Light intensity can influence broiler behavior, but discrepancies in the scientific literature remain. Furthermore, few studies have investigated the welfare implications induced by varying light intensity. We investigated the effects of providing 5 or 20 lux light intensity on broiler behavior, welfare and productivity. A total of 1,872 Ross 308 broilers of mixed sex were studied across 2 replicates. Treatments began on d 8 with one of 2 light intensity levels: 5 lux or 20 lux, using LED lights on a 16L:8D photoperiod with 30 min sunrise and sunset periods. Production data, behavioral activity, and plasma samples for corticosterone concentration analysis were collected weekly from 8 to 46 d of age. Eye weight was collected at 42 d of age. Leg strength was assessed at 35, 42 and 45 d of age using the latency to lie test and leg and foot conditions (foot pad dermatitis, hock burn, leg straightness) were assessed at 46 d. Live weight differed between light treatments, with broilers kept at 20 lux being lighter than broilers kept at 5 lux at 46 d of age (males: –5.1%, females: –2.8%, P< 0.0001), despite no significant differences in feed intake. However, broilers kept at 20 lux were more active during the photophase than broilers kept at 5 lux throughout the rearing period (P < 0.0001). Eye weight was also on average 5% lighter for broilers kept at 20 lux compared to 5 lux (P = 0.001). Nonetheless, there was no significant effect of light intensity on other measures of broiler welfare: mortality and culls, plasma corticosterone concentrations, or latency to lie reflective of leg strength. Hence, broilers kept at 20 lux compared to 5 lux were found to be more active, had slower growth, and had lighter eye weight, but other welfare measures reflective of biological functioning or leg health did not show significant changes.
As diurnal animals, lighting can undoubtedly influence broiler behavior and physiology with associated effects on welfare and productivity (for review, see Olanrewaju et al., 2006). Light exposure is a complex topic because light includes several characteristics: photoperiod, intensity, wavelength, and light source. Most research to date has focused on the effects of photoperiod lengths and schedules (Olanrewaju et al., 2006). However, many poultry welfare assurance schemes now include minimum light intensity requirements.
While there is a substantial amount of literature on the effects of light intensity on production variables, relatively few studies have examined its effects on broiler behavior. In one of the few studies that directly compared light intensity and photoperiod on broiler behavior and welfare, Blatchford et al. (2012) concluded that light intensity (1 vs. 200 lux) had a much larger effect compared to the length of the photoperiod (20 L vs. 16 L). In general, as the photophase (light) to scotophase (dark) light intensity contrast increases (50 to 200 lux photophase), broilers showed a more pronounced circadian rhythm, spending more time active, eating and drinking, walking, foraging and preening during the photophase and more time resting during the scotophase, compared to broilers kept at lower light intensities of 1 or 5 lux (Alvino et al., 2009a,b; Blatchford et al., 2009, 2012). Higher light intensity (200 lux) also resulted in a greater degree of behavioral synchrony in the flock than 5 lux, with 50 lux being intermediate (Alvino et al., 2009b). However, the effects reported in these studies could be attributed to the small contrast in light intensity between photophase and scotophase for the lower light intensity treatments, rather than light intensity per se, as broilers were never in full darkness during the scotophase: Blatchford et al. (2012) compared 1 lux and 200 lux photophase with a 0.5 lux scotophase, and Alvino et al. (2009a,b) and Blatchford et al. (2009) compared 5, 50 and 200 lux photophase with a 1 lux scotophase. However, a small light contrast may be sufficient, or a full-dark phase (i.e., 0 lux) beneficial, as Deep et al. (2012) still found similar circadian rhythm in behavior and melatonin concentration when broilers were reared with a 0 lux scotophase and 1 lux photophase as compared to photophases of 10, 20 or 40 lux, although broilers reared at 1 lux rested more and preened and foraged less over the full 24 h. Hence, discrepancies remain in the literature about the effects of light intensity on broiler behavior.
