Free-range chickens prone to disease

Chickens kept in litter-based housing systems, including free-range chickens, are more prone to disease than chickens kept in cages, according to a study published in BioMed Central's open access journal Acta Veterinaria Scandinavica.

Researchers led by Oddvar Fossum, at the National Veterinary Institute in Sweden, noted that during the switch in housing from battery cages to enriched cages and litter-based systems, including free-range, there was an increase in the number of chickens dying. During the study, the authors compared the causes of deaths in flocks of chickens kept in different types of housing across Sweden.

Scientist Live discussed Dr. Fossum's findings with him.

What prompted this study?

The study was started after noticing a marked increase in submissions for necropsies of laying hens to the National Veterinary Institute in Sweden.

This happened during the years 2001 to 2004 when most of the conventional battery cages were phased out and exchanged with alternative systems. This change of housing systems was a result of
Swedish Animal Welfare Act from 1988 which required that laying hens should have possibilities "to behave naturally". In practice this meant that they should have access to nests, perches and dust baths.

Why is the frequency of disease greater among free-range/litter based chickens than caged counterparts? 

Birds housed in litter-based systems including free range are more exposed to certain infections especially those caused by bacteria and parasites which can be transmitted via the litter. Caged birds are much less exposed as most of the droppings disappear through the netting floor. The risk of exposure to ammonia and dust is usually also higher in litter-based systems which may predispose for respiratory infections and negatively affect the immune defense. The risk of vent pecking and cannibalism is usually also higher in the litter-based systems because the size of the flocks are much bigger than in the cages. If the flock size is 10-15 birds which is common in the Swedish cages today the birds will have a fair chance to establish well functional social groups. Aside from leading to acute deaths (cannibalism), pecking may also lead to infected wounds which often develops to septicaemia (blood-poisoning).

What other types of housing were included in this study? How did they perform? 

In our study we compared cages (conventional battery cages and furnished cages) to litter-based systems with hens kept indoors and litter-based systems in which the birds had access to outdoor areas (free range or organic production). The problems were fewer in cage sytems.

Which housing system proved the most effective in maintaining healthy chickens? Why? 

During 2001-2004 we got significantly fewer submissions of hens for necropsy from farms with cages. These systems are more easy to run and the birds are less exposed to several important infections. Furthermore, many of the experienced farmers who previously had conventional cages
chose the new furnished cages.

What can be done to decrease the likelihood of disease among free-range chickens? 

Education of farmers is very important. The farmers should have knowledge about hygiene, biosecurity and different forms of specific measures to prevent infections. It is also important to give to birds possibilities to function well both socially and physically.

Do you expect an decrease in disease and mortality among free-range chickens once farmers grow more accustomed to this style of farming? If so, would that decrease ever equal the current numbers for the most efficient method (caged?)? 

We can already see indications that the farmers with laying hens in litter-based systems are getting much better to manage them as the number of submissions for necropsy from such farms are continuously decreasing. Generally, the risk of certain infectious diseases and pecking is higher in this kind of housing, but on the other hand the birds have more space and better possibilities to express a natural behavior.

Finally, what are you planning on studying next? 

We are considering to follow up with an analysis of the time after 2004, but we have not decided yet.


  (Reporting by Marc Landas)


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