Carrie J. Finno

Equine diseases caused by known genetic mutations

The recent development of equine genome maps by the equine genome community and the complete sequencing of the horse genome performed at the Broad Institute have accelerated the pace of genetic discovery. This review focuses on genetic diseases in the horse for which a mutation is currently known, including hyperkalemic periodic paralysis, severe combined immunodeficiency, overo lethal white syndrome, junctional epidermolysis bullosa, glycogen branching enzyme deficiency, malignant hyperthermia, hereditary equine regional dermal asthenia, and polysaccharide storage myopathy. Emphasis is placed on the prevalence, clinical signs, etiology, diagnosis, treatment and prognosis for each disease.

Evaluation of epidemiological, clinical, and pathological features of neuroaxonal dystrophy in Quarter Horses

OBJECTIVE To describe epidemiological, clinical, and pathological features of neuroaxonal dystrophy in Quarter Horses (QHs) on a single farm. DESIGN Prospective case series. Animals-148 horses. PROCEDURES Neurologic, pathological, and toxicological evaluations were completed in selected neurologically affected horses over a 2-year period. Descriptive statistical analysis was performed. RESULTS 87 QHs and 1 QH-crossbred horse were affected. Most (50/88 [56.8%]) affected horses were 1 to 2 years old (median age, 2 years [range, 2 months to 34 years]). Neurologic deficits included obtundation (53/88 [60%] horses), decreased to absent menace response (33/88 [37.5%]), proprioceptive positioning deficits, wide-based stance, ataxia, and dysmetria (88/88 [100%]). Most (78/88 [88.6%]) horses had mild ataxia, but some (10/88 [11.4%]) had moderate to severe ataxia. Low serum concentrations of vitamin E (≤ 2 mg/L) were detected in 3 index case horses and 16 of 17 randomly selected horses (13/14 affected and 3/3 unaffected) during study year 1. Dietary vitamin E supplementation did not improve neurologic deficits in affected horses; vitamin E administration in pregnant mares appeared to decrease but not prevent disease development among offspring born the following year. Lesions detected at necropsy included bilaterally symmetric neuroaxonal degeneration with axonal spheroids in the nucleus gracilis, nucleus cuneatus medialis, nucleus cuneatus lateralis, and nucleus thoracicus (5/5 horses). CONCLUSIONS AND CLINICAL RELEVANCE Neuroaxonal dystrophy should be considered in evaluation of young horses with ataxia and proprioceptive positioning deficits. Vitamin E deficiency may contribute to disease severity.

A Comparative Review of Vitamin E and Associated Equine Disorders

Vitamin E is a primary chain-breaking antioxidant that prevents cyclic propagation of lipid peroxidation. Across species, vitamin E is essential for normal neuromuscular function by acting as a potent antioxidant, as well as by modulating the expression of certain genes, inhibiting platelet aggregation and stabilizing plasma membranes. This review focuses on vitamin E structure, absorption, metabolism, current equine dietary recommendations, the interplay between antioxidants and exercise, a discussion of the necessity of vitamin E supplementation in the horse above the Nutritional Research Council (NRC) 2007 requirements, and a review of equine diseases that are associated with a vitamin E deficiency. Particular emphasis is placed on the proteins involved in vitamin E absorption, transport, and metabolism as potential candidates for vitamin E-associated diseases across species.

Effects of Blood Contamination of Cerebrospinal Fluid on Results of Indirect Fluorescent Antibody Tests for Detection of Antibodies against Sarcocystis Neurona and Neospora Hughesi

The purpose of this study was to determine the effect of blood contamination of cerebrospinal fluid (CSF) on the results of indirect fluorescent antibody tests (IFATs) for Sarcocystis neurona and Neospora hughesi. The in vitro study used antibody-negative CSF collected from non-neurologic horses immediately after euthanasia and blood samples from 40 healthy horses that had a range of IFAT antibody titers against S. neurona and N. hughesi. Serial dilutions of whole blood were made in seronegative CSF to generate blood-contaminated CSF with red blood cell (RBC) concentrations ranging from 10 to 100,000 RBCs/μl. The blood-contaminated CSF samples were then tested for antibodies against both pathogens using IFAT. Blood contamination of CSF had no detectable effect on IFAT results for S. neurona or N. hughesi at any serologic titer when the RBC concentration in CSF was <10,000 RBCs/μl. At concentrations of 10,000-100,000 RBCs/μl of CSF, positive CSF results (IFAT titer ≥5) for S. neurona and N. hughesi were detected only when the corresponding serum titers were ≥160 and ≥80, respectively. The IFAT performed on CSF is reliable for testing horses for equine protozoal myeloencephalitis caused by S. neurona or N. hughesi, even when blood contamination causes the RBC concentration in CSF to be up to 10,000 RBCs/μl.

