H-PSGAG concentration in the synovial fluid of the equine antebrachiocarpal, metacarpophalangeal, coronopedal and tibiotarsal joints following a 500 MG i

Eight mature horses were administered a single intramuscular injection of 500 mg polysulfated glycosaminoglycan (PSGAG) labeled with 2.044 mCi tritium. Synovial fluid samples were collected from the antebrachiocarpal (carpal), metacarpophalangeal (fetlock), tibiotarsal (hock) and coronopedal (coffin) joints prior to injection and at 2, 4, 8, 12, and 24 hours after injection. The samples were subjected to scintillation counting in decays per minute and were converted to μg PSGAG per ml. The levels achieved in the synovial fluid of the various joints were compared to levels of PSGAG described as adequate to inhibit enzymes which degrade articular cartilage matrix components and hyaluronic acid and adequate to stimulate production of new matrix components and hyaluronic acid in diseased joints.Mean synovial fluid ³H-PSGAG levels indicated that peak concentrations of ³H-PSGAG were achieved 2 hours post injection in all joints and that these concentrations were within the therapeutic range for PSGAG. The peak concentrations were not significantly different among the joints except between the antebrachiocarpal and the metacarpophalangeal joints. The areas under the concentration-time curves (AUC) for each joint were computed by the trapezoidal method from hour 0 through hour 24 and by empirical exponential decay beyond hour 24. These values were subjected to an analysis of variance (ANOVA). The overall multivariate test of AUC among all joints was not significant.The data from this study indicate that a single intramuscular 500 mg injection of PSGAG provided therapeutic levels of the drug in the equine antebrachiocarpal, metacarpophalangeal, tibiotarsal, and coronopedal joints within 2 hours of injection. While there were differences in levels between joints at certain time points, the AUC values suggest similar distribution of the drug in all joints tested.     

Computed tomographic features of the temporomandibular joint in 10 Jeju horses

BackgroundThe equine temporomandibular joint (TMJ) has a complex anatomical structure that makes diagnosis of TMJ disorders difficult. Computed tomography (CT) is now available in equine medicine; hence, TMJ evaluation has become more convenient.ObjectivesThe objectives of this study were to describe the CT features of the TMJ in Jeju horses and to compare these features with those of Thoroughbreds.MethodsIn this report, the TMJs of 10 Jeju horses (mean age: 4.5 ± 1.9 yr; mean body weight: 282.6 ± 40.3 kg) and 6 Thoroughbreds (mean age: 7.3 ± 1.6 yr; mean body weight: 479.7 ± 44.0 kg) were examined using CT. After CT scanning, the Hounsfield units (HU) and height to width ratio (H:W) of the mandibular condyle were measured.ResultsThe mean H:W in Jeju horses was significantly lower than that in Thoroughbreds. The mean HU in Jeju horses was lower than that in Thoroughbreds; however, the difference was not significant. The most frequent CT finding was an irregular medial margin of the mandibular condyle in both breeds.ConclusionsIn this study, the shape of the mandibular condyle in Jeju horses was flatter than that in Thoroughbreds. This report could be useful in evaluating the TMJ in Jeju horses. Moreover, CT could be a pragmatic choice for the examination of the TMJ in horses.     

