Evaluation of glucose tolerance and intestinal luminal membrane glucose transporter function in horses with equine motor neuron disease

OBJECTIVE: To confirm whether the plasma glucose concentration curve obtained during oral glucose tolerance tests (OGTTs) in horses with equine motor neuron disease (EMND) is decreased, compared with that obtained in clinically normal horses, and determine whether that decrease is a result of defective glucose metabolism or intestinal glucose transport dysfunction. ANIMALS: 8 horses with EMND and 44 matched control horses. PROCEDURE: Electromyography and OGTTs were performed in all 8 affected horses and 10 control horses. Intravenous GTTs (IVGTTs) were performed in 6 affected horses and another 11 control horses. The activity and levels of jejunal luminal membrane glucose transporter (Na+ / glucose cotransporter isoform 1 [SGLT1]) were measured in 2 affected horses and 23 control horses. RESULTS: In horses with EMND, generalized neuropathy was detected via quantitative electromyography; the mean increase in plasma glucose concentration during the OGTT was significantly decreased, compared with the value in control horses. During the IVGTT the mean increase in plasma glucose concentration was significantly lower than that of control horses. The activity and levels of SGLT1 in 2 affected horses were similar to those of control horses. Diagnosis of EMND was confirmed postmortem in all affected horses. CONCLUSIONS AND CLINICAL RELEVANCE: Data suggest that the decreased plasma glucose curve obtained in horses with EMND during OGTTs (compared with control horses) is a result of overall enhanced glucose metabolism or abnormalities in the facilitated glucose transporters; definitive identification of the underlying mechanisms could aid in the development of appropriate treatments of EMND in horses.     

Comparison of the diagnosis and management of unilaterally castrated and cryptorchid horses at a referral hospital: 60 cases (2002-2006)

OBJECTIVE: To determine the incidence of unilaterally castrated horses among horses admitted to the hospital for castration and to compare horses that underwent previous unilateral castration with horses that had cryptorchism. DESIGN: Retrospective case series. ANIMALS: 16 unilaterally castrated horses and 44 cryptorchid horses. PROCEDURES: Medical records of horses that were admitted to the veterinary medical teaching hospital for castration, including cryptorchid and unilaterally castrated horses, between January 2002 and December 2006 were reviewed. Medical records of unilaterally castrated horses and cryptorchid horses were examined for age, breed, history, diagnostic procedures, surgical technique of cryptorchidectomy, location of the retained testicle, and cost of surgery. RESULTS: Of 160 horses admitted for castration, 16 (10%) had undergone previous unilateral castration and 44 (27.5%) had cryptorchidism. Unilaterally castrated horses were significantly older than cryptorchid horses. No significant difference was found in left versus right distribution of testicles. No significant difference was found in abdominal versus inguinal distribution of left-sided testicles. Unilaterally castrated horses had a significantly lower proportion of right inguinal testicles, compared with cryptorchid horses. The cost of diagnosis and management of unilaterally castrated horses was significantly greater than in cryptorchid horses. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that the distribution of retained testicles is significantly different in unilaterally castrated horses, compared with cryptorchid horses, which may affect the selection of diagnostic and surgical approaches to unilaterally castrated horses.     

The Contribution of Specific and Nonspecific Biomarkers in Diagnosis of Equine Gastric Ulcer Syndrome (EGUS) Under Field Condition

