110 | Chickens strains of chickens that are better adapted for living in these facilities Rearing chickens with access to perches from an early age also mitigates some of these problems For free-range hens, the welfare implications of unexpectedly being denied access to the outdoors due to inclement weather or disease threats from wildlife (e.g., avian influenza) have not been determined To reduce contact with feces, only about one-third of the floor space in cagefree hen housing is covered with litter In contrast, broilers must be kept on all-litter floors to cushion their heavy bodies and prevent breast blisters In either case, litter must be kept dry to minimize the release of ammonia from feces, especially in warm weather Ammonia irritates the eyes and respiratory passages, and can create lesions on the feet and hocks of heavy, inactive broilers Controlling ammonia depends as much on proper ventilation and management of the drinkers as it does on the space allowance per chicken If the litter is too dry, ammonia is replaced by problems with dust prolonged periods Therefore, their feed intake is strongly restricted to control growth and promote reproductive fitness in adulthood The resultant hunger can lead to the development of unwanted behaviors such as spot pecking Feeding a high-fiber diet partially alleviates this problem Rapid Growth of Broilers Beak Trimming Broiler chickens have large appetites and grow rapidly, which places them at risk of developing cardiovascular and skeletal disorders These risks have been reduced to some extent by genetic selection and manipulation of day length to constrain early growth but stimulate rapid growth later on However, the limited mobility of modern strains of broilers, and the potential for pain from leg and joint disorders, has prompted calls for the use of slower-growing, less productively efficient broilers that display more active behavior, including use of perches Broiler breeders would become unhealthy if allowed to eat like broilers for Beak trimming (or debeaking) involves amputating up to two-thirds of the upper beak and less of the lower beak It is effective in reducing damage from feather pecking and cannibalism, which are serious welfare problems in laying hens and broiler breeder hens kept cagefree in large flocks By making manipulation of feed more difficult, beak trimming reduces feed wastage, although it may also reduce the ability of hens to remove parasitic mites through preening Unfortunately, beak trimming causes pain, fuelling bans in Sweden, Norway, Finland, and Switzerland, and a UK ban scheduled for 2011 Pain from the procedure can be Induced Molting Laying hens molt after they have been laying eggs at a high rate for about one year Until recently, molting was induced by complete feed withdrawal for up to two weeks, prompting loss of abdominal fat and leading to improved survival rates, egg production, and eggshell quality during a second laying cycle Although this increased the longevity of survivors, it put the lightest hens in the flock at the risk of anorexia and death Consequently, prolonged feed withdrawal has been outlawed in the European Union and abandoned in the United States, and molting is now induced by feeding a low-nutrient diet