Partial Arytenoidectomy in the Horse Using an Extralaryngeal Approach

An extralaryngeal approach to partial arytenoidectomy in the horse was developed by in vitro experiments on isolated larynges and then on intact equine cadavers. The goals of the approach were to preserve the laryngeal mucosa, eliminate the need for a laryngotomy or tracheotomy, and minimize postoperative complications. The new approach was evaluated in seven horses with normal upper respiratory tracts. Left laryngeal hemiplegia was surgically created, and, after a 30-day convalescence, left partial arytenoidectomy was performed using an extralaryngeal approach. The left-to-right hemilaryngeal ratio was calculated before and after left recurrent laryngeal neurectomy and 60 days after partial arytenoidectomy. Left partial arytenoidectomy was successfully completed in all horses without performing a laryngotomy or tracheotomy. Preservation of the laryngeal mucosa (6/7 horses) and apparent stabilization of the adjacent soft tissue (6/7 horses) was achieved. In one horse, a 1 -cm laryngeal mucosal tear healed without complication, and in another some collapse of adjacent soft tissue occurred when a retention suture failed. The mean left-to-right hemilaryngeal ratio was significantly increased compared to horses with left laryngeal hemiplegia, but it remained significantly less than the pre-recurrent laryngeal neurectomy ratio (p < .05). Coughing, aspiration, and airway narrowing were not observed. Partial arytenoidectomy could be reliably performed through an extralaryngeal approach in horses with a normal underlying arytenoid cartilage with preservation of the laryngeal mucosa.     

Isolation of equine herpesvirus type 5 in New Zealand

Aim. To report the first isolation of equine herpesvirus 5 (EHV-5) in New Zealand as part of a study of equine respiratory viruses in New Zealand.

Methods. Nasal swabs and peripheral blood leukocytes were collected from 114 foals and adult horses, inoculated on to equine fetal kidney, rabbit kidney and Vero cell lines and observed for cytopathic effect. EHV-5 isolates were identified using an EHV-5 specific polymerase chain reaction. All samples positive for EHV-5 were also checked for the presence of EHV-2, EHV-1 or EHV-4 DNA using published type-specific primers. The polymerase chain reaction results were further confirmed by dot blot and Southern hybridisation with specific DIG-labelled probes.

Results. EHV-5 was isolated from nasal swabs or peripheral blood leukocytes of 38 out of 114 horses sampled. From horses sampled more than once, EHV-5 was often isolated on more than one occasion. Most of the horses were infected with both EHV-2 and EHV-5 viruses. It was not possible to make an association between EHV-5 isolation and the presence of respiratory disease.

Conclusion. EHV-5 is present in the New Zealand horse population. The exact role it plays in causing, or predisposing to, respiratory disease remains to be elucidated.     

Undetectable vitamin D3 in equine skin irradiated with ultraviolet light

Vitamin D requirements for most animals are expected to be fulfilled through daily exposure of the skin to solar ultraviolet B radiation. The synthesis of vitamin D₃ in skin depends on different factors including melanin pigmentation, the amount of UVB radiation reaching the skin, type of clothing/hair coat, latitude and altitude, season, and time of day. Alternatively vitamin D₂ may be obtained from UVB irradiated pasture species. Recent studies have shown that in unsupplemented grazing horses 25-hydroxyvitamin D₂ is the predominant form of vitamin D in plasma, and that 25OHD₃ is undetectable suggesting horses may rely on diet to obtain vitamin D. In order to mimic the natural environment of skin to sunlight exposure, five equine and two ovine devitalized skin samples were irradiated with 5 J/cm² of UVB light followed by measurement of 7-dehydrocholesterol (7-DHC) and vitamin D₃ concentrations using reverse-phase high pressure liquid chromatography (HPLC). HPLC revealed the presence of 7-DHC in the skin of both horses and sheep. Vitamin D₃ was undetectable in both ovine and equine skin prior to irradiation, but after irradiation with UVB light, ovine skin showed an increase in vitamin D₃ concentration (mean 0.16 ± 0.07 µg/g), whereas vitamin D₃ was undetectable in equine skin. These results provide additional evidence that horses make negligible quantities of vitamin D₃ in their skin after exposure to UVB light and may therefore rely on their diet as a primary source of vitamin D.     

Prevalence of antibodies to equine viruses in the Netherlands

Summary

The prevalence of antibodies to various viruses was investigated in a series of serum samples collected from horses in the Netherlands between 1963 and 1966 and from 1972 onwards. Neutralizing antibodies to equine rhinopneumonitis virus, equine arteritis virus and to equine rhinovirus types 1 and 2 were detected in respectively 76%, 14%, 66% and 59% of the equine serum samples tested.

