Adenomas that developed in the pars intermedia of 1 Anglo-Arab and 4 thoroughbred horses aged 19 to 29 years were examined by light microscopy, electron microscopy and immunohistochemistry. The tumors had a nodular growth pattern separated by connective tissue and often invaded the pars nervosa irregularly. The tumor cells were spindle cells with abundant basophilic cytoplasm and proliferated in a palisade arrangement in line with the blood capillaries. Histochemically, the tumor cells were stained light red with periodic acid-Schiff-Orange G stain and purple with aldehyde thyonine, thereby showing a chromatic similarity to basophilic cells of the normal pars intermedia and the pars distalis. Immunohistochemically, the tumor cells were positive for adrenocorticotropic hormone (ACTH) and also weakly positive for α-melanocyte stimulating hormone (α-MSH), β-lipotropin (β-LPH) and β-endorphin (β-END). Since these hormones are synthesized from the prohormone, proopiomelanocortin (POMC), it has been suggested that the tumor cells may have a POMC-producing structure. But the tumor cells were positive for proliferating cell nuclear antigen, and this tumor appeared to be a nonfunctional pituitary tumor because no cell atypia or exocytosis was found ultrastructually.

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During a 2-year period from 1996 to 1997, a total of 1,089 staphylococci were isolated from the nares and skin of 99 healthy horses reared at 15 farms in the Hidaka District, Hokkaido, Japan. Identification of the 1,089 isolates resulted in the following species distribution: Staphylococcus xylosus, 883 isolates (81.1%); S. sciuri (subspecies not identified), 133 (12.2%); S. cohnii subsp. cohnii, 16; S. hominis (subspecies not identified), 11; S. haemolyticus, 10; S. gallinarum, 7; S. lentus, 7; S. simulans, 3; S. cohnii subsp. urealyticum, 2; S. epidermidis, 1; S. intermedius, 1; S. saprophyticus (subspecies not identified), 1; S. lugdunensis, 1; S. schleiferi subsp. schleiferi, 1; S. capitis (subspecies not identified), 1; S. caprae, 1; unidentifiable, 10. No difference was found between the nares and the skin regarding staphylococcal species distribution. This suggests that for the most part S. xylosus and S. sciuri comprise the staphylococcal flora in horses. For identification, 16S-23S rDNA intergenic spacer PCR analysis was used as well as the Api Staph system. It was confirmed that this method is a useful tool for identification when there are many isolates to deal with. In this study, we designed two primer sets for PCR specific for 16S rDNA of S. sciuri or S. lentus in order to distinguish the 2 species, because it is difficult to identify them definitively in terms of phenotypic characteristics alone. These primer sets were useful in distinguishing these species.

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The influence of long distance transport on various viral infections was investigated serologically by examining 29 young racehorses for infection by respiratory agents including equine herpesvirus, equine adenovirus and equine rhinovirus, as well as coronavirus which has been suggested to be an etiological agent of diarrhea and febrile disease in horses. Serological evidence of infections by these viruses was not shown in any of the 18 febrile horses. However 4 of 11 nonfebrile horses which were loaded on the same vehicle as two horses which were seropositive for coronavirus, seroconverted after transportation.

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We tested the hypothesis that frequency of intense exercise during training would affect the likelihood of bucked shins complex developing in young horses. The relative prevalence of bucked shins were examined in two groups of Anglo-Arabian horses that trainined by different training programs. One group (6 horses) exercised once per week at maximal speed, the other group (7 horses) exercised twice per week at maximal speed. They ran on similar track surface conditions on the same track. Although the group exercised twice per week at maximal speed had a prevalence, there was no significant difference in the incidence of bucked shins between the two groups. It suggest that the number of maximum gallop than the duration of intense exercise. Pathomorphogenetically, there was suggestion that focal radiolucent areas, indicating focal remodeling regions consisting of a focal conglomerate of irregular-sized osteons, at the site of the middle layer in the cortical bone beneath periosteal bony proliferation might play a role as a precursor lesion for the occurrence of otitis of the third metacarpal bone (Mclll).

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Hokkaido native horses (HH) were compared with light half-bred horses (LH) for digestibility and the number of bites and chews when fed non-chopped timothy hay at 90% of the maintenance level in the pen. Apparent digestibility of nutrient and energy in HH were similar to those in LH. The time budget of eating by HH per day was shorter than that by LH (P<0.05, 403.3 vs 557.5 min), while there was no difference between HH and LH in the eating rate. The rate of biting, bite size, chewing rate per a minute and the number of chews per 1 g DM intake in HH were similar to those in LH. Ingestion by HH was indicated to be more efficient than that by LH.

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