Renal tubular acidosis in two horses: diagnostic studies

An 11-year-old Quarter Horse mare and a 2-year-old Quarter Horse colt with clinical diagnoses of renal tubular acidosis (RTA) were donated to the University of California Veterinary Medical Teaching Hospital. A series of diagnostic tests was performed in an attempt to characterize the type and cause of RTA in these horses. Endogenous creatinine clearance and sodium sulfanilate clearance were within reference ranges; thus, no abnormality of glomerular function was detected. To assess renal tubular function in response to acid loading, each horse was given 0.1 g of NH4Cl/kg of body weight via nasogastric tube in 6 L of water. Urine acidification in response to the oral acid load was less than that observed in control horses. The urinary clearance ratio for sodium also was found to be greater for the principals than for the controls. These findings supported a diagnosis of RTA that closely resembled type 1 or distal RTA. In an attempt to determine the cause of RTA, renal ultrasonography, renal biopsy, and a mating study were performed. No abnormalities were identified, and the cause of RTA in these cases remained unknown.     

Hereditary equine regional dermal asthenia (HERDA) in Quarter Horses: A review of clinical signs,genetics and research

Hereditary equine regional dermal asthenia (HERDA) results from a genetic mutation which affects the skin and other tissues of Quarter Horses and horses with Quarter Horse lineage. The disease HERDA has an autosomal recessive mode of inheritance and has become a significant concern in the Quarter Horse industry due to the high frequency of heterozygote carriers. Affected homozygous horses appear normal at birth; however, within the first 2 years of life they usually acquire loose, hyperextensible skin and wounds which result in disfiguring scars either spontaneously or from minor trauma. Some severely affected horses also develop haematomas and seromas. Consequently, most affected horses are subjected to euthanasia at an early age. No treatment options other than palliative therapy currently exist. As part of a five panel test ( http://www.aqha.com/News/News-Articles/2013/April/04292013-Genetic-Testing.aspx ) the American Quarter Horse Association presently requires DNA testing for HERDA on all breeding stallions. There are currently no restrictions on registration of horses heterozygous or homozygous for the HERDA mutation. Due to the autosomal recessive nature of the disease, Quarter Horse mares and horses of all breeds from HERDA‐associated bloodlines should also be tested.     

Upper respiratory signs associated with Anaplasma phagocytophilum infection in two horses

An adult Quarter Horse gelding (Case 1) was evaluated for tachypnoea and acute dysphagia. A 20-year-old Quarter Horse gelding (Case 2) was evaluated for respiratory stertor and severe, acute swelling of the head in the submandibular region. A physical examination, complete blood count, blood chemistry, upper airway endoscopy, and peripheral blood Anaplasma phagocytophilum polymerase chain reaction were completed for both horses. Both horses tested positive for A. phagocytophilum. The upper airway endoscopy for Case 1 revealed a feed contaminated pharynx, absent swallowing reflex, and left laryngeal hemiplagia. The upper airway endoscopy for Case 2 revealed severe diffuse pharyngeal swelling occluding the airway. Due to increased respiratory effort in Case 2, a tracheotomy was performed. In both horses, treatment consisted of intravenous oxytetracycline 6.6 mg/kg bwt i.v. q. 24 h for 2–3 days followed by minocycline 4 mg/kg bwt per os q. 12 h for 10–14 days. Both horses made full recoveries.     

Intra-abdominal hypertension in two adult horses

Objective – To describe the clinical and pathological findings in 2 adult horses with documented increases in intra-abdominal pressure (IAP), and to describe the direct puncture technique used to measure this pressure.
Series Summary – Two adult horses developed increases in IAP secondary to large-volume abdominal effusion. A 9-year-old Quarter Horse cross gelding was presented for evaluation of urinary and neurologic signs. Abdominal ultrasonographic examination showed a hepatic abscess along with abdominal effusion. A 4-year-old Quarter Horse gelding was presented for evaluation of castration complications. A castration site infection extended into surrounding tissues, resulting in peritonitis, abdominal effusion, and severe cellulitis of the limbs. IAP measured in both horses was increased relative to reported equine reference values. Changes in hemodynamic parameters in both horses, notably increased central venous pressure, were consistent with those seen in other species in which intra-abdominal hypertension (IAH) and its sequellae have been documented.
New or Unique Information Provided – Extensive research and clinical literature guides management of humans with IAH and abdominal compartment syndrome. Knowledge of these conditions in companion animal and large domestic species is less well developed. Recent research has established reference values for standing, sedated and recumbent, anesthetized horses. Detailed reports of equine clinical cases of IAH have not been reported in the literature. This report provides information on the clinical, hemodynamic, and pathologic characteristics of 2 horses with measured increases in IAP, and describes the direct puncture technique used to perform these measurements.     