The observed incidence of serum samples positive to equine adenovirus in the complement fixation test was 39%. Precipitating antibodies to equine infectious anaemia virus were detected only in serum samples from two horses imported from abroad. Haemagglutination inhibiting antibodies to Myxovirus influenzae A / equi‐1, M. Influenzae A / equi‐2, and Reovirus types 1, 2, and 3 were present in respectively 82%, 50%, 10%, 33% and 3.6% of the serum samples tested.

The most frequently observed incidence of antibodies to the various equine respiratory viruses occurred in the groups of horses having repeatedly contact with other horses.     

Closed-Circuit Liquid Injection Isoflurane Anesthesia in the Horse

Six horses were administered isoflurane anesthesia by liquid injection into a closed breathing circuit according to the square root of time model. The unit dose (UD) was calculated using Lowe's formula to provide an end-tidal concentration of 1.3%, or the minimum alveolar concentration of isoflurane. The mean UD was 4.2 ±; 0.2 mL. The mean end-tidal isoflurane concentration (ET_1SO) for each interval after injection, and the peak and minimum concentrations for each injection interval, did not change beginning with the second injection, indicating that the square root of time model accurately predicted isoflurane uptake in the horse. Mean ET_iso measured for the interval after the first injection was 0.68 ± 0.06%, which was significantly (p < .05) lower than the mean concentration after all subsequent injections (1.1 ± 0.1%). Mean peak end-tidal concentration was 1.1 ± 0.25% after the first injection and 1.7 ± 0.26% for all other injections. Mean minimum end-tidal concentration was 0.77 ± 0.13% for all injection periods. This model proved to be an acceptable technique for administration of isoflurane anesthesia to horses.     

Cardiovascular Effects of Amphetamine in the Horse

Each of nine horses was treated with amphetamine alone, with atropine alone, and with amphetamine and atropine in combination. Cardiac effects of these drugs were studied by electrocardiography during resting and exercising states and immediately after exercise.

Although each treatment increased heart rate significantly during the resting state, only the amphetamine plus atropine treatment increased heart rate significantly during exercise. Decrease in heart rate immediately after exercise differed significantly for each treatment; the most rapid decrease in heart rate was found after the amphetamine treatment.

Amphetamine caused second-degree atrioventricular (AV) block in each horse during the postexercise period. Amphetamine also caused ectopic beats either during or immediately after exercise in six horses. Second-degree AV block was not found when atropine was used alone or when used in combination with amphetamine. Fewer ectopic beats were found when atropine was used with amphetamine.

Heart rate responses indicated that the direct effect of amphetamine was greater than the reflex effect at rest and during exercise; the opposite was true during postexercise. Second-degree AV block during the postexercise period was attributed to vagotonia due to baroreceptor stimulation. Release of norepinephrine by amphetamine probably caused many of the ectopic beats by increasing automaticity of subordinate pacemakers.

     

The Separation of Peripheral Blood Cells of the Horse

The peripheral blood cells from Standard bred horses were subjected to procedures which will separate equine peripheral blood cells with good precision and efficiency into red cell, leukocyte, and platelet fractions. The separated cells have normal morphology and the differential count of the separated granulocytes and lymphocytes is unchanged from that of the original sample.     

