Effects of color of light on preferences, performance, and welfare in broilers Anja B. Riber Department of Animal Science, Aarhus University, DK-8830 Tjele, Denmark ence between treatments was found on d 4, 10, and 22 (P > 0.07). Second, each of the 2 light conditions was applied to 6 groups of 75 chicks. BW and feed consumption were registered weekly. On d 34, we scored gait, foot pad dermatitis, and hock burns in 15 individuals/pen. At slaughter (d 35), cold carcass weight was recorded from all individuals, while yields of different body parts were collected from 9 individuals/group. Broilers from the 6,065 K treatment were 67.4 ± 19.2 g heavier on the day of slaughter (P = 0.0009), whereas no difference was found at other ages (P > 0.12). Feed intake was found to be similar for the 2 treatments (P = 0.52). Pectoralis minor was 4.1 ± 1.9 g heavier in the 6,065 K treatment (P = 0.03). There was no difference between the light treatments in any of the welfare parameters. We conclude from the results that of the 2 color temperatures examined, the most suitable for use in commercial broiler houses is 6,065 K.
Key words: broiler, color temperature, performance, preference, welfare 2015 Poultry Science 94:1767–1775 http://dx.doi.org/10.3382/ps/pev174
INTRODUCTION Light is a central environmental factor in broiler production. Light affects growth rate, animal welfare, and production economy. There are 4 important main features of light: light intensity, photoperiod, light source, and spectrum of light (Manser, 1996). Research on the effect of light intensity on broiler behavior, welfare, and production started in the early 1960s (e.g. Skoglund and Palmer, 1962), and our understanding of this topic is progressing (Deep et al., 2013). Likewise, lighting programs in broiler houses have been thoroughly investigated, especially during the last 20 yr (e.g. Lewis, 2006; Lewis et al., 2009). Some research has been put into the effect of different light sources (e.g. Lewis and Morris, 1998; D’Eath and Stone, 1999; Kristensen et al., 2007), but as new light sources are developed there is a continued need for research into this area. Finally, less attention has been addressed at the effect of the spectrum of light, and knowledge about this subject is incomplete (Prescott et al., 2003). C 2015 Poultry Science Association Inc. Received March 14, 2015. Accepted April 28, 2015. Corresponding author: [email protected]
The color of light is determined by the various outputs from the different wavelengths in the visible spectrum. White light contains all the wavelengths of the visible spectrum, but it differs in color temperature depending on the spectral characteristics, i.e., the power emitted from the different wavelengths. Color temperature is thus an indication of the color appearance of white light, with warmer colors having lower temperatures. Poultry, unlike humans, are also able to detect UV-A light, which lies immediately below the spectrum of light visible for humans (Wortel et al., 1987). Presently, the light source used in broiler houses is mainly fluorescent lighting. With the expected continued increase in energy prices, an interest has grown to use less energy consuming light sources. Light-emitting diodes (LED) are energy saving. They are more efficient, durable, and retain the light intensity for considerable longer periods (DOE, 2009; Khan and Abas, 2011). The first LEDs developed were monochromatic; they had a very narrow spectrum so that the resulting color appeared different from white. Recently, LEDs emitting white light with a range of color temperatures have been developed. Light is important for poultry as they are day-active species. Most of their behavior is mediated by vision
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ABSTRACT Broiler houses are mainly lit by fluorescent light. With the expected continued increase in energy prices, the interest in less energy consuming light sources is growing. The light-emitting diode (LED) is an energy-saving alternative. The aims of the present 2 studies were to examine 1) the preference for LED color temperature and effects on behavior, and 2) effects of LED color temperature on performance and welfare of male broilers (Ross 308). Two color temperatures were investigated: neutral-white (4,100 K) and cold-white (6,065 K). First, 6 groups of 6-day-old chicks were housed in pens consisting of 2 lightproof compartments with a pop-hole between allowing chicks to move freely between compartments. Number of broilers in each compartment and their behavior were recorded every 15 min on 6 d. A preference for 6,065 K was found (P < 0.001). On d 16, 28, and 34, more time was spent in the 6,065 K treatment (P < 0.03), whereas indiffer-
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LED color temperature 4,100 and 6,065 K on performance and welfare.
MATERIALS AND METHODS Two consecutive studies were conducted in the research facilities at the Department of Animal Science, Aarhus University, Denmark. We used male Ross 308 in both studies, and the chicks arrived 1-day-old from the hatchery (DanHatch, Sønderborg, DK). In both studies, 2 color temperatures were used: neutral-white (4,100 K; UP-T822W1200-A) and cold-white (6,065 K; UP-T822W1200-A; Up-Shine Lighting Co. Limited; Figure 1). Light intensity was kept at the same lux level, as measured with a light meter (Elma 1335) along a horizontal plane 20 cm above the litter. The flicker was kept constant at 170 Hz, which is above the limit of approximately 100 Hz that the domestic fowl can distinguish at any light intensity (Jarvis et al., 2002; Prescott et al., 2003). The photoperiod program was similar to what is commonly used under commercial conditions; at d 0 to 4, the light was switched on for 24 h and on d 5 to 34, the light:dark cycle was 18L:6D. Twilight phases of 30 min were included, occurring at the beginning and the
Figure 1. The relative spectrum of light emitted from the LED tubes with color temperatures a) 4,100 K and b) 6,065 K. In both spectra, the power emitted from 450 nm has been used as reference to the other wavelengths. Notice the relative higher power emission from the part of the spectrum with shorter wavelenghts than compared to the part with longer wavelengths at 6,065 K.
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[for a review see Collins et al. (2011)], and they have a better vision in bright than in dim light (King-Smith, 1971). Most research into the effects of color of light on behavior, welfare, and performance has been done on monochromatic light, whereas research into white light with different color temperatures is sparse. A preference for monochromatic blue light has been found in broilers reared in green, red, and white light, whereas those reared in blue light preferred green light (Prayitno et al., 1997). Xie et al. (2008) suggested that blue light may play a role in alleviating stress response in broilers due to reduction in the level of serum IL-1β . Blue and green light have been found to have a positive effect on growth in broilers (Rozenboim et al., 1999, 2004a). Thus, previous work indicates that using monochromatic blue light may potentially be beneficial to welfare and performance in broilers. However, it has been speculated whether important visual signals are lost in artificial light lacking or being low on parts of the spectrum visible for poultry, e.g., monochromatic light (Prescott et al., 2003). To avoid that, light containing emissions from the entire visible spectrum should be used in broiler houses. In the present studies, we therefore examined how LED lighting with power emissions from the full spectrum visible to poultry (although not the UV-A spectrum), but with different color temperatures, affects preference, behavior, welfare, and performance of broilers. As Rozenboim et al. (1999, 2004a) found improved growth in blue and green light we found it essential to investigate the effect of the different light treatments on important welfare indicators, i.e., leg problems and dermatitis, as the extent of these welfare problems is well-known to increase with increased growth (Bessei, 2006). We used 2 color temperatures: 4,100 and 6,065 K. The 4,100 K is specified as neutral-white, and it is close to the color temperature of the light sources typically used in Danish broiler houses. The color temperature 6,065 K is specified as cold-white, as it contains a relative higher power emission from the shorter wavelengths, including those from the blue part of the spectrum, as compared to the longer wavelengths of the spectrum. The 6,065 K was chosen as it resembles the color temperature of natural daylight on an overcast day in the tropics and, therefore, seems to be the natural choice of an ancestor of the jungle fowl. In the first study, we hypothesized that broilers prefer a color temperature resembling that of natural light and therefore would prefer the 6,065 K over 4,100 K. In the second study, we hypothesized that broilers perform better at a cold-white color temperature (6,065 K) compared to a neutral-white color temperature (4,100 K) due to the relative higher power emission from the blue part of the spectrum. We hypothesized that the expected improved performance in 6,065 K would result in increased occurrence of lameness and dermatitis. The aims of the present 2 studies were therefore to examine the 1) preference for and behavior of broilers in LED color temperatures 4,100 and 6,065 K, and 2) effects of
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Study 1: Preferences and Behavior Study setup: Six groups of 6 chicks were housed in identical pens consisting of 2 lightproof compartments (each measuring 1 × 2 × 2 m, W × L × H). The compartments were each equipped with one LED-tube with either the color temperature 4,100 or 6,065 K. Light intensity was measured in 6 fixed spots in each pen and averaged 22.7 (±2.8) lux. Upon arrival, half of the groups were placed in the 4,100 K compartment and the other half in the 6,065 K compartment. The chicks could move freely between the 2 compartments through a central pop-hole (W × H: 25 × 25 cm). The pop-hole was covered with a plastic curtain, but the first few days’ access was eased by temporarily removal of 2 of the fringes, so that a 7-cm-wide hole was free of obstacles. Feed was available from a circular feeding trough (diameter: 40 cm) placed in the center of both compartments. Water was available in both compartments from 7 nipple drinkers placed along the outer walls. We used video recordings to check that the chicks did move between the compartments during the first 2 d, and all
groups did. Light proofness was obtained by covering each compartment with black plastic (0.07 mm thick). Ventilation was secured by Pex pipes (length: 300 cm; diameter: 15 cm) used as horizontal chimneys at the top and overlaps of the wooden sides (gaps: 3 cm) at the bottom of each compartment. Light in the remaining house was only switched on during the daily caring routines. Every second day around noon, the bedding was changed and the light sources were swopped between compartments in order to avoid preferences being influenced by degree of dirtiness of the bedding or affiliations to a particular side. In each compartment, a video camera was fitted so that the entire compartment was filmed. The broilers were culled by cervical dislocation on d 35 age. Data collection: Video was recorded on 4, 10, 16, 22, 28, and 34 d age. The only disturbance in the house on recording days was staff inspecting the broilers once a day. From the videos, data were collected by scan sampling the number of broilers in each compartment and their behavior every 15 min during the 18-h photoperiod. In total, 11 types of behavior were distinguished (see Table 1).
