2018 Research Review

With the help of generous donors, the UC Davis Center for Equine Health has worked to fund research that has advanced veterinary medicine and provided a knowledge base, establishing several focused research initiatives to concentrate resources, expertise, cutting-edge technology and state-of-the-art equipment in certain areas of scientific research over the past 45 years.

Faculty Research Projects


  • Investigating Causes of Sudden Death in Racehorses
  • Study of Causes and Diagnosis of Sudden Death in Racehorses

    Francisco A. Uzal, DVM, M.Sc., Ph.D., DACVP
    Robert Poppenga, DVM, Ph.D., DABVT
    Santiago S. Diab, DVM, DACVP
    Ashley Hill, DVM, MPVM, Ph.D.
    Rick Arthur, DVM

    The number of equine sudden death cases in apparently healthy horses in California has increased over the past two years. This has created national and international negative attention on California horse racing, as sudden death adversely affects racehorse welfare, jockey safety and public perception of horseracing. Despite thorough post-mortem examinations and diagnostic work-ups, a definitive cause of death could not be established in approximately 50% of the cases of sudden death, although heart failure is suspected to be responsible for a large number of these deaths. Heart failure may be due to administration of substances such as cobalt (long known to cause cardiomyopathies in humans), vitamin B12 or levothyroxine (T4 thyroid hormone). However, no scientific evidence is available to support the claim that many of those horses die of heart failure and/or that those deaths are associated with the use of any particular substance.

    This study facilitated the microscopic examination of the hearts of horses with sudden death and an equivalent number of horses euthanized due to catastrophic leg injuries (control group) in an attempt to find a correlation between sudden death and the presence of microscopic lesions in the heart.

    Sudden death is a devastating event that severely affects all members of the equine industry and the public. This study found that non-inflammatory cardiomyocyte injury (myofibrillar degeneration and contraction band necrosis) was the most important lesion found at a higher prevalence in sudden death horses than in control animals. Inflammatory lesions, fibrosis and miscellaneous lesions were found at similar prevalence in sudden death and control horses. A baseline cardiac necropsy protocol was established. Finding specific lesions in the heart of at least some of those horses will provide a diagnostic tool to determine the mechanism of death in future cases of sudden death.

    Additionally, no significant differences in T3, T4 or liver cobalt concentrations were found between study and control horses, which suggests that at least in the group of horses studied, these substances were not associated with the cause of sudden death. If future studies are able to determine if the administration of cobalt, vitamin B12 and/or levothyroxine are a contributing factor additional preventive tools could be developed to avoid future sudden deaths.

    This research was reported in the Journal of Veterinary Diagnostic Investigation29(4):381-38229(4):442-449.
  • Can Thoroughbreds be tested for Exercise-Induced Cardiac Fatigue?
  • Identification of Asymptomatic Heart Disease in Racing Thoroughbreds and Impact on Performance and Risk for Sudden Cardiac Death

    Principal Investigator:
    Joshua Stern, DVM, Ph.D., DACVIM

    Subtle evidence of heart disease may be subclinical in high-level athletes until evaluated after extreme exercise. Changes in blood parameters that indicate heart disease, cardiac arrhythmias and heart function as seen by cardiac ultrasound may all be indicative of subtle but significant heart dysfunction after exercise. This concept, termed exercise-induced cardiac fatigue, has been documented in performance horses but never evaluated in racing Thoroughbreds as a possible explanation for poor performance and sudden cardiac death.

    This was the first study to document the cardiac biomarker, cardiac troponin I, electrocardiogram (EKG) and cardiac functional change that is expected in high-level competing Thoroughbreds. This study establishes expected changes in each of these variables and simultaneously identified that outliers exist within the population. These findings may be useful to identify screening tests that could be applied to Thoroughbred racehorses to identify those at risk of heart injury and even sudden cardiac death. With the recently reported increase in sudden death after racing, evidence for possible testing strategies is of paramount importance. This study suggests that a larger data set with long-term follow-up looking at pre- and post-race EKG parameters, as well as cardiac troponin-I, may represent a method to detect horses at risk for cardiac events.

Drug Therapies

  • Can Ketamine Calm the Excitable Horse for Routine Veterinary Care?
  • Can Ketamine be Given Intramuscularly to Horses to Aid in Standing Sedation?

    Sarah S. le Jeune, DVM, DACVS, DECVS, DACVSMR, CVA
    Laurie K. Bohannon, DVM
    Jodie Daglish, BVSc
    Alonso Guedes, DVM, M.S., Ph.D.
    Bruno Pypendop, DrMedVet, DrVetSci, DACVAA

    Ketamine, an injectable anesthetic agent, is commonly used intramuscularly (IM) to help with standard sedation in hypersensitive horses for routine treatments such as joint injections, stem cell injections and dental procedures. However, the efficacy of intramuscular ketamine as an adjunctive sedative and the disposition of intramuscular ketamine has not previously been reported in horses.

    The study showed that ketamine at a dose of 0.6mg/kg could be administered intramuscularly to horses and was well tolerated by all animals in the study, but ketamine administered alone (IV or IM) did not produce adequate levels of sedation. Administration of ketamine IM in addition to detomidine IV produced a level of sedation in horses that was similar to detomidine IV alone, but horses were less sensitive to touching of the forelimb than with detomidine alone. This effect lasted 20 minutes.

    The study successfully characterized the disposition of ketamine. It was determined that intramuscularly administered ketamine was poorly absorbed and the addition of detomidine affected the disposition of ketamine. Therefore, adding intramuscular ketamine to routine sedation protocols is a valid option for veterinarians to calm difficult or hypersensitive horses for routine procedures on the limbs and dental care.

  • Evaluating Potential Drug Therapies to Reduce Injury during Surgical Recovery
  • Evaluation of Drug Techniques to Reduce Rapid Involuntary Eye Movements Caused By General Anesthetics


    Robert J. Brosnan, DVM, Ph.D., DACVA
    Monica R. Aleman, MVZ, Ph.D., DACVIM
    D. Colette Williams, Ph.D.

    Horses recovering from general anesthesia commonly experience rapid involuntary eye movement (nystagmus) that likely is associated with the lack of coordination and dizziness, in much the same way that a person spinning in a circle develops physiologic nystagmus and associated dizziness. Nystagmus and incoordination during post-anesthetic recovery increases the risk of injury and in some cases death during the period when the anesthesia is wearing off. Dr. Brosnan and his team investigated the use of Midazolam and Romifidine, both separately and in combination together, at various doses to reduce isoflurane-induced nystagmus.

    The study showed that post-anesthetic administration of romifidine may be able to stop isoflurane-induced nystagmus and improve equine recoveries, but drug infusions (rather than a single dose as commonly administered) may be necessary to achieve these aims. Improved recovery quality will reduce complications associated with anesthesia and surgery in horses.

  • Does Chloramphenicol Combat all Equine Bacteria?
  • Pharmacokinetics of Chloramphenicol in Healthy Horses


    Trisha Patel, PharmD
    Krista E. Estell, DVM DACVIM
    Heather Knych, DVM, Ph.D., DACVCP
    Valerie Wiebe, PharmD
    Jeanne Bowers-Lepore, DVM

    Despite scarce and conflicting research on the pharmacokinetics of orally administered chloramphenicol in horses, it is commonly used in equine practice. Single dose administration has demonstrated variable oral absorption and a very short half-life using older analytical methodology, questioning the validity of its use in horses at some of the published recommended doses (as low as 25-30 mg/kg). There is a need to evaluate the pharmacokinetics of chloramphenicol, including compounded formulations which are commonly used in equine practice. Additionally, based on the pharmacokinetic results, the types of bacteria that chloramphenicol will be effective against warrants study.