The aim of this study is to investigate the diagnostic efficiency of gastrin, pepsinogen, proinflammatory cytokines (TNF-α, IL-6), and oxidative stress biomarkers in horses with equine gastric ulcer syndrome (EGUS). Thirty horses diagnosed with gastroscopic EGUS and 15 clinically healthy horses were selected for this study. The serum levels of gastrin, pepsinogen showed nonsignificant changes in horses with EGUS when compared with healthy horses. The serum levels of TNF-α, IL-6 revealed a significant increase in horses with EGUS when compared with healthy ones. Oxidative stress is evident in horses with EGUS in comparison with healthy horses as detected by higher levels of malondialdehyde (MDA) and decreased serum levels of total antioxidant capacity (TAC), Superoxide dismutase (SOD), glutathione (GSH), and nitric oxide (NO). MDA and TNF-α showed better sensitivity and specificity than IL-6 in distinguishing horses with EGUS from control horses. Conclusively, examination of serum gastrin and pepsinogen levels had a limited value in diagnosis of EGUS in horses under investigation. Moreover, this study showed that oxidative stress is evident in horses with EGUS. Higher levels of TNF-α and IL-6 indicate their role in EGUS pathogenesis in horses. Finally, MDA, TNF-α, and IL-6 could be used as biological markers for preliminary screening of horses with EGUS. Gastroscopy still accredited as the “gold standard” for diagnosis EGUS.     

MAGNETIC RESONANCE IMAGING FEATURES OF OBLIQUE AND STRAIGHT DISTAL SESAMOIDEAN DESMITIS IN 27 HORSES

Injury to the oblique and straight distal sesamoidean ligaments is becoming recognized as a more common cause of lameness in horses than was previously thought. The purpose of this study was to review the magnetic resonance (MR) imaging findings of 27 horses affected with desmitis of the oblique and/or straight distal sesamoidean ligament and determine long-term prognosis for horses with this diagnosis. Imaging was performed with horses in right lateral recumbency in a high-field 1 T magnet. All horses had lameness localized to the digit or metacarpophalangeal/metatarsophalangeal joint region with diagnostic local anesthetic blocks. Ten horses had forelimb lameness and 17 horses had hind limb lameness. MR imaging revealed abnormalities in the oblique distal sesamoidean ligaments in 18 horses, in the straight distal sesamoidean ligament in three horses, and in both the oblique and straight distal sesamoidean ligament in six horses. Treatment consisted of a 6-month rest and rehabilitation program in all horses. The digital flexor tendon sheath was injected with methylprednisolone acetate and hyaluronic acid in 22 horses to decrease inflammation in the injured ligaments before starting the rest and rehabilitation program. Two horses had ligament splitting performed, one in the oblique distal sesamoidean ligament and one in the straight distal sesamoidean ligament. MR imaging is an effective method for diagnosing injury to the oblique and straight distal sesamoidean ligaments in horses. Treatment, primarily a 6-month rest and rehabilitation program, allowed 76% of the horses to successfully resume performance.     

MRI FINDINGS IN 232 HORSES WITH LAMENESS LOCALIZED TO THE METACARPO(TARSO)PHALANGEAL REGION AND WITHOUT A RADIOGRAPHIC DIAGNOSIS

Two hundred and thirty‐two horses with lameness localized to the metacarpo(tarso)phalangeal (MCP/MTP) region without a radiographic diagnosis were evaluated. All horses had high‐field magnetic resonance (MR) imaging of the MCP/MTP region performed for the lame limb and the contralateral limb for comparison. There were 46 horses that had bilateral abnormalities in the forelimbs; 27 of these horses were not lame in the contralateral limb at the time of examination. Bilateral hind limb abnormalities were observed in 37 horses; 22 horses were not lame in the contralateral limb. Soft tissue abnormalities alone were observed in 218 limbs (162 horses). Subchondral bone and articular cartilage abnormalities alone were observed in 43 limbs (34 horses). A combination of soft tissue, subchondral bone, and cartilage abnormalities were observed in 64 limbs (36 horses). The distribution of primary abnormalities was as follows; oblique distal sesamoidean ligament desmitis (73 limbs in 56 horses), straight distal sesamoidean ligament desmitis (44 limbs in 38 horses), chronic subchondral bone injuries (15 limbs in 12 horses), suspensory ligament branch desmitis (14 limbs in 12 horses), collateral ligament desmitis (12 limbs in 12 horses), tendonitis of the superficial and deep digital flexor tendons (10 limbs in 10 horses), osteochondral defects greater than 1 cm (nine limbs in six horses), osteochondral defects less than 1 cm (eight limbs in seven horses), bone marrow lesions (six limbs in five horses), intersesamoidean ligament desmitis (five limbs in four horses). MR imaging is useful in diagnosing bone and soft tissue injuries when radiographs and ultrasound fail to yield a diagnosis.     

