The results of equine research funded by the Morris Animal Foundation (MAF) in 2007 added to scientists' understanding of foal pneumonia, hereditary muscle disorders, laminitis, and pharmacology.

Equine Center

Summaries of MAF-funded equine studies completed in 2007 are listed below.

The Morris Animal Foundation (MAF) will fund about 120 animal health studies in 2008, including 11 new and continuing studies for horses.

The complete listing of 2008 studies and their descriptions is available at www.MorrisAnimalFoundation.org, or interested parties can request a printed booklet by calling 800/243-2345.


Foal Diseases

"Prophylactic Effects of Azithromycin on Rhodococcus Equi Foal Pneumonia at Endemic Farms"

Texas A&M University, M. Keith Chaffin, DVM, MS, Dipl. ACVIM

Description:

Rhodococcus equi (R. equi) is a bacterium that causes severe pneumonia in foals. Foals usually show clinical signs of infection between three and 16 weeks of age; however, there is evidence that foals become infected within the first two weeks of life. Scientists believe that some neonatal foals have inefficient immune systems and fail to develop an effective defense against R. equi. This infection can cause illness and death and is particularly prevalent on large breeding farms. Foals that develop pneumonia are treated with lipid-soluble antimicrobials such as erythromycin or azithromycin. The investigators will test whether azithromycin, when administered to foals during the first two weeks of life, will protect foals from infection and reduce the overall incidence of R. equi-induced foal pneumonia.

Results:

This study determined that azithromycin can effectively reduce the incidence of R. equi pneumonia among foals on breeding farms. No adverse effects were identified. Due to concerns about antimicrobial resistance developing, the researchers do not recommend widespread use of the drug at breeding farms. However, the study shows that use of the drug during the first two weeks of a foal's life will effectively reduce incidence of this deadly disease. These findings will pave the way for future researchers to identify additional methods for protecting foals from R. equi pneumonia during the first weeks of life.


Hereditary Disorders

"Mapping the Recurrent Exertional Rhabdomyolysis Gene in Thoroughbred Horses"

University of Minnesota, James R. Mickelson, PhD

Completed: October 2007

Description:

A recurrent form of the heritable muscle disorder, tying-up is common in thoroughbred horses. Also called recurrent exertional rhabdomyolysis (RER), this condition causes painful cramping and muscle damage that occurs after mild to moderate exercise. Although related muscle disorders exist in other species, RER in thoroughbreds appears to be a novel genetic defect. The investigators in this study seek to locate the chromosomal position of the RER gene. Identifying a DNA marker closely associated with the RER gene would allow them to identify the precise genetic alteration that causes tying-up, predict which horses are susceptible and develop specific therapies and treatments for horses affected by this disorder.

Results:

Researchers determined that susceptibility to RER is highly heritable in thoroughbred horses and is likely a novel muscle disease that affects the regulation of muscle contraction. Although the specific RER gene and the mutation that causes that disease have not yet been identified, when its location is found, it will allow for a more accurate diagnosis of RER susceptibility. Through this study, researchers learned a great deal about how to design and implement genetic mapping studies in horses, and this knowledge has allowed them to take the leadership role in Morris Animal Foundation's Equine Consortium for Genetic Research. They feel RER will be one of the first diseases mapped using the SNP chip technology that is being developed through the consortium.


Hereditary Disorders

"Polysaccharide Storage Myopathy and Shivers in Draft and Warmblood Horses"

University of Minnesota, Stephanie J. Valberg, DVM, PhD, Dipl. ACVIM

Completed: March 2007

Description:

Shivers is a devastating disorder in draft and warmblood horses whereby horses develop muscle tremors and hyperflexion beyond normal limits of the rear limbs during shoeing, after standing still or when backing up. Many affected horses also show concurrent tail tremors. In some horses, shivers never progresses, while in others it leads to weakness, muscle atrophy and an inability to get up that may require euthanasia. The investigators are examining whether shivers is caused by another painful muscle disorder, equine polysaccharide storage myopathy (PPSM), or whether PPSM and shivers are common but separate disorders that can coexist in the same horse.

Results:

There is a high prevalence of both PSSM and shivers within the Belgian draft horse population. Researchers discovered that 36% of Belgians in the study suffered from PSSM and the same disease was found in warmblood horses. The most common signs of the disease were unexplained lameness, reluctance to engage the hindquarters, and muscle stiffness during exercise. The team also identified shivers in 20% of Belgian draft horses. This disease causes horses to have trouble backing up because their hind legs become fixed in an elevated, flexed position. Researchers learned that contrary to what was previously thought, shivers is not caused by PSSM.


