stimulated by most killed-virus vaccines.
Cell-mediated immunity protects the body against intracellular organisms using T-cells (T-lymphocytes). The T-cells will recognize a horse cell that has been infected by a virus before the virus has had a chance to replicate.
Most vaccines are able to produce a humoral immune response, but Minke said this is the only flu vaccine he knows of that has been demonstrated to produces a cell-mediated response.
Duration Researchers found that the vaccine mounted significant immunity for at least six months. They also discovered horses vaccinated with the canarypox vaccine were able to produce antibody titers within 14 days after the first vaccine dose, indicating an onset of immunity not typically seen with inactivated vaccines.
Take-home message "We have developed a state-of-the-art influenza vaccine," Minke explained. "This vaccine provides significant clinical and virological protection against the recent highly virulent U.S. strain of influenza (N/5/02).
The vaccine was capable of stimulating both humoral and cell-mediated immune responses, and significant antibody titers were already present 14 days after the first vaccination. Protection lasted at least six months after the initial vaccination program."
The study was funded by Merial.
Down the Hatch
Veterinarians at Oregon State University developed a method to get valuable calories into anorexic horses or those unable to eat normally. The process employs a couple of buckets, pelleted complete feed, water, tubing, and a bilge pump.
For horses with mouth or throat injuries, this method can be used to provide the horse's complete daily ration of both feed and water in about 15 minutes.
Shannon K. Reed, DVM, a surgery resident at Oregon State, explained the procedure. A veterinarian weighs the horse's complete daily ration of feed, dumps it into a bucket, covers the mixture with enough water to make it crumbly, and allows about 30 minutes for soaking. The ration is divided into three to four small meal amounts and stored in plastic bags until mealtime to keep the mixture from losing water.
At feeding time, the veterinarian mixes this ration with one ration of water to create a thin gruel. He places large-bore tube (about 4 cm in diameter) into the gruel and connects it to the bilge pump, and then he inserts a nasogastric tube in the horse's stomach and connects that tube to the pump's outflow valve. The pump suctions the gruel out of the bucket and into the horse's stomach via the nasogastric tube.
Reed said that the technicians at her hospital insert the nasogastric tube in the morning and leave it in all day if it's well tolerated. With the tube replaced each day, this method only requires the mixing of the gruel and pumping a few times per day to provide complete nutrition to a horse that's unable to eat.
Reed called the method easy and affordable, and said that providing sufficient calories helps speed the healing process.
Environmental Contamination Necessitates Leeway in Post-Race Cocaine Testing
The prevalence of a common metabolite of cocaine in the environment has created a need for the allowance of a minimum concentration of the substance in post-competition race testing, according to Fernanda Camargo, DVM, and Tom Tobin, DVM, PhD, DABT of the Gluck Equine Research Center at the University of Kentucky. Roberta Dwyer, DVM, MS, Dipl. ACVPM presented this study on Camargo's behalf.
According to Camargo and Tobin, exposing a horse to an amount of cocaine not uncommonly found on paper currency can result in a positive test, and 1mg of cocaine administered to a horse can produce about 100 ng/ml of Benzoylecgonine (BZE), a major urinary metabolite of cocaine.
The chances for exposure to this amount of cocaine are greater than one might imagine. According to Camargo and Tobin, one study stated that 79% of paper currency is contaminated with cocaine. (Other studies have estimated that contamination affects four out of five bills in circulation.)
"If you have a contaminated hand that touches the muzzle of a horse, puts the bit in the mouth, etc., the horse's skin may readily absorb that cocaine," Dwyer said.
Camargo and Tobin suggest that rather than a "zero tolerance" policy for BZE-positive horses, a cutoff value should be established, similar to the value allowed in human drug screening (the human workplace cutoff value for BZE is 300ng/ml for screening and 150 ng/ml for confirmatory tests).
"If trace amounts of BZE were not common in urine, then why would we have a human cutoff of 300 ng/ml, and things below that are considered negative?" Dwyer questioned.
Cocaine can be used as an equine stimulant, but doses ranging between 4mg/horse to 10mg/horse or more were required to produce any effect in previous research, Camargo and Tobin report. The ELISA test is extremely efficient in screening for BZE, and it can detect as little as 0.5ng/ml (1/2 a part per billion) of urine. The authors reported that when testing for cocaine metabolites was initiated in California, a number of horses tested positive for low concentrations of the metabolite.