Study 2: Performance and Welfare Study setup: Each of the 2 light conditions was applied to 6 groups of 75 chicks housed in pens measuring 2 × 2 m. This resulted in a density of 18.8 broilers/m2 , which is similar to commercial conditions. All groups were housed in the same room, but black plastic divided the room into 2 sections to ensure no mixture of the 2 light conditions. Light intensity was measured in 5 fixed spots in each pen and averaged 23.0 (±3.0) lux. Ventilation was kept unblocked by ending the plastic divider 1 m below the ventilators. One round pan feeder (diameter: 45 cm, corresponding to 1.9-cm feeder space per individual) and 7 nipple drinkers were available in each pen. Data collection: On d 0, 7, 14, 21, 28, and 35, each group was weighed and feed consumption registered.
Table 1. Ethogram defining the types of behavior recorded. Due to low occurrence, feather pecking, escape behavior, and aggression were pooled into the category “other,” Likewise, dust-bathing occurred infrequently and was thus pooled with other types of comfort behavior. Behavior Drinking Feeding Foraging behavior Explorative behavior Resting Locomotion Feather pecking Comfort behavior Dust-bathing Escape behavior Aggressive behavior
Definition Having the beak in touch with the drinker. Having the head in the feeder or pecking at feed in the feeder. Pecking or scratching on the floor. Pecking at objects in the pen. Sitting, lying, or standing while not engaged in other activities. Running, walking, or jumping without performing any other type of behavior. Pecking or pulling the feathers of another individual. Preening (manipulating own plumage), wing flapping, stretching, feather ruffling, or shaking (outside the context of dust-bathing). Rubbing the head and body against the ground, bill-raking, vertical wing-shaking, pecking and scratching while lying on the side, or shaking off dirt from the plumage. Running from frightening stimuli, standing alert, squatting, or freezing. Hopping orientated towards another chick, frontal threatening, leaping towards another chick, kicking, wing-flapping, or aggressive pecking.
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end of the photo phase, where the light intensity was gradually lowered and raised. We used LED lighting as the sole light source, and there was no natural light in the room. The floors of the pens were covered with a layer of approximately 4-cm-deep wood-shavings. Food and water was available ad libitum throughout the studies. Commercial starter feed for broilers was used on d 0 to 6, grower feed on d 7 to 28, and finisher feed on d 29 to 35. The starter was crumbled, whereas other feeds were pelleted. The room temperature was set to 34◦ C during the first 3 d and then gradually lowered to 20◦ C on d 28, where it remained. All procedures involving animals were approved by the Danish Animal Experiments Inspectorate in accordance with the Danish Ministry of Justice Law No. 382 (June 10, 1987) and Acts 333 (May 19, 1990), 726 (September 9, 1993), and 1016 (December 12, 2001).
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Statistical Analysis All data were subjected to repeated measurement analysis in the SAS statistical program using the Mixed procedure (SAS, 2000). The statistical unit used was group. Group-specific random effects were included in all analyses to account for the repeated measurements of the response over time from each group. Occurrence of feather pecking, escape behavior, and aggressive behavior was low and therefore pooled into the category “other.” Likewise, recordings of dust-bathing behavior were pooled with other types of comfort behavior due to low occurrence. In the analysis of the development with age of the time budget, age (n = 6), behavioral categories (n = 8), and the interaction between the 2 were used as explanatory variables. In the analysis of preference for color temperature, determined by the percentages of individuals in each compartment per scan, age (n = 6), treatment (n = 2), and the interaction between the 2 were used as explanatory variables. The same model was used in the analyses of whether specific types of behavior were performed more often in one of
the 2 tested color temperatures. In the analyses of effect of color temperature on live BW, feed intake, feed conversion ratio, and mortality, we used age (n = 5 or 6), treatment (n = 2), and the interaction between the 2 as explanatory variables. Cold carcass weight, weight of the different body parts, gait score, foot pad dermatitis, and hock burns were analyzed with treatment (n = 2) as explanatory variable. When there was an overall statistically significant difference, pairwise comparisons were made using the t-test. Results are reported as least-square means and SE, unless otherwise stated.
RESULTS Study 1: Preferences and Behavior The time budget differed between ages (F35,235 = 29.3; P < 0.001; Table 2). Time spent on locomotion and foraging decreased with age, whereas time spent resting increased with age. Also, the number of individuals engaged in comfort behavior and feeding differed between ages, whereas no difference between ages was found on the number of birds engaged in drinking, exploration, or other behavior. More time was spent in the compartment with the color temperature 6,065 K although it varied with age (treatment × age: F5,5167 = 6.08; P < 0.001; Figure 2). On d 16, 28, and 34, more time was spent in the compartment with 6,065 K, whereas indifference in use of the 2 compartments was found on d 4, 10, and 22 (−0.26 < t < 1.83; P > 0.07). Resting was found to be dependent on the interaction between treatment and age (F5,5167 = 4.66; P = 0.0003; Figure 3); on d 16 and 28, resting occurred more often in the 6,065 K compartment (−4.53 < t < −4.30; P < 0.001), whereas no differences were found on other days (−1.05 < t < 0.33; P > 0.30). Likewise, comfort behavior was found to be dependent on the interaction between treatment and age (F5,5167 = 2.75; P = 0.017; Figure 4); on d 34, comfort behavior occurred more frequently in the 6,065 K compartment (t = −2.48; P = 0.0132), whereas no differences were found on other days (−1.58 < t < 1.46; P > 0.11). All other types of behavior were found to be performed equally often in the 2 compartments (0.03 < F5,5172 < 1.30; P > 0.25).
