Immunisation of mares to control endometritis caused by Streptococcus zooepidemicus.

Normal mares were immunised by the intramuscular and intrauterine administration of an antigen with adjuvant and they and unimmunised control mares were later challenged by the intrauterine instillation of pathogenic Streptococcus zooepidemicus; the response of all the mares was monitored clinically and bacteriologically for seven days. Significantly fewer S zooepidemicus were present in cervical swabs taken from the immunised mares than from the control mares (P < 0.01) and the degree of inflammation in the genital tract of the immunised mares was also significantly less (P < 0.001). This protective effect of immunisation was associated with the specific IgG response in the serum, and an IgG and IgA response in the uterine secretions. These results are the first demonstration that a previous immunisation with a suitable antigen can reduce an infection of the reproductive tract of mares.

A comparison of ELISA, FAST-ELISA and gel diffusion tests for detecting antibody to equine infectious anaemia virus.

Sera of sixteen horses with clinical signs of EIA from six different outbreaks and sera of 100 uninfected horses were used to validate an ELISA for EIA diagnosis. The antigen used was a recombinant protein derived from the amino-terminal portion of the transmembrane envelope protein of EIA (gp45). Reactivity between positive and negative sera could be clearly distinguished. Comparison with the traditional agar gel immunodiffusion test (commonly called the Coggins test) showed that the ELISA was superior in sensitivity. Comparison of this ELISA with the FAST-ELISA system showed that the latter was less sensitive. Although the FAST-ELISA was much faster to perform, it could not be recommended as a diagnostic test in its present form, because the margin between reactivity by a positive serum and a negative serum was not high.

A soluble recombinant fusion protein of the transmembrane envelope protein of equine infectious anaemia virus for ELISA.

The use of the bacterial expression vector, pGex, to produce an abundant, soluble fusion protein of gp45 from equine infectious anaemia virus is described. Purification of the recombinant protein was achieved by one step affinity chromatography on immobilized glutathione using competitive elution so no harsh conditions were required. This provides a readily available antigen that is defined, plentiful and cheap. Yields of 3.5 mg of purified soluble protein/litre of bacterial culture were obtained. This antigen was found to be suitable for ELISA. Background reactivity to either the glutathione-S-transferase (GST) fusion partner by immune sera or the EIA-GST fusion protein by normal sera were negligible.

The role of procaine in adverse reactions to procaine penicillin in horses.

Procaine penicillin is a commonly used antibiotic in equine medicine but its use is associated with a substantial incidence of adverse reactions. Soluble procaine concentrations were determined by HPLC in several commercially available procaine penicillin preparations, including some that were involved in adverse reactions. The mean (+/- SEM) soluble procaine concentrations in the veterinary preparations was 20.18 +/- 5.07 mg/ml, which was higher than the concentration in the only procaine penicillin preparation for use in humans in Australia of 7.3 mg/ml. Heating the veterinary procaine penicillin preparations to 50 degrees C for 1 day led to a significant (P less than 0.01) increase in the amount of soluble procaine. Heating to 50 degrees C for 7 days also produced a significant (P less than 0.02) increase. Soluble procaine tended to return to baseline concentrations when veterinary procaine penicillin preparations were heated to 50 degrees C for 2 days then stored for 7 days at room temperature. Administration of procaine HCl intravenously (IV) at 2, 5, and 10 mg/kg produced behavioural, locomotor and vascular reactions, which were clinically similar to those reported in adverse reactions to procaine penicillin. The more severe reactions occurred at higher doses, although different horses responded variably at the same dose. Some adverse reactions lead to recumbency but none were fatal. The blood procaine concentrations 1 min after IV administration averaged 19.0 +/- 12.6 and 25.3 +/- 16 micrograms/ml at 2.5 mg/kg and 5 mg/kg, respectively. Ten min after administration, blood procaine concentrations were significantly higher (P less than 0.001) in the 5 mg/kg group than in the 2.5 mg/kg group. Intramuscular (IM) procaine HCl at 5 mg/kg produced significantly lower (P less than 0.001) blood concentrations than similar IV doses, and, in contrast to the IV doses, the amount of procaine in the blood was significantly higher 5 and 10 min after administration than it was after 1 min. Mild excitatory reactions in 4/5 horses were noted 5 to 10 min after IM administration. Administration of diazepam 20 s before procaine HCl prevented the excitatory adverse reaction in 2/2 horses, but administration after the procaine did not influence the outcome.

Pathological aspects of Australian Stringhalt.

Nine horses with clinical signs of Australian Stringhalt were killed and tissues collected for a detailed pathological study. Lesions were limited to peripheral nerves and muscles. The most severely affected nerves were the superficial and deep peroneal, distal tibial, plantar digital, volar and recurrent laryngeal nerve with changes characterised by a selective loss of large diameter myelinated fibres with various degrees of demyelination, fibrosis, Schwann cell proliferation and onion-bulb formation. A routine evaluation of the brain and spinal cord by light microscopy failed to reveal any consistent abnormalities. Morphometric analysis of deep peroneal and recurrent laryngeal nerves confirmed the reduced number of large diameter myelinated axons. Teased fibre preparations of these nerves did not show any abnormalities in internodal distance. The most severe muscle lesions were in the long and lateral digital extensors, cranial tibial, dorsal cricoarytenoid, gracilis and lateral deep digital flexor with extensive atrophy of fibres and diffuse fibrosis. Histochemical evaluation of the long digital extensor from 3 affected horses showed an abnormally wide distribution in fibre size and a reduction in type II fibres compared with controls. These lesions are consistent with a distal axonopathy leading to neurogenic muscle atrophy. The distribution of neuromuscular lesions in Australian Stringhalt may be explained by the susceptibility of longer, larger myelinated nerve fibres to injury, but the cause for this distal axonopathy remains unknown.

