A Review of the Aetiology and Pathology of Leg Weakness in Broilers in Relation to Welfare

Abstract

Leg disorders in broilers are a major economic and welfare problem. The aetiology of many disorders is complex but includes genetics, growth rate (due to feed restriction or lighting regime), feed conversion efficiency and body conformation, exercise, circadian rhythms, nutrition and stocking density. These categories are not mutually exclusive as one aetiological factor may affect another. Many studies of leg disorders fail to identify the specific pathological condition underlying the observed lameness. However, disorders may be classified according to underlying pathology as infectious, developmental and degenerative. This classification is difficult because these categories are not mutually exclusive. Infectious conditions include bacterial chondronecrosis with osteomyelitis (BCO or femoral head necrosis, FHN), tenosynovitis and arthritis, infectious stunting syndrome (ISS) and viral induced neoplasia. Developmental conditions include varus valgus disease (VVD), rotated tibia, tibial dyschondroplasia (TD), rickets, chondrodystrophy and spondylolisthesis. Degenerative disorders include osteochondrosis (often TD), epiphyseolosis (often classified as FHN), degenerative joint disease (DJD), spontaneous rupture of the gastrocnemius tendon and contact dermatitis. BCO, TD, dermatitis and VVD are the most common disorders. Outbreaks of leg disorders are often site / context specific. The welfare of broilers with leg disorders may be impaired due to pain from the condition, an inability to walk leading to frustration and associated problems of being unable to feed and drink due to immobility (which may result in starvation). In assessing welfare, the individual broiler must be considered irrespective of the frequency of occurrence of the disorder. Most studies of welfare in relation to leg disorders have used a subjective gait scoring method (0 is normal walking and 5 is unable to walk). Gait scoring is a practical method for assessing broiler lameness in the field. The method provides a useful tool to employ in the field without recourse to pathological investigation and, while the method conflates conformity with pathology, it is a helpful and constructive additional method to assist in welfare studies. For birds with scores greater than 3, lameness may be viewed as severe enough to potentially impair welfare. It is difficult to assess all disorders in relation to frequency of occurrence and their impact on welfare due lack of evidence. BCO (or FHN and BCN) is the most common disorder and is often severe in form. TD (incl. epiphyseolysis) and rickets is common, often sub-clinical but when severe is a considerable impact on welfare. Contact dermatitis may be common under certain conditions and causes poor welfare when severe. Gastrocnemius tendon slippage, tenosynovitis, DJD and spondylolisthesis are not so common but are likely to cause poor welfare when they occur (i.e. pain and prevention of certain behaviours). VVD and rotated tibia can be common but tend not to be directly painful unless another condition is pre...

Nutritional geometry of calcium and phosphorus nutrition in broiler chicks. Growth performance, skeletal health and intake arrays

“…Further investigation into the aetiology is required, as infectious and degenerative causes of leg weakness such as bacterial chondronecrosis with osteomyelitis (femoral head necrosis) and/or tibial dyschondroplasia (TD) could be a causative factor. Tibial dyschondroplasia is a common lesion seen in broiler leg bones (Bradshaw et al, 2002). It is characterised by an abnormal cartilage mass in the metaphyseal region below the growth plate (Pompeu et al, 2012).…”

“…It is characterised by an abnormal cartilage mass in the metaphyseal region below the growth plate (Pompeu et al, 2012). The pathogenesis of TD is not well understood, however, nutrition may influence the incidence (Bradshaw et al, 2002). Studies by Kestin et al (1994) and Vestergaard and Sanotra (1999) found that birds with TD had higher lameness scores and defect gaits.…”

The effects of <i>Saccharomyces cerevisiae</i> on the morphological and biomechanical characteristics of the tibiotarsus in broiler chickens

“…Excessive breast muscle accumulation combined with an inadequate skeletal development, gender, genetics, feeding, the composition of food, the incubation period, infectious diseases, environmental stress factors, maintenance and management factors affect the frequency and severity of leg problems (Bradshaw et al, 2002;Oviedo-Rondón et al, 2006a, b).…”

Sequential feeding with variations in energy and protein levels improves gait score in meat-type chickens

“…Many of the non-infectious disorders in poultry such as tibial dyschondroplasia and tarsal varus-valgus angulations result in abnormal gait and even lameness (Bradshaw et al, 2002;Mench, 2004). These disorders induce pain in some cases and impair birds' behavioural repertoire (McGeown et al, 1999; Danbury et al, 2000;Julian, 2004).…”