Effects of Isolation on Stress Responses to Novel Stimuli in Subadult Chickens (Gallus gallus )

Welfare of broilers on farm

This Scientific Opinion considers the welfare of domestic fowl (Gallus gallus) related to the production of meat (broilers) and includes the keeping of day-old chicks, broiler breeders, and broiler chickens. Currently used husbandry systems in the EU are described. Overall, 19 highly relevant welfare consequences (WCs) were identified based on severity, duration and frequency of occurrence: 'bone lesions', 'cold stress', 'gastro-enteric disorders', 'group stress', 'handling stress', 'heat stress', 'isolation stress', 'inability to perform comfort behaviour', 'inability to perform exploratory or foraging behaviour', 'inability to avoid unwanted sexual behaviour', 'locomotory disorders', 'prolonged hunger', 'prolonged thirst', 'predation stress', 'restriction of movement', 'resting problems', 'sensory under- and overstimulation', 'soft tissue and integument damage' and 'umbilical disorders'. These WCs and their animal-based measures (ABMs) that can identify them are described in detail. A variety of hazards related to the different husbandry systems were identified as well as ABMs for assessing the different WCs. Measures to prevent or correct the hazards and/or mitigate each of the WCs are listed. Recommendations are provided on quantitative or qualitative criteria to answer specific questions on the welfare of broilers and related to genetic selection, temperature, feed and water restriction, use of cages, light, air quality and mutilations in breeders such as beak trimming, de-toeing and comb dubbing. In addition, minimal requirements (e.g. stocking density, group size, nests, provision of litter, perches and platforms, drinkers and feeders, of covered veranda and outdoor range) for an enclosure for keeping broiler chickens (fast-growing, slower-growing and broiler breeders) are recommended. Finally, 'total mortality', 'wounds', 'carcass condemnation' and 'footpad dermatitis' are proposed as indicators for monitoring at slaughter the welfare of broilers on-farm.

Effect of Dietary Vitamin D3 and Ultraviolet B Light on Growth Performance, Blood Serum Parameters, Gut Histology, and Welfare Indicators of Broilers

Stressors are commonly encountered by all farmed species, including chickens, but the impact of these stressors on the animal and their productivity can be influenced by the environmental conditions in which they are kept. This study investigated the effects of dietary vitamin D3 (vitD3) and ultraviolet light (UVB) on growth performance, organ weight, serum corticosterone levels (CORT), serum 25-hydroxy vitamin D (25-OH-D3) status, gut histology, and welfare indicators of broiler chickens challenged with social isolation stress. One day (d) old Ross 308 broiler chicks (n = 192) were individually weighed, wing-tagged, and allocated to non-isolated (control) and isolated groups; control birds were never isolated, while isolated birds were subjected to regular sessions of social isolation for about 15-min periods over the course of 3 d a week for 2 weeks starting from d 10 (1.30 h total exposure) with inter treatment interval of 48 h. Birds were treated with either dietary vitD3 at 4,000 IU/kg (HD) or UVB light (UVB). The UVB lamp (24 Watt 12% UVB D3, 55 cm) with wavelength: 280–315 nm, intensity; 28.12 μW/cm2 hung 50 cm above the substrate was used for the broilers in all the treatment groups but were filtered to remove UVB in the HD group. Growth performance measure; body weight gain, feed intake, and feed conversion ratio were estimated at the end of starter (day 10), grower (day 24), and finisher periods (day 38). Broilers were feather and gait scored to measure welfare at 22/35 and 24/37 days of age, respectively. The selected birds were weighed and euthanized to obtain serum to determine 25-OH-D3 and CORT levels, GIT weights, and gut histology. Subjecting the birds to 2-week social isolation (for 15 min, three times per week) increased CORT levels but did not alter GP and 25-OH-D3 levels of broilers. However, UVB-treated broilers demonstrated better welfare, duodenal absorptive capacity, and reduced FCR compared to HD chickens. Results suggest some beneficial effects of UVB lighting on welfare indicators and the potential to support early life growth of commercial broilers reared indoors, which are often challenged with stressors.

Environmental complexity buffers against stress-induced negative judgement bias in female chickens

Cognitive processes are often biased by emotions. In humans, affective disorders are accompanied by pessimistic judgement, while optimistic judgement is linked to emotional stability. Similar to humans, animals tend to interpret ambiguous stimuli negatively after experiencing stressful events, although the long-lasting impact on judgement bias has rarely been investigated. We measure judgement bias in female chicks (Gallus gallus domesticus) after exposure to cold stress, and before and after exposure to additional unpredictable stressors. Additionally, we explore if brain monoamines can explain differences in judgement bias. Chicks exposed to cold stress did not differ in judgement bias compared to controls, but showed sensitivity to additional stressors by having higher motivation for social reinstatement. Environmental complexity reduced stress-induced negative judgement bias, by maintaining an optimistic bias in individuals housed in complex conditions even after stress exposure. Moreover, judgement bias was related to dopamine turnover rate in mesencephalon, with higher activity in individuals that had a more optimistic response. These results demonstrate that environmental complexity can buffer against negative effects of additive stress and that dopamine relates to judgement bias in chicks. These results reveal that both internal and external factors can mediate emotionally biased judgement in animals, thus showing similarities to findings in humans.