Intratumoral Chemotherapy Helpful in Preventing Sarcoid Recurrence
Veterinarians have attacked sarcoids with everything from scalpels to lasers, and cryotherapy to caustic chemicals. But chemotherapy administered intratumorally could be a viable new option in removing and preventing future outbreaks, according to Alain Th‚on, DVM, MS, of the University of California, Davis.
Th‚on reported this method prevented sarcoid recurrence in 97% of the 378 horses treated with it from 1996 through 2004. Th‚on injected cisplatin, a chemotherapy drug, directly into the tumor. He said this route maximizes the dose within the tumor, eliminating systemic exposure and toxicity.
Th‚on injected cisplatin (mixed with water and sesame oil to form a viscous gel) into the tumor while the horse was under heavy sedation. The outpatient procedure was repeated, with a total of four treatments given at two-week intervals for most patients. Th‚on reported the horses have tolerated this regimen well.
The intratumoral injection can also be used concurrently with surgery. Th‚on advised veterinarians to treat the entire area at risk with cisplatin, not just the tumor itself. In cases in which he removed the tumor, Th‚on treated the tumor bed and remaining affected surrounding tissues.
"You have to treat as wide as you would cut, if you were to do surgery (alone)," Th‚on said. Th‚on described one case in which he put sutures in the area surrounding the tumor to give himself a guide to the affected margin following its removal. Th‚on also advocated taking detailed photographs at each treatment to ensure the same total area received the drug. It's very important to document what you're doing because you want to treat the same volume of tissue time after time."
Overall, the cure rate (sarcoid removal with no recurrence) using cisplatin alone was 93%. Cisplatin used concurrently with surgical removal prevented recurrence in 97% of cases. In tumors up to 10cm in diameter, the control rate was 92% up to three years following treatment. Of the 378 horses treated, 18 had tumors recur.
Th‚on showed photographs from horses before and following their cisplatin treatment. In almost all cases, the hair grew back in the treatment area and maintained its original color. "The cosmetic result is very good," Th‚on said.
Known side effects of treatment include tenderness in the treated area and some edema (fluid swelling). Th‚on said other disadvantages of the treatment include the potential health risk cisplatin poses to humans, as it is a known carcinogen. Th‚on strongly advocated the use of full chemotherapy precautions in handling, mixing, and treating horses with the drug. He also suggested that practitioners not familiar with chemotherapy precautions meet with a human oncologist prior to using cisplatin on horses. The horse's owner is also required to wear gloves when handling the horse for three days following treatment.
Lactate Provides Useful Indication of Prognosis
Lactate, the ionized form of lactic acid, which is a byproduct of anaerobic metabolism, can provide objective insight into the prognoses of equine patients, according to Robert Franklin, DVM, Dipl. ACVIM, of the Equine Medical Center in Ocala, Fla.
Franklin said lactate tests are good, cheap, objective, and readily available tests for perfusion (the passage of fluid through the vessels of an organ) and tissue oxygenation. Horses with high lactate levels are more likely to require hospitalization and less likely to survive.
"How many times are we forced to make tough decisions and steer people in the right direction? Here's data that can help steer you in the right direction," Franklin said. "It helps me every day."
L-Lactate is formed in muscles, red blood cells, the brain, and gut. Healthy adult horses typically have a lactate level of under 2 mmol/l, and healthy foals measure less than 3.5 at birth, and 2.5 during their first week.
Reasons for increased lactate include impaired tissue oxygenation (caused by pulmonary or circulatory problems, intense exercise, or anemia), drugs, endotoxins, hepatic (liver) failure, hyperglycemia, or malignancy (some tumors form intense amounts of lactate). Patients with high lactate levels that fail to return to normal, or normalize very slowly in spite of appropriate therapy, have a poor outcome.
Franklin said a study performed in humans entering an emergency room showed circulating lactate concentrations greater than 4 mmol/l were 98.2% specific in predicting the need for hospitalization.
Franklin said past horse case studies revealed that colic cases seen on the farm that had lactate levels below 2 rarely needed referral. Levels over 3 suggested a need for referral, and levels above 6 were generally associated with a poor outcome.
Franklin said a first lactate sample on a horse can reveal the severity of the horse's condition, and subsequent draws can give insight into the horse's prognosis. The test result can give a good indication when to start and stop particular therapies, when to refer the horse, and when to give up, according to Franklin.
A lactate test can be performed in 60 seconds. The machine that processes tests costs about $250. Lactate is measurable in any fluid, including venous and arterial blood, joint fluid, abdominal fluid, and cerebrospinal fluid.
