Vision in the laying hen

摘要

It is important to consider the hen's vision when judging how dim artificial lighting may affect her welfare. Inappropriate lighting might constrain the quantity or quality of visual information available to the bird or adversely affect the functionaldevelopment of vision. It seems reasonable to suggest that lighting in poultry houses should allow the development of normal vision and allow hens to see well enough to carry out critical visual tasks. Understanding vision will highlight variances between the hen's visual abilities and the light environment provided. Various visual abilities are important. The colour (spectral) sensitivity of the hen is known and this has implications: first, for how brightness is measured in units relevant to a hen; second, how hens perceive notionally (to humans) white light; and third, implies that the provision of ultraviolet light in poultry houses may be beneficial. Some have argued that the 100 Hz flicker from fluorescent lights might affect poultry welfare ina similar manner to the effects that visible flicker have on humans, but in fact it is known that hens do not perceive the flicker from fluorescent lights. Ocular accommodation, buphthalmus or other abnormalities may be affected by the brightness and photoperiod of the rearing light environment, although the extent of these in laying hens housed under commercial lighting regimes is unclear. The effect of the light environment on spatial acuity is unknown, although it will determine the level of structural information that can be extracted from a visual scene. Whether or not hens possess any sensitivity to polarized light is also unknown, although its existence in other bird species is contentious. Artificial light is not polarized, but if hens have some sensitivity to it, its inclusion in poultry houses may have some benefits. Recent work indicates that pupil size fluctuations may indicate the salience of images to a hen and could provide a novel means for behavioural and welfare research. While knowledge of vision in the laying hen is deep in places, other areas need further exploration to understand fully the consequences, if any, of currently operated, commercial light environments.