Open drainage, intra-articular and systemic antibiotics in the treatment of septic arthritis/tenosynovitis in horses.

Open drainage was used to treat 26 horses with persistent or severe septic arthritis/tenosynovitis. Infected synovial structures were drained through a small (3 cm) arthrotomy incision that was left open and protected by a sterile bandage. Joint lavage was performed in all 26 horses. In addition to systemic antibiotics, 23 of these horses were also treated with intra-articular antibiotics; amikacin (17 horses), gentamycin (2 horses), cefazolin (2 horses), and 2 horses were injected at different times with gentamycin and amikacin. The infection was eliminated from the involved synovial structures in 25 of 26 horses; 24 survived and were released from the hospital. The arthrotomy incisions healed by granulation in 16 horses; in 9 horses the arthrotomy incision was sutured closed once the infection was eliminated. Seventeen horses returned to soundness and resumed athletic function. Open drainage was an effective method of achieving chronic drainage from a joint or tendon sheath. It is indicated in horses that have established intra-synovial infections or in horses that do not respond to joint lavage through needles.     

Seroprevalence of antibodies against equine arteritis virus in horses residing in the United States and imported horses

OBJECTIVE: To compare seroprevalence of antibodies against equine arteritis virus (EAV) in horses residing in the United States with that of imported horses. DESIGN: Serologic survey. SAMPLE POPULATION: Serum samples from 364 horses on 44 equine operations in California and 226 horses imported from various countries. PROCEDURE: Serum samples were collected from each imported horse and from up to 20 horses on each operation. For resident horses, the number of sampled horses on each operation was determined on the basis of the number of horses on the operation. Samples were tested for antibodies against EAV by use of a serum neutralization test. RESULTS: 1.9% of resident horses and 18.6% of imported horses were seropositive to EAV, including 16.1% of imported stallions. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that the EAV seroprevalence of horses residing in California is considerably lower than that of imported horses, including imported stallions.     

Plasma and liver copper values in horses with equine degenerative myeloencephalopathy.

Equine degenerative myeloencephalopathy (EDM) is a common spinal cord disease in the horse. The etiology of EDM currently is unknown. In other species, there are similarities in the clinical signs and neuropathological changes observed in EDM and in copper deficiency. The objective of this study was to determine if horses affected with EDM had low levels of plasma or liver copper. Plasma copper values were determined in 25 EDM affected horses and 35 normal horses. Liver copper levels were determined on 13 EDM affected horses and 22 normal horses. Plasma and liver copper values were not significantly lower in EDM affected horses than in control horses.     

The sympatho-adrenal system and plasma levels of adrenocorticotropic hormone, cortisol and catecholamines in equine grass sickness

Plasma levels of adrenocorticotropic hormone (ACTH), cortisol and catecholamines were used to study the role of the sympatho-adrenal system in equine grass sickness. Statistical evaluation determined differences of hormone levels between seven horses with grass sickness (one acute, five subacute and one chronic), six horses with colic (one with laminitis) and 16 control horses before and after mild stress. Plasma levels of the hormones were higher in horses with acute and subacute grass sickness than in the other groups. No differences were detected between horses with colic and stressed control horses but some hormone levels differed between control and colic horses and control horses before and after stress. It is possible that hyperactivation of the sympatho-adrenal system is caused by stress but it is uncertain whether the stress is only a result of the severity of the disease or also plays a role in its aetiology.     

