Survey of the Occurrence of Equine Deep Digital Flexor Tendon Contraction (Clubfoot) in the Main Thoroughbred Breeding Area in Japan

At 114 ranches in the Hidaka District of Hokkaido, a total of 1,118 Thoroughbred foals that were born from January to June 2003 were examined at different times from May to September of the same year to ascertain the occurrence of clubfoot. Clubfoot was seen in a total of 179 foals (16%) at 89 ranches (78%). Also, 124 of the 179 foals (69.3%) had clubfoot of grade II or higher, and it was found that grade I was likely to be overlooked or rapidly advance. In the present study, the occurrence of clubfoot was higher than expected in the investigated region. Hence, it is necessary to establish accurate diagnostic techniques and clubfoot guidelines to minimize the impact.     

Effects of Bedding Material on the Lying Behavior in Stabled Horses

The objective of this study was to investigate the effect of straw, sawdust, coconut husk (husk), and coconut fiber (fiber) on the welfare of stable horses by observing their resting behavior. Twenty horses with ages ranging from 3 to 21 years were used at the Equine Research Institute of the Japan Racing Association, Utsunomiya, Japan. Five horses were allocated to each bedding condition. The behavior of each horse was recorded by video camera for 3 days and was continuously sampled from 17:00 to 05:00. The total duration, the number of bouts, and the mean and the maximum duration of bouts in standing rest, sternal lying, and lateral lying were calculated and analysed by the Kruskal-Wallis test and post hoc Steel-Dwass test. There was no difference in the standing rest and the sternal lying among beddings. Significant differences were observed in these values in the lateral lying among the different beddings (P<0.05). The values of the means of the total duration, the number of bouts, and the mean and the maximum duration of bout in the lateral lying were greater when husk was used as the bedding material than when sawdust were used (P<0.05). The results of the observations show that the new bedding materials would be as usable as straw. However, lateral lying was observed less frequently when sawdust were used as bedding; this indicates that use of sawdust as bedding material will decrease the welfare of stabled horses.     

Type VII and XVII Collagen mRNA Expressions in Regenerated Epidermal Laminae in Chronic Equine Laminitis

To confirm ability forming the basement membrane of the regenerated laminar epidermis (rLE) in chronic laminitis, expression of type VII and type XVII collagen mRNAs in the rLE was studied applying sequences of two type of murine collagens. On northern blot analysis, complement DNA (cDNA) probes adjusted from the murine type VII and type XVII collagen could hybridize with the equine mRNAs, and each signal was detected as single-bands at approximately 9.5 kb and 5.6 kb, respectively. Contrasting with the expression level of equine glyceraldehyde-3-phosphate dehydrogenease mRNA, the band of type VII collagen mRNA in laminitis was stronger than normal, but the type XVII collagen mRNA in laminitis was less than normal. By in situ hybridization, positive signals in response to the murine type VII and type XVII collagen mRNA probes could be detected in the equine laminitic rLE region. From these results, it is concluded that the keratinocytes constructing the rLE in chronic stage of laminitis can express type VII and type XVII collagen mRNAs and these expression patterns were different from the normal.     

Pathological Findings in a Case of Equine T-Cell Lymphoma Associated with Ataxia

A 15-year-old Dutch Warmblood gelding suddenly developed incoordination and hindlimb stumbling. The horse had a history of eyelid lymphoma. Necropsy revealed yellow-white or dark reddish-brown masses adhering to the outer surface of the spinal dura mater from the first cervical vertebra to the seventh thoracic vertebra. The spinal cord close to the first cervical vertebra and the seventh thoracic vertebra was markedly compressed by the masses filling the epidural space. The masses were also observed in the larynx, eyelids, and adipose-rich tissues, including the joints and orbits. They appeared similar in shape. The mandibular, retropharyngeal, axillary, superficial inguinal, deep inguinal, and lateral iliac lymph nodes were solid and enlarged. Histologically, the masses were composed of small or medium-sized lymphocyte-like tumor cells, but atypical cells and mitotic figures were rare. There were moderate infiltrations of macrophages and multinucleated giant cells, which were occasionally ingesting the surrounding tumor cells. Immunohistochemically, the tumor cells were classified as T-cell-derived cells. Throughout the spinal cord, enlargement or loss of nerve axons, dilation of periaxonal spaces, and macrophage infiltration into periaxonal spaces were observed, mainly in the ventral funiculus. Spinal cord compression by the tumor mass was suggested as a cause of the locomotive dysfunction. This is the first report of equine lymphoma with ataxia located from the proximal cervical to middle thoracic dura mater and in joint cavities.     

Active expression of matrix metalloproteinase-13 mRNA in the granulation tissue of equine superficial digital flexor tendinitis

The DNA microarray analysis for matrix metalloproteinase (MMP)-related mRNA expression in equine superficial digital flexor tendinitis indicated that mRNA level of MMP-13 was apparently up-regulated in the tendinitis as compared to normal tendon. In situ hybridization also revealed that fibroblastic cells proliferated in the granulation tissue generated in the tendinitis actively expressed MMP-13 mRNA. On the other hand, in normal tendon, a few fibroblastic cells and vascular components lied in the endotenon barely expressed its mRNA, but other cellular components in the tendon bundle were not positively hybridized. As mentioned above, MMP-13 but not other collagenases or gelatinases, may play an important role in tendon injuries in the racehorses.     

A gross and histopathological study of an ectopic white line development in equine laminitis

In horses with chronic laminitis, an abnormal horny structure called lamellar wedge, is generated between the hoof wall and the laminar epidermis. To be able to manage horses with chronic laminitis correctly, more information about the pathological state of this abnormal horn is required. The aim of this study was to collect and analyze objective morphological data about the abnormal horn in order to understand its morphology and development. In the study, the abnormal horn was grossly visible on the sagittal hoof section from approximately 20 days after the onset of disease. In the histological observations, the structural characteristics of this abnormal horn were similar to the white line tissue, suggesting it is an ectopic white line. Mean value of the cross-sectional area of the abnormal horn against the distal phalanx section area (A/D) was 0.29 cm(2) SD +/- 0.14 and it finally showed an eight-fold increase over the mean value of normal white line section area against the distal phalanx section area. In conclusion, a large amount of the ectopic white line is thought to be finally able to inhibit normal hoof wall growth, so that it should be resected at the optimum time when would be after one month from the onset of the disease.