Spatial resolution threshold in layers and red jungle fowls : are there differences due to light intensity or light spectra?

Abstract: The domestic fowl (Gallus gallus domesticus) originates from the forests in South-east Asia. It may be correct to assume that the visual system of the domestic fowl is still adapted to light that is filtered through the green forest canopy. In modern poultry production, however, light is provided via artificial luminaires and in low intensities to control feather pecking and cannibalism. Compared with production and reproduc-tion, the effect of light intensity on visual abilities is not researched as much. The aim with this study was to compare spatial resolution threshold between layers and its ancestor the red jungle fowl, between different light spectra and light intensities. Chickens were held in one of three light treatments during part of the rearing, and during training and testing. One light treatment represented the light in the natural habitat of red jungle fowl, called the jungle light. Another light treatment was the standardized illuminant D65 which represents average daylight. The control light did not have UV-light, which can be discriminated by birds, included as the two other light treatments had. Twelve layers and twelve jungle fowls were trained to discrim-inate between a square-wave grating and a homogenous grey picture inside a Skin-nerbox and tested in four different light intensities. Each bird was tested with increasing spatial frequency of the grating, and when discrimination failed, the spatial resolution threshold of that chicken was said to have been reached. A significant difference in spatial resolution threshold was found between light treatments for red jungle fowls. The group with D65-light had a mean threshold of 5.023 cycles per degree of visual angle (c/deg) compared with 3.794 c/deg in the jun-gle light group (p-value < 0.05). Significant differences were also found between the breeds in the lowest light intensity in the jungle light and control light treatment. In the control light group, the mean spatial resolutions of the layers was 4.095 c/deg and 2.783 c/deg among the red jungle fowl (p-value < 0.05). In the jungle light group, the mean spatial resolution of the layers was 4.017 c/deg and 2.373 c/deg among the red jungle fowl (p-value < 0.05). A significant difference in spatial resolution threshold between the breeds in the lowest light intensity may be seen as an evidence that layers have adapted to the dim light conditions which is common in commercial layer facilities. To further deepen the understanding of how spatial resolution threshold is affected by light spectra, testing in one colour of light at a time would be interesting, as well as measuring production and welfare parameters in a larger scale behavioural study with the jungle light.