Prevalence of virulent Rhodococcus equi in isolates from 5 horse-breeding farms with endemic infection in Argentina was investigated: isolates were tested for the presence of virulence plasmid DNA and virulence-associated 15-to 17-kDa protein antigens (VapA) by colony blotting with the monoclonal antibody 10G5. R. equi was isolated from all of the soil samples obtained from the 5 farms with 2.0 × 103 to 3.7 × 10 4 colony forming units per gram of soil. Virulent R. equi at various levels (ranging from 4.0 to 24.3%) was isolated from the 5 farms and appeared in 11.4% (74 of 650 isolates). Of the 74 virulent R. equi, 8 contained an 85-kb type I plasmid and 66 contained an 87-kb type I. These results revealed that environments of the horse-breeding farms with endemic infection in Argentina were contaminated with virulent R. equi harboring a virulence plasmid of 85-kb type I or 87-kb type I, which were found in clinical isolates previously reported from Argentina.
Eight local, nondescript adult donkeys, sero-negative to EHV-1, were experimentally infected in two different experiments with EHV-1 of horse origin to study the establishment of viral infection in donkeys along with four pony mares as the control. The virus persisted up to 7 days along with clinical manifestations in pony mares in both the experiments. The virus was also detected by PCR from the spleen of one of the pony mares, but both virus isolation and PCR studies carried out on nasal discharges, peripheral blood lymphocytes and tissues of the animals sacrificed at the end of the experiment, negated the presence of EHV-1 in donkeys. The infectivity and viability of EHV-1 used as the inoculum in both donkey and pony mares was confirmed by isolation of EHV-1and detection of its DNA by PCR from the nasal swabs of pony mares. The use of dexamethasone as an immunosuppresant, failed to indicate the establishment of EHV-1 infection in the donkeys as the virus could not be revived, isolated and detected in PCR studies.
To clarify the endocrinological characteristics of mares with granulosa-theca cell tumor (GTCT), 2 mares with GTCT and a long estrous period were investigated. Before removal of the GTCT in both cases, the concentrations of testosterone, immunoreactive (ir-) inhibin and follicle stimulating hormone (FSH) in the peripheral blood were higher than those of normal mares at the follicular phase, whereas the plasma concentrations of progesterone were constantly low. In Case 1 mare, the plasma concentrations of testosterone, ir-inhibin and follicle stimulating hormone (FSH) changed to significantly high levels. In Case 2 mare, plasma concentrations of all hormones except for progesterone changed to significantly high levels. After surgical removal of the GTCT, the circulating concentration of ir-inhibin decreased rapidly to the basal level. The ir-inhibin levels in GTCT tumor fluid were similar to the follicular fluid in healthy follicles 3.5-5.0 cm in diameter. Concentrations of estradiol in the GTCT tumor fluid were low, but testosterone levels were higher than those in healthy follicles 3.5-5.0 cm in diameter. These results suggest that high levels of circulating inhibin in addition to high levels of testosterone and low levels of progesterone may be used as a clinical sign in the diagnosis of GTCT in mares.
Fecal bacteria in Hokkaido native horses were enumerated by their morphology and Gram staining, and then three major cellulolytic species were quantitated by recently developed competitive polymerase chain reaction (cPCR) assays. Fecal bacterial flora in horses showed drastic change between grazing on summer grassland pasture and grazing on winter woodland pasture mainly consisting of bamboo grass (Sasa nipponica). The number of total bacteria was decreased in winter samples, accompanied with a higher proportion of Gram negative rods and lower proportions of Gram negative cocci, Gram positive rods and cocci than those in summer. This high proportion of Gram negative rods was partly explained by the high cPCR-assay values for Fibrobacter succinogenes (a highly cellulolytic Gram negative rod) in winter samples. Of three major cellulolytic bacterial species, F. succinogenes was dominant in feces of Hokkaido native horses regardless of the sampling season. Feces of light horses mainly come from Thoroughbreds which had been kept with Hokkaido native horses, were taken in winter and employed for analysis. All three cellulolytic species were much less dominant in light horses. These results suggest that F. succinogenes contributes to fiber digestion in the hindgut of Hokkaido native horses, especially in winter woodland pasture where bamboo grass (Sasa nipponica) is mainly available.