"Anytime you're going to measure a fluid, measure a lactate," he said. Franklin encouraged other practitioners to test lactate and keep track of the results correlated to the outcome of cases in order to collect more data on its application in equine medicine.
"This may be the best predictor of outcome we have at our disposal," Franklin said.
Performing a Myelogram in 30 Minutes or Less
In the course of doing more than 80 myelograms per year during the past five years, Barrie Grant, DVM, MS, Dipl. ACVS, has the procedure down to a science. Grant explained to veterinarians how they can perform the valuable diagnostic procedure in less than 30 minutes.
A myelogram involves injecting a contrast agent, which is a solution that shows up on radiographs, into the spinal canal to reveal any compressive lesions of the spinal cord that could be affecting the horse's neurologic function. Grant advocates using myelograms not only for horses with obvious neurological dysfunction (wobblers), but also horses who have poor performance characterized by stumbling, stiffness, weak backs, knuckling when stopping, offset tail carriage, and delayed limb placement.
"We feel it's a very valuable diagnostic tool for us," Grant said, adding that the procedure helps "turn neuro case lemons into lemonade."
Grant emphasized that safety and teamwork are crucial to performing this procedure--he recommends having at least three people involved in controlling all aspects of anesthesia, positioning, and radiographs.
"It's all about teamwork and keeping it simple," he said.
Grant also explained the safety measures his team uses while performing myelograms, including reading the label of the radiographic contrast media (Grant uses iohexol) aloud by both the technician and the veterinarian while preparing to administer the solution. This is done because injecting the wrong kind of solution into an area so close to the brain can have fatal consequences.
Once the horse is anesthetized and its head is positioned on a ramp to keep the contrast media from flowing into the brain, Grant performs the spinal tap to inject the fluid.
"Try to guide it in like you're shooting pool," Grant said. "I try to really take my time while I'm doing it. Be as comfortable and relaxed as you can be."
Grant says that if the tap produces bloody fluid, it's best to be patient and wait it out a couple minutes, as many bleeds resolve on their own. He injects contrast media over three minutes, with an assistant counting down every 30 seconds.
Grant then proceeds with shooting cranial, caudal neutral, extended, caudal flexed, mid flexed, and skull radiographs. Films are processed immediately--while the horse is still down--to ensure that sufficient views and quality were achieved in the first set. Angles can be re-shot if necessary.
"Don't just quit after (finding) the first lesion," he said. "Many horses have multiple lesions, so you need to keep going."
If the radiographs are sufficient, he allows the horse to recover from anesthesia.
Grant estimated a well-practiced team can perform the entire procedure in under 30 minutes. This technique gives veterinarians another way to detect causes of illness in some of the most difficult neurologic cases.
Peritoneal Dialysis Provides New Hope for Horses in Acute Renal Failure
Acute renal failure used to be a death sentence for a horse, but a new procedure pioneered by Laurie Gallatin, DVM, Dipl. ACVIM, of Purdue University School of Veterinary Medicine, and successfully used by Sarah Reuss, VMD, a veterinary resident instructor at Texas A&M University, could be a viable option for getting horses with this condition through the most dangerous period.
Reuss has used continuous peritoneal dialysis to allow the toxins that the kidneys usually filter to diffuse across the peritoneum (lining of the abdominal cavity), into the dialysate (material that passes through the membrane in dialysis), then out into a collection bag.
This method relies on the permeability of the peritoneum to filter toxins and gives horses a fighting chance in cases where they are unable to produce urine.
Reuss' method uses a fluid drip from an ingress portal (the opening where fluid flows in) in the left flank area to an egress portal (place for excess fluid to escape) along the middle of the belly.
The fluid washes across the peritoneum and toxins diffuse into the fluid that is collected via gravity in a urine collection bag under the horse. Reuss uses 1.5% dextrose in a balanced polyionic solution. While solutions containing up to 5% dextrose have been used in human dialysis, Reuss said this might be irritating to the horse's peritoneum.
According to Reuss, this method can be used continuously for several days with the horse loose in a stall. Both portals should be checked for leakage, and the egress portal should be checked for obstruction. So long as sterility can be maintained, Reuss said to leave the system in place until the horse is producing urine and the azotemia (excess of creatinine and urea) is resolved.
Overall, Reuss calls this method a "viable treatment option for horses in acute renal failure," and she encouraged veterinarians in referral and university hospitals to initiate it early to significantly reduce the morbidity and mortality associated with the condition.
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POLL: Enriching Your Horse's Environment