Racing Performance in 72 Racehorses Treated with Prosthetic Laryngoplasty for Laryngeal Hemiplegia

The purpose of this study was to compare racing performance before and after prosthetic laryngoplasty for treatment of laryngeal hemiplegia in inexperienced (horses without at least one start before surgery) and experienced (horses with at least one start before surgery) Thoroughbred and Quarter Horse racehorses. Medical records of 54 Thoroughbred and 18 Quarter Horse racehorses or horses intended for racing treated with prosthetic laryngoplasty and unilateral ventriculectomy for laryngeal hemiplegia were reviewed. Signalment, age at the time of surgery, resting endoscopic grade of laryngeal function, surgical procedure, and type of suture were recorded. Median performance index (PI), earnings, distance, and Beyer speed figure (BSF) per start for three races before and after surgery were compared, and factors associated with improved postsurgical performance were evaluated. Seventy-three percent of horses that had not raced before surgery and 84% of horses that competed in at least one race before surgery were able to return to racing after surgery. Fifty-nine percent and 27% of Thoroughbreds and Quarter Horses, respectively, were able to improve their PI after surgery. Sixty-two percent and 20% of Thoroughbreds and Quarter Horses, respectively, significantly increased their distance after surgery. Additionally, 61% and 66% of racehorses were able to increase their earnings and BSF after surgery, respectively. Horses treated with laryngoplasty and unilateral ventriculectomy have a good prognosis for return to racing. Inexperienced racehorses have a better prognosis for improvement after surgery than do experienced racehorses. Thoroughbred racehorses have a better success rate than Quarter Horse racehorses.     

Hyperkalaemic periodic paralysis in Australian Quarter Horses

SUMMARY Three Quarter Horse stallions and 5 of their 11 tested progeny were diagnosed as affected with the inherited autosomal dominant defect hyperkalaemic periodic paralysis in Victoria in 1992. The diagnoses were based on the appearance of clinical signs and associated increased plasma potassium concentrations in response to oral potassium loading. All affected horses were descendants of the American Quarter Horse Impressive. Indirect evidence indicates that at least 3 other affected Quarter Horse stallions have stood or are standing at stud in Australia. The clinical details of the affected horses are described and the size of the affected population in Australia is discussed.     

Occipitoatlantoaxial malformation in two non-Arabian horses

Occipitoatlantoaxial malformation was diagnosed in a 19-month-old mare of Appaloosa breeding and in a 3-year-old Quarter Horse gelding. Both horses had abnormal head and neck carriage since birth, but neurologic deficits did not become evident clinically until the horses reached 2 and 3 years of age, respectively. Palpation and manipulation of the base of the skull and cervical area proved to be useful diagnostically. Movement could not be elicited at the atlantooccipital joint but, in comparison with clinically normal horses, the range of dorsoventral motion at the atlantoaxial joint was increased. Alternate subluxation and relocation of this joint generated audible clicking sounds. Radiography revealed symmetric atlantooccipital fusion, with modification of the atlas, atlantoaxial joint, and axis. These findings were confirmed at necropsy.     

Penicillin-induced immune-mediated hemolytic anemia in a horse.

A 5-year-old female American Quarter Horse was determined to have immune-mediated hemolytic anemia after detection of a positive response to a direct Coombs' test. Penicillin-induced immune-mediated hemolytic anemia was confirmed via a direct antiglobulin test, using penicillin-coated RBC. The horse was clinically improved and the anemia resolved in response to supportive care and discontinuation of penicillin treatment. Penicillin should be considered a possible cause of immune-mediated hemolytic anemia in horses.     

Transient Fanconi syndrome in Quarter horses

Two Quarter horses with weight loss had glucosuria, euglycemia, and a mild metabolic acidosis suggesting a proximal renal tubular defect. Further testing revealed transient generalized aminoaciduria, lactic aciduria, and glucosuria, indicating Fanconi syndrome. Both horses recovered with supportive therapy. This is the first report of acquired Fanconi syndrome in horses.     