In addition, the implications of light intensity on broiler welfare remain relatively unknown. Deep et al. (2013) concluded that 0.1 lux was an unacceptably low level, returning 3.3% mortality within wk 2 after abruptly changing from the first 7 d at 40 lux, whereas keeping broilers at 0.5 to 10 lux did not significantly differ on mortality over the whole period. Broilers kept at 0.5 and 1 lux had more severe footpad lesions and heavier and larger eyes than broilers kept at 5 and 10 lux, whereas 5 and 10 lux levels returned similar values (Deep et al., 2013). Light intensities lower than 5 lux are well-recognized to cause retinal degeneration, eye enlargement, myopia, glaucoma and blindness in other poultry such as broiler breeders, layer strains and turkeys (Olanrewaju et al., 2006). Other studies confirmed that broilers kept at 1 lux have both larger eyes (Deep et al., 2010, comparing 1, 10, 20, and 40 lux; Blatchford et al., 2012, comparing 1 to 200 lux), and heavier eyes (Blatchford et al. (2009); Deep et al., 2010 comparing 5, 50 and 200 lux; Blatchford et al., 2012). Nonetheless, Blatchford et al. (2009) found no effect of 5 lux on eye diameter or the corneal radii that have been reported under lower intensities (Deep et al. 2013). It is not possible to determine whether this discrepancy in eye weight difference between Blatchford et al. (2009, comparing 5 to 50 and 200 lux) and Deep et al. (2013, comparing in the range of 0.5 to 10 lux) is due to the scotophase of 1 lux used by Blatchford et al. (2009), as mentioned earlier, or the difference in the range of comparison studied. Regardless, the welfare implications of these changes in eye morphology for broiler's vision remain unclear.
The determination of an optimal light intensity for broiler welfare is further complicated by the fact that broilers seem to have different preferences at different ages: 2-week-old broilers preferred the brightest environment of 200 lux whereas 6-week-old broilers preferred the dimmest environment of 6 lux (Davis et al., 1999). This may correspond to the increased level of inactivity in older broilers, which prefer dim lights (Newberry et al., 1985), but it appears contradictory to recommendations that a minimum of 20 lux should be provided at all ages (Farm Animal Welfare Committee, 1992).
Overall, there is evidence that light intensity affects broiler behavior, but the implications of these behavioral changes on broiler welfare remain poorly understood. This experiment investigated the effects of light intensity on broiler behavior, welfare and productivity, by comparing a minimum of 20 lux requirement commonly reported in the literature (European Commission, 2000), and recommended by some poultry welfare assurance schemes in commercial production, to a 5 lux treatment representative of industry practices at the time of the study, using LED lighting.
MATERIALS AND METHODS
The project was approved by the University of Sydney Animal Ethics Committee in accordance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes.
The experiment was conducted over 2 replicates in time, with 8 wk between commencement of each replicate. A total of 1,872 Ross 308 day-old broilers of mixed sex were obtained from the same commercial hatchery, transported to the research facility, and distributed into 24 pens with equal numbers of individuals per pen. Chicks were sexed at the hatchery and packed in separate transport boxes for delivery to the research site. At arrival, broilers were randomly distributed into 24, 1.52 × 1.51 m pens, with 12 pens per side, in single-sex groups, and wing tagged for identification. On d 4, mixed-sex groups were formed with approximately equal numbers of males and females per pen, by combining chicks from one pen of males and one pen of females. Any chicks that died before the start of the light intensity treatments were replaced with chicks of the same sex from a pool of spare chicks, to keep 39 broilers per pen by the start of the experiment, equivalent to 17 chicks per square meter. Each pen was equipped with a nipple drinker line equipped with 4 nipple drinkers, linked to a water dispenser shared between 2 adjacent pens, a 45-cm diameter bell feeder that provided approximately 141 cm feed-trough circumference, and an even depth of hardwood shavings of 7 cm at the start of the trial. No litter was subsequently added during the trial. Broilers were provided access to water and a formulated broiler diet ad libitum. The feed was formulated according to Ross Nutrition Specifications to provide feed in 3 phases (starter; d 1–14 of age: 12.55 MJ and 23.0% CP, grower; d 15–26: 12.97 MJ and 21.5% CP, finisher; d 27 onwards: 13.39 MJ and 20.0% CP) and mixed by the source farm. The shed was temperature controlled, with room temperature decreasing over the experimental period from about 32 to 20°C and relative humidity fluctuating between 50 to 60%.