Experimental Leptospira interrogans Serovar Kennewicki Infection of Horses

Background: Little information is available about experimental induction of leptospirosis in horses. Objectives: Determine serologic, hematologic responses of horses to Leptospira interrogans serovar Kennewicki infection. Animals: Four adult horses seronegative for leptospirosis. Methods: Experimental and observational study. Horses were challenged with an equine isolate of L. interrogans serovar Kennewicki at 2 different doses and different inoculation sites. After challenge, the horses were monitored for 60 days. Blood, urine, and aqueous humor samples were collected at intervals until euthanasia 60 days after infection. Results: Pyrexia (39.3–40°C) occurred as early as 1 day after challenge with 10 × 10⁸Leptospira divided equally between topical ocular and intraperitoneal injection in 2 horses. Leptospires were recovered from the blood and urine but not from the aqueous humor of the 2 febrile horses. The sera of all 4 challenged horses developed microscopic agglutination test antibody after challenge and remained relatively constant for 21 days. Titer to cross‐reacting strains declined earlier than titer to the challenge strain. Conclusions: Clinical disease in experimentally infected horses can be mild or inapparent in Leptospira infected horses. Repeated serologic testing can allow recognition of the infecting serovar. In febrile horses, Leptospira can be isolated from blood while isolation from the urine can occur after fever has subsided.     

Evaluation of the Perkins handheld applanation tonometer in horses and cattle

The objective of this study was to evaluate and validate the accuracy of the Perkins handheld applanation tonometer for measuring intraocular pressure (IOP) in horses and cattle. Both eyes of 10 adult horses and cattle were evaluated in a postmortem study. The eyes from 10 clinically normal adult horses and cattle were also examined after bilateral auriculopalpebral nerve block and topical anesthesia for an in vivo study. IOP was measured postmortem using direct manometry (measured with an aneroid manometer) and tonometry (measured with a Perkins handheld applanation tonometer). The correlation coefficients (r²) for the data from the postmortem manometry and Perkins tonometer study were 0.866 for horses and 0.864 for cattle. In the in vivo study, IOP in horses was 25.1 ± 2.9 mmHg (range 19.0~30.0 mmHg) as measured by manometry and 23.4 ± 3.2 mmHg (range 18.6~28.4 mmHg) according to tonometry. In cattle, IOP was found to be 19.7 ± 1.2 mmHg (range 18.0~22.0 mmHg) by manometry and 18.8 ± 1.7 mmHg (range 15.9~20.8 mmHg) by tonometry. There was a strong correlation between the IOP values obtained by direct ocular manometry and the tonometer in both horses and cattle. Our results demonstrate that the Perkins handheld tonometer could be an additional tool for accurately measuring IOP in equine and bovine eyes.     

The Effect of a Seaweed-Derived Calcium Supplement on Gastric Juice pH in the Horse

Low gastric pH for extended periods of time can increase the risk of gastric ulceration in horses. Therefore, nutritional interventions that buffer stomach acid may be helpful to decrease ulcer risk. The objective of this trial was to evaluate whether the incorporation of calcified Lithothamnion corallioides and Phymatolithon calcareum (Calmin; Celtic Sea Minerals, Cork, Ireland) into an equine ration would buffer equine gastric juice. Nine mature, Thoroughbred-cross horses, including 6 geldings and 3 mares (524 ± 49 kg) were housed in stalls and fed 2 kg/day of a texturized concentrate (Purina Omolene 100) and 1.5% BW grass hay/day. On testing days 0, 7, and 14, the horses received one of three pelleted dietary treatments (CON, MIN1 ×, MIN2 ×) in a randomized, crossover design. CON contained no added Calmin, MIN1 × provided Calmin at a 1 × concentration, and MIN2 × provided a 2 × dose. All horses underwent gastroscopy (Karl Storz, El Segundo, CA) prior to feeding the treatments, and at 2 and 4 hours postfeeding. Gastric juice was aspirated and pH measured using a benchtop pH meter (ThermoOrion pH Meter Model 410A). Overall, there was a significant time effect (P < .0001) with an increase in gastric juice pH from time 0 (2.31 ± 0.58) to 2 hours (5.52 ± 0.48) and 4 hours (3.59 ± 0.48). Gastric juice pH at 2 hours was higher (P = .0122) in MIN1 × (5.92 ± 0.58) and MIN2 × (5.92 ± 0.57) than CON (5.08 ± 0.58). These results demonstrate that adding Calmin to a meal increases buffering capacity at 2 hours postfeeding.     