Study 2: Performance and Welfare Live BW was found to depend on the interaction between treatment and age (F5,50 = 2.58; P = 0.04; Figure 5). On the day of slaughter, broilers from the 6,065 K treatment were 67.4 ± 19.2 g heavier (t = 3.52; P < 0.001), whereas no difference was found at other ages (−1.59 < t < −0.03, P > 0.12). Feed intake was found to be similar for the 2 treatments (F1,44 = 0.42; P = 0.52). There was a tendency for the weekly feed conversion ratio to be dependent on the interaction between treatment and age (F4,40 = 2.55; P = 0.054); at
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Weekly BW gain was calculated by subtracting the weight recorded at the end of the previous week from the current weight of the birds. It was corrected by adding total weight of the dead birds to total live weight. The age at death of birds dying during the course of the study was used to adjust the feed conversion ratio. Feed conversion ratio was calculated by dividing feed intake with BW gain. On d 34, we did a welfare assessment of the broilers according to the following procedure. Fifteen individuals/pen were randomly selected by taking out the remaining individuals from different parts of each pen, leaving the 15 individuals intended for the welfare assessment. The gait of each individual was scored according to the scoring system of Kestin et al. (1992), where a score of 0 corresponds to normal gait and 5 describes a bird that is completely unable to walk. The gait scoring was done in the pen in order to avoid lifting and removing the bird from the flock, and to keep it on a known ground material. After assessment of gait, the bird was picked up and scored for contact dermatitis on hocks and foot pads. Hock burns were scored on a 4-point scale (Sherlock et al., 2010), whereas foot pad dermatitis was scored on a 3-point scale (Ekstrand et al., 1998). Foot pads and hock burns of both legs were scored. All individuals were scored by the same observer. Mortality was registered continuously. On d 35 age, the broilers were transported 1.5 h to a small-scale slaughterhouse (Raunsmed Fjerkræ, Denmark). Cold carcass weight was registered for all individuals, whereas 9 individuals from each group were randomly selected (the second individual in the slaughterline and thereafter every ninth individual) and deboned to obtain yields for Pectoralis minor, Pectoralis major, wings, thighs, drums, abdominal fat, and the remaining carcass.
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EFFECTS OF COLOR OF LIGHT IN BROILERS Table 2. The different categories of behavior as percentages of observed behavior at 4, 10, 16, 22, 28, and 34 d age. Other = occurrence of feather pecking, escape behaviour, and aggression that all occurred at low frequencies. Age (d)
Resting (%)
Locomotion (%)
Drinking (%)
Foraging (%)
Feeding (%)
Exploring (%)
Comfort behaviors (%)
Other (%)
4 10 16 22 28 34
22.5a 43.7b 44.9b 46.3b 48.5c 53.1d
7.1a 7.5a 5.3a,b 4.0b,c 2.0c 1.8c
10.2 10.0 10.0 9.2 8.5 8.1
25.5a 18.2b 13.5c 8.6d 9.9d 8.3d
11.8a 4.4b 6.1b,c 8.1c 8.8c 11.1a
0.9 1.0 1.8 1.5 1.0 0.5
21.3a 13.3b 16.9b 21.2a 20.4a 16.6b
0.7 1.9 1.6 1.1 0.8 0.6
a–d Different superscripts within a columns indicate significant differences between ages within behavioral categories.
5 wk age, feed conversion ratio was found to be lower in the 6,065 K treatment (t = 2.60; P = 0.013). Pectoralis minor was heavier in the 6,065 K treatment (F1,96 = 4.64; P = 0.03; Table 3). Higher numeric, but not significant, values were found in the 6,065 K treatment for all the remaining performance parameters (Table 3). With regard to mortality, there was no difference between treatments [overall mortality: 3.4% ± 2.5% (mean ± SD); F1,44 = 0.02; P = 0.89] or ages (F4,44 = 0.24; P = 0.91). We found no differences between treatments in gait score [1.32 ± 0.65 (mean ± SD); F1,168 = 0.56; P = 0.46], foot pad dermatitis [0.03 ± 0.19 (mean ± SD); F1,168 = 0.27; P = 0.61], or hock burns [1.16 ± 0.95 (mean ± SD); F1,168 = 0.80; P = 0.37].
DISCUSSION In the preference study, broilers spent more time in the color temperature with the proportional highest power emission from the blue part of the spectrum (6,065 K). Specifically, the categories of behavior performed more often in the 6,065 K treatment were resting and comfort behavior. In the performance exper-
iment, an increased BW at slaughter age was found in the 6,065 K treatment, with Pectoralis minor being significantly heavier when yields for the different body parts were obtained. Interestingly, this improvement in performance in the 6,065 K treatment was not found to affect the chosen welfare indicators, i.e., lameness and dermatitis, negatively. The broilers were found to become increasingly inactive with age, as has been shown in numerous previous studies (Newberry et al., 1988; Weeks et al., 2000; Cornetto and Estevez, 2001; Bizeray et al., 2002; Kristensen et al., 2007). Few studies exist on preferences for color temperatures and how different color temperatures affect behavior of domestic fowl. Mendes et al. (2013) found indifference in broilers in time spent in compartments with either yellow or white light provided by LED bulbs. Prayitno et al. (1997) reared broiler chicks in white, red, green, or blue light filtered from tungsten filament bulbs. In the fifth week, they were given a choice between red, blue, or green light. Preference developed over time, and after a week, all broilers preferred the blue light, except those reared in blue light; they preferred green light. In our preference study, the broilers
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Figure 2. Mean percentage (±SE) of broilers in the 6,065 K compartment on observation days (n = 6). The intersection at 50% on the y-axis indicates a complete indifference between the 2 color temperatures. If bars are above 50% on particular observation days, more individuals have been observed in the 6,065 K treatment than in the 4,100 K treatment and vice versa. Asterisks indicate where differences were significant (∗ = P < 0.05; ∗∗∗ = P < 0.001).
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Figure 4. Mean percentage (±SE) of broilers observed engaged in comfort behavior during scans in either the 4,100 K compartment or the 6,065 K compartment on observation days (n = 6). Asterisks indicate where differences were significant (∗ = P < 0.5).
used the 2 compartments differing in color temperature equally on d 4 and 10, suggesting that a preference had not yet been established. Similarly, Kristensen et al. (2007) showed that broilers have a preference for certain light sources at 6 wk age, but not at 1 wk age, and Senaratna et al. (2012) found no establishment of preference for 4 different light colors before the broilers were 21 d age. In the present study, a significant preference was found for 6,065 K on 3 of the 4 remaining observation days (d 16, 28, and 34), whereas indifference was found on the remaining day (d 22). Thus, whenever a preference was shown it was for the color temperature 6,065 K. However, the broilers never spent
more than 56.2% of their time during a day in the preferred color temperature; consequently, the preference cannot be categorized as strong. We speculate whether the preference for 6,065 K was due to its closer resemblance to natural light than the 4,100 K. Looking more detailed into which categories of behavior that differed between the color temperatures, we found resting and comfort behavior to be more commonly performed in the 6,065 K. Sultana et al. (2013) housed broilers under different colors of monochromatic LED light and found differences between light treatments in time allocated feeding, sitting, walking, and standing. Broilers in blue light were sitting and
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Figure 3. Mean percentage (±SE) of broilers observed resting during scans in either the 4,100 K compartment or the 6,065 K compartment on observation days (n = 6). Asterisks indicate where differences were significant (∗∗ = P < 0.01; ∗∗∗ = P < 0.001).
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Table 3. Means and SD (or SE)1 for the weight of the different body parts. Data on cold carcass weight was obtained from all individuals (n = 856), whereas data on the different body parts were obtained from 9 individuals/pen (n = 108). Body part Cold carcass; all Cold carcass; individuals selected for detailed slaughter data Pectoralis major Pectoralis minor Wings Thighs Drums Abdominal fat Remaining carcass
Treatment
Mean
SD or SE1
dfn, dfd
4,100 K 6,065 K 4,100 K
1,652.4 1,686.3 1,626.4
163.3 163.7 155.2
6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K
1,657.7 379.1 389.6 84.3 88.3 165.6 167.5 306.0 309.5 213.4 218.4 4.3 4.6 473.5 479.9
159.8 50.2 49.6 1.3 1.3 13.3 14.6 33.6 31.4 20.7 21.6 4.9 4.4 43.2 47.0
F
P
1, 844
1.99
0.16
1, 96
0.58
0.45
1, 96
0.59
0.44
1, 96
4.64
0.03
1, 96
0.42
0.52
1, 96
0.17
0.68
1, 96
0.82
0.37
1, 96
0.05
0.83
1, 96
0.33
0.57
1 Values in italic font are the SE, not the SD; dfn = degrees of freedom numerator; dfd = degrees of freedom denominator.
standing more than broilers in red and red–yellow light. This corresponds well with our observation that the 6,065 K compartment, providing light with a larger proportion of power emission from the blue part of the spectrum, was used significantly more for resting than the 4,100 K compartment. Sultana et al. (2013) did not find differences between broilers housed in different colors of light in time allocated wing flapping or wing stretching. We found that broilers spent more time in the 6,065 K compartment on comfort behavior, but only on d 34. There is a general trend in the literature as to how color temperature affects growth. Most studies show an increased growth in broilers reared in light with a
high proportion of short wavelengths (i.e., the green and blue part of the spectrum; see below), although yellow light has also been found to have a stimulating effect on growth (Jiang et al., 2012; Kim et al., 2012). A few studies find no effects of light spectrum on growth (Prayitno et al., 1997). Broilers reared under monochromatic blue and green LED light were significantly heavier at 35 d age than broilers reared under red and white light (Rozenboim et al., 1999). Ke et al. (2011) found a higher BW at 49 d age in broilers reared in blue LED light compared to broilers reared in green, red, and white light. Also blue and green fluorescent lights have been found to increase BW of broilers compared to red and white light (Wabeck and Skoglund, 1974).
