Today we have more possibilities to choose when purchasing eggs. Several types compete on the market that are differentiated by the form of raising the chickens (in a cage, on the ground, free range or organic). The egg shells are subsequently marked with their corresponding code.
For that reason, it is normal for consumers to wonder if the form of raising chickens influences the quality of the egg, and if some types of eggs have advantages over others. Moreover, with certain frequency, consumers receive contradictory opinions that almost never correspond to the knowledge provided by the abundant scientific research of the last 20 years.
For the vast majority of consumers, as shown in all surveys, the most important factor about the quality of the egg is the safety of consuming it, that is, that the egg is free of health risks due to microbial contamination, especially Salmonella, as well as the presence of waste and chemical contaminants. This aspect is the one we will address here.
Eggs and microbial contamination
In general, the content of the recently laid egg is practically sterile. It is on the surface of the shell where there is a range of microorganisms, mainly bacteria. Most are innocuous, but sometimes microbes can be present that are capable of altering the product or causing infections in humans, which in some cases may reach inside through pores on the shell, or due to crossed contamination in kitchens.
In studies published over 40 years ago, the contamination of cageless chicken eggs was much greater than in chickens kept in cages. However, this data tended to belong to small groups of chickens kept in the rural environment for self-consumption (“coops”).
The studies carried out in practical conditions in several research projects, in parallel with the progressive development of the commercial production of cageless chicken eggs in Europe, have clearly shown that in these eggs, the microbial load on the shell is more variable—10 times greater on average. However, in most cases, it continues to be below the limits considered correct.
These differences are due to different conditions of hygiene and biosafety amongst farmers (sometimes between facilities belonging to the same poultry farmer), and in general, due to the presence of a bed, which implies a greater contact of the cageless chickens with their feces, and greater contamination of the air inside their shelters.
It is more important to clarify whether or not there are theoretical differences in the risk of eggs being more likely to be contaminated with Salmonella in cageless chickens due to the same reasons, compared to chickens that go outside, due to coming into contact with transmitting animals. The intense research carried out in the EU 10-15 years ago showed that in all raising systems, there were flocks of chickens that tested positive for Salmonella. Nevertheless, at that time, the incidence in cageless systems tended to be lower. This was due to their greater size, having more recent buildings, and the early and massive use of effective vaccines, which was also later done by the poultry farmers that worked with laying cages.
However, today this question is no longer relevant. Today in Spain, the proportion of flocks that tested positive for potentially pathogenic Salmonella is below 1%, as required by the EU. These flocks are tested through periodic self-controls that are supervised by the Administration and official controls. In case of infection, all birds are sacrificed, and until that time, their eggs cannot go to direct consumption. These standards are the same for all raising systems. Thanks to them, the number of egg consumers affected by salmonellosis has drastically dropped in recent years in Spain.
To minimize the risks of microbial contamination, the integrity and cleaning of the shell are essential. The comparative studies between raising systems offer quite variable results, as the quality of the shell is much more influenced by the nutrition and handling of birds than by the system of sheltering the chickens in it.
In general, at the farm level, more broken eggs tend to be obtained in cages and dirtier eggs in alternative systems. For the consumer, this does not have any practical importance, as all commercialized eggs must comply with the same strict limits for these defects.
Eggs and chemical contamination
Each year, the results of the European Waste Monitoring Plan are published, obtained from samples representing the commercial production of each country. However, until now for eggs, the system of raising the chickens has not been identified. In Spain, the same conclusions have always been reached: there is a total absence of illegal products and the tiny proportion of non-compliant samples (on the order of 1 per 1,000) is one of the lowest of all foods originating from animals.
The scarce non-compliant samples are almost always due to the accidental contamination in the chicken feed plant with antibiotic waste used in feeds from other animal species, though in quantities lower than those considered safe. Research carried out in several countries has shown that this could occur in all types of eggs, though it appears to be slightly higher in organic eggs, probably due to the lower level of current technology of the factories specialized in producing food for organic chickens.
The low use of antibiotics in Spanish egg-producing poultry farming is recognized at the official level for its excellent health situation. Although in theory, free-range chickens are more exposed to certain bacterial infections, and therefore, the need to use therapeutic antibiotics may be greater than in those raised in cages, there is no data to confirm this possibility.
The presence of pesticide residue and contaminants like dioxins and PCBs is currently practically null. Isolated cases have been cited in free-range, organic eggs, especially in Central Europe, if the chickens’ fields have been close to pollutant industries or located on contaminated lands.
The case of Fipronil, a pesticide used to fight parasitic mites in chickens, which in 2017, was found mainly in organic eggs in Holland and Germany, was due to a very different reason: organic poultry farmers, obliged to use natural products for this purpose, were victims of fraud by a company that provided them with a product that wasn’t what it was supposed to be, and didn’t report that it included an illegal compound. The European alert systems quickly identified and removed the contaminated eggs from the market, which did not reach Spain.
In conclusion, all eggs that are put on the Spanish market, independent of the system of raising the chickens, are safe for the consumer. The great professionalism of Spanish poultry farmers and the application of demanding official control plans guarantee it.
Ricardo Cepero Briz: Doctor in Veterinary, Professor of the Department of Animal Production of the Faculty of Veterinary Medicine of the University of Zaragoza and member of the Advisory Council of the Institute of Egg Studies.