Comparison of serum parathyroid hormone and ionized calcium and magnesium concentrations and fractional urinary clearance of calcium and phosphorus in healthy horses and horses with enterocolitis

OBJECTIVE: To evaluate calcium balance and parathyroid gland function in healthy horses and horses with enterocolitis and compare results of an immunochemiluminometric assay (ICMA) with those of an immunoradiometric assay (IRMA) for determination of serum intact parathyroid hormone (PTH) concentrations in horses. ANIMALS: 64 horses with enterocolitis and 62 healthy horses. PROCEDURES: Blood and urine samples were collected for determination of serum total calcium, ionized calcium (Ca2+) and magnesium (Mg2+), phosphorus, BUN, total protein, creatinine, albumin, and PTH concentrations, venous blood gases, and fractional urinary clearance of calcium (FCa) and phosphorus (FP). Serum concentrations of PTH were measured in 40 horses by use of both the IRMA and ICMA. RESULTS: Most (48/64; 75%) horses with enterocolitis had decreased serum total calcium, Ca2+, and Mg2+ concentrations and increased phosphorus concentrations, compared with healthy horses. Serum PTH concentration was increased in most (36/51; 70.6%) horses with hypocalcemia. In addition, FCa was significantly decreased and FP significantly increased in horses with enterocolitis, compared with healthy horses. Results of ICMA were in agreement with results of IRMA. CONCLUSIONS AND CLINICAL RELEVANCE: Enterocolitis in horses is often associated with hypocalcemia; 79.7% of affected horses had ionized hypocalcemia. Because FCa was low, it is unlikely that renal calcium loss was the cause of hypocalcemia. Serum PTH concentrations varied in horses with enterocolitis and concomitant hypocalcemia. However, we believe low PTH concentration in some hypocalcemic horses may be the result of impaired parathyroid gland function.     

Prevalence of gastric ulcers in endurance horses--a preliminary report

Gastric endoscopy was performed at the end of a 50 or 80 km endurance ride. Gastric ulceration was evident in 67% of the horses with ulcers on the squamous region of the stomach found in 57% of the horses and active bleeding of the glandular mucosa in 27%. Three horses (10%) had lesions only on the glandular mucosa. Values of albumin, creatinine and glucose were higher in horses without gastric lesions. We conclude that horses from endurance competitions have a high prevalence of gastric ulceration that is similar to that observed in performance horses. However the severity of ulceration is less severe than has been reported in Thoroughbred race horses in active training. Owners should be aware of the high prevalence of gastric ulceration in horses that perform in endurance competitions. The high incidence of active bleeding from the glandular mucosa of the stomach in these horses requires further investigation.     

Pulmonary epithelial lining fluid and plasma ascorbic acid concentrations in horses affected by recurrent airway obstruction

OBJECTIVE: To determine the pulmonary epithelial lining fluid (ELF) concentrations and degree of oxidation of ascorbic acid in horses affected by recurrent airway obstruction (RAO) in the presence and absence of neutrophilic airway inflammation. ANIMALS: 6 RAO-affected horses and 8 healthy control horses. PROCEDURE: Nonenzymatic antioxidant concentrations were determined in RBC, plasma, and ELF samples of control horses and RAO-affected horses in the presence and absence of airway inflammation. RESULTS: ELF ascorbic acid concentration was decreased in RAO-affected horses with airway inflammation (median, 0.06 mmol/L; 25th and 75th percentiles, 0.0 and 0.4 mmol/L), compared with RAO-affected horses without airway inflammation (1.0 mmol/L; 0.7 and 1.5 mmol/L) and control horses (2.2 mmol/L; 1.4 and 2.2 mmol/L). Epithelial lining fluid ascorbic acid remained significantly lower in RAO-affected horses without airway inflammation than in control horses. Moreover, the ELF ascorbic acid redox ratio (ie, ratio of the concentrations of dehydroascorbate to total ascorbic acid) was higher in RAO-affected horses with airway inflammation (median, 0.85; 25th and 75th percentiles, 0.25 and 1.00), compared with RAO-affected horses without airway inflammation (0.04; 0.02 and 0.22). The number of neutrophils in bronchoalveolar lavage fluid was inversely related to the ELF ascorbic acid concentration (r = -0.81) and positively correlated with the ascorbic acid redox ratio (r = 0.65). CONCLUSIONS AND CLINICAL RELEVANCE: Neutrophilic inflammation in horses affected by RAO is associated with a reduction in the ELF ascorbic acid pool. Nutritional supplementation with ascorbic acid derivatives in horses affected by RAO is an area for further investigation.     