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Figure 5. Mean (±SE) live BW (g) measured weekly (n = 6) for broilers in the 4,100 K treatment and the 6,065 K treatment, respectively. Asterisks indicate where differences were significant (∗∗∗ = P < 0.001).
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the same treatment and between different spots within compartments, suggesting that if a difference in clux existed, it was too small to have a biological relevance.
CONCLUSION We conclude that of the 2 color temperatures examined in the present studies, the most suitable for use in commercial broiler houses is 6,065 K. We base our conclusion on the findings that when the broilers demonstrated a preference it was for the 6,065 K. In addition, the 6,065 K also improved the final live BW and the yield from the breast muscle tenders (Pectoralis minor) without compromising the measured welfare indicators.
ACKNOWLEDGMENTS We would like to thank TA-Elteknik ApS for technical support with the lighting equipment. We are grateful to Jens Askov Jensen, Aarhus University, Denmark, for chopping the cold carcasses into the different body parts for detailed body part yields. We also thank Dr. Ulrik Halekoh, Aarhus University, Denmark, for his statistical advice and Raunsmed Fjerkræ for excellent and flexible service during slaughter. The work was financed by the Green Development and Demonstration Program, established under the Ministry of Food, Agriculture, and Fisheries, Denmark.
REFERENCES Bessei, W. 2006. Welfare of broilers: A review. World’s Poult. Sci. J. 62:455–466. Bizeray, D., I. Estevez, C. Leterrier, and J. M. Faure. 2002. Influence of increased environmental complexity on leg condition, performance, and level of fearfulness in broilers. Poult. Sci. 81:767–773. Cao, J., W. Liu, Z. Wang, D. Xie, L. Jia, and Y. Chen. 2008. Green and blue monochromatic lights promote growth and development of broilers via stimulating testosterone secretion and myofiber growth. J. Appl. Poult. Res. 17:211–218. Collins, S., B. Forkman, H. H. Kristensen, P. Sandoe, and P. M. Hocking. 2011. Investigating the importance of vision in poultry: Comparing the behaviour of blind and sighted chickens. Appl. Anim. Behav. Sci. 133:60–69. Cornetto, T., and I. Estevez. 2001. Behavior of the domestic fowl in the presence of vertical panels. Poult. Sci. 80:1455–1462. D’Eath, R. B., and R. J. Stone. 1999. Chickens use visual cues in social discrimination: An experiment with coloured lighting. Appl. Anim. Behav. Sci. 62:233–242. Deep, A., C. Raginski, K. Schwean-Lardner, B. I. Fancher, and H. L. Classen. 2013. Minimum light intensity threshold to prevent negative effects on broiler production and welfare. Br. Poult. Sci. 54:686–694. DOE (US Department of Energy), 2009. LED measurement series: LED luminaire reliability. http://www2.unca.edu/environment/ documents/luminaire-reliability.pdf. Accessed 12 Dec. 2013. Ekstrand, C., T. E. Carpenter, I. Andersson, and B. Algers. 1998. Prevalence and control of foot-pad dermatitis in broilers in Sweden. Br. Poult. Sci. 39:318–324. Hassan, M. R., S. Sultana, H. S. Choe, and K. S. Ryu. 2014. A comparison of monochromatic and mixed LED light color on performance, bone mineral density, meat and blood properties, and immunity of broiler chicks. J. Poult. Sci. 51:195–201.
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Photostimulation with monochromatic green LED light during incubation has been found to accelerate growth rate pos hatch in broilers (Rozenboim et al., 2004b; Zhang et al., 2012). Experiments have shown that blue light enhances growth at the later growth stage in broilers, probably by stimulating testosterone secretion (Rozenboim et al., 1999; Cao et al., 2008; Hassan et al., 2014). Our results are consistent with this, as the BW only differed on the last day of weighing, i.e., d 34, with the broilers reared in the color temperature containing the proportional highest power emission from the blue part of the spectrum (6,065 K) being heaviest. The effects on welfare of the light spectrum offered to broilers have been investigated in a few studies. Xie et al. (2008) suggested that blue light may play a role in alleviating stress response in broilers due to reduction in the level of serum IL-1β . Blue light has also been found to attenuate the fear reaction in a tonic immobility test displayed as decreased duration of tonic immobility, whereas red and red-yellow light increased the duration (Sultana et al., 2013). Prayitno et al. (1997) found a higher occurrence of aggressive interactions in broilers housed in red light compared to those housed in blue, green, and white light. Finally, blue light (Prayitno et al., 1997) or light containing a high power emission from the blue part of the spectrum (present study) is preferred by broilers. Thus, summing these studies up, blue light seems to have a positive effect on welfare. On the other hand, Levenick and Leighton (1988) noted that in turkeys, blue light seemed to reduce activity compared with white, green, or red light. Similarly, Sultana et al. (2013) found broilers housed in blue light to sit and stand longer than broilers in red and red– yellow light. Also, the often reported increase in BW of broilers housed in blue light may affect leg problems negatively (Kristensen et al., 2006). Thus, an important concern about using blue light in broiler houses is whether there is a greater risk of leg problems due to decreased activity and increased BW. However, our results in study 2 revealed no difference in lameness or dermatitis between broilers housed in light differing in proportional amount of power emission from the blue part of the spectrum. The observed increase in BW at slaughter age may have been too small to cause deterioration of leg problems. Attention should be drawn to the fact that chickens perceive light intensity differently than humans due to differences in spectral sensitivity (Prescott and Wathes, 1999). In the present study, we measured light intensity in lux (as perceived by humans) and not clux (as perceived by broilers). This was unintended as we planned to convert lux into clux to establish similar light intensities in clux prior to the startup of the studies. However, we were unsuccessful in obtaining the necessary data for the conversion from the manufacturer. Nevertheless, the potential difference in light intensity between the 2 color temperatures is likely to be less than 2 lux, which is less than the variation between compartments within
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Prayitno, D. S., C. J. C. Phillips, and H. Omed. 1997. The effects of color of lighting on the behavior and production of meat chickens. Poult. Sci. 76:452–457. Prescott, N. B., and C. M. Wathes. 1999. Spectral sensitivity of the domestic fowl (Gallus g. domesticus). Br. Poult. Sci. 40:332–339. Prescott, N. B., C. M. Wathes, and J. R. Jarvis. 2003. Light, vision and the welfare of poultry. Anim. Welf. 12:269–288. Rozenboim, I., I. Biran, Y. Chaiseha, S. Yahav, A. Rosenstrauch, D. Sklan, and O. Halevy. 2004a. The effect of a green and blue monochromatic light combination on broiler growth and development. Poult. Sci. 83:842–845. Rozenboim, I., I. Biran, Z. Uni, B. Robinzon, and O. Halevy. 1999. The effect of monochromatic light on broiler growth and development. Poult. Sci. 78:135–138. Rozenboim, I., Y. Piestun, N. Mobarkey, M. Barak, A. Hoyzman, and O. Halevy. 2004b. Monochromatic light stimuli during embryogenesis enhance embryo development and posthatch growth. Poult. Sci. 83:1413–1419. SAS. 2000. SAS OnlineDoc1, Version 8 with PDF Files. SAS Institute Inc., Cary, NC. Senaratna, D., T. S. Samarakone, A. A. P. Madusanka, and W. W. D. A. Gunawardane. 2012. Preference of broiler chicken for different light colors in relation to age, session of the day and behaviour. Tropical Agric. Res. 23:193–203. Sherlock, L., T. G. M. Demmers, A. E. Goodship, I. D. Mccarthy, and C. M. Wathes. 2010. The relationship between physical activity and leg health in the broiler chicken. Br. Poult. Sci. 51:22–30. Skoglund, W. C., and D. H. Palmer. 1962. Light intensity studies with broilers. Poult. Sci. 41:1839–1842. Sultana, S., M. R. Hassan, H. S. Choe, and K. S. Ryu. 2013. The effect of monochromatic and mixed LED light colour on the behaviour and fear responses of broiler chicken. Avian Biol. Res. 6:207–214. Wabeck, C. J., and W. C. Skoglund. 1974. Influence of radiant energy from fluorescent light-sources on growth, mortality, and feed conversion of broilers. Poult. Sci. 53:2055–2059. Weeks, C. A., T. D. Danbury, H. C. Davies, P. Hunt, and S. C. Kestin. 2000. The behaviour of broiler chickens and its modification by lameness. Appl. Anim. Behav. Sci. 67:111–125. Wortel, J. F., H. Rugenbrink, and J. F. W. Nuboer. 1987. The photopic spectral sensitivity of the dorsal and ventral retinae of the chicken. J. Compar. Physiol. A Sensory Neural Behav. Physiol. 160:151–154. Zhang, L., H. J. Zhang, X. Qiao, H. Y. Yue, S. G. Wu, J. H. Yao, and G. H. Qi. 2012. Effect of monochromatic light stimuli during embryogenesis on muscular growth, chemical composition, and meat quality of breast muscle in male broilers. Poult. Sci. 91:1026–1031. Xie, D., Z. X. Wang, Y. L. Dong, J. Cao, J. F. Wang, J. L. Chen, and Y. X. Chen. 2008. Effects of monochromatic light on immune response of broilers. Poult. Sci. 87:1535–1539.
