In a riding stable keeping about one hundred horses, a high incidence of white line disease (WLD) related to diet variations was examined from 1992 through 1997. During the first year, the jumping horses (group A) and the dressage horses (group B) were fed mainly with alfalfa hay cubes, timothy hay, barley, salt and calcium supplements. In contrast, the school horses (group C) were fed with Yuusyun® (YS), a pelleted feed, instead of barley, and no salt or calcium supplement. WLD was then detected only in groups A and B. Since the second year, the diets for groups A and B have been changed to supply YS, and after the third year the incidence of WLD decreased significantly. The typical diet fed to groups A and B before the change (P-diet) was short of zinc and copper, and the improved diet (N-diet) provided enough zinc and copper. The other nutrients contained in either diet were enough. It is therefore inferred that the high incidence of WLD which appeared in this stable was caused by feeding low-zinc and low-copper diets to adult performance horses for a long time.

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The distribution of immunocompetent cells (CD4, CD5, CD8, and IgM positive cells) in the immuno-organs of healthy nulliparous mares was investigated by the immunohistological technique with monoclonal antibodies. Aggregated CD4⁺ or CD8⁺ T cells were observed in the thymic cortex, and a small number of CD4⁺ or CD8⁺ T cells were found in the thymic medulla. CD5⁺ T cells were observed widely in the thymus, they were detected at higher frequencies in the medulla than the cortex, but, a small number of IgM⁺ B cells were scattered only in the thymic medulla. T cell-dependent areas of the spleen, lymph nodes and ileum were identified by CD5⁺ T cells. In T cell-dependent areas of these organs, the number of CD4⁺ T cells was slightly greater than that of CD8⁺ T cells. In the center of the follicles of these organs, IgM⁺ B cells aggregated, and these follicles adjoined the T cell-dependent areas. These findings suggested that T and B cells differentiate and mature in thymic and peripheral lymphoid tissues, respectively, and also suggested that immunological actions of peripheral lymphoid tissues would be related to humoral immune responses.

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Most class II genes show a wide genetic variation both in the number of loci and the number of alleles among and within species. Sequence conservation during evolution has proven to be high enough in domestic animals for primer sequences developed for one species to be employed to amplify sequences of another. The aim of this work was to develop a PCR-RFLP method for MHC DRB DNA typing in horses by using bovine designed primers. The analysis of the ELA-DRB sequences revealed that all the eleven alleles previously described could be differentiated by the PCR-RFLP method with the restriction enzymes Hae III and Rsa I. The use of other restriction enzymes could be useful in recognizing other variants, improving the accuracy of this DNA-based typing method.

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A 15-year-old pony mare showed signs of inactivity, dehydration, weight loss, hyperglycemia and glucosuria. After 4 years from the first hospitalization, the pony had the same clinical signs and hirsutism, and died in spite of the treatment. Plasma concentrations of cortisol and insulin in the case had increased to extremely high levels. Necropsy revealed enlargement of the pars intermedia of the pituitary gland and hyperplasia of the adrenal cortex. We concluded that this case was Cushing’s disease.

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To study changes in L-proline uptake at different stages of gestation in mares, L-proline uptake into the maternal-facing microvillous plasma membrane was examined. The placental microvillous membrane vesicles (PMV) were isolated at three stages of gestation (6th, 8th and 10th month), characterized for their purity, and measured L-proline uptake. The uptake of L-proline into the PMV was demonstrated in a sodium-dependent manner. From apparent K_m and V_max values, it was considered that the degree of L-proline uptake by the active transport mechanism in the equine placenta tended to be higher at the 8th month than at the 6th and 10th month of gestation. These results suggest that the changes in L-proline uptake at different stages of gestation might be related to fetal growth in mares.

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