The shed was divided lengthwise using light-proof polyethylene curtain into 2 treatment sides, and treatment sides were reversed between replicates to control for side effects.
Light Intensity Treatments
Following placement, broilers were kept at 30–50 lux (Mean ± SD: 37 ± 5.1 lux) on a 23L:1D photoperiod for the wk 1. At d 8, the broilers were exposed to one of 2 light intensity levels: 5 lux (common Australian industry practice at the time of the study) or 20 lux (European Commission, 2000), on a 16L:8D photoperiod with 30 min sunrise and sunset periods and 7 h of uninterrupted darkness. Lighting was delivered with LED lights placed above each pen (SMD LED 3528 Warm light, Jaycar Campbelltown NSW, Australia; manufacturer specifications: 2 peaks of wavelengths at 455 nm and 585 nm). Light intensity was checked weekly at 3 positions in each pen along a horizontal plane 25 cm above the litter with the photoreceptor sensor of a light meter (Meter lux 400 K Pro, Jaycar, Campbelltown NSW, Australia) pointed toward the light sources, according to the methodology of Blatchford et al. (2009). The measurements for the 5 lux treatments averaged 4.4 (±SD: 0.53) lux and 4.8 (±SD: 0.69) lux for replicates 1 and 2 respectively, and for the 20 lux treatments, the measurements averaged 22.4 (±SD: 2.66) lux and 24.0 (±SD: 2.58) lux in replicates 1 and 2 respectively. The LED lights were dusted weekly after the light intensity check to reduce interference. The 2 ‘light treatment rooms’ were light-proof, and there was no observable leakage of light from outside the shed into the rooms or between rooms. Pens between treatments were visually isolated from each other, but birds from pens within the same treatment could see neighboring pens. All light from outside the shed was excluded by covering air inlets and exhaust fans with ‘PERIdark’ light filters (Protective Fabrications, Werombi, NSW, Australia). Light intensity in the scotophase was measured at 0 lux.
Pink noise (noise of equal energy per octave) was provided in the background from d 1 and played continuously through 2 speakers placed on each treatment side in order to cover possible vocal and activity noise effects between treatments. The broadcast sound was measured at 70 dB directly below the speakers and 68 dB at both ends of the rows of pens (4.5 m distant from the perpendicular line below the speakers). Sound level measurements were taken weekly using a Pro Sound Level Meter (Jaycar Electronics, Campbelltown NSW, Australia) 1 m above floor level at the front of pens. The sound system was professionally designed to provide a relatively even spread of pink noise across the 24 pens, to mimic fan and other equipment noises present in commercial settings.
Most measurements were taken weekly from the day before treatment started (d 7) to final pick-up (d 46), for a total of 7 time-points: 7, 14, 21, 28, 35, 42, and 46 d of age, with exceptions listed below.
Production and Litter Measures
Body weight data were collected through weekly weighing estimates of 10 broilers per pen (>25% of the pen population), selected at random with an equal number of each sex, and on all broilers at the start (d 7) and end (d 45 or 46) of the trial. Using the weights of this sample of randomly chosen birds provided an unbiased estimate of the average pen weight, confirmed by similar means and 95% confidence intervals between pen weight at d 46 and 3 random 25% subsets of weights. Feed intake was measured by weighing the feeder in each pen weekly, and recording the weight of all feed added during the week. Water intake was measured through the use of graduated cylinders connected to the water line, and the difference over 24 h once weekly assessed, and the value divided by 2 to account for the shared water lines in adjacent pens from the same treatment. Litter samples were collected in 3 different locations in each pen along the midline of the pen, 15 cm from the drinker line, at the center of the pen and 15 cm from the opposite pen fence, for the full depth of 5 cm to the floor and samples were subsequently pooled. Litter moisture was assessed through the determination of litter dry matter through oven desiccation over 24 h at 70°C. Mortality and culls were recorded daily, but due to the low numbers, reasons for culls or causes of death have not been reported here.