Colic in geriatric compared to mature nongeriatric horses. Part 1: Retrospective review of clinical and laboratory data

Reason for performing study: It is the impression of some surgeons that geriatric horses have a lower survival rate compared to mature nongeriatric horses following colic surgery. One possible reason for this is that geriatric horses may be more critically ill at admission and have more severe disease than mature nongeriatric horses. Objective: To compare admission historical, physical examination and laboratory data for geriatric and mature nongeriatric horses referred for signs of colic. Methods: Medical records of horses admitted with a presenting complaint of colic between 2000 and 2006 were reviewed. Geriatric horses ≥16 years (n = 300) and mature nongeriatric horses 4–15 years (n = 300). Information obtained included duration of colic prior to admission, admission level of pain, heart rate, intestinal borborygmi, packed cell volume (PCV), plasma creatinine and blood lactate concentrations and peritoneal fluid total protein. Data were analysed using a Chi‐squared test or an analysis of variance. Level of significance was P<0.05. Results: There was no difference between geriatric and mature horses in the duration of colic prior to admission or in admission heart rate, PCV, or plasma creatinine or blood lactate concentrations. However, geriatric horses were more likely to be moderately painful and less likely to be bright and alert than mature horses; and less likely to have normal intestinal borborygmi than mature horses. Peritoneal fluid total protein concentration was higher in geriatric than mature horses. Conclusions and potential relevance: Geriatric horses presenting with signs of colic had a similar admission cardiovascular status based on heart rate, PCV, and plasma creatinine and blood lactate concentration to mature horses. Geriatric horses, however, may have different causes of colic, which may be more serious than mature horses based on pain, lack of intestinal borborygmi and peritoneal fluid total protein concentration.     

Thyroid Function in Anhidrotic Horses

Background: This study was performed to determine whether anhidrotic horses have altered thyroid function compared with horses that sweat normally.
Hypothesis: Anhidrotic horses have normal thyroid function.
Animals: Ten client-owned horses with clinical signs of anhidrosis were paired with 10 horses living in the same environment that had normal sweat production.
Methods: Horses were diagnosed as having normal sweat production or being anhidrotic based on responses to intradermal injections of terbutaline and physiologic responses to lunging exercise. Control horses were selected from the same environment and matched as closely as possible to anhidrotic horses in terms of age, sex, breed, and athletic condition. Thyrotropin-releasing hormone (TRH) stimulation tests were performed in both horses at the same time, once in the summer or fall, and once again in winter.
Results: Anhidrotic horses produced less sweat in response to intradermal injections of terbutaline and exercise than did control horses. They also had greater increases in body temperature and respiratory rate in response to exercise. Resting concentrations of thyroid hormones and thyroid-stimulating hormone (TSH) were not different between anhidrotic and control horses. Thyroid hormone responses to TRH also were not different between the 2 groups of horses. However, anhidrotic horses had a significantly different TSH response to TRH compared with control horses, particularly in the winter.
Conclusions and Clinical Importance: The biologic relevance of the altered TSH response to TRH in anhidrotic horses is uncertain, considering that TSH concentrations remained within previously reported normal ranges and thyroid hormone responses were not different between anhidrotic and control horses.     

