In barn and free-range egg production systems, hens have access to a nest in which to lay their eggs. This is a key behavioural need for layer hens. In egg production systems where hens are housed in battery cages, the hens do not have access to a nest and instead have to lay their eggs on the sloped wire mesh floor.
In the majority of commercial egg production systems (cage, barn and free range), eggs are collected automatically and transported along a conveyer belt to a packing shed. Following collection, eggs are washed, checked for cracks, and packed according to size. These ‘whole eggs’ are what you buy at the supermarket. Cracked eggs and eggs that are otherwise rejected usually end up in manufactured egg products including liquid egg, or sauces, cakes, etc.
Eggs have natural defences to protect microorganisms from entering which include the shell and inner membranes. Even the white of the egg presents a hostile environment for microorganisms. However, the tiny pores in the shell may allow some microorganisms to get through. Appropriate on-farm cleaning and disinfection procedures reduce the chance of Salmonella being introduced into the birds’ environment. A report produced by FSANZ (2009) found that Salmonella is the most common cause of food poisoning related to eggs. An egg can be contaminated by Salmonella as it is laid (the source of contamination is either the bird’s vent or the surface upon which the egg is laid) or the egg becomes contaminated as it is being formed inside the bird. Fortunately, this latter method of contamination is by types of Salmonella that are not present in Australia.
The FSANZ report mentions no risk factors pertaining to the type of production systems used – i.e. no difference in risk between cage, barn or free-range systems – rather, the risks relate to consumption of contaminated eggs that are either raw or undercooked, or dirty eggs cross-contaminating other foods or surfaces during food preparation. Overall, the frequency of eggs contaminated with Salmonella is very low in Australia and any food safety risk can be significantly reduced by cooking.