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

最近，奶牛中各种蹄病的发病率有所增加，这对日本的奶牛场造成了重大的经济损失。从以往的报道来看，慢性或亚临床的板层炎已被认为是该问题的重要诱发因素，瘤胃产生的内毒素可能被认为是板层炎的病因之一。在这个研究项目中，我们最初从屠宰场获得了奶牛的手指，这些奶牛被认为是在典型的日本奶牛场饲养的，并调查了慢性或亚临床板膜炎的存在。结果，52.9%的手指在组织学上表现为亚临床板炎，29%为慢性板炎。足趾动脉造影显示敏感椎间动脉延伸或狭窄，提示慢性循环障碍是足趾各种疾病的重要因素。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。根据分娩后饲粮精料的增加，瘤胃ET明显升高，血液ET在分娩后的前两周呈间歇性升高。然而，每个ET水平并不一定是一致的。通过瘤胃瘘管给予浓缩淀粉的山羊，瘤胃和血液ET水平变化相似，且两者之间具有更好的符合性。这些结果可能表明，高精料饲喂增加的ET通过消化道吸收，在慢性或亚临床足板炎的病因学中起重要作用，从而导致角质量差和足底溃疡等蹄部疾病。

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.