As the debate over housing for layers and egg safety continues, the Poultry Science Association (PSA) has put its weight behind those calling for the need for further research.

This comes as international pressure grows on the egg industry to shift from conventional cages to non-cage housing systems for layers.

The European Union (EU) voted for a ban on traditional cage systems back in 1999 and the industry there is scheduled to have completed the transition to non-cage housing by the start of 2012.

But the PSA, a global scientific society that is dedicated to the discovery and dissemination of knowledge generated by poultry research, says: “It is important to recognise that there is currently no scientific basis for believing that such a move would improve either egg safety, or quality.

“In fact, given the conflicting nature of the findings of a number of recent studies in the US and EU, such a move could conceivably have the opposite effect.”

The association’s view is based on a new paper called “The Impact of Different Housing Systems on Egg Safety and Quality”, that is due to be published in “Poultry Science” early in 2011.

The authors of this document, who include Dr Pete Holt at USDA’s Egg safety and Quality Research Unit, and several other researchers and scientists from government poultry research bodies and university departments in Europe and America, believe that any move from conventional cages could affect the safety and quality of eggs laid by hens raised in the new environment.

The paper provides a summary of the current knowledge of how different hen housing systems may influence egg production and how this could affect the safety of egg products flowing into the human food chain and points out that “a paucity of information is available in the United States as in the EU with regard to alternative hen housing systems and the safety and quality of eggs produced on farms using such systems”.

The authors feel that a far greater understanding of the effects of these systems is desirable before any large-scale transfer is undertaken.

Agreeing with the authors of the paper, PSA president Dr Michael S Lilburn says: “Housing is an emotional issue and the question of which is preferable – conventional vs non-cage – clearly hinges on a wide variety of important issues. But given that the very reason for the existence of layer housing systems is the production of safe and high quality eggs for human consumption, it is the PSA’s view that any decisions involving changes that might impact on these parameters of egg production should be objective and science-based.

“Unfortunately, there is currently no consensus in the scientific community as to which side the weight of evidence favours, so further work needs to be done before there is any move to follow the EU’s ban on conventional cages here in the US.”

Safety issues  

The overriding microbiological concern regarding the safety of eggs meant for human consumption is, according to the authors of the paper, the potential for possible human infection by Salmonella, which could cause severe gastrointestinal distress, or even death in some cases.

While thorough heating through cooking can destroy the bacterium, they maintain that good protocol calls for the industry to take steps to minimize the presence of risk through the egg-to-table production process. However, they point out that, unfortunately, data on the prevalence of Salmonella in either cage or non-cage housing systems is often contradictory.

For example, the white paper reveals that a number of recent studies conducted in the EU revealed a higher incidence rate in traditional housing systems. But one study showed a higher incidence in free-range systems, while another one showed no difference.

Meanwhile, a study in California showed a much higher incidence rate of Salmonella enteritidis (SE)-contaminated eggs among free-range birds than birds raised in traditional cage systems. And, a nation-wide survey by USDA showed that pullets (pre-lay hens) that were raised on the floor of a housing facility had a five-fold higher incidence rate of SE than cage-raised pullets.


The authors’ conclusion, therefore, is that “many factors (including flock size, stress and bio-security issues) which could affect the prevalence of SE with a flock need to be assessed before the superiority of one housing system over another one can be determined.

They also note that while many similarities exist between EU and US egg production systems, there are also significant differences and they state: “Care must, therefore, be exercised when applying results from one system to another.”

Chemical contamination and contamination by pesticides are also possible egg safety factors that could be impacted by the choice of housing systems.

The paper cites multiple studies conducted in the EU showing, for example, that free-range eggs have a higher incidence of PCBs (polychlorinated biphenyls, or dioxins) and heavy metals than conventional cage hens.

It also provides details of a study in Brazil that showed an incidence rate of the now-banned DDT in free-range eggs that was 1,000 times that of caged hens, even though DDT had not been used in the location of the free-range site in the previous nine years.

The paper’s authors say this also serves as a warning for producers, pointing to the environmental persistence of some chemicals and the need for great care to be taken when considering land for free-range housing.

Generally, they feel that the various housing systems for layers all exhibited different strengths and weaknesses under differing seasonal and climatic situations with regard to Salmonella contamination.

“As a consequence, sampling regimens need to be developed to ensure equal representation of all housing types under different seasonal situations,” that say.

Quality issues  

On the subject of quality, the authors point out that current evidence showing that the quality of eggs produced under different housing systems might vary is also conflicting.

Egg quality is usually measured along a number of parameters, including size, functional and nutritional quality and the integrity of an egg’s shell, yolk and albumen.

According to the comprehensive paper, one study showed fewer cracked eggs in free-range than conventional housing, while a separate one yielded precisely the opposite conclusion. A third concluded that free-range eggs had higher levels of Vitamin E and omega-3 fatty acids than conventional eggs, while yet another said that there were no differences between conventional cages, free-range or floor-raised eggs.

Even studies originating from the same laboratory yielded contradictory results when investigating internal quality issue.

As lead author Dr Holt explained at a recent presentation on the authors’ findings: “Many factors besides housing type can affect the safety and quality of eggs. As a result, the effect of housing type on egg safety and quality is not clear cut. They all need to be taken into account before hard conclusions can be made (regarding the efficacy of different housing systems vis-à-vis egg safety and quality).”

The paper concludes with this message for Americans: “Ultimate US housing decisions need to be based on sound scientific data and this information currently does not exist. It is incumbent upon the US egg industry, allied industries and government regulatory agencies to provide the means necessary to ensure the expeditious performance of the needed studies.”