    This study discovered that due to relatively poor absorption when administered orally, the resulting concentrations of the drug in the blood will only eliminate certain bacteria, such as Streptococcus and non-enteric bacteria. Specifically, chloramphenicol should be used only for treating bacteria with MIC values of ≤ 2 μg/mL, with dosing at 50 mg/kg q 6 hours. The results of this study provide equine practitioners with valuable information regarding dosing and appropriate use of chloramphenicol in the horse.

  • What Impacts on Behavior Does the Drug Trazodone Produce in Horses?
  • Pharmacokinetics and Selected Physiological and Behavioral Responses of Trazodone Following Intravenous Administration to Exercised Horses


    Heather Knych, DVM, Ph.D., DACVCP
    Khursheed Mama, DVM, DACVA
    Eugene P Steffey, VMD, Ph.D.

    Trazodone is a selective serotonin reuptake inhibitor that has the potential to be used as a calming medication in horses. There are no reports documenting the pharmacology of trazodone in horses but, given its pharmacological profile in both humans and dogs, it is likely to have applicability as a behavioral modifier in horses as a calming medication in a variety of circumstances, and could also be used to modulate performance. Knowledge of the pharmacodynamic profile of trazodone is essential to further elucidating beneficial and potential side effects. Characterization of the pharmacokinetic profile of trazodone and, if produced by horses, its active metabolite will additionally facilitate detection in the event of its inappropriate use in performance animals.

    In this study, pharmacokinetic parameters were determined for trazadone following intravenous and oral administration. Following intravenous administration, horses were ataxic and exhibited whole body tremors while horses appeared sedate following oral administration. The results of this study provide baseline information to encourage its appropriate use in horses as a calming medication. The results will also facilitate detection of this drug in situations of inappropriate administration.

  • Recent publications:
  • Pharmacokinetics and pharmacodynamics of intravenous romifidine and propranolol administered alone or in combination for equine sedation
    Soluble epoxide hydrolase activity and pharmacologic inhibition in horses with chronic severe laminitis
    Electroencephalogram of Healthy Horses During Inhaled Anesthesia
    Desflurane and sevoflurane elimination kinetics and recovery quality in horses
    Pharmacokinetics of metronidazole in foals: influence of age within the neonatal period
    Pharmacokinetics and physiological effects of repeated oral administrations of tramadol in horses


  • Unlocking the Genetic Puzzle Associated with Equine Neuroaxonal Dystrophy
  • Identification of Putative Genetic Mutations Associated with Equine Neuroaxonal Dystrophy


    Carrie Finno, DVM, Ph.D., DACVIM
    Erin Burns, B.S.

    Equine neuroaxonal dystrophy (eNAD) is a devastating neurological condition that develops during the first year of life in genetically predisposed foals maintained on a vitamin E deficient diet. Affected horses suffer from incoordination, preventing their use as a riding animal. To develop a genetic test for eNAD, an adequate number of horses (eNAD-affected and unaffected) and genetic markers (DNA sequence on a chromosome) are required. Previous attempts at identifying the gene involved in eNAD were limited to only 54,000-70,000 genetic markers, whereas the newest marker test contains 670,000 markers. Horses affected with eNAD have very low vitamin E levels, supporting the idea that a genetic mutation involved in vitamin E transport or metabolism is responsible for the disease.

    This study identified a region on equine chromosome 7 for further evaluation for eNAD. Using the combination of genotyping and sequencing data, the region was explored for haplotypes (i.e. markers on stretches of chromosome that are inherited together) that could be associated with the disease. With continued investigation of the region on chromosome 7, investigators hope to develop a genetic test for eNAD, thereby allowing breeders to determine the need for supplementation of pregnant mares and foals to prevent the disease.

  • Is there a Genetic Cause of Juvenile Idiopathic Epilepsy in Arabians?
  • Genetic Investigation of Juvenile Idiopathic Epilepsy in Arabian Foals


    Monica Aleman, MVZ, Ph.D., DACVIM
    Carrie Finno, DVM, Ph.D., DACVIM

    Juvenile ldiopathic Epilepsy (JIE) is a disorder in Egyptian Arabian foals that causes seizures. Potential life-threatening complications include head injury and aspiration pneumonia. Although the disorder is heritable, the genetic mutation is not yet identified. This project investigated the genetic cause of JIE by performing a genome-wide association study. A region on chromosome 1 was identified as significantly associated with the JIE phenotype. Two JIE-affected horses underwent whole genome sequencing and candidate genetic mutations have been identified.

    The identification of a region on chromosome 1 is a significant step forward. Additional studies are underway to determine which of these genetic mutations may be responsible for JIE in Arabian foals and allow for the development of a genetic test. This will provide breeders the ability to screen mares and stallions for JIE prior to breeding.

  • Does Sudden Death in Racehorses have a Genetic Basis?
  • Identifying a Genetic Basis of Unexplained Sudden Death in Racehorses


    Joshua Stern, DVM, Ph.D., DACVIM

    Despite thorough pathologic and toxicologic investigations, no unifying, definitive cause has been identified to explain the increase in sudden cardiac death events of racing Thoroughbred. Similar events are observed in human athletes and are often attributed to genetic mutations and predisposition to abnormal conduction within their hearts, yet no genetic investigation into these equine sudden death cases has been performed. This study sought to identify genetic markers associated with sudden death to provide a foundation for future investigations.

    The DNA was obtained from 20 horses that died suddenly with no clear cause of death and compared to DNA of 28 matched control horses that were euthanized due to orthopedic injury and then compared across the entire genome to obtain a list of genetic markers for analysis. The study’s results did not identify a significant area of the genome associated with sudden death.

    This work confirmed that future genetic investigations of sudden death require fresh tissue samples or blood samples to be stored and high-quality DNA samples extracted as soon as possible. The study also showed that the number of cases and controls was insufficient and future evaluations should aim for a sample size that considers this condition to be polygenic or multifactorial. Finally, this data supports that continued efforts looking for environmental causes of sudden death in the Thoroughbred racehorse are warranted.

  • Is Squamous Cell Carcinoma (SCC) Eye Cancer Caused by a Genetic Mutation?
  • Genetic Investigation of Limbal Squamous Cell Carcinoma in Haflinger Horses

    Rebecca Bellone, Ph.D.
    Mary Lassaline, DVM, Ph.D., M.A., DACVO

    Squamous cell carcinoma (SCC) is the most common cancer of the equine eye and the second most common tumor of the horse overall. SCC frequently originates in a region of the eye known as the limbus and can quickly spread to other parts of the eye, leading to vision loss and destruction of the eye. Haflinger horses are over-represented for this disease, on average are affected at a younger age, and affected horses trace back to a common ancestor; making this an important breed to study the genetics of the disease. This study sought to identify and investigate the DNA mutations that cause this disease. A genetic variant was identified with a strongly associated risk for cancer in Haflingers.

    This work led to the development of a commercially available DNA test offered at the Veterinary Genetics Laboratory, UC Davis. Clinicians are utilizing the DNA test to identifying Haflinger horses at highest risk for this cancer so that these animals can be examined earlier and more frequently. Breeders are also utilizing this test to make informed breeding decisions, which should help to lower the incidence of cancer in the breed.

    Because this genetic variant does not explain all of the limbal SCC cases observed, data analysis is in progress to determine if additional genetic variants are involved. In the long term, understanding the genes and biological pathways disrupted in ocular SCC may lead to the development of new and more effective treatments and thereby prevent visual impairment associated with loss of the eye.

    The study was published in the International Journal of Cancer 141(2):342-353.

