Can UV light induce movement in cage-free laying hens?

Housing and Birds

A total of 1,800 Lohmann Brown hens were obtained as day-old-chicks from Hy-line hatchery (Hy-line North America, LLC, GA) and transported to the Poultry Teaching and Research Center. The study began when hens were 56 wk of age and was conducted in 4 identical rooms measuring 19.81 m × 4.57 m × 3.20 m (length × width × height). All rooms had an equal number of hens and equal number of hens per aviary section. Hens were randomly divided into each room (450 hens/room) and were further divided into 3 sections (150 hens/section; 0.093 m² per bird) of the multitier aviary system (NATURA60, Big Dutchman Inc., Holland, MI). The aviary system was internally divided into 4 sections and had approximately 120 to 130 hens/section; hen housing capacity of system per section was 144 hens/section. To mimic a commercial stocking density, hens from fourth section were divided and placed into remaining 3 sections to obtain approximately 150 hens/section (United Egg Producers, 2017).

The aviary was located in middle of each room, with each aviary section facing the wall; each section was of equal size and equipment (i.e., each section has 3 tiers, water lines, feeders, etc.), refer to Figure 1. The first tier included a water line, feeders, outer perch, and main opening to floor area; second tier included feeders and outer perch; and third tier included one water line, nest boxes, and inner and outer perches. Within each section, there was an open litter area in front of the aviary and litter area underneath the system. Birds were able to freely move within their respective sections but could not access another section of the aviary. For a detailed description of the aviary offered to birds, please see Ali et al. (2016). Hens were provided with ad libitum access to water, fed 3 times a day (with 2 stimulations), and were under a lighting schedule of 16L:8D; room lights were turned on at 0800 (dawn). Doors on the system that restricted access to the floor area during the night (dark period) were opened prior to the start of study and kept open for the full duration of study. However, there was equipment malfunction in control room and one of the rail doors in tier 3 (nest boxes) remained closed. Although a portion remained closed, hens still had access to floor by using main opening to floor area located in tier 1.

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Figure 1. Aerial view of room layout. Room layout was identical between the treatments. Aviary system was in the middle of room and consisted of 4 sections, each with corresponding floor area; however, only 3 sections were used to house hens in present study. Bird side depicts where hens were located. Man side represents area workers used for egg collection and side where UV lights were placed. Front end of room contained entrance door and 2 air inlets, whereas 2 exhaust fans were located on backend of room. Diagram not drawn to scale.

Lighting Treatments and Light Intensity

Due to room setup and takedown, the experiment was conducted over the span of 4 d (1 room/d; 1 treatment/d). Each room was randomly assigned to a lighting treatment: 1) control (C), UV light flash and/or darkened floor area were not utilized, 2) UV lights flashed for one 10-sec per morning/afternoon (UV), 3) floors of the system were darkened plus UV lights flashed for one 10-sec per morning/afternoon (DF + UV), and 4) floors of the system were darkened (DF). The floor areas were darkened by turning off the floor lights on the controller, causing the floor area and tier 1 to be darker compared to the rest of the system (Figure 2). Treatments were applied once in the morning (AM) between 8 am and 9:30 am and once in the afternoon (PM) between 12 pm and 1 pm each day to observe if diurnal rhythm would influence treatment response. For the DF + UV treatment, floors were darkened 5 to 10-min prior to the UV flash. In the DF treatment, after the AM application, floor lights were turned on 60-min prior to PM application. Because in treatment C nothing was applied (i.e., no utilization of UV light flash and/or darkened floor area), bird distribution and behavior at times when other treatments were applied were used for comparison. Two rooms were equipped with 6 UV-LED purple blacklight bars (INWT504014650Dc, Barrina Lighting, Paris, France) in the UVA light spectrum (395–400 nm). UV lights were positioned on the back side of the system to encourage hens to vacate the aviary through the opened doors and onto the floor. When floor lights in UV treatment remained on, UV flash was partially observed in tier 1, whereas in tier 2 and 3 (nest box) UV flash was more noticeable. Additionally, in treatment DF + UV the UV lights illuminated all 3 tiers. The hens did not have prior exposure to UV light.

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Figure 2. Aviary system offered to hens. The levels of the aviary (from bottom to top) are floor, tier 1, tier 2, and tier 3 (nest boxes). UV lights were placed right above feed trough. Source: Zhao, Yang & Zhao, Deiling & Xin, Hongwei. 2013. Characterizing Manure and Litter Properties and Their Carbon Dioxide Production in an Aviary Laying-Hen Housing System. American Society of Agricultural and Biological Engineers Annual International Meeting 2013, ASABE 2013. 4. 10.13031/aim.20131618601.