Ubiquitin expression in muscle from horses with polysaccharide storage myopathy

Serial sections of formalin-fixed, paraffin-embedded muscle biopsy specimens from 28 Quarter Horse, Paint, and draft-related breeds, aged 0.5-23 years, were treated with periodic acid-Schiff (PAS) stain for glycogen and were immunostained to detect ubiquitin expression. On the basis of findings in PAS-stained sections, a diagnosis of equine polysaccharide storage myopathy (EPSSM) was made in 22 horses aged 2-23 years (mean, 9.4 years); samples from 6 horses aged 0.5-15 years (mean, 7.3 years) had a normal PAS staining pattern, with no relevant lesions. Ubiquitin expression was detected in all but a 2-year-old EPSSM-affected horse and was not detected in the non-EPSSM-affected horses. Ubiquitin expression was greater than the degree of PAS-positive, amylase-resistant material, and ubiquitin was detected in aggregates of amylase-sensitive glycogen as well as in aggregates of amylase-resistant material. Results suggest that glycogen aggregates develop and are ubiquitinated prior to development of amylase-resistant inclusions. Ubiquitin immunostaining may be most useful for confirming the diagnosis of EPSSM in horses with only amylase-sensitive glycogen aggregates and in horses with early amylase-resistant inclusions. However, ubiquitin immunostaining is no more sensitive than is PAS staining for diagnosis of EPSSM.     

Vascular hamartoma in the tongue of a horse

Hamartoma is defined as a benign tumor-like nodule composed of an overgrowth of mature cells and tissues that normally occur in the affected part but with disorganization. Vascular hamartomas are defined as disorganized and excessive proliferations of vascular tissue. Most vascular hamartomas are present at birth or during early infancy and are considered developmental lesions rather than true neoplasms. Vascular hamartomas are rarely described in horses, and reports have been limited to the dorsal carpal region, the ovary, and the face. In this report, we describe a vascular hamartoma arising from the tongue of a 2-year-old Quarter Horse.     

Differentiation of Chronic Lymphocytic Leukemia in the Horse: A Report of Two Cases

Chronic lymphocytic leukemia (CLL) was diagnosed in two horses: an 18-year-old Quarter Horse gelding that was examined because of edema of the prepuce and ventral abdomen; and a 20-year-old mixed breed gelding that was referred because of lymphocytosis, ventral edema, and weight loss. The first horse had enlarged peripheral lymph nodes and cool nonpainful pitting edema of the ventral abdomen and prepuce. The second horse had enlarged peripheral lymph nodes, cool nonpainful pitting edema of the ventral thorax and cranial ventral abdomen, and a 3/5 holosystolic heart murmur. The diagnosis of CLL was based on increased blood lymphocyte counts and infiltration of marrow and other tissues by lymphocytes. In horse 1, the lymphocytosis persisted for 2 months between initial examination and death. The results of flow cytometric analysis on blood lymphocytes using anti-lymphocyte antibodies suggested that horse 1 had T-cell CLL, and horse 2 had B-cell CLL. In addition, the second horse had a monoclonal gammopathy (IgG), with light-chain proteinuria.     

Bilateral arytenoid cartilage paralysis after inhalation anesthesia in a horse

An 8-year-old Quarter Horse gelding was anesthetized for surgical exploration and debridement of a chronic draining wound in the intermandibular space. Anesthesia was without complication other than persistently low PaO2. Severe airway obstruction was evident immediately after extubation, requiring tracheostomy. Endoscopic diagnosis was bilateral arytenoid paralysis, which gradually resolved over the next 7 days. Compression, trauma, or tension of the recurrent laryngeal nerves are the postulated causes of idiopathic laryngeal hemiplegia in horses. The extremely extended position of the head and neck during anesthesia, perhaps compounded by low arterial oxygen content, may have resulted in a hypoxemic insult to the recurrent laryngeal nerves and caused bilateral arytenoid paralysis in this horse.     

Small intestinal strangulation caused by Meckel's diverticulum in a horse

Necropsy of a 12-year-old Quarter Horse mare revealed a blind-end segment of intestine originating from the antimesenteric border of the ileum. The blind-end segment had looped around and strangulated the ileum and 3.5 m of the jejunum.     

Hyperkalaemic periodic paralysis‐like syndrome in a Criollo Argentino horse

Hyperkalaemic periodic paralysis (HYPP) is a relatively new genetic disease that, so far, appears to be confined to descendants of the American Quarter Horse Impressive, a stallion identified as the link between the pedigrees of all affected horses, and that predominantly affects Quarter Horses but also Paint horses, Appaloosas and Palominos. This study suggests that an episode of muscle weakness, which was reported in a Criollo Argentino genetically unrelated to Impressive, was related to marked hyperkalaemia. The symptoms in this case were reproducible following a KCI challenge test although DNA testing for HYPP was negative. Based on these findings, a diagnosis of a HYPP‐like syndrome was made.     