Transmission studies of Hendra virus (equine morbilli-virus) in fruit bats, horses and cats

Objective To determine the infectivity and transmissibility of Hendra virus (HeV). Design A disease transmission study using fruit bats, horses and cats. Procedure Eight grey-headed fruit bats (Pteropus poliocephalus) were inoculated and housed in contact with three uninfected bats and two uninfected horses. In a second exper iment, four horses were inoculated by subcutaneous injection and intranasal inoculation and housed in contact with three uninfected horses and six uninfected cats. In a third experi ment, 12 cats were inoculated and housed in contact with three uninfected horses. Two surviving horses were inoculated at the conclusion of the third experiment: the first orally and the second by nasal swabbing. All animals were necropsied and examined by gross and microscopic pathological methods, immunoperoxidase to detect viral antigen in formalin-fixed tissues, virus isolation was attempted on tissues and SNT and ELISA methods were used to detect HeV-specific antibody. Results Clinical disease was not observed in the fruit bats, although six of eight inoculated bats developed antibody against HeV, and two of six developed vascular lesions which contained viral antigen. The in-contact bats and horses did not seroconvert. Three of four horses that were inoculated devel oped acute disease, but in-contact horses and cats were not infected. In the third experiment, one of three in-contact horses contracted disease. At the time of necropsy, high titres of HeV were detected in the kidneys of six acutely infected horses, in the urine of four horses and the mouth of two, but not in the nasal cavities or tracheas. Conclusions Grey-headed fruit bats seroconvert and develop subclinical disease when inoculated with HeV. Horses can be infected by oronasal routes and can excrete HeV in urine and saliva. It is possible to transmit HeV from cats to horses. Transmission from P poliocephalus t o horses could not be proven and neither could transmission from horses to horses or horses to cats. Under the experimental conditions of the study the virus is not highly contagious.     

Influence of age of horse on results of quantitative electromyographic needle examination of skeletal muscles in Dutch Warmblood horses

OBJECTIVE: To determine the influence of age on results of quantitative analysis of electromyographic (EMG) needle examination in the subclavian, triceps, and lateral vastus muscles of Dutch Warmblood horses. ANIMALS: 7 healthy young Dutch Warmblood horses (range, 13 to 18 months old), 7 healthy adult Dutch Warmblood horses (range, 4 to 10 years old), and 7 healthy elderly Dutch Warmblood horses (range, 18 to 21 years old). PROCEDURE: An EMG needle examination was performed to evaluate insertional activity, spontaneous activity, and motor unit action potential (MUAP) variables. Although all horses were conscious, young horses were sedated prior to examination. RESULTS: Mean insertional activity in young horses was significantly lower than in elderly horses. Pathologic spontaneous activity was rarely found in young and adult horses but was frequently evident in all muscles in all elderly horses. The MUAP duration and amplitude were significantly lower in all muscles of young horses, compared with values for adult and elderly horses. The MUAP duration and number of phases and turns were significantly lower in adult horses than in elderly horses. Group differences for percentages of polyphasic and complex MUAPs were also found. The 95% confidence intervals for MUAP duration, MUAP amplitude, and number of phases and turns for the subclavian, triceps, and lateral vastus muscles were significantly lower in young horses than in adult or elderly horses. CONCLUSIONS AND CLINICAL RELEVANCE: Age of the horse being examined should be considered when EMG examination is performed.     

West Nile virus encephalomyelitis in horses: 46 cases (2001)

OBJECTIVE: To determine signalment, clinical findings, results of diagnostic testing, outcome, and postmortem findings in horses with West Nile virus (WNV) encephalomyelitis. DESIGN: Retrospective study. ANIMALS: 46 horses with WNV encephalomyelitis. PROCEDURE: Clinical data were extracted from medical records of affected horses. RESULTS: On the basis of clinical signs and results of serologic testing, WNV encephalomyelitis was diagnosed in 46 of 56 horses with CNS signs. Significantly more males than females were affected. Increased rectal temperature, weakness or ataxia, and muscle fasciculations were the most common clinical signs. Paresis was more common than ataxia, although both could be asymmetrical and multifocal. Supportive treatment included anti-inflammatory medications, fluids, antimicrobials, and slinging of recumbent horses. Results of the IgM capture ELISA and the plaque reduction neutralization test provided a diagnosis in 43 horses, and only results of the plaque reduction neutralization test were positive in 3 horses. Mortality rate was 30%, and 71% of recumbent horses were euthanatized. One horse that had received 2 vaccinations for WNV developed the disease and was euthanatized. Follow-up communications with 19 owners revealed that most horses had residual deficits at 1 month after release from the hospital; abnormalities were resolved in all but 2 horses by 12 months after release. CONCLUSIONS AND CLINICAL RELEVANCE: Our findings were similar to those of previous WNV outbreaks in horses but provided additional clinical details from monitored hospitalized horses. Diagnostic testing is essential to diagnosis, treatment is supportive, and recovery rate of discharged ambulatory horses is < 100%.     