Behavioral activity was recorded though infra-red video cameras (Sony CCD 1/3” Sensor Camera, model 600TVL, CCTV Central, Mount Waverly, VIC, Australia) positioned 3.1 m above each pair of pens and providing a view of the whole of each pen's floor space. Video footage was recorded continuously for all pens during the experiment using MSH VClient software (M Safro & Co., Latvia) via 2 computers at a rate of 7 frames per second.
A software program (Chicken Monitor v1.1, Leading Edge Research, Moggill Qld Australia), specifically designed for our use, estimated broilers’ activity based on movement as assessed through mean pixel count changes per frame of video over a 5-min period each hour during the photophase. The field of view covered approximately one-third of the floor space per pen, avoiding ‘non-usable’ space that contained the feeder or drinker, and was consistent across pens. We validated the software through concurrent manual observations by an experienced observer, which returned an R-squared value of 0.90 between manual observations and results from the software. The software could only detect changes during the photophase. During the scotophase, the cameras’ built-in infrared capability enabled the broilers to be visible on the monitor. However, the Chicken Monitor software was unable to register the very low number of pixel changes due to the broilers’ inactivity combined with the digital video technology which only records frames when a set minimal number of pixel changes occurs.
Therefore, behavioral activity during the scotophase was visually analyzed using video records at 8 and 29 d of age by one observer in order to verify broiler inactivity during the scotophase by recording bird activity, measured as the mean number of birds per pen with their head over the feed tray at one time point per hour over 24 h. Only feeding was considered for general activity during the scotophase as one of the only behaviors birds were observed doing during that period, apart from repositioning themselves which only involves subtle movements and no obvious activity (e.g., locomotion).
Blood samples were collected weekly from 2 random broilers per pen per time point between 1200 and 1330 h. The investigators avoided being in the vicinity of pens for 40 min prior to capture and sampling of broilers from the pens. Blood was collected from the jugular vein of 9-day-old broilers using 26-gauge needles, and the brachial wing vein of broilers older than 9 d using 23-gauge needles, in 5 mL Vacuette lithium heparin tubes (Greiner Bio-One GmBH, Austria) within 3 min of the humans entering the pen to avoid effects of human presence and handling. Blood samples were collected from the broilers on average 62.1 s ± 20.3 (±SD) after the human entered the respective pen (min = 25 s; max = 175 s; median = 56 s). Blood samples were subsequently centrifuged at 2,400 RPM for 20 min, and the plasma fraction was stored at -20°C. Plasma samples were analyzed for corticosterone concentrations using a RIA kit (ImmuChemTM Double Antibody Corticosterone 125I RIA Kit, MP Biomedicals LLC, Orangeburg, NY), following the manufacturer's manual and using a 1:4 dilution. Sample results with coefficient of variation superior to 5% between duplicates were reanalyzed.
At 35, 42 and 45 d of age, 4 broilers per pen, with an unequal number of each sex, were randomly selected to undergo the latency to lie test (Berg and Sanotra, 2003), as an indirect and objective assessment of gait score, which consists of placing broilers standing in a 2–3 cm deep warm water bath (31-33°C) for 300 s or until they squat in the water. The broilers that underwent the latency to lie tests were not returned to their pens, thereby reducing the stocking density to help maintain pen stocking density as birds grew.
At 42 d of age, 2 broilers per pen, from the individuals tested for the latency to lie test and with an unequal number of each sex, were euthanized using cervical dislocation and both of their eyes were extracted whole and the optic nerves and their surrounding tissues removed close to the eye ball. The eyes were trimmed of extraneous tissue, and both eyes were individually weighed to the nearest 0.1 g within 1 min of completing the trimming process.
