In the United States, about 99% of laying hens are housed in so-called battery (or conventional) cages (Fig. 1). This type of housing provides the hen with protection against predators and soil-borne diseases, and although hens are kept in natural-sized social groups of 3 10 birds, their behavior is also restricted. A space allowance of about 72 in2 is required for a hen to be able to stand, turn around, and lie comfortably, although hens may be given less than this amount. Even more space is required, however, for the hen to groom herself and perform other behaviors such as wing-flapping. Even given sufficient space, typical conventional cages are barren and lack the features that the hen needs to perform dustbathing, perching, and nestbuilding behaviors, all considered important for welfare.[3,4]
Because of concerns about behavioral restriction, conventional cages will be outlawed in Europe as of 2012. Potential alternatives are free-range systems and barn-type systems similar to those in which broilers are raised (as described in the next section), with or without access to range. These systems are not perfect alternatives, however, and they can present other welfare problems, including poorer air quality, much larger group sizes, more cannibalism, and generally higher mortality than for chickens in cages. A middle ground is the furnished (or modified) cage, which contains a perch, dustbath, and nesting area. The feasibility of using these cages on a commercial scale is currently being evaluated.1-2-1
Most laying hens are beak-trimmed to reduce injuries and mortality associated with feather pecking and cannibalism. These are abnormal behaviors whose causes are still incompletely understood, but large group size (as in free-range and barn systems) and lack of foraging opportunity (as in cages) are both contributing factors.1-1-1 Beak trimming involves removal of one-third to one-half of the upper beak. Birds explore their environment using their beaks, and consequently the beak is highly enervated. Although cannibalism is a serious welfare issue, beak trimming causes acute pain and can also cause chronic pain if the bird is trimmed when older. Genetic selection for hens that do not show these behaviors has been successful experimentally, and it may be possible for the industry to discontinue beak trimming by using selected stocks.[2,5]
Another controversial practice is induced molting. Birds in the wild normally molt their feathers periodically. The function of a natural molt is to improve feather condition, but the molt is also associated with changes in the hen's reproductive system. The industry uses this link between molting and reproduction to control egg production rates. By inducing the molt artificially when egg
production starts to decline, all hens molt simultaneously and subsequently return to a higher rate of egg production. Although in the wild the trigger for a molt is declining daylength, the most common method to induce the molt is to withdraw feed from the hens for periods ranging from 4 21 days. This causes hunger, and since fowl normally spend a considerable portion of their day in activities associated with foraging, it can also lead to boredom, frustration, and the development of abnormal behaviors like stereotyped pecking and pacing. Molt programs that do not involve feed withdrawal are being developed and evaluated.
A final concern relates to the disposal of hens at the end of their productive life (spent hens). These hens used to be sent to a nearby processing plant to be used in products such as pet foods, but since broiler meat is so inexpensive, spent hen meat now has little economic value. Spent hens may have to be transported long distances to places where there are specialty markets for their meat, or be killed on-farm. Hens have osteoporosis because of their high rates of calcium utilization for formation of eggshell, and many hens suffer broken bones during catching and transport, so the transport process is particularly stressful for them. Current on-farm killing methods are not optimal, and there is an urgent need for the development of practical and humane methods for on-farm depopulation.
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