CHAPTER I: LITERATURE REVIEW - Repository.lib.ncsu.edu

Several surveys have been performed to evaluate the prevalence of leg problems indifferent regions, especially in Europe. A recent study of over 50% of UK broiler productionindicated that 28% of chickens suffered locomotion problems and 3% were almost unable towalk (Knowles et al., 2008). Previous European surveys of walking impairment resulted in arange from 26 to 30% (Kestin et al., 1992; Sanotra et al., 2001). Estimation of the total culledbirds due to lameness was 2.6% relative to the total UK annual broiler production that wasabout 750 million birds (Pattison, 1992; Yogaratnam, 1995). The high prevalence of legproblems motivated the European Commission to declare leg problems a serious welfareissue in broiler production in 1992 (Jensen, 2000). In contrast, there have been nationwidesurveys that determine prevalence of leg problems in the United States. The main concernhas been the economic losses due to leg abnormalities. Lame broilers have poor growthperformance (Kestin et al., 1999; Kestin et al., 2001) and are likely to be downgraded atslaughter. The most recent large scale survey of leg health in broilers in the U.S. indicatedthat leg problems accounted for 1.1% of mortality and 2.1% of carcass condemnations anddowngrades annually (Morris, 1993). The annual cost of leg problems to the U.S. poultryindustry has been estimated to be $80 to $120 million for broilers, and $32 to $40 million forturkeys (Sullivan, 1994). These findings confirm the worldwide importance of doing researchto reduce leg health issues, and suggest that there is a higher awareness of leg problems inEurope compared with the USA.Therefore, adequate internal structure of bones, morphological and biomechanicalproperties of legs should be in optimal conditions to enable locomotion and amelioratewelfare issues that also can cause reductions in growth performance.SKELETAL DISORDERS OF BROILERSLeg abnormalities can be categorized as infectious and non-infectious (Oviedo-Rondón etal., 2006). The non-infectious type is the most relevant disorder in terms of economic3