Medical and surgical management of small-colon impaction in horses: 28 cases (1984-1989).

Medical records of 28 horses with impaction of the small colon were reviewed; 20 horses were admitted during the winter months. Diagnosis of small-colon impaction was made in 21 horses by rectal examination, and in 7 horses at exploratory celiotomy. Ten horses were treated medically, and 18 were treated surgically. Horses that were treated surgically were more likely to have abdominal distention than were those that responded to medical treatment (P less than 0.025). Signs of greater degree of abdominal pain and higher heart rate were seen in horses treated surgically, but these values were not significantly different from values in medically treated horses. Duration of hospitalization was less in horses treated medically (P less than 0.025). Long-term survival was higher for horses treated medically (P less than 0.025). All horses treated medically and 7 of the horses treated surgically were alive at follow-up evaluation, at least 1 year after discharge. Fever and diarrhea were common complications after surgery. Four horses were fecal culture-positive for Salmonella sp after surgery. Early and aggressive medical management of horses with impaction of the small colon is recommended.     

A survey of respiratory viruses in New Zealand horses

AIMS: To determine which viruses circulate among selected populations of New Zealand horses and whether or not viral infections were associated with development of respiratory disease.

METHODS: Nasal swabs were collected from 33 healthy horses and 52 horses with respiratory disease and tested by virus isolation and/or PCR for the presence of equine herpesviruses (EHV) and equine rhinitis viruses.

RESULTS: Herpesviruses were the only viruses detected in nasal swab samples. When both the results of nasal swab PCR and virus isolation were considered together, a total of 41/52 (79%) horses with respiratory disease and 2/32 (6%) healthy horses were positive for at least one virus. As such, rates of virus detection were significantly higher (p<0.001) in samples from horses with respiratory disease than from healthy horses. More than half of the virus-positive horses were infected with multiple viruses. Infection with EHV-5 was most common (28 horses), followed by EHV-2 (27 horses), EHV-4 (21 horses) and EHV-1 (3 horses).

CONCLUSIONS: Herpesviruses were more commonly detected in nasal swabs from horses with respiratory disease than from healthy horses suggesting their aetiological involvement in the development of clinical signs among sampled horses. Further investigation to elucidate the exact relationships between these viruses and respiratory disease in horses is warranted.

CLINICAL RELEVANCE: Equine respiratory disease has been recognised as an important cause of wastage for the equine industry worldwide. It is likely multifactorial, involving complex interactions between different microorganisms, the environment and the host. Ability to control, or minimise, the adverse effects of equine respiratory disease is critically dependent on our understanding of microbial agents involved in these interactions. The results of the present study update our knowledge on the equine respiratory viruses currently circulating among selected populations of horses in New Zealand.     

Activities of Enzymes Related to the Malate–Aspartate Shuttle in the Blood Cells of Thoroughbred Horses Undergoing Training Exercise

The activities of the enzymes related to the malate–aspartate shuttle, which convert cytosolic NADH into mitochondrial NADH, were measured in red and white blood cells from thoroughbred horses undergoing continuous training (race horses) and compared with those in blood cells from riding horses. The activities of malate dehydrogenase (MDH), a rate-limiting enzyme for the malate-aspartate shuttle, were significantly elevated in the white blood cells (WBC) from race horses compared with those from riding horses. There were no significant differences in the activities of the enzymes in the red blood cells between race horses and riding horses. This increase in the MDH activity in their WBC is considered to reflect the increased metabolic activity in the race horses resulting from the training.