At 45 or 46 d of age, all remaining broilers (approximately 28 broilers per pen) were scored for foot pad dermatitis (Berg, 1998; combining score of mild (1) and severe (2) foot pad dermatitis to assess its overall prevalence), hock burns, and leg straightness by visual assessment on whether the 2 leg bones below the knee joint were parallel. Two experienced persons conducted the scoring, and trained prior to scoring to ensure intra- and inter-observer consistency. Broilers were subsequently weighed and checked for sex identification. This final sex identification was used to correct for possible incorrect sexing for previous measurements at younger time-points.
All continuous data met the criteria for normality and homogeneity of variance. Data were analyzed using a mixed model (Proc Mixed, SAS Inst. Inc., Cary, NC), which included the fixed effects of treatment, age (if the variable was collected repeatedly), sex (if data were collected on individuals) or sex ratio (if data collected on a group), all interactions between treatment, age and sex to the second and third levels of interaction if significant; and the random effect of time replicate. Pen was considered the experimental unit, accounting for repeated measures when applicable. For the behavioral data, the model accounted for repeated measures between hours nested within age. For the behavioral activity data during the scotophase, the model included the fixed effects of treatment, light phase (photophase vs. scotophase), age and their interactions if significant; and the random effect of replicate and accounting for repeated measures. When significant differences (P < 0.05) were detected, Tukey–Kramer tests were used for pairwise comparisons between treatments. Categorical data (foot pad dermatitis, hock burn, and leg straightness) were analyzed using Chi-square tests, testing for light treatment effects, per replicate if replicate was significant. Data for the latency to lie tests were analyzed using a Kaplan-Meier Survival Analysis in Genstat (Genstat, ver 17, VSN International, UK), including the same effects as the mixed model. Data are presented as least squares means ± SE unless otherwise noted.
Mortality and Culls
Over the course of the experiment, 3.15% of the birds died or were culled for health reasons over the 2 replicates, with 20.3% of these mortalities occurring in wk 1 of life prior to the start of treatment imposition. The number of broilers per pen, as a result of mortality and culls, did not differ according to treatment (means over the course of the experiment: 5 lux: 36.4 ± 0.11 broilers per pen vs. 20 lux: 36.4 ± 0.11 broilers per pen, P = 0.80), but differed according to age (P < 0.0001), with broilers number decreasing at 35, 42 and 45 d of age due to the latency to lie test on those d after which tested broilers were culled to help maintain stocking density.
Live weight differed according to the interaction of treatment, sex and age (P = 0.005; Figure 1), with males kept at 20 lux being lighter than males kept at 5 lux at 28, 42 and 45/46 d of age (all P < 0.0001), and females kept at 20 lux being lighter than females kept at 5 lux at 45/46 d of age (P < 0.0001). At final weight (45/46 d of age), males kept at 20 lux were on average 5.1% lighter than males kept at 5 lux, and females kept at 20 lux were on average 2.8% lighter than females kept at 5 lux.
Live weight for each week according to light intensity and sex (LS-means ± SEM; ***P < 0.001).
Feed intake did not differ according to treatment (5 lux: 135.6 ± 2.42 g/broiler/d vs.20 lux: 131.5 ± 2.42 g/broiler/d, P = 0.23), but differed according to age (P < 0.0001), as feed intake increased until wk 5 and decreased thereafter (wk 2: 36.4 g/broiler/d, wk 3: 38.8 g/broiler/d, wk 4: 38.6 g/broiler/d, wk 5: 38.5 g/broiler/d, wk 6: 34.3 g/broiler/d, wk 7: 29.3 g/broiler/d, SEM: 0.11 g/broiler/d). Feed intake did not differ between replicates (P = 0.62). The drop between 5 and 7 wk corresponded to the removal of birds for the latency to lie tests.
