Providing a gradient from low to high light intensity did not clearly affect the behavior, welfare or performance of either fast- or slower-growing broilers compared with a uniform low light intensity.

One of the most important senses in chickens is vision and light (intensity, spectrum, etc.) influences broiler behavior, welfare and performance. However, a lot remains unknown about offering a choice in light intensity and how this affects behavior, welfare and performance, especially for slower-growing broilers which are increasingly used in broiler production systems. Therefore, we studied the effect of control (uniform 20 lux) versus gradient (range from 20 (dim) to 200 (bright) lux) lighting on behavior, welfare and performance of fast- and slower-growing broilers. Day-old chicks from a fast-growing (Ross 308) and slower-growing (Hubbard JA757) breed were housed until an approximate weight of 2.6 kg (33 kg/m2) in groups of 346 per pen (27.3 m2) with 8 pens per breed x light treatment combination. We assessed effects on behavior, responses to behavioral tests, activity, distribution, litter quality, welfare scores and performance. Slower-growing broilers had lower (better) scores for cleanliness compared to fast-growing broilers at 2.6 kg, but only in the gradient lighting. Slower-growing broilers showed more activity in bright lighting while activity of fast-growing broilers was not affected by light treatment. More fast-growing broilers were present in bright lighting while more slower-growing broilers were present in dim lighting. Thus, fast- and slower-growing broilers did not differ greatly in their responses to gradient lighting, with only minor differences in cleanliness, activity and distribution. Regardless of breed, gradient lighting reduced body weight and feed intake, and had no clear effects on welfare scores or litter quality compared to control lighting. Furthermore, gradient lighting reduced drinking behavior and increased fear of humans and play behavior (specific weights) compared to control lighting. Dim lighting reduced activity close to the wall and in gradient lighting, broilers seemed to be less uniformly distributed over the zones studied than in control lighting. Thus, offering broilers a choice in light intensity from low to high had no clear negative or positive effects on behavior, welfare or performance compared with a uniform low light intensity.