  • Can a Genetic Cause of Melanoma Cancer be Identified?
  • Study of Genetic Cause of Melanoma Cancers in Connemara Ponies

    Alain Theon, DVM, MS, Ph.D., DACVR

    Connemara Ponies, similar to other horses with a graying hair coat, have an 80% lifetime risk of developing melanomas. Although Connemara ponies are not predisposed to melanoma cancer, they have an increased risk due to selective breeding for gray phenotype. The study focused on identifying actionable genomic targets associated with melanoma that could be manipulated through genetic screening and careful breeding to decrease or eliminate the risk of developing melanomas in Connemara ponies and other breeds. The investigation also sought to further define the molecular mechanisms responsible for development of melanomas in patients at risk, which will aid in targeting treatment development efforts.

    The study required the establishment of a biobank to provide quality samples for research. Through the support of the American Connemara Pony Society, the UC Davis Center for Equine Health and the Cunningham and Doyle Charitable Trust Fund, biospecimens of 72 pure-bred Connemara ponies were collected from across the U.S.

    Preliminary identification of genetic variants was accomplished, which will help to guide future studies with the ultimate goal of being able to develop genetic testing tools to inform the Connemara pony community and potentially breeding decisions to decrease the disease prevalence. The establishment of the biobank with the Connemara pony biospecimens will aide future genetic studies targeted to this breed.

  • Do Draft Horses have a Genetic Predisposition to Chronic Progressive Lymphedema?
  • Chronic Progressive Lymphedema

    Danika L. Bannasch, DVM, Ph.D.
    Verena K. Affolter, DVM, Ph.D.
    Claudia Sonder, DVM
    Brittany Dally, M.S. student

    Chronic progressive lymphedema (CPL) in the horse is a disabling condition that stems from a buildup of lymph fluid in the lower limbs. Draft horses (especially Shires, Belgians, Clydesdales, Gypsy Vanners, and Friesians) are most commonly affected by this condition, with the majority of animals presenting with varying severities of clinical signs. Due to the large number of horses displaying clinical signs of CPL in affected breeds, a genetic predisposition is suspected.

    Two genome-wide association studies were conducted to identify a genetic component within the Friesian horse breed that may cause CPL or predispose them to the condition. Unfortunately, neither of these studies was able to identify a genomic region on a chromosome that was associated with CPL. As this form of lymphedema appears to be predominantly in draft horse breeds, the size of the horse was investigated as a potential contributing factor or indicator of CPL development. Height, weight, and limb measurements at four locations were obtained from a total of 37 horses (28 cases and 9 controls). Of these measurements, significance was achieved for two measurement locations, forearm (radius and ulna) and gaskin lengths, demonstrating a potential correlation between animal size and CPL status within the Friesian breed.

    Increased understanding of the cause and predisposition of this condition in draft horse breeds will assist veterinarians in developing more consistent treatment plans to manage this condition and provide lifelong support to keep affected horses comfortable and mobile. These study results will help to inform future studies aimed at identifying a genetic cause and the potential development of a genetic test which would assist breeders.

  • Recent publications:
  • Investigation of Known Genetic Mutations of Arabian Horses in Egyptian Arabian Foals with Juvenile Idiopathic Epilepsy
    Identification of long non-coding RNA in the horse transcriptome
    Tissue resolved, gene structure refined equine transcriptome
    Transcriptome profiling of equine vitamin E deficient neuroaxonal dystrophy identifies upregulation of liver X receptor target genes
    Blood and Cerebrospinal Fluid α-Tocopherol and Selenium Concentrations in Neonatal Foals with Neuroaxonal Dystrophy
    SERPINB11 frameshift variant associated with novel hoof specific phenotype in Connemara ponies
    Risk of false positive genetic associations in complex traits with underlying population structure: a case study
    RNA-seq transcriptome profiling of equine inner cell mass and trophectoderm

Medicine and Infectious Disease

  • Establishing Prevalence of Equine Coronavirus in the United States
  • Frequency of Antibody Detection to Equine Coronavirus (ECoV) in Healthy Horses Living in the U.S.

    Nicola Pusterla, DVM, Ph.D., DACVIM
    Samantha Barnum, M.S.
    Kaitlyn James, M.S.

    Despite the sporadic occurrence of Equine Coronavirus (ECoV) outbreaks in adult horses, the overall number of horses testing positive for this virus in horse populations has remained poorly investigated. Seroprevalence data, based on blood serum specimens, is needed to better understand the epidemiology of ECoV, evaluate diagnostic modalities and develop preventive measures. Study results revealed the seroprevalence to ECoV was 9.6% in 5,247 healthy adult horses from 18 different states. Seropositivity was significantly associated with horses from the Midwest, particularly in draft horses.

    This study represents the first known and most comprehensive seroprevalence study on ECoV in healthy adult horses. Factors contributing to a higher ECoV seroprevalence in the Midwest could be related to a higher population of ECoV seropositive draft horses used for farm and ranch work and breeding in this geographic region. Longitudinal studies are needed to further investigate the various observations and risk factors.

    This research was reported in the Veterinary Journal.

  • Developing Diagnostic Tools for Equine Coronavirus
  • Development of a Serological Test to Detect Antibodies to Equine Coronavirus in Adult Horses

    Nicola Pusterla, DVM, Ph.D., DACVIM
    Samantha Barnum, M.S.

    Recently, equine coronavirus (ECoV) has been associated with febrile and enteric disease in adult horses. Since 2011, the laboratory team has been involved with several outbreaks of ECoV across the U.S. The main clinical signs reported were anorexia, lethargy and fever. Although polymerase chain reaction (PCR) testing detects the antigen during the acute disease phase, this project set out to develop an equine-specific antibody-test which would allow determination of exposure amongst infected and asymptomatic horses.

    The study established and validated a new S protein-based ELISA test to detect specific antibodies to ECoV. Although RT-PCR on feces is considered the best diagnostic modality to support ECoV infection, this new test will facilitate investigation of disease and infection rates in various horse populations in order to better understand the epidemiology of this emerging equine virus.

  • How Does the Underlying Infection Transition to Become Equine Protozoal Myeloencephalitis?
  • Toxoplasma Gondii Seroprevalence and Association with Equine Protozoal Myeloencephalitis (EPM): A Case-Control Study amongst California Horses

    Nicola Pusterla, DVM, Ph.D., DACVIM
    Patricia A. Conrad, DVM, Ph.D.
    Woutrina Smith, DVM, MPVM, Ph.D.
    Kaitlyn James, M.S.

    While the causative agents of equine protozoal myeloencephalitis (EPM) are known, the transition from infection with Sarcocystis neurona and Neospora hughesi to the clinical disease of EPM is not yet understood. Marine mammals infected with both S. Neurona and Toxoplasma gondii have shown increased severity of neurologic disease. Co-infection between the causative agents of EPM and T. gondii may contribute to the transition from infection to clinical disease in horses. This study sought to determine the seroprevalence, frequency of blood serum samples, with T. gondii amongst California horses with neurologic signs compatible with EPM and neurologically normal horses.

    In this study, horses with higher titers to T. gondii (80, 160, 320) were more likely to have clinical signs compatible with EPM than healthy, non-neurologic horses. While there was no evidence that co-infections by T. gondii and S. neurona/N. hughesi were required for clinical signs of EPM to develop, the association between T. gondii seropositivity and clinical EPM suggested that T. gondii was associated with neurologic signs in the study population of California horses. Serologic testing of cerebrospinal fluid and isolation of T. gondii in EPM suspect cases should be considered. Future studies investigating the relationship between T. gondii and EPM are warranted.

    This research was reported in the Veterinary Journal.

  • Is EPM More Prevalent in Certain Areas of the U.S.?
  • Frequency of Antibody Detection to Sarcocystis neurona and Neospora hughesi in Healthy Horses from various areas of the U. S.

