It is safe to say that the transition from cages to cage-free systems is the most important global trend for the egg sector since the removal of conventional cages. Having started in Europe, the cage-free movement has since gained momentum in many countries throughout the world, as well as in the United States where it is expected that the share of cage-free eggs will increase to about two thirds of the market by 2026. Indeed, numerous major egg producers, retailers, food service companies and hotel chains have already committed to switch entirely to cage-free eggs by 2025.
Dust and ammonia exposure
Chickens housed in cage-free systems have contact with the floor. Increased bird activity will also increase the amount of dust in the air. Consequently, dust levels in cage-free buildings can be 5-15 times greater than in houses equipped with cages.
Ammonia (NH3) is generated from manure. The complete removal of manure is frequent in cage systems, especially in automated houses, but the full removal of manure in cage-free systems can only be done after the premises have been vacated. Not surprisingly, therefore, ammonia levels are usually greater in cage-free than in cage houses. Litter-based systems are also associated with a greater frequency of intestinal disorders which, in turn, lead to higher ammonia levels due to the lower absorption of nutrients and the increased moisture content of manure.
The higher aerial pollution in cage-free buildings can depress the immune system and increase the load of infectious agents. Indeed, it has been reported that total bacteria concentrations in the indoor air of cage-free houses can be 5-9 times greater than in sheds equipped with cages, especially in winter. High levels of ammonia damage the epithelium of the respiratory tract, thereby favouring the colonisation of air sacs and lungs with airborne E. coli and predisposing the flock to higher mortality. E. coli also attaches to dust particles which then serve as pathogen disseminators inside the poultry shed.
De-Odorase is formulated from proprietary extracts of Yucca schidigera, a desert plant that is sustainably grown and harvested by Alltech. Supplementing the feed with De-Odorase can help to maintain a consistently lower air ammonia level in poultry houses with no detrimental effects on flock productivity. Wet litter and high ammonia content can lead to footpad dermatitis and bumblefoot, a painful footpad infection. While uncommon in furnished cages, the frequency of bumblefoot can be 3-4 times greater in litter-based houses.
On average, the hen mortality rate is greater in cage-free systems, especially free-range, compared to furnished cages. A thorough study conducted in the United Kingdom reviewed the on-farm mortality of nearly 1,500 flocks, comprising over 13 million layers. It provided striking evidence for this general trend. Despite a considerable variation between flocks, under all systems, the average cumulative mortality rate was clearly lower in cage (5.39%) than in cage-free production (8.55%, 8.68% and 9.52%, respectively, for barn, organic and free-range flocks).
The greater prevalence of cannibalism, various bacterial infections and internal parasites, plus the occasional occurrence of smothering, can help to explain the higher average mortality rate associated with cage-free farms. Free-range chickens are also at risk of predation and can become infected with serious diseases, such as avian influenza and Newcastle disease, through contact with wild birds.
Chickens have no contact with soil, litter and manure in cages, but this is not so in cage-free housing. Therefore, the natural (faecal-oral) transmission route of several intestinal parasites, such as coccidia and worms, is interrupted in cages but not in litter-based systems. Not surprisingly, these parasites are much more common in cage-free farms, and the resulting increase in mortality rate can be significant, thereby negatively affecting bird welfare.
Histomoniasis (also known as blackhead), a disease that affects the caeca and liver of chickens and turkeys, provides a good example of the re-emergence of parasitic diseases in cage-free farms. This problem is greatly aggravated by the ban on traditional treatment options in Europe, North America and many other countries, due to human health concerns. In the absence of treatment, flock mortality can be very high. The frequency with which certain bacterial infections occur, namely colibacillosis, erysipelas and pasteurellosis, is also greater in cage-free systems.
Behaviour and welfare
Feather pecking (FP) is a major welfare issue in laying hens. In its severest form, characterised by feather removal, FP can result in denuded body areas, often followed by pecking of the skin, wounding, bleeding and, in extreme cases, mortality due to cannibalism. Pecking around the cloaca (vent pecking), another type of injurious pecking, can also be a critical cause of internal infections, cannibalism and mortality in layer flocks.
Injurious pecking is a learned behaviour passed on from one chicken to another and is very difficult to control once an outbreak starts. Although it can occur in any housing system, this behavioural problem can spread more easily and become even more serious in cage-free flocks – given the larger group size, there are more birds to learn the behaviour or to fall victim to it. Accordingly, several surveys have reported that a high percentage of cage-free flocks suffer from FP (40-80%). Similarly, the reported percentage of cage-free flocks affected by cannibalism is also substantial (up to 40%).
Apart from the larger group size, other specificities of cage-free housing may contribute to the greater magnitude of injurious pecking (severe FP and vent pecking) on these farms. Free-range flocks are exposed to outdoor light which is much more intense than indoor light, even on a cloudy day – higher light intensities increase the risk of injurious pecking. Ammonia levels are usually greater in cage-free sheds; elevated levels of ammonia have been linked to the onset of FP. Infestation by worms has also been associated with the triggering of injurious pecking.
Apart from the associated pain and stress, there is another crucial welfare aspect of severe FP: feather loss. Without proper feathering, the skin is at greater risk of injury and birds lose insulation from draughts and cold weather. In addition, damage to the tail and flight feathers of the wings affects flying ability which, in turn, may increase the risk of bone fractures in cage-free layers.
Several authors have reported that bone strength is higher in cage-free than in caged hens. Paradoxically, the prevalence of keel bone fractures (KBF) is greater in cage-free layer flocks. Accordingly, KBF is a particular welfare concern in cage-free farms. It has even been suggested that this might be the most critical welfare issue currently faced by the egg production industry. Although the exact causes for its development have not been fully identified, it has been proposed that housing and equipment features may contribute to KBF.
Attention to details
Although laying hens housed in cage-free systems can move more freely and better express their natural behaviour, some factors can turn their welfare into a challenge. Air quality, foot health, higher mortality rate, feather pecking and keel bone fractures are therefore important welfare concerns in cage-free egg production that need to be addressed by egg producers.