44. Hens must be provided with acceptable environmental conditions in which to live. The various systems described earlier offer these in different measures. If managed well, most can minimise environmental discomfort. The important environmental factors include temperature, climate, ventilation, dust and gas levels, litter quality and light levels.
45. Hens are most biologically energy efficient at temperatures well above those normally experienced outdoors in the UK. In intensive houses in this country they are usually kept within the range 18C to 24C. This does not necessarily mean that they are uncomfortable at temperatures outside this range. Hens with access to feed available ad libitum can withstand a very wide range of temperatures.
46. In cool conditions good insulation is provided by clean, dry feathers, unruffled by outdoor wind or indoor draughts. Free range birds benefit from shelter from wind and rain and need access to clean pasture which will not dirty the plumage. Birds in both intensive and extensive systems benefit from management conducive to the maintenance of good plumage quality.
47. Hens suffer discomfort at temperatures high enough to cause heat stress, as indicated by deep and prolonged panting; this should be avoided. The temperature above which such panting occurs varies with several factors including body weight, standard of feather cover, acclimatisation, stocking density, air speed, humidity, radiant environment, level of performance and breed. The degree of discomfort during severe panting is likely to vary, in particular, with humidity. In both intensive and extensive systems hens benefit from protection from hot sun.
48. Current practice, which does not appear to cause welfare problems, usually incorporates the use of "daylengths" within the range of 8 to 17 hours of light per day but the intensity, colour and source of light required for optimum hen welfare are uncertain. Whilst it appears that the egg production of modern strains of hen may be less sensitive to low light intensity than that of earlier stocks, low intensities may be insufficient for normal behavioural expression, inspection and good hen welfare. It is important that houses have light levels sufficient to allow birds to see and be seen. It is well established that the optimum working of all visual systems depends upon a certain minimum level of light. High intensities and uneven light intensity within a building are undesirable because they may increase the risk of injurious pecking. In multi-level systems there is an unavoidable variation in light intensity between levels. There is a need for a balance between providing sufficient light at lower levels and avoiding excessive light intensity at levels closest to the light source which might cause injurious behaviour. In battery cage systems, industry practice restricts light intensity at any feed trough level to a maximum of about 35 lux yet still achieves 5 lux at the darkest feed trough level.
49. In battery cage and multi-level systems, light intensity should be at least 5 lux, and preferably not less than 10 lux, measured at any feed trough level; in other systems, light intensity in the perching, walking and feeding areas should be at least 10 lux measured at bird eye height.
50. Research is required into the physiological and behavioural responses in hens at different light intensities and wavelengths with particular reference to the incidence of injurious pecking. More information is required to determine the minimum light levels required for hens to perform normal investigative behaviour and how visual acuity is affected by lighting conditions.
51. Hens require a supply of fresh air, either by access to the outdoor environment or by provision of ventilation. In indoor systems, the latter is normally specified and designed to provide sufficient oxygen and adequately dilute and disperse metabolic heat, moisture, carbon dioxide, dust, ammonia and odour. Minimising concentrations of dust and ammonia is important to both hens and to the people who care for them. Concentrations of dust vary widely within and across systems but they are generally highest in litter based systems, though litter is not the only source of dust. High levels of ammonia tend to occur in systems where undried manure accumulates within the house. High concentrations of dust and ammonia are respiratory irritants, which increase the risk of respiratory diseases in hens.