A new study into mortality in laying hens suggests that free range birds need not be at any greater risk than hens in cage systems.
The study, which contradicts some long held beliefs about hen welfare, concluded that the chance of a mortality outbreak did not differ between hens kept in battery cages and those housed in alternative systems like barn or free range. Dr Raf Freire, who carried out the work, took a new approach to comparing the impact of different egg production systems, and he said he believed that the method he had used had produced more objective results.
“We adopted a different way of looking at this controversial animal welfare area,” he said. “We have taken the raw numbers from the studies in peer reviewed journals and quantitatively compared the two systems of keeping egg-laying hens.
This quantitative approach reduces or removes the chance of bias or value judgements when interpreting findings, and provides a truly objective appraisal of the effect of cages on laying hen welfare,” said Dr Freire, who works at Charles Sturt University in Australia.
His findings certainly seem to be at odds with conventional thinking. Mortality has normally been thought to be higher in alternative egg production systems.
Professor Christine Nicol, who has conducted many research projects on laying hens in her role at the veterinary school at the University of Bristol, said that Dr Freire’s work was very interesting. “It’s a useful exercise and should provoke some debate,” said Professor Nicol, who published results of research into hen mortality in 2010. Her study found that mortality was lowest in enriched }}
cages, next best were conventional cages and free range systems, which produced similar results, with the worst mortality rates being produced by barn systems.
“We all know that good free range systems can have low mortality; we just know that it’s extremely variable, but we are getting more data all the time,” she said. “Raf has taken an interesting approach.”
In a recent article for the journal Veterinary Record, David Burch of Octagon Services in Berkshire pointed to the results of another piece of research at the University of Bristol, which indicated that both hen mortality and variability were significantly lower in caged systems when compared with barn, organic or free range. The researchers used records of dead-on-arrival birds collected by the Meat Hygiene Services at five slaughterhouses in 2009, derived from nearly 1,500 flocks. The study found that mortality over a 52-week laying period was 5.39 per cent in cage hens, compared with 9.52 per cent in free range, 8.68 per cent in organic and 8.55 per cent in barn.
“This should not be of any great surprise,” he said in the article, “because the reasons hens were moved into cages were, first, to facilitate intensification of production, but also to remove the hens from direct faecal-oral contact. Chicken-sick land could be infected with a variety of bacteria, such as salmonella, clostridium and brachyspira species, protozoa such as eimeria species and helminth eggs. Free range hens have a propensity to drink from potentially contaminated puddles, aiding the transmission of infections.”
He said that in a recent survey in Great Britain, free range flocks developed brachyspira species infections as early as 22 weeks of age, whilst cage flocks became infected with brachyspira species much later, at 36 weeks of age. Free range flocks were also statistically significantly associated with poor performance (less than 285 eggs/hen housed) in comparison with cage flocks, he said.
David Burch said that not all free range flocks were bad. “All systems, if they are well managed and remain disease free, can have low mortality. However, those systems that have outdoor access have additional management difficulties, such as the weather, predators, lack of biosecurity and direct contact with faecal material, which makes the responsibilities of management even greater and more necessary if they truly want to be considered more welfare friendly.”
In the new Australian study, Dr Freire collected information from previous studies about the effect of conventional battery cages on a hen’s behaviour, physical condition, physiology and }}
production. He used a quantitative analysis to compare them with studies on egg-laying hens in alternative systems such as furnished cages, barns and free range. The studies he analysed were published between 1974 and 2011.
“What was most interesting in our study was that the chance of a mortality outbreak may be no greater in alternative systems than in battery cages,” he said. “The long held belief that hen mortality is higher in alternative systems indicates the magnitude of the problem once an outbreak occurs. This means that if we learn to manage alternative egg production systems better, we can potentially avoid unnecessary mortalities.”
The analysis resulted in a series of other conclusions. Dr Freire found that egg production was higher in conventional cages; that bones were stronger in hens kept in alternative systems; that birds showed more comfort behaviour such as wing flapping, body shaping, stretching, and possibly dust-bathing in alternative systems than had been previously reported; and, surprisingly, that feather and aggressive pecking did not differ between the different systems.
The research, which was conducted by Dr Freire and Dr Ann Cowling, a statistician from CSU, was funded by RSPCA Australia.