    Nicola Pusterla, DVM, Ph.D., DACVIM
    Patricia A. Conrad, DVM, Ph.D.
    Heather Fritz, DVM, Ph.D.
    Andrea Packham, M.S.
    Kaitlyn James, M.S.

    Equine protozoal myeloencephalitis (EPM) is a debilitating cause of neurologic disease in horses across the U.S. Two protozoa pathogens, Sarcocystis neurona and Neospora hughesi, can cause EPM; however, N. hughesi is most frequently reported in the western half of the U.S. This study investigated the prevalence of antibodies to both protozoa across the United States.

    This study discovered that horses in regions previously considered at lower risk of infection with S. neurona, and perhaps more importantly, N. hughesi, experienced higher rates of infection than previously thought. Practitioners in all regions of the U.S. should therefore consider testing for both causative agents when presented with a suspect EPM case based on the seroprevalence of S. neurona and N. hughesi in healthy equines.

  • Can Iodide be used to Prevent Pneumonia in Foals?
  • Iodide Supplementation as a Strategy for Enhancing Equine Innate Airway Defenses: A Possible Preventative Therapy for R. equi Pneumonia in Foals

    Meera Heller, DVM, Ph.D., DACVIM
    Fauna Smith, DVM
    Ken Jackson, M.S.
    Johanna L. Watson, DVM, Ph.D., DACVIM

    Rhodococcus equi causes pneumonia in foals and is a major cause of illness and even death. It also costs the equine industry millions of dollars for treatment and prevention. Sodium Iodide has been used to treat similar types of infections in humans and animals for over a hundred years, before the discovery of antibiotics. A recent study showed that oral supplementation with iodine in humans increases the levels of hypoiodous acid (HOI) on the surfaces of the respiratory tract, and this is a potent anti-bacterial and antiviral defense mechanism. There are two potential roles for iodine in the augmentation of the immune response; one is as a treatment for R. equi infections and the other is to prevent infection via respiratory tract surfaces. 

    The study demonstrated that live R. equi bacteria could be killed in vitro by sodium iodide. Additionally, when cells from horse’s lungs were experimentally infected with R. equi in vitro, sodium iodide slowed the rate of infection. However, when those same cells were infected with R. equi and then treated with sodium iodide, killing of R. equi was not enhanced. Therefore, sodium iodide may play a preventative role in the development of clinical R. equi pneumonia in foals.

    The killing of bacteria in the airways and resulting decrease in the rate of infection could aid in the prevention of R. equi pneumonia in foals. Based on these findings, the use of sodium iodide as a preventative treatment for R. equi pneumonia in foals warrants further investigation.

  • Recent publications:
  • Pharmacokinetics and antinociceptive effects of the soluble epoxide hydrolase inhibitor t-TUCB in horses with experimentally induced radiocarpal synovitis
    Comparison of flocked and rayon swabs for the molecular detection of selected equine viruses and bacteria from nasal secretions of healthy horses
    Modeling the effect of race surface and racehorse limb parameters on in silico fetlock motion and propensity for injury
    Development of an equine coronavirus-specific enzyme-linked immunosorbent assay to determine serologic responses in naturally infected horses
    Hitting the ground running: Evaluating an integrated racehorse limb and race surface computational model
    Qualitative and Quantitative Characteristics of the Electroencephalogram in Normal Horses during Administration of Inhaled Anesthesia
    Daily feeding of diclazuril top dress pellets in foals reduces seroconversion to Sarcocystis neurona
    Association of Factor V  Secretion with Protein Kinase B Signaling in Platelets from Horses with Atypical  Equine Thrombasthenia
    Detection of modified-live equine intranasal vaccine pathogens in adult horses using quantitative PCR


  • Looking for New Glaucoma Medications
  • Effect of Brimonidine and Brimonidine-Timolol on Intraocular Pressure in Normal Equine Eyes

    Mary Lassaline, DVM, Ph.D., M.A., DACVO
    Sara Thomasy, DVM, Ph.D., DACVO

    Glaucoma is a disease characterized by elevated intraocular pressure (IOP) and is a common cause of blindness in horses. Medications such as brimonidine and brimonidine-timolol have been developed to reduce IOP in people with glaucoma by decreasing the amount of fluid within the eye, thereby preserving functional vision and controlling pain associated with this disease. This study investigated the efficacy and safety of two glaucoma drugs, brimonidine and brimonidine-timolol, at lowering intraocular pressure in horses.

    The study showed that there were no adverse effects in normal equine eyes treated with brimonidine or brimonidine-timolol. While both medications are well tolerated in normal horses, treatment with these medications did not result in a significant decrease in IOP in the normal horses tested. It is not known whether these drugs would decrease intraocular pressure in horses with glaucoma. It was noted that horses with glaucoma may respond differently than normal horses.

    Now that the safety of these two medications has been established, the next step is to test their efficacy in treating the disease in glaucomatous horses. Identifying new ophthalmic medications that successfully lower IOP in horses with glaucoma may decrease the severity of pain and the incidence of blindness in horses with this devastating disease.

    This research was reported in the Equine Veterinary Journal.

  • Recent publications:
  • Field use of N-butylscopolammonium bromide to facilitate thorough ophthalmic examination in horses

Orthopedics & Lameness

  • Understanding Bone Loss in Silicate Associated Osteoporosis Could Lead to Treatment and Prevention
  • Mechanisms of Bone Loss (Osteoporosis) in Horses from Geographic Regions with Soils High in Toxic Silicate

    Susan Stover, DVM, Ph.D.

    Silicate Associated Osteoporosis (also known as Bone Fragility Syndrome) is a devastating disease that causes nonspecific chronic lameness and neck pain, bone deformities and fractures, and death or humane euthanasia of horses that breathe dust from soil containing toxic silicate particles (cristobalite).  Most horses have concurrent lung disease caused by the inhalation of the cristobalite, but the reason for the skeletal disease in horses with this lung disease is unknown. If the mechanism that links the bone disease to the lung disease can be discovered, further research for the treatment and prevention of the bone disease can be pursued.

    The study identified extensive bone loss, decrease in bone mineral, and abnormal bone architecture in the ribs of affected horses which explains the markedly weakened bones and the high fracture risk in affected horses. The bone abnormalities were consistent with abnormal function of cells responsible for bone resorption (osteoclasts). Vigorous attempts by bone-forming cells (osteoblasts) to form new bone were also present, but insufficient to compensate for the marked and disorganized bone loss.

    Horse owners with horses suffering from SAO incur financial and emotional loss and, in some instances, devaluation of real estate with soil containing toxic substances. Information obtained from this study will add to the body of knowledge surrounding the disease. Determination of the major dysfunction in the disease is expected to guide further studies into disease mechanisms. Understanding these mechanisms could help to identify potential targets for the development of treatment and preventive strategies. This investigation was a first step in understanding the nature of the bone loss in affected horses.

  • Looking for Genetic Links between Lung and Bone Disease
  • Deciphering Mechanisms of Bone Loss (Osteoporosis) in Horses from Geographic Regions with Soils High in Toxic Silicates

    Susan Stover, DVM, Ph.D.
    Regina Zavodovskaya, M.S., DVM, DACVP

    SAO is a devastating disease of horses that breathe dust from soil containing toxic silicates (cristobalite). The disease results in extensive bone loss, painful skeletal deformities, bone fractures, and death or humane euthanasia. Most horses with SAO have a concurrent lung disease called silicosis, which is caused by the inhaled cristobalite. Investigating the link between the lung disease and bone loss could ultimately lead to treatment and prevention strategies for SAO.

    This study utilized computer programs to determine the genetic differences between SAO affected and control horses. Differences in the gene profiles were found that affect bone health, but surprisingly the genetic differences highlighted bone formation activation and not bone resorption activation.

