Lately, animal activists are claiming that conventional cages are creating health risks from increased incidence of Salmonella. Like their welfare claims, this is unfounded and illogical. Consider the following:
1) The claims that caged layers increases Salmonella is not even logical. The Food & Drug Administration has issued a regulation entitled Prevention of Salmonella Enteritidis in Shell Eggs During Production, Storage, and Transportation (21 CFR part 118) on July 9, 2009 requiring shell egg farmers to implement measures to prevent SE from contaminating eggs on the farm. If caged environments increased Salmonella, it's inconceivable that FDA would issue regulations governing the production of eggs in caged environments.
2) The Coalition for Sustainable Egg Supply finished their two-year study of the available research including food safety. The conclusions from their analysis of the research is that eggs produced in caged environments had less fecal contamination compared to cage-free eggs. This is logical since cages allow for the eggs to be removed from the environment of the hen compared to cage-free where the eggs come into contact with manure. Any reasoning person would conclude that keeping eggs clean and away from manure is better from a food safety perspective. Caged eggs allow for cleaner eggs.
3) The Journal Poultry Science in 2011 [90, pp. 1586-1593] published "Comparison of shell bacteria from unwashed and washed table eggs harvested from caged laying hens and cage-free floor-housed laying hens." This study found that the numbers of bacteria on eggs was lower in housing systems that separated hens from manure and shavings.
4) The Journal Food Control published a study June 17, 2014 entitled "Microbiological Contamination of Shell Eggs Produced in Conventional and Free-Range Housing Systems" The conclusions state "Battery caged hens are standing on wire slats that allow feces to fall to a manure collection system beneath the hens. Conversely, free-range hens laid their eggs in nest boxes on shavings and the eggs remained in contact with hens, shavings and fecal material until they are collected. The longer contact time with free-range hens, shavings and feces would explain the higher enterobacteriaceae counts (pathogenic bacteria) on free-range eggs as compared to battery caged eggs."
5) As to the welfare of caged hens compared to cage-free, any reasoning person can see just watching that hens peck each other to establish the pecking order. In a caged environment, the number of hens are minimized compared to the hundreds on the floor where the lower hen on the pecking order is pecked more often. That would help explain what mortality among cage-free hens at the University of Bristol (UK) showed 19.1% compared to 3% for caged layers. In the U.S. the comparison is even greater with cage-free at 28% compared to 9% for caged layers (North Carolina State University). Furthermore, the immune response (measured from hematological and immunological indices at NC State) showed free-range chickens with poorer immune response thus leaving the chicken more vulnerable to disease. Logically then, caged layers have lower stress when noting the mortality and immune response investigations.