Equine Protozoal Myeloencephalitis Associated with Neosporosis in 3 Horses

A 24-year-old Appaloosa gelding was evaluated for a 2-month history of pelvic limb incoordination. The gelding had been administered phenylbutazone (2 mg/kg PO q12h) for 1 week before admission, and no improvement was apparent. Two months before presentation, the gelding had been vaccinated against Eastern and Western equine encephalitis (EEE, WEE), tetanus, influenza, West Nile virus (WNV), and rabies. Deworming was adequate, with oral dewormers rotated between ivermectin and pyrantel pamoate every 2 months. On admission, the gelding was tachycardic (52 beats per minute), normothermic (37uC, 99.0uF), and eupneic (16 breaths per minute). Muscling appeared symmetric; however, the gelding placed more weight on the right pelvic limb than on the left and the tail was held to the right side. A complete neurologic evaluation revealed asymmetric hypermetria, characterized by a grade 2 of 5 ataxia on the left thoracic and left pelvic limbs and a grade 3 of 5 ataxia on the right thoracic and right pelvic limbs. There were no cranial nerve deficits, and both tail tone and were normal. The gelding was observed to urinate and defecate normally. A CBC revealed a leukocytosis (14,000/mL; reference range, 5,000–11,600/mL) characterized by a mature neutrophilia (12,200/mL; reference range, 2,600–6,800/ mL). Serum biochemical abnormalities included hyper-glycemia (124 mg/dL; reference range, 50–107 mg/dL). Findings of cervical radiographs revealed mild osteoar-throsis of the articular facets at C4-5 and C5-6. Lumbosacral cerebrospinal collection was performed, and clear cerebrospinal fluid (CSF) fluid was obtained and submitted for cytology, serology (immunoglobulin M [IgM] capture ELISA) for WNV, and indirect fluorescent antibody testing (IFAT) for equine pro-tozoal myeloencephalitis (EPM) (Sarcocystis neurona and Neospora hughesi). The CSF total nucleated cell count (TNCC) was normal (1/mL; reference range, ,6/ mL) with the cell population consisting primarily of small mononuclear cells (70%), large mononuclear cells (17%), and neutrophils (13%). The CSF protein concentration was normal (47 mg/dL; reference range, 20– 70 mg/dL). Red blood cell (RBC) concentration within the CSF was 8/mL. The IgM capture ELISA was negative for WNV. S neurona IFAT titers were negative in serum (,40) and CSF (,5), whereas the serum and CSF tested positive for N hughesi, with titers of 2,560 and 5, respectively. A diagnosis of EPM associated with N hughesi was made, and the gelding was started on a course of ponazuril (5 mg/kg PO q24h for 30 days) and phenylbutazone (2 mg/kg PO sid for 14 days). A repeat examination was performed after …

Applied equine genetics

Genome sequencing of the domestic horse and subsequent advancements in the field of equine genomics have led to an explosion in the development of tools for mapping traits and diseases and evaluating gene expression. The objective of this review is to discuss the current progress in the field of equine genomics, with specific emphasis on assembly and analysis of the reference sequence and subsequent sequencing of a Quarter Horse mare; the genomic tools currently available to researchers and their implications in genomic investigations in the horse; the genomics of Mendelian and non-Mendelian traits; the genomics of performance traits and considerations regarding genetic testing in the horse. The whole-genome sequencing of a Quarter Horse mare has provided additional variants within the equine genome that extend past single nucleotide polymorphisms to include insertions/deletions and copy number variants. Equine single nucleotide polymorphism arrays have allowed for the investigation of both simple and complex genetic traits while DNA microarrays have provided a tool for examining gene expression across various tissues and with certain disease conditions. Recently, next-generation sequencing has become more affordable and both whole-genome DNA sequencing and transcriptome-wide RNA sequencing are methodologies that are being applied to equine genomic research. Research in the field of equine genomics continues to expand rapidly as the cost of genotyping and sequencing decreases, resulting in a need for quality bioinformatics software and expertise to appropriately handle both the size and complexity of these data.

Equine Degenerative Myeloencephalopathy in Lusitano Horses

BACKGROUND Equine degenerative myeloencephalopathy (EDM) is a neurodegenerative disorder that has been previously associated with low vitamin E concentrations. OBJECTIVE To describe the clinical, electrophysiologic, and pathologic features of EDM in a group of related Lusitano horses. ANIMALS Fifteen Lusitano horses. PROCEDURES Neurologic examinations were conducted, and serum vitamin E concentrations were measured. Three neurologically abnormal horses were further evaluated by ophthalmologic examination, electroretinography, electroencephalography, muscle and nerve biopsies, and post-mortem examination. RESULTS Six horses appeared neurologically normal, 6 were neurologically abnormal, and 3 had equivocal gait abnormalities. Abnormal horses demonstrated ataxia and paresis. An inconsistent menace response was noted in 4 neurologically abnormal horses and in 1 horse with equivocal findings. All horses had low serum vitamin E concentrations (<1.5 ppm). Ophthalmologic examinations, electroretinograms, electroencephalograms, and muscle and peripheral nerve biopsies were unremarkable in 3 neurologically abnormal horses. At necropsy, major neuropathological findings in these horses were bilaterally symmetric, severe, neuro axonal degeneration in the gracilis, cuneatus medialis, cuneatus lateralis, and thoracicus nuclei and bilaterally symmetric axonal loss and demyelination mainly in the dorsolateral and ventromedial tracts of the spinal cord. A diagnosis of EDM was made based on these findings. Pedigree analysis identified 2 sires among the affected horses. CONCLUSIONS AND CLINICAL RELEVANCE Equine degenerative myeloencephalopathy is a neurodegenerative disorder that causes ataxia and, in severe cases, paresis, in young Lusitano horses. The disease appears to have a genetic basis, and although vitamin E deficiency is a common finding, low serum vitamin E concentrations also may occur in apparently unaffected related individuals.

