-Equine herpesvirus types 2 and 5 (EHV-2 and EHV-5) have a rather unclear pathogenicity and distribution within the equid population. In order to gain more information on the prevalence of these two viruses, type-specific PCR assays were developed to detect viral DNA in nasal specimens and in peripheral blood leukocytes (PBLs) of adult horses and foals from various regions of Europe, i.e. Sweden, Hungary and the United Kingdom. In adult horses, the prevalence of EHV-2 in PBLs was up to 68% in Sweden and 71% in the United Kingdom. EHV-2 DNA was detected in the PBLs from all the foals tested in all countries and most (93%) of the nasal specimens also yielded positive results. The prevalence of EHV-5 DNA in the PBLs of foals in Hungary was 15 and 24% in adult horses in the United Kingdom. This observation was among the very few reports of the presence of EHV-5 in horses. In summary, the specific PCR assays revealed important data on the occurrence and distribution of EHV-2 and EHV-5 in large horse populations. The findings indicated that infection with EHV-5 occurred later than EHV-2 in foals. This study may contribute to a better understanding of the etiological role of these gammaherpesviruses in equine diseases. Chez les chevaux adultes, la prévalence de EHV-2 dans les LSP atteignait 68 % en Suède et 71 % au Royaume-Uni. L'ADN de EHV-2 a été détecté dans les LSP de tous les poulains testés, et la plupart (93 %) des prélèvements nasaux étaient également positifs. La préva-lence de l'ADN de EHV-5 dans les LSP des poulains en Hongrie était de 15 % et de 24 % chez les chevaux adultes au Royaume-Uni. Cette observation fait partie des très rares signalements de la présence de EHV-5 chez les chevaux. En résumé, les tests PCR spécifiques ont révélé des données importantes sur la présence et la distribution de EHV-2 et EHV-5 dans d'importantes populations de chevaux. Les résultats ont montré que l'infection par le EHV-5 se produisait plus tard que celle par le EHV-2 chez le poulain. Cette étude apporte une meilleure compréhension du rôle étiologique de ces herpesvirus gamma dans les maladies équines.infections équines / Gammaherpesvirinae / EHV-2 / EHV-5 / PCR

Summary Clostridium (C.) difficile, or its cytoxin, was demonstrated in faecal samples from 10 of 25 (40%) mature horses investigated with acute colitis treated primarily with antibiotics for disorders other than diarrhoea. C. difficile was not found in faecal samples from 140 horses without signs of enteric disorders, from 21 nondiarrhoeic horses treated with antibiotics, nor from 22 horses with colitis untreated with antibiotics. Except for C. difficile neither Salmonella nor any other investigated intestinal pathogen was isolated in any of the diarrhoeic horses. The findings strongly support some earlier reports that C. difficile is associated with acute colitis in mature horses treated with antibiotics. Of the 10 horses, 4 proved positive for C. difficile both in culture and in the cytotoxin test, 4 in culture only and 2 only in the cytotoxin test. Eight of 10 horses positive for C. difficile were or had recently been hospitalised, indicating that C. difficile may be a nosocomial infection in horses. All horses positive for C. difficile were treated with β‐lactam antibiotics. The authors are grateful to A. Hellander‐Edman, B. Green and J. Skidell for fruitful cooperation and for providing specimens and to G. Holmström, G. Sigstam and H. Ljung for excellent technical assistance. This research was supported by ATG (the Swedish Horserace Totalizator Board) and the AGRIA Foundation for Research.