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Jarvis, J. R., N. R. Taylor, N. B. Prescott, I. Meeks, and C. M. Wathes. 2002. Measuring and modelling the photopic flicker sensitivity of the chicken (Gallus g. domesticus). Vision Res. 42:99–106. Jiang, J., P. Jinming, W. Yue, Y. Zhangyin, and Y. Yibin. 2012. Effect of light color on growth and waste emission of broilers. Proc., 9th Int. Livestock Environment Symposium (ILES IX), Paper No. ILES12-0394, 8-12 July 2012, Valencia, Spain. Ke, Y. Y., W. J. Liu, Z. X. Wang, and Y. X. Chen. 2011. Effects of monochromatic light on quality properties and antioxidation of meat in broilers. Poult. Sci. 90:2632–2637. Kestin, S.C., T. G. Knowles, A. E. Tinch, and N. G. Gregory. 1992. Prevalence of leg weakness in broiler chickens and its relationship with genotype. Vet. Rec. 131:190–194. Khan, N., and N. Abas. 2011. Comparative study of energy saving light sources. Renew. Sust. Energy Rev. 15:296–309. Kim, M., J. Kim, H. Kang, D. Kim, J. Na, J. Hwanbo, and H. Choi. 2012. Effect of monochromatic light on growth performance of broilers. Poult. Sci. 91(E-Suppl. 1):98. (Abstr.) King-Smith, P. E. 1971. Special senses. Pages 1040–1060 in Physiology and Biochemistry of the Domestic Fowl. D. J. Bell, and B. M. Freeman, eds. Academic Press, London. Kristensen, H. H., G. C. Perry, N. B. Prescott, J. Ladewig, A. K. Ersboll, and C. M. Wathes. 2006. Leg health and performance of broiler chickens reared in different light environments. Br. Poult. Sci. 47:257–263. Kristensen, H. H., N. B. Prescott, G. C. Perry, J. Ladewig, A. K. Ersboll, K. C. Overvad, and C. M. Wathes. 2007. The behaviour of broiler chickens in different light sources and illuminances. Appl. Anim. Behav. Sci. 103:75–89. Levenick, C. K., and A. T. Leighton. 1988. Effects of photoperiod and filtered light on growth, reproduction, and mating behavior of turkeys, 1. Growth performance of 2 lines of males and females. Poult. Sci. 67:1505–1513. Lewis, P. D. 2006. A review of lighting for broiler breeders. Br. Poult. Sci. 47:393–404. Lewis, P. D., R. Danisman, and R. M. Gous. 2009. Photoperiodic responses of broilers. I. Growth, feeding behaviour, breast meat yield, and testicular growth. Br. Poult. Sci. 50:657–666. Lewis, P. D., and T. R. Morris. 1998. Responses of domestic poultry to various light sources. World’s Poult. Sci. J. 54:7–25. Manser, C. 1996. Effects of lighting on the welfare of domestic poultry: A review. Anim. Welf. 5:341–360. Mendes, A. S., S. J. Paixao, R. Restelatto, G. M. Morello, D. J. de Moura, and J. C. Possenti. 2013. Performance and preference of broiler chickens exposed to different lighting sources. J. Appl. Poult. Res. 22:62–70. Newberry, R. C., J. R. Hunt, and E. E. Gardiner. 1988. Influence of light intensity on behavior and performance of broiler chickens. Poult. Sci. 67:1020–1025.
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Key words: broiler, color temperature, performance, preference, welfare 2015 Poultry Science 94:1767–1775 http://dx.doi.org/10.3382/ps/pev174
INTRODUCTION Light is a central environmental factor in broiler production. Light affects growth rate, animal welfare, and production economy. There are 4 important main features of light: light intensity, photoperiod, light source, and spectrum of light (Manser, 1996). Research on the effect of light intensity on broiler behavior, welfare, and production started in the early 1960s (e.g. Skoglund and Palmer, 1962), and our understanding of this topic is progressing (Deep et al., 2013). Likewise, lighting programs in broiler houses have been thoroughly investigated, especially during the last 20 yr (e.g. Lewis, 2006; Lewis et al., 2009). Some research has been put into the effect of different light sources (e.g. Lewis and Morris, 1998; D’Eath and Stone, 1999; Kristensen et al., 2007), but as new light sources are developed there is a continued need for research into this area. Finally, less attention has been addressed at the effect of the spectrum of light, and knowledge about this subject is incomplete (Prescott et al., 2003). C 2015 Poultry Science Association Inc. Received March 14, 2015. Accepted April 28, 2015. Corresponding author: [email protected]
The color of light is determined by the various outputs from the different wavelengths in the visible spectrum. White light contains all the wavelengths of the visible spectrum, but it differs in color temperature depending on the spectral characteristics, i.e., the power emitted from the different wavelengths. Color temperature is thus an indication of the color appearance of white light, with warmer colors having lower temperatures. Poultry, unlike humans, are also able to detect UV-A light, which lies immediately below the spectrum of light visible for humans (Wortel et al., 1987). Presently, the light source used in broiler houses is mainly fluorescent lighting. With the expected continued increase in energy prices, an interest has grown to use less energy consuming light sources. Light-emitting diodes (LED) are energy saving. They are more efficient, durable, and retain the light intensity for considerable longer periods (DOE, 2009; Khan and Abas, 2011). The first LEDs developed were monochromatic; they had a very narrow spectrum so that the resulting color appeared different from white. Recently, LEDs emitting white light with a range of color temperatures have been developed. Light is important for poultry as they are day-active species. Most of their behavior is mediated by vision
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ABSTRACT Broiler houses are mainly lit by fluorescent light. With the expected continued increase in energy prices, the interest in less energy consuming light sources is growing. The light-emitting diode (LED) is an energy-saving alternative. The aims of the present 2 studies were to examine 1) the preference for LED color temperature and effects on behavior, and 2) effects of LED color temperature on performance and welfare of male broilers (Ross 308). Two color temperatures were investigated: neutral-white (4,100 K) and cold-white (6,065 K). First, 6 groups of 6-day-old chicks were housed in pens consisting of 2 lightproof compartments with a pop-hole between allowing chicks to move freely between compartments. Number of broilers in each compartment and their behavior were recorded every 15 min on 6 d. A preference for 6,065 K was found (P < 0.001). On d 16, 28, and 34, more time was spent in the 6,065 K treatment (P < 0.03), whereas indiffer-
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LED color temperature 4,100 and 6,065 K on performance and welfare.