Detection of reserpine in horses by high-performance liquid chromatography.

A high-performance liquid chromatography (HPLC) assay was developed for the detection of reserpine. The assay was used to monitor the plasma concentrations of the drug given intramuscularly on one or two occasions to five horses. The blood concentrations of reserpine varied quite considerably between horses given the same dose of the drug. However, on average, reserpine could be detected consistently, and quantified, for 48 h after a single dose of 2.5 mg, and for a similar period after the second of two 2.5 mg doses given 13 d apart. Because of the apparently large variability in the pharmacokinetics of reserpine in horses, exact times cannot be given beyond which the drug will no longer be detectable in the plasma. However, following two doses of 2.5 mg reserpine given 13 d apart, at least 7 d must elapse after the second dose before there is no drug detectable in the plasma of most horses.

Use of phenytoin to treat horses with Australian stringhalt.

Five horses with Australian stringhalt were treated with 15 mg/kg phenytoin orally for 2 weeks. During the second week of the trial, 3 of the horses were given an additional dose of 10 mg/kg phenytoin. The response to treatment was clinically assessed by grading the severity of the gait abnormality at the walk, trot, turning and backing twice daily. There was a significant (P less than 0.05) improvement in the gait abnormality when pre-treatment values were compared with the mean of the last 3 assessments before treatment stopped. When reassessed 2 weeks after treatment ceased, there remained a significant (P less than 0.05) improvement compared with pre-treatment values at the trot and on backing, but not at the walk or turning. Surface electromyographic recordings were made weekly from the long digital extensor muscle, and there was a change to a near normal recording by the end of treatment. Plasma phenytoin concentrations were monitored during the trial, and the dose rates used achieved a steady state with a mean plasma level of 37 +/- 7 mumol/l. There was wide variability between plasma concentrations in different horses, although there was no difference in absorption between administration of the phenytoin as a paste, or when it was mixed in the feed. Although mild tranquilization was seen after treatment, there were no clinical, haematological or biochemical signs of toxicity from the phenytoin therapy.

The occurrence of equine arteritis virus in Australia.

This paper reports the first isolation of equine arteritis virus (EAV) in Australia and serological evidence of exposure to EAV in Australian horses. Twelve Standardbred stallions imported from North America were found to shed EAV in semen. One hundred and seven stallions were tested for serum antibodies to EAV and 73% of Standardbred stallions tested were seropositive as compared to 8% of Thoroughbred stallions. Serum antibody was detected in 71% of Standardbred mares, 6% of Standardbred racehorses and 1% of Thoroughbred mares and racehorses. Examination of stored serums demonstrated that EAV had been present in Australia since at least 1975.

Australian Stringhalt--epidemiological, clinical and neurological investigations.

An investigation of 78 cases of typical Australian Stringhalt from 52 properties in Victoria was carried out from 1985 to 1987. Horses were either examined in the field (n = 52), referred to the Veterinary Clinical Centre (n = 13) or clinical details were obtained verbally (n = 13). In addition 10 cases of false or atypical stringhalt were examined. Detailed soil and pasture analysis was carried out on 14 properties where Australian Stringhalt had occurred. Information was also obtained on epidemiology of the condition from a survey of practitioners. Fifty of the 52 cases examined in the field occurred in horses that were dependent upon poor quality unimproved dry pasture. In all but a few cases, there was no pasture improvement or fertiliser application, leading to the development of weed-dominated pastures, particularly by flatweed, Hypochaeris radicata. The range of clinical signs exhibited by horses with Australian Stringhalt was described and a grading system proposed to classify horses according to severity of signs. Laryngeal abnormalities were present in 10 of 11 cases examined endoscopically and these horses exhibited increased electromyographic (EMG) activity in the long digital extensor muscle at rest and during hindlimb flexion. To a large extent, the EMG changes disappeared and digital extensor muscle atrophy improved in two horses that were monitored to recovery. Deep peroneal nerve conduction studies in four horses with Australian Stringhalt showed a substantial reduction in nerve conduction velocity and when stimulated at 50 Hz were unable to sustain activation of the long digital extensor muscle. EMG and evoked responses appeared to be sensitive indicators of the state of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Adverse reaction to procaine penicillin G in horses.

Adverse reactions to intramuscular injections of procaine penicillin G are reported in 11 horses, five of which died. The clinical findings are presented and suggest central nervous involvement in most cases. Post mortem findings in one horse were consistent with anaphylaxis whereas in other cases the clinical findings, duration of treatment, speed of onset and subsequent completion of treatment supports diagnosis of an acute procaine toxicity syndrome.

Body condition scoring and weight estimation of horses.

Three hundred and seventy two horses of varying breeds, height and fatness were weighed and measured for height at the withers. They were assessed for condition score by adaptation of a previously published method. The heart girth and length of 281 of the horses were also measured. Weight of horses was highly correlated (P less than 0.001) with height (r2 = 0.62), condition score (r2 = 0.22) and girth2 x length (r2 = 0.90). Nomograms were constructed to predict weight from height and condition score, and girth and length measurements. Weight can also be accurately estimated from the formula: (formula, see text) The average value of 'Y' in this experiment was 11900 and this estimated weight with more accuracy than some previously published values of 'Y'. Racing Thoroughbred horses were found to be significantly lighter than non-racing Thoroughbreds of the same height and condition score. The method of assessment of condition score was shown to be repeatable between different operators with varying degrees of experience.