An excellent paper in Veterinary Record by Weeks and others (2012) reviewed the levels of hen mortality over the laying period by different systems of housing, writes David Burch, BVetMed, FRCVS, in a 'Viewpoint', published in the same journal. He continues that they showed that the highest hen mortality was found in free-range and organic flocks, closely followed by barns; almost double that of caged flocks. Have we really got our assessment of what is good welfare right?

The mortality of hens in cages over usually a 52-week laying period was 5.39 per cent and the mortality in free-range hens was 9.52 per cent, 77 per cent higher. The variability in flock mortality or standard deviation (sd) was also higher, with cages at 3.05 per cent and free range at 7.41 per cent, a 143 per cent increase.

This should not be of any great surprise, 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, continues Mr Burch, aiding the transmission of infections.

In a recent survey in Great Britain (Burch and others 2009), free-range flocks developed Brachyspira species infections, the cause of avian intestinal spirochaetosis, as early as 22 weeks of age, soon after point of lay at 20 weeks of age. Caged 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 per hen housed) in comparison with caged flocks.

Interestingly, organic free-range flocks had a slightly lower mortality and sd variation in comparison with free-range flocks; this might reflect a smaller flock size or hopefully better range management and lower stocking density. Surprisingly, barns showed quite a high mortality in comparison with cages (59 per cent) but had the largest variation in mortality of all. Some countries, for example, the Netherlands, have adopted this form of production as a major replacement for caged production?

Since the ban on traditional cages in the EU from January 2012, there has been a change over to the more enriched cages or furnished colony cages, housing groups of approximately 60 hens and containing perches, laying areas and dusting/scratching areas. In Weeks and others (2012), only 16 of 375 cage systems were using the new system and were not separately reported.

Comments from colleagues in the field (Peter Cargill, Richard Turner, Claire Knott; personal communications) have described the mortality as being similar to the old cage system but with greater variation. Although the flocks have been described as calmer, there can be outbreaks of cannibalism. Infections, such as Mycoplasma species and secondary Escherichia coli, appear to spread through the colony more quickly and severely if outbreaks occur. Otherwise, the system is working well and the birds have good feather cover, good body condition and better health, which may help with reducing transport mortality, as shown by Weeks and others (2012).

Not all free-range flocks are bad, concludes Mr Burch. 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'.

Reference

Burch, D.G.S., 2012. Laying hen mortality by system – a welfare guide? Veterinary Record, 171:649-650. doi:10.1136/vr.e8582

Further Reading You can view the full paper by clicking here.

March 2013