MATERIALS AND METHODS Two consecutive studies were conducted in the research facilities at the Department of Animal Science, Aarhus University, Denmark. We used male Ross 308 in both studies, and the chicks arrived 1-day-old from the hatchery (DanHatch, Sønderborg, DK). In both studies, 2 color temperatures were used: neutral-white (4,100 K; UP-T822W1200-A) and cold-white (6,065 K; UP-T822W1200-A; Up-Shine Lighting Co. Limited; Figure 1). Light intensity was kept at the same lux level, as measured with a light meter (Elma 1335) along a horizontal plane 20 cm above the litter. The flicker was kept constant at 170 Hz, which is above the limit of approximately 100 Hz that the domestic fowl can distinguish at any light intensity (Jarvis et al., 2002; Prescott et al., 2003). The photoperiod program was similar to what is commonly used under commercial conditions; at d 0 to 4, the light was switched on for 24 h and on d 5 to 34, the light:dark cycle was 18L:6D. Twilight phases of 30 min were included, occurring at the beginning and the
Figure 1. The relative spectrum of light emitted from the LED tubes with color temperatures a) 4,100 K and b) 6,065 K. In both spectra, the power emitted from 450 nm has been used as reference to the other wavelengths. Notice the relative higher power emission from the part of the spectrum with shorter wavelenghts than compared to the part with longer wavelengths at 6,065 K.
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[for a review see Collins et al. (2011)], and they have a better vision in bright than in dim light (King-Smith, 1971). Most research into the effects of color of light on behavior, welfare, and performance has been done on monochromatic light, whereas research into white light with different color temperatures is sparse. A preference for monochromatic blue light has been found in broilers reared in green, red, and white light, whereas those reared in blue light preferred green light (Prayitno et al., 1997). Xie et al. (2008) suggested that blue light may play a role in alleviating stress response in broilers due to reduction in the level of serum IL-1β . Blue and green light have been found to have a positive effect on growth in broilers (Rozenboim et al., 1999, 2004a). Thus, previous work indicates that using monochromatic blue light may potentially be beneficial to welfare and performance in broilers. However, it has been speculated whether important visual signals are lost in artificial light lacking or being low on parts of the spectrum visible for poultry, e.g., monochromatic light (Prescott et al., 2003). To avoid that, light containing emissions from the entire visible spectrum should be used in broiler houses. In the present studies, we therefore examined how LED lighting with power emissions from the full spectrum visible to poultry (although not the UV-A spectrum), but with different color temperatures, affects preference, behavior, welfare, and performance of broilers. As Rozenboim et al. (1999, 2004a) found improved growth in blue and green light we found it essential to investigate the effect of the different light treatments on important welfare indicators, i.e., leg problems and dermatitis, as the extent of these welfare problems is well-known to increase with increased growth (Bessei, 2006). We used 2 color temperatures: 4,100 and 6,065 K. The 4,100 K is specified as neutral-white, and it is close to the color temperature of the light sources typically used in Danish broiler houses. The color temperature 6,065 K is specified as cold-white, as it contains a relative higher power emission from the shorter wavelengths, including those from the blue part of the spectrum, as compared to the longer wavelengths of the spectrum. The 6,065 K was chosen as it resembles the color temperature of natural daylight on an overcast day in the tropics and, therefore, seems to be the natural choice of an ancestor of the jungle fowl. In the first study, we hypothesized that broilers prefer a color temperature resembling that of natural light and therefore would prefer the 6,065 K over 4,100 K. In the second study, we hypothesized that broilers perform better at a cold-white color temperature (6,065 K) compared to a neutral-white color temperature (4,100 K) due to the relative higher power emission from the blue part of the spectrum. We hypothesized that the expected improved performance in 6,065 K would result in increased occurrence of lameness and dermatitis. The aims of the present 2 studies were therefore to examine the 1) preference for and behavior of broilers in LED color temperatures 4,100 and 6,065 K, and 2) effects of
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Study 1: Preferences and Behavior Study setup: Six groups of 6 chicks were housed in identical pens consisting of 2 lightproof compartments (each measuring 1 × 2 × 2 m, W × L × H). The compartments were each equipped with one LED-tube with either the color temperature 4,100 or 6,065 K. Light intensity was measured in 6 fixed spots in each pen and averaged 22.7 (±2.8) lux. Upon arrival, half of the groups were placed in the 4,100 K compartment and the other half in the 6,065 K compartment. The chicks could move freely between the 2 compartments through a central pop-hole (W × H: 25 × 25 cm). The pop-hole was covered with a plastic curtain, but the first few days’ access was eased by temporarily removal of 2 of the fringes, so that a 7-cm-wide hole was free of obstacles. Feed was available from a circular feeding trough (diameter: 40 cm) placed in the center of both compartments. Water was available in both compartments from 7 nipple drinkers placed along the outer walls. We used video recordings to check that the chicks did move between the compartments during the first 2 d, and all
groups did. Light proofness was obtained by covering each compartment with black plastic (0.07 mm thick). Ventilation was secured by Pex pipes (length: 300 cm; diameter: 15 cm) used as horizontal chimneys at the top and overlaps of the wooden sides (gaps: 3 cm) at the bottom of each compartment. Light in the remaining house was only switched on during the daily caring routines. Every second day around noon, the bedding was changed and the light sources were swopped between compartments in order to avoid preferences being influenced by degree of dirtiness of the bedding or affiliations to a particular side. In each compartment, a video camera was fitted so that the entire compartment was filmed. The broilers were culled by cervical dislocation on d 35 age. Data collection: Video was recorded on 4, 10, 16, 22, 28, and 34 d age. The only disturbance in the house on recording days was staff inspecting the broilers once a day. From the videos, data were collected by scan sampling the number of broilers in each compartment and their behavior every 15 min during the 18-h photoperiod. In total, 11 types of behavior were distinguished (see Table 1).
Study 2: Performance and Welfare Study setup: Each of the 2 light conditions was applied to 6 groups of 75 chicks housed in pens measuring 2 × 2 m. This resulted in a density of 18.8 broilers/m2 , which is similar to commercial conditions. All groups were housed in the same room, but black plastic divided the room into 2 sections to ensure no mixture of the 2 light conditions. Light intensity was measured in 5 fixed spots in each pen and averaged 23.0 (±3.0) lux. Ventilation was kept unblocked by ending the plastic divider 1 m below the ventilators. One round pan feeder (diameter: 45 cm, corresponding to 1.9-cm feeder space per individual) and 7 nipple drinkers were available in each pen. Data collection: On d 0, 7, 14, 21, 28, and 35, each group was weighed and feed consumption registered.
Table 1. Ethogram defining the types of behavior recorded. Due to low occurrence, feather pecking, escape behavior, and aggression were pooled into the category “other,” Likewise, dust-bathing occurred infrequently and was thus pooled with other types of comfort behavior. Behavior Drinking Feeding Foraging behavior Explorative behavior Resting Locomotion Feather pecking Comfort behavior Dust-bathing Escape behavior Aggressive behavior
Definition Having the beak in touch with the drinker. Having the head in the feeder or pecking at feed in the feeder. Pecking or scratching on the floor. Pecking at objects in the pen. Sitting, lying, or standing while not engaged in other activities. Running, walking, or jumping without performing any other type of behavior. Pecking or pulling the feathers of another individual. Preening (manipulating own plumage), wing flapping, stretching, feather ruffling, or shaking (outside the context of dust-bathing). Rubbing the head and body against the ground, bill-raking, vertical wing-shaking, pecking and scratching while lying on the side, or shaking off dirt from the plumage. Running from frightening stimuli, standing alert, squatting, or freezing. Hopping orientated towards another chick, frontal threatening, leaping towards another chick, kicking, wing-flapping, or aggressive pecking.
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end of the photo phase, where the light intensity was gradually lowered and raised. We used LED lighting as the sole light source, and there was no natural light in the room. The floors of the pens were covered with a layer of approximately 4-cm-deep wood-shavings. Food and water was available ad libitum throughout the studies. Commercial starter feed for broilers was used on d 0 to 6, grower feed on d 7 to 28, and finisher feed on d 29 to 35. The starter was crumbled, whereas other feeds were pelleted. The room temperature was set to 34◦ C during the first 3 d and then gradually lowered to 20◦ C on d 28, where it remained. All procedures involving animals were approved by the Danish Animal Experiments Inspectorate in accordance with the Danish Ministry of Justice Law No. 382 (June 10, 1987) and Acts 333 (May 19, 1990), 726 (September 9, 1993), and 1016 (December 12, 2001).
