Predisposing factors of sheep lameness

Abstract

Lameness is a major health problem in sheep flocks worldwide. It is associated with reduced productivity and welfare of lame animals within a flock. The consequences of lameness on production have been studied in meat and wool producing breeds, but the available research studies are limited. In dairy breeds of sheep the problem has not been investigated. Lameness can be the result of many causes, but it is mostly associated with foot lesions. With the exception of systemic diseases, a number of predisposing factors seem to dictate the epidemiology of lameness. Here, these factors are grouped in two major categories: a) genetic factors that are attributed to individual animals and b) environmental factors that affect the prevalence of lameness within the flock. In this review, different approaches to counteract those factors are presented. In principle, appropriate genetic selection, together with the implementation of preventive measures, could reduce the negative consequences of those factors. Nutrition is a fundamental factor associated with the health of the foot and the animal in general. Hence, the formulation of a balanced rationis crucial, because deficiencies in specific nutrients, involved in the keratinization of hoof wall, could predispose to lameness. The latter could be also associated with inappropriate housing conditions (e.g. bedding, ventilation). In particular, moisture has been identified as an important predisposing factor for foot lesions. Flock management (e.g. foot trimming, foot bathing), particularly in intensively reared sheep, can also affect the prevalence of lameness. Moreover, the implementation of biosecurity measures at farm level could eliminate the possibility of infectious footrot from purchased animals. In conclusion, the implementation of any preventive measures against the predisposing factors of lameness implies that the farmer is aware of the importance and the consequences of lameness in his flock. The role of the veterinarian is also important. The veterinarian should not focus only on the diagnosis and the treatment of lame animals, but should also try to educate the farmer on the epizootiology of the problem.

Aetiology, Risk Factors, Diagnosis and Control of Foot-Related Lameness in Dairy Sheep

“…Lameness is the deviation from normal gait, accompanied or not by pain and distress. It is a sign rather than a disease itself, usually caused by injuries, lesions, defects, and diseases affecting the limbs, the joints, or other parts of the body [3,21,22,23]. Several etiological factors are associated with lameness in sheep.…”

“…Laminitis due to ruminal acidosis is uncommon in meat and wool sheep. Its occurrence in dairy sheep has not been investigated thoroughly; however, it is likely to be higher due to the increased consumption of concentrates and the commonly disrupted roughages to concentrates ratio in high producing flocks [23,47].…”

“…Accumulatiοn of grass, mud, and manure in feet may cause the impaction of interdigital space (soil balling) or the occlusion of the interdigital gland, leading to foot-related lameness [12,23,48]. Other less common causes of lameness include injuries and foreign bodies, ergotism (due to the toxins ergotoxine, ergotamine, ergometrine, ergocornine, ergocristine, and ergosine produced by the ergot fungus Claviceps purpurea) [49], fescue toxicosis with gangrenous necrosis and sloughing of the hoof (caused by ergovaline and lolitrem B toxins found in endophyte-infected tall fescue and perennial ryegrass, respectively) [50,51], dermatophilosis or strawberry footrot caused by Dermatophilus congolensis [52], and post-dipping lameness in adult sheep caused by Erysipelothrix rhusiopathiae [53].…”

“…Differences among these breeds in production systems, feeding regimes, available infrastructures, husbandry practices, hygiene measures, and flock health management schemes may offer an explanation. Irrespective of the etiology of foot-related lameness, the risk factors associated with its occurrence can be either genetic or environmental and interact between them [23].…”

“…For molecular screening, the use of extensively polymorphic genetic markers has been suggested [57]. These markers have been identified on the chromosome 20 at the DQA2 and DQA2-like loci in the ovine Major Histocompatibility Complex (MHC-ovar) genes, which have been found to be associated with various degree of susceptibility/resistance to footrot [19,23,58] via modulation of the cellular immune response against D. nodosus [57,59,60]. It is well known in most vertebrates that the loci of MHC genes are the most polymorphic of any chromosomal region.…”