Hen Responses to Indoor Ultraviolet Light Supplementation and Sunlight Effects on Hen Ranging Behaviour in Free-Range Systems in Australia

Abstract

<p>In laying hen housing systems, light critically affects laying hen behaviour, production, and health. Deviations in fulfilling the lighting requirements of hens may have multiple negative consequences. Thus, it is important to consider birds' visual spectral sensitivity and physiological processes in the provision of typical lighting regimens. Based on the housing system, hens can be exposed to either artificial indoor lights (intensive system) or both artificial indoor lights and sunlight outdoors (free-range system). The traditional artificial lights used in current practices are based on human specifications and are mostly deficient in the ultraviolet (UV) spectrums, but birds have broader spectral sensitivity, including UVA perceptual capabilities. Additionally, the biological regulation of endogenous vitamin D formation is driven by the UVB spectrum, which birds can attain from sunlight during free-range outdoor ranging, but indoor hens are unlikely to be exposed. The daily requirements of vitamin D in indoor hens therefore require supplementation by synthetic dietary formulations. Similar to sunlight, supplementing full-spectral artificial UV light (UVA/B) may fulfill hens' natural lighting requirements in intensive systems. But the effects of UV light indoors need to be verified before practical implementation. At the same time, the modern evolution of free-range systems already facilitates visual and physiological benefits from sunlight containing UV radiation while ranging outside. Despite these benefits, over-exposure or high UV radiation may cause skin damage and deter hens from going outside. Concurrent studies in recent years demonstrated that numerous factors affected hen ranging behaviours, while the direct impact of sunlight on hen range use is still not clearly understood. Therefore, the aim of this dissertation was to examine the effects of UV radiation on the hens' physiological and ranging behavior in indoor and free-range systems, respectively, through an integrated approach.</p> <p>This dissertation contains a total of seven chapters. Chapter 1 provides broad background information based on existing literature and synthesises the current research gaps related to indoor UV lighting provision and the factors affecting free-range hen ranging behaviour in relation to sunlight. Chapter 2 is a comprehensive review providing in-depth discussion of the behavioural and physiological effects of supplementing UV lights in indoor poultry production systems, including laying hens, broiler chickens, and other poultry species. The outcome of this review identified the broad research gaps and future research directions across poultry to justify the application of UV in poultry housing. Based on the literature, it was evident that UV lights could have some benefits, but these varied across intensity levels and the negative consequences of UV supplementation negated immediate widespread implementation</p> <p>The first experiment, comprising Chapter 3, uses preference testing to determine how hens respond to different spectral lights (visible spectrum with infrared radiation (VIS), UVA spectrum, and UVA/B spectrum) of varying intensity levels (low, medium, and high) over control standard lighting. This testing was applied to infer whether hens have any spectral preferences or aversion to high intensity of UVA/B light (spectrally similar to sunlight) that hens would be exposed to while ranging outside during intense sun. Eighty-four caged-reared ISA-Brown laying hens of 44 weeks underwent a series of tests across six choice apparatuses divided into equal halves connected through a tunnel on both sides to choose between standard LED-white light (control) versus LED-white light plus one of three supplemental treatment lights of different intensity level. Each light treatment group had 28 hens that were tested individually for a 2 h test period, sequentially for low, medium, and high intensity on different days. Hen preferences were measured from video recordings based on their time spent and behavioural repertoires in the control or treatment compartment of the testing apparatus. Hens showed a greater preference for the low and medium intensities of the UVA/B light treatment in terms of time spent (62%, P = 0.03 and 60%, P = 0.02, respectively) and displayed more comfort and exploratory behaviours (e.g., low intensity: ground pecking and preening, medium intensity: foraging) when compared with control light. Hens also preferred the medium intensity of UVA light (59%), and both low (61%) and high intensities of the VIS light (58%) over control light (all P < 0.05). However, hens did not actively avoid the high intensity of UVA/B light (P = 0.17). This suggests UVA/B light (sunlight) up to a certain intensity level might have behavioural and physiological health benefits which could correspond with increased range use, but during periods of peak