Differential Expression of IGF1, IGFBP5, MSTN,and MYH1 Across Different Age Classes in American Quarter Horses

The objective of this study was to determine the influence of age on expression of insulin-like growth factor 1 (IGF1), insulin-like growth factor binding protein (IGFBP5), myostatin (MSTN), and myosin (MYH1) genes which are related to growth and muscle development in the American Quarter Horse. Thus, horses (n = 10) from weanling, yearling, 2-, 3-, and 10-year-old age classes were sampled and gene expression was assessed by RT-qPCR. ΔC_T was calculated using the hypoxanthine-guanine phosphoribosyltransferase gene as an internal normalizer. The generalized linear model was used to determine differentially expressed genes, by pairwise comparison between ages. Among technical replicates, the coefficient of variation ranged from 1.0 to 5.2% and was lower than the variation observed between biological replicates (2.1–12.9%). IGF1 demonstrated significantly lower expression in the 3-year-old age class than in weanlings and yearlings, but the 10-year-old age class displayed a significantly higher level than 2- and 3-year-old age classes. Expression of IGFBP5 was highest in weanlings compared with all other age classes. Expression of MSTN was significantly higher in weanlings than in other age classes, whereas 10-year-old horses had an intermediate level of expression, but significantly different from yearlings, 2- and 3-year-old fillies. Finally, expression of MYH1 was lower in 2- and 10-year-old horses than in weanlings and yearlings, whereas 3-year-old fillies demonstrated an intermediate level of expression. Differential expression patterns observed in this preliminary study provide insight into the physiological changes occurring throughout the life span of horses. These patterns could also help explain the variation in performance and endurance between individuals at different developmental stages.     

Unusual response following use of succinylcholine in a horse anesthetized with halothane

A syndrome similar to malignant hyperthermia developed in a 545-kg Quarter Horse while anesthetized with halothane for cataract removal. Succinylcholine administration caused prolonged, severe muscle fasciculations followed by tachycardia, and an elevated blood pressure. Later, while the horse was still under anesthesia, its body temperature rose 2 degrees C, and respiratory acidosis developed. Myositis developed after surgery, but the horse recovered.     

Inheritance of hereditary equine regional dermal asthenia in Quarter Horses

OBJECTIVE: To assess heritability and mode of inheritance for hereditary equine regional dermal asthenia (HERDA) in Quarter Horses. ANIMALS: 1,295 horses with Quarter Horse bloodlines, including 58 horses affected with HERDA. PROCEDURE: Horses were classified as affected or unaffected or as undetermined when data were insufficient to assess phenotype. Pedigree data were analyzed to determine the probable mode of inheritance. Heritability was estimated by use of Bayesian statistical methods. RESULTS: Heritability (mean+/-SD) of HERDA was estimated to be 0.38+/-0.13, with both sexes having an equal probability of being affected. Results for evaluation of the pedigrees were consistent with a single Mendelian autosomal recessive mode of inheritance. CONCLUSIONS AND CLINICAL RELEVANCE: HERDA in Quarter Horses is an inherited disease, and affected horses are more likely to produce affected offspring. An autosomal recessive mode of inheritance should be considered by people making breeding decisions involving Quarter Horses when a first-degree relative has been confirmed with HERDA or has produced affected offspring. In addition, breeders whose horses have produced affected offspring can reduce the likelihood of producing affected horses in the future by avoiding inbreeding.     

Behavior of stabled horses provided continuous or intermittent access to drinking water

OBJECTIVE: To compare quantitative measures and clinical assessments of behavior as an indication of psychologic well-being of stabled horses provided drinking water continuously or via 1 of 3 intermittent delivery systems. ANIMALS: 22 Quarter Horse (QH) or QH-crossbred mares and 17 Belgian or Belgian-crossbred mares (study 1) and 24 QH or QH-crossbred mares and 18 Belgian or Belgian-crossbred mares (study 2). PROCEDURE: Stabled horses were provided water continuously or via 1 of 3 intermittent water delivery systems in 2 study periods during a 2-year period. Continuous 24-hour videotaped samples were used to compare quantitative measures and clinical assessments of behavior among groups provided water by the various water delivery systems. RESULTS: All horses had clinically normal behavior. Significant differences in well being were not detected among groups provided water by the various delivery systems. CONCLUSIONS AND CLINICAL RELEVANCE: Various continuous and intermittent water delivery systems can provide adequately for the psychologic well-being of stabled horses.     

Ileocecocolic intussusception as a sequel to jejunocecostomy in a mare

An excessively long ileal stump, the result of a previous jejunocecostomy, had intussuscepted into the cecum and subsequently obstructed the cecocolic orifice of a 12-year-old Quarter Horse mare. Clinical signs were dehydration, ileus, and endotoxemia. The diagnosis was made at necropsy.