Laminitis

"Load and Thermal Effects on Equine Digital Hemodynamics Measured Using Microspheres"

Louisiana State University, Ashley M. Stokes, DVM, PhD Completed: June 2007

Description:

Laminitis is a painful and debilitating disease of the horse's foot, causing lameness and sometimes leading to death. It usually occurs when a horse suffers from gastrointestinal tract disease, such as colic and grain overload, or other diseases. Laminitis is extremely frustrating for veterinarians because understanding of its cause and progression is incomplete, making it difficult to prevent and treat. The investigators are studying a new technique that may prevent vascular changes in the foot that occur in the earliest stages of the diseases development and stop clinical signs of laminitis. Discoveries made during this study may offer insight into preventing and treating this disease.

Results:

Often a horse that has surgery or an injury to a limb might develop laminitis in the contralateral foot that provides support because the horse puts increased weight on the healthy leg. Researchers learned a great deal about how weight-bearing and thermal conditions in the foot can change the blood flow reaching the horse's digit, and specifically the laminar tissues. This change in blood flow might be linked to the development of laminitis. They learned that the more weight put onto a horse's supporting hoof, the more problems there are with blood flow, which may increase the risk for development of laminitis. In addition, applying ice therapy decreases the blood flow while warm compresses increase blood flow, which may be important findings pertaining to therapeutic efforts. The techniques used in this study were found to be very sound and provided critical information that will help in further studies of this often deadly disease.


Pharmacology

"Pilot Study: Pharmacokinetics of Transdermal Fentanyl in Neonatal Foals"

Washington State University, Melissa T. Hines, DVM, PhD, Dipl. ACVIM

Completed: August 2007

Description:

Options for managing pain in neonatal foals are very limited and often cause undesirable side effects such as gastric ulcers, kidney damage, hypotension and need for sedation. Safer options for controlling pain in foals are urgently needed. The use of fentanyl patches is considered safe and effective in adult horses, but no information is available for their use in foals. Investigators will study the pharmacokinetics and possible adverse effects of fentanyl, a potent pain reliever, in neonatal foals. This pilot project is the first step toward developing guidelines for the use of fentanyl patches to treat pain in foals.

Results:

Researchers determined that fentanyl is safe for use in foals and appears to have no adverse effects. When given intravenously, the drug reached effective concentrations in the bloodstream for controlling pain; however, these concentrations were short-lived. When given as a transdermal patch, which would be the easiest way to administer the drug, fentanyl did not reach what would be considered effective concentrations in the bloodstream. Further researcher is needed to determine whether therapeutic concentrations can be obtained by increasing the dose without increasing side effects.


Pharmacology

"Pharmacokinetics of Intravenous Lidocaine Administered as a Prolonged Infusion in Horses"

Virginia Tech, Harold C. McKenzie, DVM, MS

Completed: October 2007

Description:

Colic is a major cause of disease and death in horses. Animals suffering from colic are prone to intestinal obstruction called ileus. This complication usually occurs after colic surgery and is often treated with intravenous lidocaine. This therapy is generally well tolerated, but in some patients, lidocaine and its metabolites build up, creating toxicity. The risk of toxicity appears to increase with prolonged therapy. Many horses require prolonged infusions, but the effects haven't been fully evaluated. This study will assess the elimination of lidocaine and its active metabolites when lidocaine is given over a four-day period. The information learned may be used to revise lidocaine dosage recommendations and reduce the risk of toxicity in sick horses.

Results:

Researchers learned that horses appear to metabolize lidocaine much differently than other species that often develop toxicity when the drug is used over a prolonged period of time. They found that levels of lidocaine in the blood reached a steady state within three hours, did not accumulate over time and decreased rapidly as soon as the infusion was discontinued. None of the horses showed severe signs of toxicity, therefore, suggesting that use of a prolonged lidocaine infusion appears safe. However, one of lidocaine's two active metabolites did increase rapidly in the first 48 hours after infusion, reaching levels greater than the concentration of lidocaine itself, and remained elevated during the final 48 hours of the protocol. Researchers caution that this accumulation could lead to adverse side effects. They recommend further research into the active metabolites of lidocaine to determine whether these metabolites can become toxic and at what levels.


For more information see www.MorrisAnimalFoundation.org.

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