To know whether light intensity was similar across treatments, it was measured at 3 locations at approximately bird level in each aviary section (middle of floor area, middle of tier 1, and middle of tier 2) using a light meter (cal-LIGHT 400, The Cooke Corp., San Diego, CA).

Video Data Collection, Spatial Distribution, and Behavior Analysis

Dome CCTV cameras with 4k ultra-HD resolution (LNE9292B, LOREX Corp., Linthicum, MD) and an NVR recording system (N882A63B, LOREX Corp., Linthicum, MD) were used, with 4 cameras per section, for 12 total cameras per room. Two cameras were mounted on the wall to record each tier of the aviary, one mounted on the ceiling for an aerial view of the floor area, and one on the backside of the aviary to record tier 1 and floor area underneath system. This set up enabled video recordings of almost the entire housing system, visibility was reduced in some areas due to space limitations of aviary equipment.

To determine the spatial distribution of hens, video recordings were observed by one observer at 1-min intervals during a 12-min observation period (6-min pre-treatment and 6-min post-treatment) per camera. Hens observed within the system and floor area were counted at each time point. In order to be counted, hens had to be clearly visible in the video frame. Then, the difference of hens for floor area was calculated by subtracting the number of hens pre- and post-treatment application.

Statistical Analysis

Data analyses were carried out using the GLM procedure of SPSS 27 (IBM, Armonk, NY). The study was a completely randomized design, and the experimental unit was an aviary section (N = 3 aviary sections/room). Data were examined for normality and analyzed for interaction between treatment, position in aviary, and main treatment effects, distribution time of day, time post treatment. Statistical significance was considered at P ≤ 0.05. Means were separated with Tukey’s Least Significant Difference Test.

Spatial Distribution of Hens

Based on the location of UV lights (i.e., to stimulate hens’ movement towards the floor area) the UV light may had been perceived as an environmental stressor that was followed by a fleeing response from hens’ movement to the floor area to escape the UV light. There may be 2 possible explanations as to why hens reacted in such a manner. When an animal encounters a short-term challenge (i.e., predation attempt or change to the immediate environment) “the physiological stress response, coordinated by the activation of the hypothalamic-pituitary-adrenal axis, provides an essential mechanism for survival designed to help the animal escape the stressor and return to stable conditions” (Pusch et al., 2018). The first explanation is related to the personality of brown hens (i.e., proactive personality) (Cockrem, 2013; Pusch et al., 2018). Personality is defined here as “birds’ response to changes in their immediate environment that is consistent with individual behavioral and physiological responses” (Cockrem, 2013). Proactive animals tend to have a bold and fast response to unfamiliar environments or stimuli (i.e., quick explorers, less fearful and more aggressive) and produce smaller physiological responses (e.g., corticosterone elevations) to acute stressors (Cockrem, 2013; Pusch et al., 2018).

A second explanation for the hens’ reaction could be related to the flicker rate of the UV lights. While a statement can be found in the manual of UV lights used, stating that these lights do not flicker, and no flickering was detected by the naked human eye, the avian eye can perceive rapid movements (high flicker fusion frequency) (Rubene et al., 2010; Korbel, 2012; Lisney et al., 2012). Flicker fusion frequency is defined as “the rate of successive light flashes from a stationary light source at which the sensation of flicker disappears, and the light becomes ‘steady’” (Simonson and Brozek, 1952). In the study by Lisney et al., (2012) the retina of adult laying hens was examined, via electroretinograms, to determine whether the chicken retina can detect flicker at higher frequencies. The results showed the retina of hens can at least respond to flicker frequencies in the 100 to 200 Hz range, although Lisney et al., 2011, found that hens do not appear to be able to consciously detect flicker above approximately 90 Hz. The retina’s ability to respond to flicker frequencies higher than 100 Hz may result in distress for the animals (Lisney et al., 2012). Although a light meter was not used to determine if flickering was apparent in the UV lights, there was a quick and effective way this was resolved by, using the slow-motion video setting (240 frames per second) in a standard iPhone. While the frequency of the flicker cannot be determined with this procedure, flickering can be detected and indeed, the UV light did flicker. Therefore, flickering may have caused hens to experience general stress and move to the floor area away from UV light (Greenwood et al., 2004; Lisney et al., 2011). A second plausible explanation, related to light flickering, may give insight as to why hens reacted to such an extent. Rubene et al., (2010) concluded that when some UV light is added to regular white light, birds can detect higher frequencies of flickering light, compared to only white light, meaning that the temporal resolution was enhanced by the addition of UV wavelengths. Because hens in the present study had no prior exposure to UV light, it may be plausible that the UV light flash caused some distress due to improved temporal resolution during those 10-sec.