    SAO in horses is associated with certain regions of California and results in the loss of affected horses, as well as the financial loss and emotional burden for horse owners. The identified genes could be used as a much-needed tool for the detection of affected horses at an early stage of the disease when they can be treated to slow progression of SAO, and as markers for future studies that may link similar diseases in other animals and humans. The discovery of the genes specific to affected horses will guide future research on the path to understanding the mechanism by which the lung disease causes the bone disease. Early diagnosis, targeted therapy for osteoporosis and potential preventive strategies may emerge as a result of the discovery of the SAO associated genes.

  • Evaluating Tendons and Ligaments with New MRI
  • New Magnetic Resonance Imaging Approach to Evaluation of Tendons and Ligaments in the Equine Foot

    Mathieu Spriet, DVM, M.S., DACVR, DECVDI
    Brian Murphy, DVM, Ph.D., DACVP
    Anthony DeRouen, DVM

    Ligament and tendon lesions in the foot are common causes of equine lameness. Magnetic resonance imaging (MRI) has markedly contributed to better recognition and characterization of these lesions, however subtle and early lesions remain a diagnostic challenge. New quantitative MRI techniques have shown promising results in the human Achilles tendon and equine metacarpal tendon disorders. It was hypothesized that this new MRI technique will increase sensitivity for detection of subtle lesions and lesions at an earlier stage of progression while also providing quantitative diagnostic information to more accurately and consistently characterize the nature of the lesions.

    The study results showed that abnormal tendons had a different appearance than normal tendons using this new quantitative MRI technique. These tendons were more heterogeneous, with areas displaying increased values of the measured MRI parameter. The increased MRI parameter correlated with an increase glycosaminoglycan content of the tendon, which is known to be related to degenerative changes of the tendon.

    This study confirms that changes at the molecular level can be appreciated with this new MRI approach. This technique might provide additional information regarding the underlying mechanisms leading to lesion development and possible earlier intervention in soft tissue injury.

  • Can Tendon Repair and Recovery be improved by Certain Proteins?
  • The Effect of Decorin and Biglycan Modulation on Equine Tendon Formation

    Michael J. Mienaltowski, DVM, Ph.D.
    Keith Baar, Ph.D.

    Under normal development and growth conditions, tendon formation in the horse involves the creation of a strong, highly organized collagen-rich tissue capable of withstanding great tension during locomotion. Recovery outcomes for horses suffering from a tendon injury are generally incomplete and result in chronic lameness, thus having a huge impact on performance. When compared to healthy conditions, the repair response mounted by the cells of the tendon, and its surrounding tissue, is inferior and would benefit from strategies that bolster the response of these cell populations and strengthen the organization of the tissue to a state closer to that of healthy tendon. One strategy for improving tendon healing is the introduction of exogenous proteins that act to promote and stimulate tendon formation. Molecules like biglycan and decorin play several roles in maintaining tendon structure and function; they inform cells in the tendon as to their fate and they regulate collagen fibril organization.

    The study results showed that the addition of purified bovine biglycan and decorin did stimulate tendon formation. These findings are encouraging and support a role for the utilization of exogenous biglycan and decorin as a cost-effective treatment strategy to improve tendon repair. Ongoing studies will provide additional information to aid in the development of strategies to add biglycan and/or decorin to the site of an injured tendon.

  • How do Horseshoes Impact Toe and Heel Conformation in Racehorses?
  • Heel Movement and Hoof Wall Deformation with Different Nail Positions applied to the Horse Shoe

    Susan Stover, DVM, Ph.D.
    Vanessa Dahl, M.S. (Ph.D. student)

    Racehorses exhibit long toe/low heel conformation which has been associated with increased risk for fetlock injuries and breakdown. Shoeing techniques have an impact on hoof growth which can lead to this long toe/low heel hoof conformation.

    We hypothesize that the number and position of nails used to attach the shoe to the hoof affect hoof expansion, hoof wall distortion, and fetlock extension. Furthermore, we hypothesize that nails placed closer to the heels of the hoof will produce effects that could promote the development of the long toe/low heel hoof conformation.

    The effect of nail distribution on hoof heel expansion, heel distortion, and fetlock extension was studied in the forelimbs from 9 horses. Each limb was tested a total of 5 times under the following conditions: unshod; shod with 10 nails, 6 nails, and 2 nails; and again unshod for comparison to initial conditions.

    It was discovered that nails placed closer to the heels of the hoof decreased the amount of expansion in the heels and quarters of the hoof during limb loading. Additionally, nails placed closer to the heels resulted in hoof wall distortion, leading to the heels moving more dorsally (i.e. forward) than without a shoe. Fetlock angle decreased with nails placed closer to the heels of the hoof. Application of horseshoes is a factor that can be easily managed and could be a viable method to prevent injury in racehorses and performance horses.

  • Can a New Imaging Technique Provide Evidence for Active Pain in the Equine Foot?
  • Assessment of a New Imaging Technique to Detect Active Lesions in the Horse Foot

    Mathieu Spriet, DVM, MS, DACVR, DECVDI
    Larry Galuppo, DVM, DACVS

    Imaging of the horse foot has markedly improved over the past 15 years with the development of computed tomography (CT) and magnetic resonance imaging (MRI). Lesions that were unrecognized in the past can now be detected.  The current challenge is to distinguish between active lesions and chronic inactive lesions in order to design appropriate treatment plans and for the assessment of the effectiveness of those therapies. This study assessed the effectiveness of positron emission tomography (PET) imaging for both soft tissue and bone lesions.

    The study demonstrated that the PET imaging technology produced high-quality images of the feet and fetlock and the imaging procedures were safe for both the horse and the staff. A wide range of lesions were identified including tendon, ligament, bone and joint lesions not identified with other imaging modalities and abnormal activity in the hoof of a horse with laminitis. The investigators predict that PET will become an invaluable research tool in particular for tendon and laminitis research. PET also has direct clinical applications for the early identification of bone and joint lesions.

  • Do Different Arena Surfaces Contribute to Equine Injuries?
  • Using Stem Cells to Engineer Cartilage for Joint Repair in Horses

    Principal Investigator:

    Kyriacos A. Athanasiou, M.S., Ph.M., Ph.D.

    Joint injuries occur frequently in the equine athlete, but effective treatments for cartilage repair are yet to be discovered due to the tissue’s inherent lack of healing response. Tissue engineering seeks to grow healthy new cartilage constructs in a controlled laboratory environment; however, methods need to be developed not only to select an appropriate cell source, but also to ensure that the engineered cartilage possesses adequate properties for implantation. The study determined that Mesenchymal Stem Cells (MSCs) derived from umbilical cord blood formed superior neocartilage than MSCs from equine bone marrow.


    Using tissue engineering for cartilage repair is a potential tool to increase the success rate of surgical intervention as well as to hasten recovery times by replacing defective cartilage with a healthy neocartilage implant. Identifying an ideal cell source is the first step toward generating a viable cartilage repair product. This study demonstrated that cord-blood-derived MSCs may be used to produce viable cartilage grafts, as neocartilage produced from these MSCs have properties that resemble native equine articular cartilage in terms of composition and mechanical properties.  This work holds exciting translational applications for human joint resurfacing.

    Susan Stover, DVM, Ph.D.

    Injuries to structures that support the fetlock, pastern, and hoof (suspensory ligament, superficial and deep digital flexor tendons) are the primary causes of performance limitations in show jumpers. The likelihood of injury to these structures increases with high limb loads and greater fetlock extension. Characteristics of the arena surface affect maximum limb loads, and thus the risk for injury. Knowledge of how arena surfaces contribute to the risk for injury can lead to recommendations for arena surface composition and management for injury prevention.