Water intake did not differ according to treatment (5 lux: 307.7 ± 4.16 mL/broiler/d vs. 20 lux: 303.1 ± 4.18 mL/broiler/d, P = 0.44), but differed according to age (P< 0.0001), as water intake increased until wk 7 (wk 2: 134.6 mL/broiler/d, wk 3: 196.3 mL/broiler/d, wk 4: 271.3 mL/broiler/d, wk 5: 357.2 mL/broiler/d, wk 6: 428.2 mL/broiler/d, wk 7: 445.0 mL/broiler/d, SEM: 5.18 mL/broiler/d). Water intake also differed between replicates (P < 0.001; Table 1), being higher in replicate 1 compared to replicate 2 (317.7 ± 2.2 mL/broiler/d vs. 293.5 ± 2.2 mL/broiler/d).
Legs and feet conditions, water intake and litter moisture according to treatment and replicate.
| ||Replicate 1 ||Replicate 2 || || || || |
| || || || ||P-value ||P-value ||P-value |
|Variables ||5 lux ||20 lux ||5 lux ||20 lux ||SEM ||Treatment effect ||Replicate effect ||Treatment × Replicate effect |
|Water intake (mL/broiler/d) ||320.2 ||315.2 ||295.2 ||292.8 ||3.06 ||0.19 ||<0.0001 ||NS |
|Litter moisture (%) ||47.5 ||46.9 ||32.1 ||31.4 ||0.81 ||0.42 ||<0.0001 ||NS |
|Foot pad dermatitis (%) ||50.8 ||47.9 ||14.5 ||0 ||- ||0.008 ||<0.0001 ||NA1 |
|Hock burn (%) ||48.9 ||24.1 ||51.0 ||67.9 ||- ||0.14 ||<0.001 ||NA1 |
|Bent leg (%) ||0.3 ||0.0 ||7.4 ||7.8 ||- ||0.86 ||<0.0001 ||NA1 |
Litter moisture did not differ according to treatment (P = 0.79), but differed according to age (P < 0.0001), as it increased over time (wk 2: 22.3%, wk 3: 37.8%, wk 4: 40.6%, wk 5: 40.8%, wk 6: 45.5%, wk 7: 49.8%, SEM: 1.39%). Litter moisture also differed between replicates (P < 0.001; Table 1), being higher in replicate 1 than in replicate 2 (47.2 ± 0.6% vs. 31.7 ± 0.6%).
Foot Pad Dermatitis, Hock Burns, Leg Straightness and Bumblefoot
The prevalence of foot pad dermatitis differed according to treatment (P = 0.008; Table 1), and replicate (P < 0.0001). When broken down by replicate, the prevalence of foot pad dermatitis between broilers kept at 5 and 20 lux did not differ in replicate 1 (P = 0.47), in which about half the broilers showed signs of foot pad dermatitis, whereas broilers kept at 5 lux had a higher prevalence of foot pad dermatitis compared to broilers kept at 20 lux in replicate 2 (P < 0.001).
Hock burn prevalence did not differ according to treatment (P = 0.14; Table 1), but differed according to replicate (P < 0.0001). When broken down by replicate, broilers kept at 20 lux showing a lower prevalence of hock burn compared to broilers kept at 5 lux in replicate 1 (P < 0.0001), but higher prevalence in replicate 2 (P < 0.0001), whereas broilers kept at 5 lux had stable prevalence across both replicates.
Leg straightness did not differ according to treatments (P = 0.86; Table 1), but differed according to replicate (P < 0.0001), with no significant differences between treatments in replicate 1 (P = 0.32) or replicate 2 (P = 0.86).
Bumblefoot was never observed.
Behavioral activity during the photophase differed according to treatment (P< 0.0001), age (P < 0.0001), and the interaction of treatment and age (P < 0.0001). All broilers increased their activity with age, but broilers kept at 20 lux were always significantly more active than broilers kept at 5 lux at all time points (P < 0.001; Figure 2). Behavioral activity also differed according to the hour of the photophase (P< 0.0001), being highest on the 1st and 15th hour of the photophase (corresponding to light on and off), then on the 2nd and 16th hour, and remaining uniform across all other times (all P < 0.05).