The kinetics of hematopoiesis in the light horse II. The hematological response to hemorrhagic anemia.

Hemorrhagic anemia was experimentally produced in three Standardbred horses by removing approximately 63% of the red cell mass and the accompanying plasma during a three day interval. Red cell parameters were examined daily for 45 days and then weekly until termination of the experiment 250 days after production of the anemia. Leukocytes, platelets and bone marrow aspirates were examined at regular intervals for 25 days after the final phlebotomy. At 24 hours after the last bleeding, 75-selenomethionine was injected intravenously to measure the lifespan of the newly produced erythrocytes. The erythrocyte lifespan was found to be 139 days as compared to the 155 day erythrocyte lifespan for three normal standardbred horses measured previously by similar techniques. The maximum decrease in erythrocyte numbers occurred four, two and two days following the last phlebotomy to 43, 39 and 44% of the original values. The prebleeding erythrocyte levels were regained at approximately 63, 91 and 98 days respectively. During the initial 45 days post phlebotomy the maximum increase in mean cell colume was 2, 4 and 7 mj-3 respectively. During the recovery period there was erythrocyte production of 6.84, 6.99, and 6.12 x 10-9 cells/kg/day. At the same time the absolute production of hemoglobin was 44.6, 50.0, and 51.0/gm/day or on a relative basis 0.096, 0.114 and 0.113 gm/kg/day.     

Evaluation of intra-articular injection of autologous platelet lysate (PL) in horses with osteoarthritis of the distal interphalangeal joint

Background: Regenerative medicine has become one of the most promising therapies of equine osteoarthritis. Platelet lysate (PL) is rich in bioactive proteins and growth factors that play a crucial role in tissue healing.

Objective: To evaluate the efficacy of intra-articularly injected autologous PL in equine athletes with naturally occurring osteoarthritis.

Animals and methods: Fifteen warmblood geldings aged 8–19 years with osteoarthritis of the distal interphalangeal joint were included in this study. They were randomly divided into two groups; 10 horses received intra-articular injections of PL and 5 of normal saline (controls). Before treatment, platelet-derived growth factor (PDGF) levels in basal plasma and prepared PL were estimated. Each joint was injected twice within a three-week period. Lameness was evaluated using the American Association of Equine Practitioners grading system, before treatment and 10 days after each intra-articular injection. Horses were examined fortnightly for one year. Radiographic examination was performed six months post-treatment. The generalized estimating equation test was used for statistical analysis.

Results: Acceptable levels of PDGF were detected in PLs (mean ± SD: 258.0 ± 52.3 pg/ml). The majority of horses (9/10) responded positively to PL treatment presenting lower lameness grades (p < 0.0005) compared to controls 10 days after the second injection, and returned to normal athletic activity. Radiographs revealed no changes in osteoarthritis lesions six months after treatment. One year post-injections, however, all horses relapsed to their initial degree of lameness.

Conclusion: Intra-articularly injected autologous PL is an efficient method for temporarily managing osteoarthritis of the distal interphalangeal joint in athletic horses.     

Cobalt metabolism in horse. Serum level and biosynthesis of vitamin B12.

The levels of serum vitamin B₁₂ were determined on 16 mature partly warm-blooded, partly Finnish rural-race horses by the radioisotopic competitive inhibition assay method. The mean value from three samplings carried out in dupli- or triplicate was 1.54 ± 0.16 ng/ml. The utilization of serum inorganic cobalt for cyanocobalamin synthesis was studied on two geldings, which received a dose of 200 µCi ⁵⁸CoGl₂ i.v. A Sephadex G-100 gel filtration was carried out with the serum proteins from serial blood samplings at different time intervals 15 min. to 48 hrs. after administration. The gel filtration showed the presence of two labelled proteins in the serum, one of them appearing some time after administration and disappearing almost completely towards the end of the experimental period. The two elution peaks are considered to represent inorganic ⁵⁸Co and ⁵⁸Co labelled vitamin B₁₂. The appearance of labelling in serum vitamin B₁₂ indicates the passing of cobalt into the intestine, and reabsorption into blood in the form of vitamin B₁₂.     