    The project studied both dirt and synthetic arena surfaces testing with the approach that a less stiff, more compliant arena surface, with sufficient strength to support the hoof, could result in lower limb loads and lesser fetlock joint hyperextension, and thus have a lower likelihood of inducing common injuries.

    Investigators found that the dirt arena surface was stiffer and had higher vertical impact loads than the synthetic surface. Therefore, the dirt arena had more resistance to deformation of the hoof into the surface. However, the synthetic arena surface had higher cohesion (i.e. resistance to horizontal motion or slide of the hoof). During take-off for the jump, fetlock extension and hoof movement were greater on the synthetic arena than the dirt arena surface. During landing, fetlock extension was greater and the toe of the hoof penetrated further into the synthetic arena than the dirt arena surface.

    Fetlock and hoof motions were found to differ during take-off and during landing from a jump between different arena surfaces that had different mechanical behaviors. Because extreme fetlock and hoof motions increase the risk for injury, arena surface design and management have the potential to prevent injuries in show jumping horses. However, further work is needed to determine the optimum arena surface design and management for injury prevention.

  • Recent publications:
  • F-sodium fluoride positron emission tomography of the equine distal limb: Exploratory study in three horses

Regenerative Medicine


  • Evaluating Antibiotic Treatment for Endometriosis
  • How long Does the Antibiotic Ceftiofur Remain Effective in the Uterus after Intrauterine Infusion in Both Healthy Mares and mares with a Uterine Infection?

    Camilla J. Scott, BVetMed, MRCVS, DACT
    Ghislaine A. Dujovne, DVM, M.S., DACT
    Bruce W. Christensen, DVM, M.S., DACT

    Bacterial endometritis is a leading cause of infertility in the mare and a major cause of economic loss to the equine industry. The use of intrauterine ceftiofur to treat endometritis is common practice; however, its efficacy had not been evaluated, especially in clinical cases of endometritis. A primary question was how long the ceftiofur remained at an effective concentration following administration for successful targeting of the infection in both healthy mares and mares with a uterine infection. The study showed that endometrial tissue concentrations of ceftiofur in healthy mares were above the concentration required to target common uterine infections for the 48 hour testing period. But in infected mares, tissue concentrations of ceftiofur were only above target concentrations for Escherichia coli for 6 hours and Streptococcus zooepidemicus for 24 hours.

    The results of this study suggest that healthy endometrial tissue retains target concentrations of ceftiofur for longer than inflamed tissue. In healthy mares, a prophylactic ceftiofur infusion would appear to be effective for at least 48 hours; however, in mares infected with S. zooepidemicus, a daily infusion protocol is required to avoid treatment failure. Knowing the length of time the antibiotic remains effective will provide veterinarians important information to design and implement treatment plans for their patients. Future studies to evaluate intrauterine antibiotic treatment for endometritis on mares with endometritis is a logical next step.


Resident Research Projects

Infectious Disease

  • Could a Vaccine for Cattle Be Effective in Horses to Combat Equine Coronavirus?
  • Evaluation of Safety, Humoral Immune Response and Fecal Shedding of a Modified-Live Bovine Coronavirus Vaccine Given to Adult Healthy Horses.


    James Prutton, DVM (Resident)
    Nicola Pusterla, DVM, Ph.D., DACVIM (Mentor)
    Samantha Barnum, M.S. (Staff Research Associate)

    Equine coronavirus is an emerging disease with a mortality rate of 7-27%. Investigating a vaccination protocol could allow for a reduction on the spread of equine coronavirus in the equine population.


    In this pilot study, 25% of horses vaccinated with modified live bovine coronavirus seroconverted, indicating an immune response was mounted in a subset of horses. The project demonstrated the safety of the bovine coronavirus vaccination in horses and demonstrated a limited immune response in certain individuals.

  • Developing Better Tools to Assess Infectious Disease in Horses
  • Use of Serum Amyloid A to Differentiate Between Infectious and Non-Infectious Diseases in Horses


    Fiona Wensley, DVM (Resident)
    Nicola Pusterla, DVM, Ph.D., DACVIM (Mentor)
    Philip Kass, DVM, MPVM, MS, Ph.D. (Mentor)
    Danielle Carrade-Holt, Ph.D. (Research/Development Analyst)
    Julie Burges, MS (Clinical Diagnostic Lab Manager)
    Kaitlyn James, Ph.D. (Graduate Student)

    Serum amyloid A (SAA) is an acute phase protein that has been used in equine practice to assess and monitor horses for inflammation. The researchers in this study hypothesized that SAA alone, or in combination with white blood cell count and fibrinogen, would be a better indicator to differentiate infectious from non-infectious inflammatory disease. Horses were categorized by disease conditions as healthy, healthy vaccinated, inflammatory non-infectious (i.e. osteoarthritis, uveitis, laminitis, strangulating or ischemic colic), inflammatory infectious (i.e. abscess, cellulitis, sepsis) or non-infectious non-inflammatory non-healthy (i.e. neoplasia, Cushing’s disease, non-strangulating colic cases such as impactions and enteroliths). 


    In this study, SAA performance held a greater overall accuracy when compared to neutrophil count and fibrinogen, both individually and combined, for defining infectious versus non-infectious diseases. When used in conjunction with neutrophil count and fibrinogen, SAA further enhanced the accuracy of differentiating disease status. Use of this assessment tool by veterinarians would enhance their diagnostic evaluation and lead to a more accurate and rapid treatment plan for equine patients.

  • Looking for Anti-Viral Drug Therapy for Horses with Equine Herpesvirus-5
  • Effect of Valacyclovir (Anti-Viral) Treatment in an Equine Herpesvirus-5 (EHV-5) Related Lung Disease (Equine Multinodular Pulmonary Fibrosis)


    Charlotte Easton-Jones, DVM (Resident)
    John Madigan, DVM, M.S., DACVIM (Mentor)
    Nicola Pusterla, DVM, Ph.D., DACVIM (Mentor)
    Samantha Barnum, M.S. (Staff Research Associate)

    Recent studies have revealed that equine herpesvirus-5 (EHV-5) is commonly isolated from the lungs of horses diagnosed with Equine Multinodular Pulmonary Fibrosis (EMPF), suggesting that EHV-5 is linked and may be the cause of EMPF. The current theory is that the damage to the lungs from the viral infection may provide the health incident that the horse reacts to with an exaggerated inflammatory response. There are currently no studies assessing the impact of valacyclovir (anti-viral) treatment on the amounts of the virus, EHV-5, in EMPF cases.  Researchers hypothesized that anti-viral therapy with valacyclovir will lead to a decrease in the viral load of EHV-5 in whole blood, nasal secretions and bronchoalveolar lavage fluid of horses with EMPF.


    In this study of horses with naturally occurring EMPF treated with valacyclovir, there were no significant differences between the median EHV-5 viral load between day 0 and day 10 for all three of the sample types tested (blood, nasal secretions and bronchoalveolar lavage fluid). Treatment with valacyclovir did not appear to have a significant effect on EHV-5 viral load in EMPF affected horses. Therefore, while valacyclovir is a relatively expensive drug that is routinely used to treat horses with EMPF, this study revealed that 10 days of valacyclovir treatment did not significantly alter the viral amounts of EHV-5 in EMPF horses and therefore may not be a clinically effective treatment.

  • Evaluating Infectious Disease Risk from Imported Horses
  • Do Imported Horses Represent a Significant Risk for the Spread of Respiratory Disease to Resident Equids in the United States?