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Statistical Analysis All data were subjected to repeated measurement analysis in the SAS statistical program using the Mixed procedure (SAS, 2000). The statistical unit used was group. Group-specific random effects were included in all analyses to account for the repeated measurements of the response over time from each group. Occurrence of feather pecking, escape behavior, and aggressive behavior was low and therefore pooled into the category “other.” Likewise, recordings of dust-bathing behavior were pooled with other types of comfort behavior due to low occurrence. In the analysis of the development with age of the time budget, age (n = 6), behavioral categories (n = 8), and the interaction between the 2 were used as explanatory variables. In the analysis of preference for color temperature, determined by the percentages of individuals in each compartment per scan, age (n = 6), treatment (n = 2), and the interaction between the 2 were used as explanatory variables. The same model was used in the analyses of whether specific types of behavior were performed more often in one of
the 2 tested color temperatures. In the analyses of effect of color temperature on live BW, feed intake, feed conversion ratio, and mortality, we used age (n = 5 or 6), treatment (n = 2), and the interaction between the 2 as explanatory variables. Cold carcass weight, weight of the different body parts, gait score, foot pad dermatitis, and hock burns were analyzed with treatment (n = 2) as explanatory variable. When there was an overall statistically significant difference, pairwise comparisons were made using the t-test. Results are reported as least-square means and SE, unless otherwise stated.
RESULTS Study 1: Preferences and Behavior The time budget differed between ages (F35,235 = 29.3; P < 0.001; Table 2). Time spent on locomotion and foraging decreased with age, whereas time spent resting increased with age. Also, the number of individuals engaged in comfort behavior and feeding differed between ages, whereas no difference between ages was found on the number of birds engaged in drinking, exploration, or other behavior. More time was spent in the compartment with the color temperature 6,065 K although it varied with age (treatment × age: F5,5167 = 6.08; P < 0.001; Figure 2). On d 16, 28, and 34, more time was spent in the compartment with 6,065 K, whereas indifference in use of the 2 compartments was found on d 4, 10, and 22 (−0.26 < t < 1.83; P > 0.07). Resting was found to be dependent on the interaction between treatment and age (F5,5167 = 4.66; P = 0.0003; Figure 3); on d 16 and 28, resting occurred more often in the 6,065 K compartment (−4.53 < t < −4.30; P < 0.001), whereas no differences were found on other days (−1.05 < t < 0.33; P > 0.30). Likewise, comfort behavior was found to be dependent on the interaction between treatment and age (F5,5167 = 2.75; P = 0.017; Figure 4); on d 34, comfort behavior occurred more frequently in the 6,065 K compartment (t = −2.48; P = 0.0132), whereas no differences were found on other days (−1.58 < t < 1.46; P > 0.11). All other types of behavior were found to be performed equally often in the 2 compartments (0.03 < F5,5172 < 1.30; P > 0.25).
Study 2: Performance and Welfare Live BW was found to depend on the interaction between treatment and age (F5,50 = 2.58; P = 0.04; Figure 5). On the day of slaughter, broilers from the 6,065 K treatment were 67.4 ± 19.2 g heavier (t = 3.52; P < 0.001), whereas no difference was found at other ages (−1.59 < t < −0.03, P > 0.12). Feed intake was found to be similar for the 2 treatments (F1,44 = 0.42; P = 0.52). There was a tendency for the weekly feed conversion ratio to be dependent on the interaction between treatment and age (F4,40 = 2.55; P = 0.054); at
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Weekly BW gain was calculated by subtracting the weight recorded at the end of the previous week from the current weight of the birds. It was corrected by adding total weight of the dead birds to total live weight. The age at death of birds dying during the course of the study was used to adjust the feed conversion ratio. Feed conversion ratio was calculated by dividing feed intake with BW gain. On d 34, we did a welfare assessment of the broilers according to the following procedure. Fifteen individuals/pen were randomly selected by taking out the remaining individuals from different parts of each pen, leaving the 15 individuals intended for the welfare assessment. The gait of each individual was scored according to the scoring system of Kestin et al. (1992), where a score of 0 corresponds to normal gait and 5 describes a bird that is completely unable to walk. The gait scoring was done in the pen in order to avoid lifting and removing the bird from the flock, and to keep it on a known ground material. After assessment of gait, the bird was picked up and scored for contact dermatitis on hocks and foot pads. Hock burns were scored on a 4-point scale (Sherlock et al., 2010), whereas foot pad dermatitis was scored on a 3-point scale (Ekstrand et al., 1998). Foot pads and hock burns of both legs were scored. All individuals were scored by the same observer. Mortality was registered continuously. On d 35 age, the broilers were transported 1.5 h to a small-scale slaughterhouse (Raunsmed Fjerkræ, Denmark). Cold carcass weight was registered for all individuals, whereas 9 individuals from each group were randomly selected (the second individual in the slaughterline and thereafter every ninth individual) and deboned to obtain yields for Pectoralis minor, Pectoralis major, wings, thighs, drums, abdominal fat, and the remaining carcass.
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EFFECTS OF COLOR OF LIGHT IN BROILERS Table 2. The different categories of behavior as percentages of observed behavior at 4, 10, 16, 22, 28, and 34 d age. Other = occurrence of feather pecking, escape behaviour, and aggression that all occurred at low frequencies. Age (d)
Resting (%)
Locomotion (%)
Drinking (%)
Foraging (%)
Feeding (%)
Exploring (%)
Comfort behaviors (%)
Other (%)
4 10 16 22 28 34
22.5a 43.7b 44.9b 46.3b 48.5c 53.1d
7.1a 7.5a 5.3a,b 4.0b,c 2.0c 1.8c
10.2 10.0 10.0 9.2 8.5 8.1
25.5a 18.2b 13.5c 8.6d 9.9d 8.3d
11.8a 4.4b 6.1b,c 8.1c 8.8c 11.1a
0.9 1.0 1.8 1.5 1.0 0.5
21.3a 13.3b 16.9b 21.2a 20.4a 16.6b
0.7 1.9 1.6 1.1 0.8 0.6
a–d Different superscripts within a columns indicate significant differences between ages within behavioral categories.
5 wk age, feed conversion ratio was found to be lower in the 6,065 K treatment (t = 2.60; P = 0.013). Pectoralis minor was heavier in the 6,065 K treatment (F1,96 = 4.64; P = 0.03; Table 3). Higher numeric, but not significant, values were found in the 6,065 K treatment for all the remaining performance parameters (Table 3). With regard to mortality, there was no difference between treatments [overall mortality: 3.4% ± 2.5% (mean ± SD); F1,44 = 0.02; P = 0.89] or ages (F4,44 = 0.24; P = 0.91). We found no differences between treatments in gait score [1.32 ± 0.65 (mean ± SD); F1,168 = 0.56; P = 0.46], foot pad dermatitis [0.03 ± 0.19 (mean ± SD); F1,168 = 0.27; P = 0.61], or hock burns [1.16 ± 0.95 (mean ± SD); F1,168 = 0.80; P = 0.37].
DISCUSSION In the preference study, broilers spent more time in the color temperature with the proportional highest power emission from the blue part of the spectrum (6,065 K). Specifically, the categories of behavior performed more often in the 6,065 K treatment were resting and comfort behavior. In the performance exper-
iment, an increased BW at slaughter age was found in the 6,065 K treatment, with Pectoralis minor being significantly heavier when yields for the different body parts were obtained. Interestingly, this improvement in performance in the 6,065 K treatment was not found to affect the chosen welfare indicators, i.e., lameness and dermatitis, negatively. The broilers were found to become increasingly inactive with age, as has been shown in numerous previous studies (Newberry et al., 1988; Weeks et al., 2000; Cornetto and Estevez, 2001; Bizeray et al., 2002; Kristensen et al., 2007). Few studies exist on preferences for color temperatures and how different color temperatures affect behavior of domestic fowl. Mendes et al. (2013) found indifference in broilers in time spent in compartments with either yellow or white light provided by LED bulbs. Prayitno et al. (1997) reared broiler chicks in white, red, green, or blue light filtered from tungsten filament bulbs. In the fifth week, they were given a choice between red, blue, or green light. Preference developed over time, and after a week, all broilers preferred the blue light, except those reared in blue light; they preferred green light. In our preference study, the broilers
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Figure 2. Mean percentage (±SE) of broilers in the 6,065 K compartment on observation days (n = 6). The intersection at 50% on the y-axis indicates a complete indifference between the 2 color temperatures. If bars are above 50% on particular observation days, more individuals have been observed in the 6,065 K treatment than in the 4,100 K treatment and vice versa. Asterisks indicate where differences were significant (∗ = P < 0.05; ∗∗∗ = P < 0.001).