Effect of fitness on glucose, insulin and cortisol responses to diets varying in starch and fat content in Thoroughbred horses with recurrent exertional rhabdomyolysis

REASONS FOR PERFORMING STUDY Recurrent exertional rhabdomyolysis (RER) occurs in fit, nervous Thoroughbreds fed high nonstructural carbohydrate (NSC) diets. Clinical signs are diminished by feeding low NSC, high fat diets; however, the mechanism is unclear. OBJECTIVE To determine if the glucose, insulin and cortisol response to isocaloric diets varying in fat and NSC availability differ in fit vs. unfit Thoroughbreds with RER. MATERIALS AND METHODS Four fit (10 weeks treadmill training) RER Thoroughbred mares were exercised and fed 3 isocaloric (121 MJ/day) diets in a 5 day/diet block design. Two high NSC concentrates, sweet feed (SF) and a processed pelleted feed (PL) and a low starch high fat feed (FAT) were used. After 24 h of rest and a 12 h fast, horses ate half their daily concentrate. Blood sampled for [glucose], [insulin] and [cortisol] was obtained before, immediately after and at 30-60 min intervals for 420 min. After 3-6 months detraining period, the block design was repeated. RESULTS Results for SF and PL were similar. Regardless of diet, cortisol was higher in fit vs. unfit horses. Fit horses on SF/PL had higher post prandial [insulin] and insulin:glucose ratio than unfit horses. FAT resulted in lower post prandial [glucose] and [insulin] vs. SF/PL. Higher [insulin] in fit vs. unfit horses was not seen on the FAT diet. CONCLUSIONS Increased post prandial [glucose], [insulin] and [cortisol] induced by high NSC, but not high fat, feeds are enhanced by fitness in RER horses. This combination may trigger rhabdomyolysis through increased excitability in RER Thoroughbreds.

Electrophysiological studies in American Quarter horses with neuroaxonal dystrophy.

OBJECTIVE Neuroaxonal dystrophy (NAD) is a disease characterized by the sudden onset of neurologic signs in horses ranging from 4 to 36 months of age. Equine degenerative myeloencephalopathy (EDM), a disease that has been associated with low vitamin E concentrations, is considered a more advanced form of NAD. The objective of this report is to describe the electrophysiological features of NAD/EDM in American Quarter horses (QHs). HORSES: Six NAD/EDM-affected QHs and six unaffected QHs were evaluated by ophthalmic examination and electroretinography. Five of the NAD/EDM-affected QH and five unaffected QHs were also evaluated by electroencephalography (EEG). RESULTS Ophthalmic examination, ERGs, and EEGs were unremarkable in NAD/EDM cases. CONCLUSIONS Neuroaxonal dystrophy/EDM does not appear to cause clinical signs of ocular disease or functional ERG/EEG deficits in QHs.

Equine protozoal myeloencephalitis due to Neospora hughesi and equine motor neuron disease in a mule.

CASE DESCRIPTION A 23-year-old female mule was presented for bilateral ocular abnormalities and an abnormal pelvic limb gait. CLINICAL FINDINGS Anisocoria, unilateral enophthalmos, medial strabismus, ptosis, pupillary light reflex deficits, and bilateral reticulated pigmentary retinopathy were observed on ophthalmic examination. Neurologic abnormalities included right-sided facial nerve paralysis, extensive symmetric muscle atrophy, and asymmetric pelvic limb ataxia with an abnormal pelvic limb gait. A positive titer (1:40) for equine protozoal myeloencephalitis (EPM) associated with Neospora hughesi was obtained from cerebrospinal fluid with minimal (<1 red blood cell/microL) blood contamination. Muscle biopsies of the sacrocaudalis dorsalis medialis muscle revealed predominantly type I neurogenic muscle atrophy, consistent with a diagnosis of equine motor neuron disease (EMND). TREATMENT AND OUTCOME Treatment included a 2-month course of ponazuril (5 mg/kg PO q24 h), vitamin E (8000 IU PO q24 h), and selenium (2 mg PO q24 h). Clinical improvement was not observed after 2 months although the mule remained stable. Clinical deterioration was reported upon discontinuation of the ponazuril after a 2-month course. CONCLUSION Concurrent disease with EPM associated with N. hughesi and EMND should be considered in cases demonstrating cranial nerve abnormalities, pronounced symmetric muscle atrophy, unusual asymmetric gait abnormalities, and reticulated pigmentary retinopathy.