    Fauna Smith, DVM (Resident)
    Nicola Pusterla, DVM, Ph.D., DACVIM (Mentor)
    Johanna Watson, DVM, Ph.D., DACVIM (Mentor)
    Isabelle Kilcoyne, DVM, DACVS (Mentor)
    Claudia Sonder, DVM (Mentor)

    Imported horses are likely to be stressed during transport and may be at a higher risk of exposure to infectious respiratory pathogens, due to comingling with other horses at sales and shipping barns, during transport and at quarantine facilities. These horses may, therefore, represent a risk for spreading infectious respiratory pathogens into equine populations in the United States.

    This study assessed the prevalence of respiratory disease in 166 horses entering the Contagious Equine Metritis quarantine facility at the UC Davis, Center for Equine Health between October 2014 and June 2016. 


    Approximately 3.6% of horses were shedding either equine herpesvirus 1 (EHV-1) or EHV-4, which could have serious consequences if introduced into a large barn. Equine influenza positive horses were not identified; however, many samples for influenza testing failed quality control. EHV-2 and -5 were commonly shed in imported horses. At this time, the significance of EHV-2 and -5 in the development of respiratory disease remains poorly understood.

    While equine influenza was not identified in any sample, the two important implications from this study are that sampling technique and environmental conditions can affect the quality of the sample and due to the high failure rate, it is possible to miss positive animals.


  • Investigators Seek to Validate a New Test for Inflammation in Horses
  • Validation of a New Stall-side Test for Serum Amyloid A in Horses


    Diana Schwartz, DVM (Resident)
    Nicola Pusterla, DVM, Ph.D., DACVIM (Mentor)
    Mary Christopher, DVM, Ph.D. (Mentor)

    Serum amyloid A (SAA) is an acute phase protein that has been used in equine practice to assess and monitor horses for inflammation. Validation of a stall-side SAA test in horses provides an opportunity for equine practitioners to rapidly and accurately identify abnormalities in SAA concentrations that can facilitate disease diagnosis, evaluate response to therapy, and assess overall prognosis in horses with a variety of inflammatory diseases.


    Based on the results of this study, the stall-side SAA test should be accurate for use by veterinarians to detect inflammation in horses, but with less precision at high concentrations, if performing serial measurements between batches. Interpretation of SAA results obtained using this stall-side test and other SAA laboratory tests should be undertaken with acknowledgment of differences in results between methods and between test kit batches.

  • Can a Heart Muscle Marker Indicate the Presence of a Rib Fracture in Foals?
  • Levels of a Heart Muscle Damage Marker (Cardiac Troponin) in Healthy Neonatal Thoroughbred Foals and Thoroughbred Foals with Rib Fractures


    Rana Bozorgmanesh, B.Sc., BVetMed, DACVIM, MRCVS, (Resident)
    Gary Magdesian, DVM, DACVIM, DACVECC, DACVCP (Mentor)
    Nathan M. Slovis DVM, DACVIM, CHT (Collaborator)
    Jeanne Bowers-Lepore, DVM (Collaborator)

    Rib fractures sustained during birth are not uncommon injuries in neonatal foals. In some foals, they can have severe effects including death from heart or lung damage. Prompt identification and assessment of rib fractures are necessary to determine if surgical management is warranted. Thoracic ultrasound is most commonly used to identify fractured ribs, but requires expertise and is time-consuming. Therefore, a quick and cost-effective method of identification of potentially fatal rib fractures would be a valuable clinical aid for the equine veterinarian.


    In this study, cardiac troponin was determined to not be a specific indicator of rib fractures. This may be due to a low rate of direct damage to the heart muscle in foals in this study and the mortality rate for foals with rib fractures was lower than previously reported. Potential reasons for the low mortality include increased awareness, earlier identification, or improved management of rib fractures.

  • What do Glucose and Insulin Levels Tell us About Neonatal Foals?
  • Temporal Variability in Serum Glucose and Insulin Concentrations in Neonatal Foals


    Emily Berryhill, DVM, DACVIM (Resident)
    Gary Magdesian, DVM, DACVIM, DACVECC, DACVCP (Mentor)
    Judy Edman, B.S. (Staff Research Associate)

    Insulin dynamics are associated with metabolic diseases such as Equine Metabolic Syndrome and insulin resistance. It is well established that serum glucose and insulin concentrations in adult horses and foals are affected by many variables, including feed intake, stress, and metabolic phenotype. However, there are no studies that serially measure insulin and glucose concentrations in healthy foals of differing ages to establish normal daily variability, how insulin and glucose are associated with other metabolic parameters (i.e. serum triglycerides), and how they change with age. The researchers in this study hypothesized that newborn foals have highly variable serum glucose and insulin concentrations compared to adult horses.


    The study confirmed the hypothesis that serum glucose and insulin concentrations in neonatal foals of different ages can have a high degree of variation when measured serially over several hours. For instance, the maximum serum insulin concentration over a 16-hour sampling period was almost double that of the lowest insulin concentration for individual foals at all ages analyzed.

    Documenting and understanding insulin and glucose dynamics in healthy foals is imperative to understanding metabolic changes that occur with critical illness, including insulin resistance secondary to neonatal infection, and may influence treatment of sick foals.

  • Preventive Treatment for Equine Protozoal Myeloencephalitis
  • Assessing Plasma Concentrations Of 1.56% Diclazuril given Twice a Week to Adult Horses

    Laszlo M. Hunyadi, DVM, M.S., Ph.D.
    Nicola Pusterla, DVM, Ph.D., DACVIM
    Mark Papich, DVM, MS, DACVCP

    EPM is a commonly diagnosed and economically costly neurologic disease affecting horses of all ages, but young performance horses appear to be at greater risk for developing this condition. Opossums are the definitive hosts of the major causative parasite, Sarcocystis neurona. The equine industry is in need of a preventive protocol that is both sustainable and cost-effective.

    The administration of a low dose diclazuril every 3 to 4 days was shown to be safe and caused no adverse effects in the study horses. Administration of diclazuril at the lower dose twice a week provided plasma concentrations to effectively inhibit in vitro concentrations for Sarcocystis neurona, a single-celled parasite and the most common cause of EPM in horses in the United States.

    On ranches with a high incidence of EPM, the newly established protocol resulting from this study will improve compliance (twice weekly drug administration instead of daily drug administration) and reduce the total amount of diclazuril administered. Overall, this new protocol may reduce the negative effects associated with the use of compounded antiprotozoal drugs for the prevention of EPM.


  • Determining Impact of Pain Medicine on Semen Quality
  • Effect of local anesthetic (lidocaine) on the quality of semen collected from the testicles of castrated stallions


    Jenny Boye, DVM, DACT (Resident)
    Bruce Christensen, DVM, MS, DACT (Mentor)

    Sperm from castrated horses can be saved if the testicles and epididymides (ducts that help to store sperm) are processed after they are removed from the stallion. During this procedure, the sperm is frozen and stored for future insemination. Castration surgery can be performed with or without the local pain medicine injected into the testicles when the horse is under general anesthesia. Lidocaine is the most commonly used drug for local pain relief during castration. The standard dose typically used in a routine castration is 10mls of Lidocaine 2% in each testicle.

    If the sperm is to be harvested, however, the castration is often performed without lidocaine due to concern that the local pain medicine may affect the sperm quality. There is, however, no published evidence that shows any effect of lidocaine on equine sperm quality, fertility, or demonstrates actual contact between the lidocaine and the sperm. The project sought to determine the effect of lidocaine exposure on sperm quality, determine if there are measurable amounts of lidocaine in the sperm, when the lidocaine is injected into the testicles, and determine what the amount is; and determine if castration with lidocaine affects quality of sperm saved from the epididymis after castration, freezing and thawing.


