The equine influenza vaccine in Japan, has been used since 1985. The vaccine contains inactivated virus strains, A/equine/Newmarket/1/77 (H7N7), A/equine/Tokyo/2/71 (H3N8) and A/equine/Kentucky/1/81 (H3N8). Viruses which have currently spread worldwide are predominantly H3N8 viruses. Influenza epidemics involving vaccinated horses have occurred in Europe and the United States after 1989. Some of the current field isolates are antigenically and genetically distinct from the vaccine strains. Therefore, four field isolates were analyzed for their antigenicity and immunogenicity. Among those, A/equine/La Plata/93 (H3N8) showed ideal properties as a new vaccine strain, and A/equine/Kentucky/1/81 was still immunogenic against some of the field isolates. A/equine/Newmarket/1/77, A/equine/Kentucky/1/81 and A/equine/La Plata/93 were, therefore, contained in the test vaccine. The test vaccine (containing these 2 strains) induced sufficient immune response to current field isolates in horses. The new vaccine has been marketed since September of 1996.

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Neutralization antigenic sites of equine arteritis virus (EAV) were examined with neutralization resistant (NR) mutants generated by two monoclonal antibodies (MAbs; 1A1 and 4G8). From the result of the neutralization test with NR mutants, each MAb was found to recognize a distinct neutralization antigenic site. Immunofluorescent test revealed that the MAbs bound to antigen expressed on the cell surface and envelope protein of the parental EAV-infected cells, but they lost binding activity to antigen in NR mutant-infected cells. The two neutralization MAbs were found to recognize ORF5-coding protein, G_L protein, by sequence analysis of the structural protein-cording region of the parental virus and NR mutant genome. 1A1 and 4G8 recognized neutralization epitope including amino acid positions 60-61 and 84 of G_L protein, respectively. The amino acid positions were located in or near the hydrophilic domain of G_L protein, and hydrophilicity of the positions of NR mutants was distinct from the parental virus.

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A partial cDNA fragment of equine (Thoroughbred) c-ski gene (exon 1) was cloned by means of the polymerase chain reaction (PCR) amplification, and its nucleotide sequence was determined. The nucleotide and the deduced amino acid sequences of equine c-ski showed very high homology (>90%) with human and mouse c-ski, suggesting that this gene is highly conserved in different species of mammals. Genomic DNAs from other breeds of horse, e.g., Breton, New Zealand Pony, Shire, Anglo-Arab and Tokara Horse, were also subjected to PCR analysis. No difference, however, was observed in the nucleotide sequences of the partial c-ski DNA fragments examined. The patterns of c-ski gene expression in various male fetal equine tissues, i.e., cerebrum, lung, heart, skeletal muscles etc., obtained on day 180 of pregnancy, were analyzed by means of reverse transcriptase-mediated PCR (RT-PCR). In all the tissues examined, the expression of c-ski genes was confirmed. Northern blot analysis was carried out to assess the relative expression levels of c-ski genes in the male fetal equine tissues. In all tissues examined, two forms of the transcripts were detected at molecular sizes of 7.8 kb and 6 kb, respectively. In the cerebellum and the lung, the relative expression levels were high. The expression levels in skeletal muscles were moderate compared to the other tissues. The small population size of satellite cells may explain the relatively low expression levels of c-ski genes in the well developed skeletal muscles.

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We investigated the effects of low intensity exercise during the breaking period on cardiorespiratory function in twelve Thoroughbred yearlings. The horses were broken to handling and riding according to typical breaking program, and breaking was defined as a period of about 8 weeks covering bitting, saddling, longeing exercise and track exercise at trot and slow canter. Each horse performed an incremental exercise test on a treadmill before (pre-test) and after (post-test) the breaking period. Vo_2max was increased significantly after the breaking period (pre-test: 134.8 ± 8.9 ml/kg/min, post-test: 151.3 ± 7.9 ml/kg/min). There were no significant difference between the peak HR and La values before and after breaking. Breaking also caused no change in the relationship between speed and HR or La. The peak PCV value was significantly higher after breaking period. These results suggest that Thoroughbreds already have considerably high cardiorespiratory function at the early stage of their lives before breaking, and also suggest that cardiorespiratory function is enhanced through the breaking period, which is necessarily experienced by young racehorses.

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To measure levels of antibody to Japanese encephalitis virus (JEV) in equine serum, an enzyme-linked immunosorbent assay (ELISA) was applied. Purified JEV particles of BMIII strain, derived from Beijing-1 strain, were physically adsorbed onto an immunoplate and the ability to react with anti-JEV antibody was tested. Whole virus particles reacted with the antibody, but the NP-40 lysed antigen did not. The ELISA titer correlated with the virus neutralization (VN) titer and the hemagglutination inhibition (HI) titer, although correlation coefficients were not very high. When the time course of the sera of immunized horses was measured by these three assays, the ELISA response was detected later than the VN and HI responses in 3 of 4 horses. This system can be useful for screening antibody to JEV.

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