Chronic laminitis as the predisposing factor for other digital diseases in dairy cows

近年来，奶牛各种蹄病的发病率不断上升，给日本的奶牛养殖场造成了巨大的经济损失。根据以往的报道，慢性或亚临床乳房炎是这一问题的重要易感因素，瘤胃产生的内毒素可能是乳房炎的病因之一。在本研究项目中，我们首先从屠宰场获得了被认为是典型日本奶牛场饲养的奶牛的手指，并对慢性或亚临床乳房炎的存在进行了调查。结果：52.9%的指甲组织学表现为亚临床型椎板炎，29%为慢性椎板炎。这些手指的动脉造影还显示了敏感板层的动脉延长或狭窄，这可能表明慢性循环障碍是各种蹄疾病的重要因素。下一步测定产前和产后瘤胃液和外周血中的内毒素(ET)水平。根据产后饲喂精料的增加，产后前两周瘤胃ET显著升高，血液ET呈间歇性升高。然而，每个ET水平并不一定是一致的。通过瘤胃瘘管饲喂浓缩淀粉的山羊，瘤胃和血液中的ET水平也有相似的变化，两者之间有较好的一致性。这些结果可能表明，随着高精料摄入量的增加，ET的增加可能通过消化道被吸收，并在慢性或亚临床板炎的病因中发挥重要作用，这些板炎可能导致角质量差和其他蹄疾病，如足底溃疡。

A recent increase in incidence of various types of hoof disease in dairy cows has caused a significant ecomic damage on the dairy farms in Japan. From previous reports, chronic or subclinical laminitis has been indicated as an important predisposing factor for this problem and endotoxin produced in the rumen may be thought as one of the etiologic factors for laminitis.In this research project, we initially obtained the digits of dairy cows, which were thought to be raised in the typical Japanese dairy farms, from slaughterhouses and the presence of chronic or subclinical laminitis was investigated. As a result, 52.9% of the digits were demonstrated revealed histologically as subclinical laminitis and 29% as chronic laminitis. Arteriography of these digits also revealed the extended or narrowed artery to the sensitive laminae, which may indicate that the chronic circulatory disturbance is the important factor of the various hoof diseases. In the next step, the endotoxin (ET) levels in the ruminal fluid and peripheral blood during the pre- and postparturient period were determined. According to the increase in feeding concentrates after parturition, ruminal ET considerably rised and the blood ET showed episodic increase during the first two weeks after parturition. However, each ET levels did not necessarily coincided. In goats given starch as a concentrate via the rumen fistula, the similar changes in ruminal and blood ET levels were observed and better coincidence could be observed between the two levels. These results might indicate the hypothesis that the increased ET according to the increase in high concentrate feeding is absorbed via the digestive tract and plays an important roll in the etiology of chronic or subclinical laminitis which may result in poor horn quality and other hoof diseases such as sole ulcer.