Summary Fibre characteristics and enzyme activities were determined for the gluteus, semitendinosus, vastus lateralis and triceps brachil muscles of 55 Standardbred trotters of different ages. Four fibre types (I, IIA, IIB, IIC) were demonstrated by histochemical staining of myofibrillar adenosine triphosphatase after preincubation at different pH values. Type II fibres predominated in all the muscles and the type IIA/IIB ratio was higher in horses over 5 years than in younger horses, except in the vastus in which the IIA/IIB ratio did not change with age. The vastus had the highest proportion of type IIA fibres and the semitendinosus the highest proportion of type IIB fibres. Histochemical demonstration of NADH dehydrogenase disclosed that almost 100 per cent of the type IIA and many of the type I and IIB fibres were medium‐stained; the remaining type I fibres were darkly stained and the type IIB fibres lightly stained. In older horses more fibres were stained for NADH dehydrogenase. The activity of triosephosphate dehydrogenase decreased and that of 3‐hydroxy‐acyl‐coA dehydrogenase and citrate synthase increased in all the muscles except the vastus with increasing age. The greatest increase in oxidative capacity occurred in the gluteus and triceps. Training, rather than age, was regarded as the factor inducing these changes. The results emphasise that histochemical data are only semiquantitative, and there are apparent discrepancies in the intensities of histochemical staining and the biochemical evaluation of various enzymes. Résumé Les caractéristiques des fibres et les activités enzymatiques ont été déterminées pour les muscles glutéal, semi tendineux, long vaste et triceps brachial chez 55 trotteurs de race standardbred, d'âges différents. Quatre types de fibres (I, IIA, IIB, IIC) ont été identifiés par coloration histochimique de la triphosphatase adénosique myofibrillaire, après incubation à des pH variables. Les fibres de type II étaient les plus nombreuses dans tous les muscles, et le rapport entre les fibres IIA/IIB a été trouve plus élevé chez les chevaux agés de plus de 5 ans, à l'exclusion du long vaste où ce rapport n'a pas varié avec l'âge. Le long vaste avait la proportion la plus élevée de type, IIA, le semi tendineux la proportion la plus élevée de type IIB. La mise en évidence histochimique de NADH déshydrogénase a révélé que presque 100% des fibres de type IIA, et beaucoup des fibres de type I et IIB étaient colorées modérément. Les fibres de type I restant étaient fortement colorées et celles du type IIB légèrement colorées. Chez les chevaux les plus âgés, les fibres à NDH déshydrogénase étaient plus nombreuses. L'activité de la triosephosphate déshydrogénase diminuait, l'activité de 3‐hydroxyacyl‐coA‐déshydrogénase et de la citrase synthase augmentait dans tous les muscles sauf le long vaste, quand l'âge augmentait. La plus grande augmentation du pouvoir d'oxydation se produisit dans les muscles glutéal et triceps. C'est l'entraînement, plus que l'âge, qui est tenu pour responsable de ces c...

This study investigated mechanisms used by horses and steers to increase O2 uptake and delivery (VO2) from resting to maximal rates and identified the mechanisms that enable horses to achieve higher maximal rates of O2 consumption (VO2max) than steers. VO2 and circulatory variables were measured while Standardbred trotting horses and steers (450-kg body mass) stood quietly and ran on a treadmill at speeds up to those eliciting VO2max. As VO2 increased in both species, heart rate and circulating hemoglobin (Hb) concentration increased, thereby increasing O2 delivery by the circulation, while cardiac stroke volume remained unchanged. At VO2max arterial PCO2 increased from its resting value in horses but was unchanged in steers, and arterial PO2 decreased in both species. Although the horses hypoventilated and were hypoxemic at VO2max, no significant decrease in arterial Hb saturation occurred. VO2max of the horses was 2.6 times higher than that of the steers and was associated with a 100% larger cardiac output, 100% larger stroke volume, and 40% higher Hb concentration, whereas heart rates at VO2max were identical in the two species. The higher cardiac output of the horses at VO2max resulted from a 1.2-fold higher mean arterial pressure and 1.6-fold lower peripheral tissue resistance (associated with a larger skeletal muscle capillary bed). Both the magnitude of the difference in VO2max between horses and steers and the mechanisms used to achieve it are the same as observed in smaller pairs of mammalian species with large variation in aerobic capacity.

Summary In Sweden there are several reports of mares developing acute colitis while their foals were being treated orally for Rhodococcus equi pneumonia with the combination of erythromycin and rifampicin. In this study 6 adult horses were given low oral dosages of these antibiotics, singly or in combination. Within 3 days post administration of erythromycin, in one case in combination with rifampicin, 2 horses developed severe colitis (one fatal). Clostridium difficile was isolated from one of the horses, whereas no specific pathogens were isolated from the other. Both horses had typical changes in blood parameters seen in acute colitis. Clostridium difficile was also isolated from the faeces of a third horse given an even lower dosage of erythromycin in combination with rifampicin. This horse developed very mild clinical symptoms and recovered spontaneously. In the fourth horse given erythromycin only, very high numbers of Clostridium perfringens were isolated. The horses given rifampicin only did not develop any clinical symptoms and there were no major changes in their faecal flora. In conclusion, it has been demonstrated that low dosages of erythromycin ethylsuccinate can induce severe colitis in horses associated with major changes of the intestinal microflora. Clostridium difficile has been demonstrated as a potential aetiological agent in antibiotic‐induced acute colitis.