Dark brooders during rearing affect fearfulness but not production parameters of broiler chickens

Dark brooders are often suggested as enrichment for broiler chickens because they promote natural motivated behaviors compared to conventional barren environments in broiler production. Although the use of brooders is thought to convey benefits for animal welfare, it is not well described how they might affect parameters related to production and health. The objective of this study was to investigate if providing dark brooders affects production, health, behavior, and welfare compared to a control group without dark brooders. Six pens of each treatment were used, keeping 60 mixed-sex chickens (Ross 308) per pen for a full rearing period of 35 days. Data on growth, mortality, gait score, litter quality, infectious bronchitis virus (IBV)-specific antibody titers, and fearfulness were collected. There were no differences in BW at day 35 (brooders: 2857.3 ± 40.8 g, control: 2831.9 ± 39.6 g, p = 0.55) or feed conversion ratio (FCR) (brooders: 1.44, control: 1.45, P = 0.87). Nor were there any differences in mortality, gait score, or litter quality (P > 0.05). However, birds reared with brooders showed lower IBV titers compared to the control at 15 days after vaccination (P = 0.0448), although there were no other differences between treatments at 0, 22, or 29 days after vaccination. Chickens reared with dark brooders were less fearful as shown by shorter latency to first head movement in the tonic immobility test (brooders: 197.2 ± 15.9 s, control: 307.6 ± 17.9 s, P = 0.0002), shorter latency to turn itself around in tonic immobility test (brooders: 234 ± 19.7 s, control: 351 ± 29.5 s, P = 0.0012), more chickens near the object in the novel object test (brooders: 2.6 ± 0.25 birds, control: 1.5 ± 0.16 birds, P < 0.0001), and more chickens near the observer in the adapted touch test (brooders: 9.8 ± 0.28 birds, control: 4.8 ± 0.28 birds, P < 0.0001). The results of this study indicate that the use of dark brooders does not affect production or health of broiler chickens, however, birds with brooders were less fearful. Fear is a negative emotion and thus reducing fear should increase bird welfare. Therefore, dark brooders may be a useful tool to increase broiler welfare without negatively affecting production or health.