A new UK study concludes that the huge increase in growth rates of broiler chickens means that more than a quarter of these intensively-reared birds have difficulty walking, raising serious animal welfare and consumer acceptance issues.
According to the study, which was funded by DEFRA and published in the journal PLoS ONE today, consumers currently know little about how broiler chickens are reared but they can be shocked when presented with information about current commercial practices.
The study warns: "Since the sustainability of intensive broiler production depends on continued consumer acceptance of the farming practices involved, the broiler industry will need to work with the scientific community to develop more robust and healthier genotypes and to ensure that optimal husbandry and management practices are fully implemented."
Animal welfare groups such as the RSPCA or Compassion in World Farming are already advising customers and the public about the negative aspects of the broiler industry.
Broiler chickens are reared for their meat and used in a range of processed meat products.
Doctor Toby Knowles of Bristol University's Division of Food Animal Science, who carried out the research with colleagues, said that worldwide approximately 20 billion broilers are reared within husbandry systems that are "biased towards economics of production and detrimental to poultry welfare".
The study states that due to their short reproductive cycle and their popularity as food, poultry represent the most highly selected livestock. Selection of broilers has been primarily directed at economic traits which have reduced costs of production.
Throughout the world the majority of broilers are reared using modern, intensive systems of production where birds are confined for their lifetime within high density housing and reared from hatch to slaughter weight within about 40 days.
"However, 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, with poor walking ability, or locomotion, a primary concern," wrote the authors.
The researchers studied broiler flocks belonging to five major UK producers who together account for over 50 per cent of UK production. They assessed the walking ability of 51,000 chickens within 176 flocks, and obtained information on about 150 different management factors associated with each flock.
At an average age of 40 days, over 27.6 per cent of birds showed poor locomotion and 3.3 per cent were almost unable to walk.
Dr Knowles said that broiler chickens have been subject to intense genetic selection and "in the past 50 years broiler growth rates have increased by over 300 per cent from 25g per day to 100g per day…..Our research shows that the primary risk factors associated with impaired locomotion and poor leg health are those specifically associated with rate of growth."
Other factors include age of the bird, bird genotype, feed, antibiotic regime, and length of dark period during the day.
The study called for an informed debate of current practices, for a balance to be drawn "between profitability and our moral obligation to maintain good standards of animal welfare"
Journal: PLoS ONE 3(2): e1545
Title: Leg Disorders in Broiler Chickens: Prevalence, Risk Factors and Prevention
Authors: Toby Knowles, Steve Kestin, Susan Haslam, Steven Brown, Laura Green, Andrew Butterworth, Stuart Pope, Dirk Pfeiffer, Christine Nicol