sun, some protective measures may be needed. Chapter 4 investigates the effects of supplementing low intensity of UVA/B light indoors for laying hens during early lay, with the hypothesis that UVB exposure will improve hen-day egg production, egg and bone quality, and external health parameters in comparison to UVdeficient standard control light or supplementing UVA spectral light. A total of 252 ISA brown pullets of 16 weeks were housed under three different lighting treatments across eighteen pens (14 birds/pen, 6 pens/treatment) up to 27 weeks: UVO (control, UV-deficient LED-white light), UVA (LED-white plus supplemental UVA daylight), and UVA/B (LED-white plus supplemental full spectral light containing both UVA and UVB). Measurements were made on hen-day egg production, egg quality, plasma Ca and P, and serum 25(OH)D₃, external health scores, and tibia bones. In the results, supplementing UVA/B light showed few beneficial effects with a small increase in hen-day egg production and serum 25(OH)D₃ concentrations relative to control hens (P < 0.05). There was high pen variation within treatment groups.However, the interaction between light treatments and age showed more comb wounds at some age points under both UV supplemental lights (P = 0.0004). These results suggest UVB exposure during hens' early lay might have some positive physiological effects but also some negative behavioural consequences. Optimal intensity and duration of exposure must be further quantified to ensure benefits. </p> <p>Leading on from Chapter 3, the effect of sunlight on hen range use and the relationship between sunlight spectrums and hen ranging behaviours was investigated in commercial free-range settings in Chapter 5. Three individual commercial layer farms in diverse regions of Australia (Tasmania, Queensland, and Western Australia) were video recorded across the summer months. Hens' range distribution was measured by counting the hens every 30 mins during ranging hours under the direct sunlight ('sun') or 'cloud' parts and in the shaded areas ('sunshade' or 'cloud-shade') depending on the sunny or cloudy conditions, respectively. The sunlight spectral intensities (irradiance), including UV_AB (288-432 nm), photosynthetically active radiation or visible spectrum (PAR, 400-700 nm), and total solar radiation (TSR, 285 nm-3000 nm) along with weather variables (ambient temperature and relative humidity) were recorded through on-site weather stations. Analyses of the individual farm datasets showed that hen range distribution was impacted by the time of day and months across all farms (all P < 0.0001). The number of hens ranging in the 'sun' showing a diurnal pattern of increasing in the early morning and late afternoon to evening but decreasing during the midday period, and viceversa in the 'sun-shade.' The linear increase in hens' outdoor range use and ranging on the 'sun' part across the months from summer to autumn indicated that hen ranging behaviour could be also impacted by seasonal sunlight effects. However, the models establishing the relationship between sunlight spectrums including weather variables, and hen ranging behaviours revealed ambient temperature, UVAB, and PAR were the predominant factors for demotivating hens to use the range under direct sunlight. The effect of shade/shelters for increasing hen range use in relation to sunlight was verified in Chapter 6 using different sunlight-filtering (literally UV-filtering) shade cloth shelters in one of the previously studied commercial farms in Queensland across two flocks. Three different densities of cloth shade shelters (50%, 70%, and 90% UV block) built-in horizontal orientation, each with 3 replications, were placed 10.5 m away from the pop holes in each flock. The same sunlight spectrums and weather variables (UV_AB, PAR, TSR, ambient temperature, and relative humidity) were recorded through on-site weather stations. The number of birds under and on top of the shelter was counted at 30 min intervals during the ranging hours for 14 to17 days from pre-recorded video files. Then the use of shelters by hens and its correlation with sunlight and weather variables was established by fitting the regression models. The study showed that hens had a greater preference for higher densities of sunlight-filtering cloth shelter across the day time (both Flocks, P < 0.0001). The ambient temperature resulted in large variations in hens' shelter preferences, while sunlight spectrums had varying effects. Moreover, irrespective of shelter types, fewer hens used the range during the midday periods, suggesting shelters may not be sufficient to attract hens outside during the most prevalent sunny conditions.</p> <p>Overall, this dissertation gives a better understanding of the role of UV for layer industries from the perspective of both intensive and free-range production systems. The findings of the dissertation have highlighted the future prospects for UV light's practical implications and recommend long-term studies for the sustainability of layer production systems.</p>