Abstract
Broiler (meat) chickens have been subjected to intense genetic selection. In the past 50 years, broiler growth rates have increased by over 300% (from 25 g per day to 100 g per day). There is growing societal concern that many broiler chickens have impaired locomotion or are even unable to walk. Here we present the results of a comprehensive survey of commercial flocks which quantifies the risk factors for poor locomotion in broiler chickens. We assessed the walking ability of 51,000 birds, representing 4.8 million birds within 176 flocks. We also obtained information on approximately 150 different management factors associated with each flock. At a mean age of 40 days, over 27.6% of birds in our study showed poor locomotion and 3.3% were almost unable to walk. The high prevalence of poor locomotion occurred despite culling policies designed to remove severely lame birds from flocks. We show that the primary risk factors associated with impaired locomotion and poor leg health are those specifically associated with rate of growth. Factors significantly associated with high gait score included the age of the bird (older birds), visit (second visit to same flock), bird genotype, not feeding whole wheat, a shorter dark period during the day, higher stocking density at the time of assessment, no use of antibiotic, and the use of intact feed pellets. The welfare implications are profound. Worldwide approximately 2×1010 broilers are reared within similar husbandry systems. We identify a range of management factors that could be altered to reduce leg health problems, but implementation of these changes would be likely to reduce growth rate and production. A debate on the sustainability of current practice in the production of this important food source is required.
Highlights
Due to their short reproductive cycle and their worldwide popularity as a food, poultry represent the most highly selected livestock
Despite a large body of work investigating the effects of specific risk factors [reviewed in 16], there has been little previous work to examine how these practices interact on real commercial farms to determine the overall level of leg disorders in particular flocks
For comparison with previous surveys we draw attention to the prevalence of birds in our survey that had gait scores of 3 or above. This cut-off point is important because there is evidence from studies of the effects of analgesic drugs that birds in these categories can be in pain [19,20,21,22], Other surveys have reported between 14.1% and 30.1% of birds with gait scores of 3 or above in different European countries, it is not always clear whether weighted or unweighted estimates have been used [7,23,24]
Summary
Due to their short reproductive cycle and their worldwide popularity as a food, poultry represent the most highly selected livestock. Selection of broiler chickens (chickens grown for their meat) has been primarily directed at economic traits which have reduced costs of production [1,2,3]. There is evidence that in optimising traits for production the resulting birds, whilst producing meat at a low cost, have a reduced viability and reduced welfare [5,6,7], with poor walking ability, or locomotion, a primary concern. Previous research has highlighted associations between management practices and levels of leg disorders. Despite a large body of work investigating the effects of specific risk factors [reviewed in 16], there has been little previous work to examine how these practices interact on real commercial farms to determine the overall level of leg disorders in particular flocks.
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