Interferon-gamma, interleukin-4 and interleukin-10 production by T helper cells reveals intact Th1 and regulatory TR1 cell activation and a delay of the Th2 cell response in equine neonates and foals

Cytokines produced by T helper (Th) cells are important in orchestrating the immune response during health and disease. Recent reports indicated that cytokine mRNA expression in foals is often quantitatively lower than that of adult horses suggesting that foal T cells are not fully mature. Here, peripheral blood mononuclear cells from foals and adult horses were stimulated with phorbol 12-myristate 13-acetate and analyzed for intracellular interferon-gamma (IFN-γ), interleukin-4 (IL-4) and IL-10 production, representing the Th1, Th2 and regulatory T_R1 cell phenotypes respectively, by flow cytometry. In agreement with previous reports, all three cytokines were quantitatively reduced in foals compared to adults. However, the balance between Th1 and Th2 cytokines (IFN-γ/IL-4 ratio) showed a clear Th1-biased response in foals by 6 and 12 weeks of life, while similar IFN-γ/IL-10 ratios were found in foals and adult horses. By day 5 after birth, intracellular IFN-γ production by foal CD4⁺ and CD8⁺ T cells resembled that in adults. Overall, IL-4 production was low in foals. IL-4⁺ cells peaked at day 5 of age when IL-4 was mainly produced by IgE⁺ cells. Relative percentages of IL-4⁺ Th2 cells were significantly lower in foals at all time points. The data suggested that equine neonates and young foals have an impaired Th2 response, that the immune response of foals is Th1 biased, that IFN-γ production by Th and cytotoxic T cells is qualitatively similar to adult horses, and regulatory IL-10 production by T cells is developmentally mature in foals during the first three months of life.     

Volume of the Synovia in Certain Joint Cavities in the Horse

A method of determining the volumes of synovia in certain articular cavities in the horse is described. The method is based on the degree of dilution of human serum albumin labelled with ¹²⁵I that is injected into the joint. It is shown that uniform distribution of the injected substance is attained within 20 min post injection. The elimination of the labelled substance was found to follow the pattern of a single exponential function. The following volumes of synovia were determined (mean ± s) : hock, 39.8 ± 2.1 ml; radio-carpal, 12.6 ±1.5 ml; intercarpal, 14.9 ± 0.6 ml; foreleg fetlock joint, 12.5 ± 1.0 ml.     

Abdominal Adhesions after Small Intestinal Surgery in the Horse

One hundred thirteen of 172 horses (66%) undergoing exploratory celiotomy for a small intestinal lesion survived 4 or more days after surgery. Intra-abdominal adhesions causing clinical problems requiring additional surgery or euthanasia were documented in 25 horses (22.1%). Problems developed in significantly more males than females. The most common initial small bowel lesion was ileal impaction (12 horses); 21 horses underwent small intestinal resection or bypass. However, there was no significant difference in the incidence of intra-abdominal adhesions between horses that underwent intestinal resection or bypass and those that did not. Only 4 of the 25 horses (16%) with problems associated with postoperative adhesions survived. The mean interval between surgical procedures or between the initial procedure and euthanasia for all horses was 84 days (range, 7–512 days; median, 25 days). However, 70% of the subsequent celiotomies were performed within 60 days of the previous surgery. The mean interval between celiotomies was 221 days (range, 9–512 days) for the survivors and 61 days (range, 7–358 days) for the nonsurvivors. These results indicated that most of the problems related to postoperative intra-abdominal adhesions occurred within 2 months of the initial small intestinal surgery. Furthermore, the earlier development of postoperative adhesions was associated with a poorer prognosis for survival.     

