Causes, risk factors, and prevention of laminitis and related claw lesions.

Introduction Laminitis is an inflammation of the laminar corium of the hoof wall. In general, the term laminitis is used to describe a systemic disease affecting not only the hooves, but also the general condition of the animal. Researchers believe the inflammation is primarily associated with a dysfunction of the digital vasculatory system that results in hypoxia and malnutrition of the sensitive laminar structure in the hoof wall. The etiology of the circulatory disturbance is not fully understood and there are some possible explanations often related to nutrition, which I will discuss further. Due to mechanical stretching of the attachment between the inner and outer laminar structures of the hoof wall, which has been affected by the inflammation (i.e. laminitis), the claw bone can rotate and or sink inside the hoof. Depending on the severity of the laminitis, the mobility of the claw bone inside the capsule and the counter pressure on the sole from hard floors, the sole corium can be contused and secondary lesions of the sole area can develop (Ossent & Lisher 1998). The pathological alterations inside the rigid hoof capsule cause considerable pain and, therefore, results in lameness, which is an animal welfare issue. A United Kingdom survey (Clarkson et al. 1996) revealed a yearly lameness incidence of 55%, of which sole ulcers (40%) and white line lesions (29%) were the most prevalent lesions (Murray et al. 1996). Such laminitis-related lesions have a greater economic effect than infectious diseases, for example, (Esslemont & Spincer 1993), due to severe influence on reproduction and consequently a higher risk for culling (Sprecher et al. 1997). Other common lesions associated with laminitis are: hemorrhages, fissures and abscesses of the white line, sole hemorrhages and double soles, toe ulcers and toe necrosis, and under-running of the heels. Thus, laminitis has a great economic impact on dairy operations, and all over the world dairy producers are moving towards housing cows in intensive, confined conditions. As we understand the causes of laminitis and identify the risk factors better, it is possible to prevent and reduce the effects of the laminitis syndrome.