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Figure 4. Mean percentage (±SE) of broilers observed engaged in comfort behavior during scans in either the 4,100 K compartment or the 6,065 K compartment on observation days (n = 6). Asterisks indicate where differences were significant (∗ = P < 0.5).
used the 2 compartments differing in color temperature equally on d 4 and 10, suggesting that a preference had not yet been established. Similarly, Kristensen et al. (2007) showed that broilers have a preference for certain light sources at 6 wk age, but not at 1 wk age, and Senaratna et al. (2012) found no establishment of preference for 4 different light colors before the broilers were 21 d age. In the present study, a significant preference was found for 6,065 K on 3 of the 4 remaining observation days (d 16, 28, and 34), whereas indifference was found on the remaining day (d 22). Thus, whenever a preference was shown it was for the color temperature 6,065 K. However, the broilers never spent
more than 56.2% of their time during a day in the preferred color temperature; consequently, the preference cannot be categorized as strong. We speculate whether the preference for 6,065 K was due to its closer resemblance to natural light than the 4,100 K. Looking more detailed into which categories of behavior that differed between the color temperatures, we found resting and comfort behavior to be more commonly performed in the 6,065 K. Sultana et al. (2013) housed broilers under different colors of monochromatic LED light and found differences between light treatments in time allocated feeding, sitting, walking, and standing. Broilers in blue light were sitting and
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Figure 3. Mean percentage (±SE) of broilers observed resting during scans in either the 4,100 K compartment or the 6,065 K compartment on observation days (n = 6). Asterisks indicate where differences were significant (∗∗ = P < 0.01; ∗∗∗ = P < 0.001).
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Table 3. Means and SD (or SE)1 for the weight of the different body parts. Data on cold carcass weight was obtained from all individuals (n = 856), whereas data on the different body parts were obtained from 9 individuals/pen (n = 108). Body part Cold carcass; all Cold carcass; individuals selected for detailed slaughter data Pectoralis major Pectoralis minor Wings Thighs Drums Abdominal fat Remaining carcass
Treatment
Mean
SD or SE1
dfn, dfd
4,100 K 6,065 K 4,100 K
1,652.4 1,686.3 1,626.4
163.3 163.7 155.2
6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K 4,100 K 6,065 K
1,657.7 379.1 389.6 84.3 88.3 165.6 167.5 306.0 309.5 213.4 218.4 4.3 4.6 473.5 479.9
159.8 50.2 49.6 1.3 1.3 13.3 14.6 33.6 31.4 20.7 21.6 4.9 4.4 43.2 47.0
F
P
1, 844
1.99
0.16
1, 96
0.58
0.45
1, 96
0.59
0.44
1, 96
4.64
0.03
1, 96
0.42
0.52
1, 96
0.17
0.68
1, 96
0.82
0.37
1, 96
0.05
0.83
1, 96
0.33
0.57
1 Values in italic font are the SE, not the SD; dfn = degrees of freedom numerator; dfd = degrees of freedom denominator.
standing more than broilers in red and red–yellow light. This corresponds well with our observation that the 6,065 K compartment, providing light with a larger proportion of power emission from the blue part of the spectrum, was used significantly more for resting than the 4,100 K compartment. Sultana et al. (2013) did not find differences between broilers housed in different colors of light in time allocated wing flapping or wing stretching. We found that broilers spent more time in the 6,065 K compartment on comfort behavior, but only on d 34. There is a general trend in the literature as to how color temperature affects growth. Most studies show an increased growth in broilers reared in light with a
high proportion of short wavelengths (i.e., the green and blue part of the spectrum; see below), although yellow light has also been found to have a stimulating effect on growth (Jiang et al., 2012; Kim et al., 2012). A few studies find no effects of light spectrum on growth (Prayitno et al., 1997). Broilers reared under monochromatic blue and green LED light were significantly heavier at 35 d age than broilers reared under red and white light (Rozenboim et al., 1999). Ke et al. (2011) found a higher BW at 49 d age in broilers reared in blue LED light compared to broilers reared in green, red, and white light. Also blue and green fluorescent lights have been found to increase BW of broilers compared to red and white light (Wabeck and Skoglund, 1974).
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Figure 5. Mean (±SE) live BW (g) measured weekly (n = 6) for broilers in the 4,100 K treatment and the 6,065 K treatment, respectively. Asterisks indicate where differences were significant (∗∗∗ = P < 0.001).
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the same treatment and between different spots within compartments, suggesting that if a difference in clux existed, it was too small to have a biological relevance.
CONCLUSION We conclude that of the 2 color temperatures examined in the present studies, the most suitable for use in commercial broiler houses is 6,065 K. We base our conclusion on the findings that when the broilers demonstrated a preference it was for the 6,065 K. In addition, the 6,065 K also improved the final live BW and the yield from the breast muscle tenders (Pectoralis minor) without compromising the measured welfare indicators.
ACKNOWLEDGMENTS We would like to thank TA-Elteknik ApS for technical support with the lighting equipment. We are grateful to Jens Askov Jensen, Aarhus University, Denmark, for chopping the cold carcasses into the different body parts for detailed body part yields. We also thank Dr. Ulrik Halekoh, Aarhus University, Denmark, for his statistical advice and Raunsmed Fjerkræ for excellent and flexible service during slaughter. The work was financed by the Green Development and Demonstration Program, established under the Ministry of Food, Agriculture, and Fisheries, Denmark.
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Photostimulation with monochromatic green LED light during incubation has been found to accelerate growth rate pos hatch in broilers (Rozenboim et al., 2004b; Zhang et al., 2012). Experiments have shown that blue light enhances growth at the later growth stage in broilers, probably by stimulating testosterone secretion (Rozenboim et al., 1999; Cao et al., 2008; Hassan et al., 2014). Our results are consistent with this, as the BW only differed on the last day of weighing, i.e., d 34, with the broilers reared in the color temperature containing the proportional highest power emission from the blue part of the spectrum (6,065 K) being heaviest. The effects on welfare of the light spectrum offered to broilers have been investigated in a few studies. Xie et al. (2008) suggested that blue light may play a role in alleviating stress response in broilers due to reduction in the level of serum IL-1β . Blue light has also been found to attenuate the fear reaction in a tonic immobility test displayed as decreased duration of tonic immobility, whereas red and red-yellow light increased the duration (Sultana et al., 2013). Prayitno et al. (1997) found a higher occurrence of aggressive interactions in broilers housed in red light compared to those housed in blue, green, and white light. Finally, blue light (Prayitno et al., 1997) or light containing a high power emission from the blue part of the spectrum (present study) is preferred by broilers. Thus, summing these studies up, blue light seems to have a positive effect on welfare. On the other hand, Levenick and Leighton (1988) noted that in turkeys, blue light seemed to reduce activity compared with white, green, or red light. Similarly, Sultana et al. (2013) found broilers housed in blue light to sit and stand longer than broilers in red and red– yellow light. Also, the often reported increase in BW of broilers housed in blue light may affect leg problems negatively (Kristensen et al., 2006). Thus, an important concern about using blue light in broiler houses is whether there is a greater risk of leg problems due to decreased activity and increased BW. However, our results in study 2 revealed no difference in lameness or dermatitis between broilers housed in light differing in proportional amount of power emission from the blue part of the spectrum. The observed increase in BW at slaughter age may have been too small to cause deterioration of leg problems. Attention should be drawn to the fact that chickens perceive light intensity differently than humans due to differences in spectral sensitivity (Prescott and Wathes, 1999). In the present study, we measured light intensity in lux (as perceived by humans) and not clux (as perceived by broilers). This was unintended as we planned to convert lux into clux to establish similar light intensities in clux prior to the startup of the studies. However, we were unsuccessful in obtaining the necessary data for the conversion from the manufacturer. Nevertheless, the potential difference in light intensity between the 2 color temperatures is likely to be less than 2 lux, which is less than the variation between compartments within
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