Distribution of immunocompetent cells in lymphoid tissues of healthy nulliparous horses were revealed by the double-staining indirect immunofluorescence antibody technique with monoclonal antibodies. In the thymus, immature T cells (CD4⁺ 8⁺ T cells) aggregated in the cortex, while a few mature T cells (CD4⁺ 8^- or CD4^- 8⁺ T cells) were scattered in the medulla. MHC class II⁺ cells aggregated in the cortico medullary region were considered to be macrophages and dendritic cells, while the MHC class II⁺ cells in the cortex were thought to be macrophages, dendritic cells or cortical epithelial cells. The existence of T cell-dependent areas in the spleen, lymph nodes and ileum was confirmed by the presence of CD5⁺ T cells. The number of helper T cells (CD4⁺ 5⁺ T cells) was slightly greater than that of killer T cells (CD5⁺ 8⁺ T cells) in these areas. Within the follicles of the spleen, lymph nodes and ileum, aggregated MHC class II⁺ cells were considered to be B cells and dendritic cells. Almost all the IgM⁺ MHC class II⁺ B cells aggregated within the center of the follicles, whereas IgM^- MHC class II⁺ B cells were found in the marginal zone of the follicles. These findings suggest that activated B cells are contained in the center of the follicle and inactivated B cells in the marginal zone of the follicle and that the follicles are adjoined to T cell-dependent areas.

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A comparative study was carried out to assess the effect of total feed deprivation on various biochemical indices in donkeys and mules, kept off feed continuously for ten days with free access to water. Blood samples were collected during the control period, feed deprivation and recovery period for different biochemical evaluations. All the animals in both the groups were observed to be calm and lethargic during deprivation with significant low water intake as compared to the pre-deprivation period. Feed deprivation resulted in almost total cloudiness of serum at the 7th and 8th days post feed deprivation in mules and donkeys, respectively. Lactate dehydrogenase (LDH), isocitrate dehydrogenase, creatine kinase and aspartate aminotransferase activities decreased significantly in both the groups, but changes were comparatively more pronounced in mules. Activities of sorbitol dehydrogenase and gamma glutamyl transferase as well as levels of potassium remained almost the same as the pre-fasting values in both the groups. Among metabolites, cholesterol, blood urea nitrogen, total serum protein, albumin and creatinine increased significantly in both the groups. Further both the species differed significantly in their albumin and direct bilirubin during the feed stress and recovery periods but LDH, cholesterol and bilirubin total differed even during the control period. Fasting did not seem to have any deleterious effect on major body organs and all the animals recovered by the 6th day of the recovery period. Donkeys were observed to be more adaptable than mules under feed stress conditions.

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Cell division cycles of equine lymphocytes were studied in in vitro cultures of blood samples from seven horses. The first peak of the mitotic index was observed at 36-42 hr after incubation, and the population of mitotic cells at the time consisted of many at the first (97-62%) and the others at the second (3-38%) division. The frequency of cells at the second division increased gradually and reached a peak at 48 hr (62%) after incubation. The third division started at 48 hr after incubation and frequency reached 55% at 60 hr and 80% or more at 72 hr.

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In recent years, there have been reports that uric acid has an antioxidative effect, producing allantoin in a non-enzymatic fashion by reacting with uric acid, as the level of active oxygen increases in the body. We analyzed the changes in the serum concentration of uric acid and allantoin in horses before and after exercise by subjecting horses to kinetic loads in exhaustive treadmill exercise. The uric acid value showed an increase until 60 min after the exhaustive exercise was completed, and declined after 120 min almost to the pre-exercise value. Concentration of allantoin increased after starting exercise, reached maximum values at 30-60 min, and then decreased. No significant difference in the allantoin-uric acid ratio was observed. This suggested that the increase in the allantoin level was closely associated with uric acid present before exercise as well as uric acid produced during exercise.

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To determine whether the guttural pouches in clinically healthy horses contain fungi, especially Emericella nidulans (E. nidulans) and Aspergillus fumigatus (A. fumigatus), that could possibly be pathogenic fungi, microbiological and cytological analyses were conducted. The results obtained were as follows: two fungal species, Eurotium sp. and Penicillium sp. were isolated from guttural pouch lavages in 1 and 2 out of 6 healthy horses respectively, whereas neither E. nidulans nor A. fumigatus were isolated. Eight species of bacteria were isolated from guttural pouch lavages in 1 to 6 cases, respectively. Staphylococcus xylosus was the most dominant species. The average number of nucleated cells in guttural pouch lavages was 0.89 ± 0.36 × 10⁴ cells/ml. Most of the cells were cylindrical ciliated epithelial cells (82.4%). The findings suggest that the guttural pouches of clinically healthy horses contain a small number of fungi and bacteria, which normally reside in the equine environment and the ciliated epithelial cells in the organ may be related to the clearance of pathogenetic micro-organisms.

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