Effects of extracorporeal shock wave therapy on desmitis of the accessory ligament of the deep digital flexor tendon in the horse

Objective: To evaluate the effects of extracorporeal shock wave therapy (ESWT) on collagenase‐induced lesions in the accessory ligament of the deep digital flexor tendon (ALDDFT) of horses. Study Design: Paired, blinded controlled study. Animals: Eight Thoroughbred horses (3 mares, 5 geldings; mean±SD weight, 464±26 kg, mean age, 8±1.7 years). Methods: Lesions were created in both ALDDFTs of all horses by injection of 2 × 10³ IU of collagenase type I. Percent lesion and structure (fiber alignment and echogenicity) were quantified with ultrasonographic imaging 3, 6, and 9 weeks after collagenase injection. After ultrasound examinations, ESWT (1000 shocks at 0.15 mJ/mm²) was applied to 1 ALDDFT in each horse. ALDDFT were harvested 15 weeks after collagenase injection and the microstructure, mRNA levels of collagen types I and III, and collagen and glycosaminoglycan content were evaluated. Results: There were no differences in percent lesion, echogenicity, or fiber alignment between control‐ and ESWT‐treated ligaments at each evaluation time; however, compared with 3‐week values, there was a significant increase in percent lesion and echogenicity for EWST treated ligaments at 6 weeks and significant decrease in both variables for treated and control ligaments at 12 weeks. Fiber alignment improved significantly at 9 weeks in controls and at 12 weeks in treated and control ligaments. Collagen type I mRNA levels were significantly higher in the ESWT treatment group compared with the control group 15 weeks after collagenase injection though differences in other mRNA levels, microstructure, and composition were not significant. Conclusions: Our results do not support an effect of ESWT on collagenase‐induced lesions in the equine ALDDFT.     

Viruses associated with outbreaks of equine respiratory disease in New Zealand

AIM: To identify viruses associated with respiratory disease in young horses in New Zealand.

METHODS: Nasal swabs and blood samples were collected from 45 foals or horses from five separate outbreaks of respiratory disease that occurred in New Zealand in 1996, and from 37 yearlings at the time of the annual yearling sales in January that same year. Virus isolation from nasal swabs and peripheral blood leukocytes (PBL) was undertaken and serum samples were tested for antibodies against equine herpesviruses (EHV-1, EHV-2, EHV-4 and EHV-5), equine rhinitis-A virus (ERAV), equine rhinitis-B virus (ERBV), equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), reovirus 3 and parainfluenza virus type 3 (PIV3).

RESULTS: Viruses were isolated from 24/94 (26%) nasal swab samples and from 77/80 (96%) PBL samples collected from both healthy horses and horses showing clinical signs of respiratory disease. All isolates were identified as EHV-2, EHV-4, EHV-5 or untyped EHV. Of the horses and foals tested, 59/82 (72%) were positive for EHV-1 and/or EHV-4 serum neutralising (SN) antibody on at least one sampling occasion, 52/82 (63%) for EHV-1-specific antibody tested by enzyme-linked immunosorbent assay (ELISA), 10/80 (13%) for ERAV SN antibody, 60/80 (75%) for ERBV SN antibody, and 42/80 (53%) for haemagglutination inhibition (HI) antibody to EAdV-1. None of the 64 serum samples tested were positive for antibodies to EAV, reovirus 3 or PIV3. Evidence of infection with all viruses tested was detected in both healthy horses and in horses showing clinical signs of respiratory disease. Recent EHV-2 infection was associated with the development of signs of respiratory disease among yearlings [relative risk (RR)=2.67, 95% CI=1.59-4.47, p=0.017].

CONCLUSIONS: Of the equine respiratory viruses detected in horses in New Zealand during this study, EHV-2 was most likely to be associated with respiratory disease. However, factors other than viral infection are probably important in the development of clinical signs of disease.