    During the in-vitro study, there was no significant difference for any of the measured motility parameters for lidocaine concentrations at low concentrations (1-10 μg/ml) compared with the lidocaine-free control sample. There were significant decreases in motility parameters in samples with high and very high lidocaine concentrations (100 μg/ml - 10,000 μg/ml) compared to the lidocaine-free control sample. Morphology was not affected by lidocaine at any concentration and membrane permeability was only affected at the highest concentration of lidocaine (10,000 μg/ml).

    After castration, an average concentration of 1.027 ± 0.422 μg /ml lidocaine was detected in the epididymal flush of stallions treated with lidocaine during surgery. There was no effect on sperm quality parameters in sperm obtained from testicles with the use of lidocaine compared with the ones without the lidocaine during castration.

    Based on these results, it should be considered safe to castrate a stallion with local anesthesia injected into the testicle before castration if an epididymal flush is intended post-castration. This would allow veterinarians to perform castrations with lower levels of pain as well as reducing the need for higher amounts of general anesthetic and pain medication post-surgery.

Surgery, Lameness and Imaging

  • Do Horses get TMJ?
  • Jaw Joint Arthritis in Horses: Comparison of Advanced Imaging with Gross and Microscopic Findings


    Jacqueline Tanner, DVM, MS, DACVR (Resident)
    Derek Cissell, VMD, PhD, DACVR (Mentor)
    Boaz Arzi, DVM, DAVDC, DEVDC (Mentor)

    Temporomandibular joint (i.e., jaw joint or TMJ) arthritis in the horse is poorly understood and difficult to diagnose using conventional imaging techniques such as radiographs. Interest in advanced imaging to evaluate the TMJ has been growing; although up to 25% of horses are suspected to have evidence of TMJ arthritis on advanced imaging exams, very little has been published regarding the significance of these findings. Furthermore, there are no descriptions of abnormal advanced imaging findings in the TMJ and their relationship to TMJ arthritis.

    Advanced imaging through computed tomography (CT), gross examination, and microscopic examination of the jaw joints of 18 deceased adult horses of varying ages were performed. CT images were scored for evidence of arthritis. These scores were compared to gross and microscopic evaluation of the jaw joints to confirm the presence of arthritis.


    Advanced imaging through CT showed abnormalities that correlated strongly with evidence of arthritis in the postmortem examinations of adult horses of varying ages. Jaw joint arthritis has been proposed as a cause of reduced performance and behavior problems in horses. This study establishes advanced imaging findings through CT associated with jaw joint arthritis, providing a foundation for predicting clinically significant jaw joint arthritis. This will help identify patients that may benefit from treatment of the jaw joint to restore or improve performance.

  • Developing Better Understanding of Painful Dental Disease
  • Characterizing Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) Lesions through Radiographic and Histological Methods.


    Amanda L. Johnson, DVM, MPH (Resident)
    Travis J, Henry, DVM (Mentor)
    Brian G. Murphy, DVM, Ph.D., DACVP (Mentor)
    Verena K. Affolter, DVM, Ph.D., DECVP (Mentor)

    Equine odontoclastic tooth resorption and hypercementosis (EOTRH) is a commonly recognized, but poorly characterized disease in middle-aged and older horses. The underlying cause remains elusive, and at present, the only therapeutic option is surgical extraction of affected teeth. Loss of incisor teeth can have a negative impact on athletic performance as well as the ability to grasp food material. The goal of this study was to identify microscopic changes in teeth and paradental tissues characteristic of EOTRH that relate to specific radiographic changes. An improved understanding of the pathogenesis of EOTRH may aid in the development of future treatments.

    The study evaluated tissues and radiographic evidence of equine odontoclastic tooth resorption and hypercementosis as well as the affected tooth, adjacent teeth and surrounding bone and soft tissue structures.


    The data collected demonstrated the histopathologic features of EOTRH and information was gained in how to process tissues to avoid loss of cellular detail.  To avoid loss of cellular detail associated with decalcification of tissue, future studies should focus on acrylic embedding of tissues, which allows processing and staining of hard tissues without decalcification. This study additionally provided preliminary data for a larger scale project on EOTRH. A greater understanding of the underlying mechanisms of EOTRH could provide the ability to sustain a full complement of incisor teeth in the older horse, and may provide a path forward to novel treatment strategies.

  • Determining Proper Amikacin Antibiotic Dose for Wound Infection Treatment
  • Comparison of Duration of Target Intra-Articular Concentrations Following Intravenous Regional Limb Perfusion with Two Doses of Amikacin Sulfate in Horses


    Alison Harvey, BVSc, MRCVS
    Isabelle Kilcoyne, MVB DACVS
    Barbara A. Byrne, DVM, Ph.D., DACVIM, DACVM
    Jorge Nieto, MVZ, Ph.D., DACVS, DACVSMR

    Traumatic wounds in the limbs of horses are common and frequently involve synovial (joint) structures that can affect the life and athletic career of the horse. Intravenous regional limb perfusion (IVRLP) with antibiotics is a simple procedure, which allows effective levels of antibiotics to be administered locally with minimal systemic effects.

    To date, there is limited information available on the duration of targeted antibiotic concentrations within joints following IVRLP with amikacin, and how this is affected by the dose used. Determining the length of time that antibiotic concentrations remain above adequate protective levels based on hospital-established minimum inhibitory concentrations (MICs) would guide clinical decisions on the appropriate dosage and frequency of treatment for horses with synovial sepsis, and potentially reducing the frequency of treatment and incidence of unwanted side effects. Study results showed that a 2-gram dose of amikacin, administered through IVRLP, is likely appropriate for most injuries. A 3-gram dose is feasible but may not be justified in the majority of distal limb injuries and should be reserved for cases where culture and sensitivity of the bacterial infections reveals MICs above those achievable with a routine dose range


    The study results will guide veterinary decisions on use of the antibiotic amikacin for treatment of wound infections in joints and reduce the use of more antibiotic than is productive. For most infectious conditions, a daily IVRLP 2 gram dose will be sufficient. There were no adverse effects noted using either dose.

  • Evaluating Optimal Tourniquet Time
  • Evaluation of 10 Minute vs. 30 Minute Tourniquet Time for Intravenous Regional Limb Perfusion (IVRLP) with Amikacin Sulfate in Standing Sedated Horses


    Isabelle Kilcoyne, MVB, DACVS
    Julie E. Dechant, DVM, M.S., DACVS, DACVECC
    Jorge E. Nieto, MVZ, Ph.D., DACVS, DACVSMR

    To address traumatic wounds in the limbs of horses involving synovial structures in a joint, veterinarians often administer 2 grams of amikacin in 60 mL of 0.9% Saline, which allows effective levels of antibiotics to be administered locally with minimal systemic effects. Tourniquets have been used on the distal limb of horses undergoing surgery to maintain a bloodless surgical field for up to 1-2 hours with minimal adverse effects being reported. When performing IVRLP to deliver antibiotics locally, tourniquet times of up to 25-30 minutes have been reported in previous studies. Use of a shorter tourniquet time could greatly reduce the discomfort experienced by the horse and the level of sedation required to perform the procedure in the standing animal.


    The study showed that there was no significant difference between the synovial amikacin concentrations noted between 10 minute and 30 minute IVRLP. Based on these results, 10 minute tourniquet time may be sufficient to achieve peak synovial amikacin concentrations when performing IVRLP.

    To further investigate the actual time required to reach peak synovial concentrations of antibiotics during intravenous regional limb perfusion the group performed a second study in which samples of joint fluid were taken every five minutes after the IVRLP was performed. This study demonstrated the time to reach peak concentrations within the joint was 15 minutes, thereby only necessitating tourniquet application for 15 minutes.

    This study was reported in Veterinary Record.

Recent Publications

Newly Funded Projects