When examining the mean difference of hens in floor area between AM and PM application (Table 2 and Table 3, respectively), it is evident that treatments had a stronger effect on hens in the AM application than PM application. A potential justification for this is that in AM application, treatments were novel to hens as they did not have prior exposure to UV lights. In a study conducted by Jones (1977), 909 male chicks were separated into groups that were presented with different rearing cues (red crosses or black circles) on the walls of their home environment from 2 to 7 d old; behaviors were measured during an open field test in absence or presence of familiar rearing cues. After chicks reached 7 d of age, they were tested individually in a test box; the researcher found fearfulness (freezing, sitting time, lying time, and time spent with eyes closed) was reduced in the presence of familiar rearing cue, meaning that familiarity decreased fearfulness (Zajonc et al., 1974; Jones, 1977). An interesting finding was that when chicks were in the presence of their familiar cue, they spent more time drinking and eating, which could potentially support notion that chicks were less fearful (Jones, 1977). Campbell et al. (2016a) studied hen pattern movements between the aviary system and floor area at various times (morning, afternoon, and evening) throughout 2 different flock cycles (peak lay, mid lay, and end of lay). For both flocks, more hens per unit moved from the system onto floor area in the morning period as soon as hens gained access to it; but a higher occupancy of the floor area was more apparent and consistent during afternoon period (Campbell et al., 2016a).

Light Intensity

Furthermore, observations of hens’ reaction after UV flash were used revealed that hens who had their backs to the UV light, or had their heads in feed trough, did not react to UV light in the same manner as hens who were in direct contact (i.e., fleeing response). Instead, those hens stayed in aviary system looking around being vigilant.

Behavioral Data Collected From Hens

Overall, UV light influenced the behavior of hens as both groups in rooms with UV lights had lower frequencies of preening and wing flapping (comfort behaviors) but had a higher expression of standing alert (stress behavior), whereas more hens exhibited comfort behaviors in the non-UV light treatments. Interestingly, an increase in preening (comfort behavior) expression was anticipated after UV light utilization as disruption to hen environment occurred (i.e., stressful situation), this occurrence is referred to as displacement behavior. Displacement behaviors such as preening, head shaking or vocalization, are behaviors birds will do to show signs of frustration, stress, and overall discomfort (Duncan and Wood-Gush, 1972; Kuhne et al., 2013). Results from present study demonstrated that although hens in UV treatments exhibited signs of stress (i.e., higher standing alert frequency), hens were still comfortable in the environment as displacement behavior, such as preening, was not apparent. Moreover, Zimmerman et al. (2011) conducted a study in 17-wk old hens to find behavioral expressions specific to the anticipation of a positive, neutral, and negative event. The authors observed that anticipation of a positive event was associated with an increase in comfort behaviors (preening, wing flapping, feather ruffling and body scratching), whereas hens in the negative event showed more head movements and higher locomotion. Although hens in the present study were not anticipating a positive or negative event, it could be inferred that natural comfort behaviors are expressed to reflect how well the animal is feeling in the current environment and why lower frequencies of these behaviors were lowest in both UV treatments (Linares and Martin, 2010; Bhanja and Bhadauria, 2018).

Domestication may have played a role in hens displaying a higher frequency of standing alert behavior. Domestication is defined as a process by which a population of animals becomes adapted to a captive environment by the combination of genetic changes and environmentally induced developmental events (Price, 2002). The Red Junglefowl is considered the wild ancestor of domestic chickens (Fumihito et al., 1994; Hartcher and Jones, 2017; Tixier-Boichard, 2020). In a study conducted by Campler et al., (2009) domesticated White Leghorn chickens and Red Junglefowl were tested for behavioral reactions to 4 different types of potentially fearful stimuli. Results indicated Red Junglefowl had higher fear levels than White Leghorn across the 4 fear tests and performed more stand/sit alert and less locomotion, fly/jump, and vocalizations. Whether it was a conscious or unconscious decision to select for less fearfulness in chickens, domestication contributes to this phenomenon as indicated by the results presented. However, molecular studies show that a consequence of intensive selection is the loss of genetic diversity at the DNA level (Tixier-Boichard, 2020).

Overall results indicated that a flash of UV light combined with darkened floors (DF + UV treatment) was the most effective in moving hens out of an aviary system and onto floor area. However, the treatment used might not be effective for long term movement because hen concentration varied within a 6-min observation period.