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The effect of light intensity on the behavior, eye and leg health, and immune function of broiler chickens

R. A. Blatchford^*,, K. C. Klasing, H. L. Shivaprasad, P. S. Wakenell, G. S. Archer and J. A. Mench^*,,1

^* Animal Behavior Graduate Group, Department of Animal Science, University of California, Davis 95616; Department of Animal Science, University of California, Davis 95616; California Animal Health & Food Safety Laboratory System, Fresno 93725; and School of Veterinary Medicine, University of California, Davis 95616

¹ Corresponding author: jamench{at}ucdavis.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Broilers are typically raised commercially in dim lighting. It has been suggested that providing brighter light intensity could improve health and provide opportunities for more normal behavioral rhythms. We examined the effects of 3 photophase light intensities (5, 50, and 200 lx) on activity patterns, immune function, and eye and leg condition of broilers (n = 753; 6 replicate pens/treatment). Broilers were reared with one of these intensities from 1 to 6 wk of age; photoperiod consisted of 16L:8D with 1 lx intensity during the scotophase. Broilers reared with 5 lx were less active (P = 0.023) during the day than 50 or 200 lx and showed less (P < 0.0001) change in activity between day and night than 50 or 200 lx. There was no difference between treatments for final BW (2.30 ± 0.02 kg) or for most immune parameters (IgG primary and secondary responses to keyhole limpet hemocyanin, B and T lymphocyte proliferation, plasma lysozyme, haptoglobin, NO, whole blood killing of Escherichia coli and Staphylococcus aureus), but there was a trend (P = 0.072) for a greater IgM response in 50 lx (6.21 titer) than 5 lx (5.78 titer), with 200 lx (5.92 titer) intermediate. There was no effect of light intensity on back-to-front (1.13 ± 0.01 cm) or side-to-side (1.48 ± 0.01 cm) diameter of the eyes or on corneal radii (0.82 ± 0.01 cm), but 5 lx (2.33 ± 0.07 g) had heavier eyes (P = 0.002) than 50 lx (2.09 ± 0.04 g) or 200 lx (2.11 ± 0.04 g). There were no differences in gait score, although 200 lx broilers had more hock and footpad bruising (P = 0.038) but fewer erosions (P = 0.006) than 5 or 50 lx. Increased daylight intensity had little effect on broiler health but resulted in more pronounced behavioral rhythms.

Key Words: broiler • welfare • behavior • lighting • health

	INTRODUCTION

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Artificial lighting regimens are a critical aspect of the management of poultry reared in environmentally controlled buildings. Although a great deal of research has been conducted on the effects of lighting on the performance of poultry, relatively little attention has been given to its effects on behavior and well-being (Manser, 1996; Prescott et al., 2003). Lighting intensity is often kept low (generally below 10 lx) in commercial broiler houses to inhibit bird activity and increase feed efficiency, as well as to save energy (Appleby et al., 1992; Prescott et al., 2003). Poultry have good color vision (Nuboer, 1993), which suggests that broilers may experience a better quality of vision in brightly lit than dimly lit environments. Therefore, intensity is one aspect of light management that could have important consequences for broiler behavior, performance, and welfare (Prescott et al., 2004).

Only a few studies have examined the effects of light intensity on broiler behavior. When broilers were reared in pens containing areas of 12 and 0.5 lx intensity, they performed more of their active behaviors (e.g., moving, standing) in the brighter areas and more of their nonactive behaviors (e.g., lying) in the dimmer areas (Newberry et al., 1985). Similarly, broilers reared with light intensities that alternated between 100 and 5 lx were more active during the periods of high intensity lighting (Davis et al., 1999; Kristensen et al., 2006a). Broilers reared under high (180 lx) intensity light were also found to be more active than broilers reared under low (6 lx) intensity light (Newberry et al., 1988).

Light intensity appears to have little effect on broiler food intake, with broilers consuming the same overall amount of feed regardless of lighting treatment (Charles et al., 1992; Downs et al., 2006; Kristensen et al., 2006b). Lighting does, however, affect rhythms of feeding behavior (Weaver and Siegel, 1968; Savory, 1976; May and Lott, 1992), although few studies have examined lighting effects on the distribution of feeding patterns over a 24-h period.

Most studies report that there is no effect of light intensity on final BW (Newberry et al., 1988; Charles et al., 1992; Downs et al., 2006; Kristensen et al., 2006b). However, Downs et al. (2006) did find a transitory effect of light intensity on BW gain. They observed that broilers reared under a dim lighting regimen where the light was reduced in intensity during grow out (~10 lx reduced to 2.7 lx by d 15) gained more by d 15 and 36 than broilers reared under 21.5 lx intensity. Charles et al. (1992) also reported that broilers reared under high intensity light (150 lx) had lower BW at 6 and 8 wk of age than broilers reared under low intensity light (5 lx). Both of these studies attributed the lower BW of broilers reared under higher light intensities to greater activity levels, although activity was not quantified in either study.

The potential for bright light to increase activity could also have an effect on leg health. Prayitno et al. (1997) observed improved gait scores and less angular deformity of the legs of female broilers that were reared under high intensity red light early in the growth period, although the same effect was not seen in broilers raised under high intensity blue light. Prayitno et al. (1997) speculated that this improvement in leg health may have been due to the increased activity of the broilers reared with high intensity red light, but in other studies no differences in leg health were observed even when greater light intensities were associated with greater activity levels (Newberry et al., 1985; Kristensen et al., 2006a).

The light environment has also been shown to affect eye health and immunocompetence. A long photophase, like that used in continuous lighting regimens, can disrupt the functional development of the avian eye (Oishi and Murakami, 1985; Li et al., 1995). Problems affecting the vision of broilers such as buphthalmia (in which the eyes become enlarged) and blindness can also occur with continuous lighting regimens (Whitley et al., 1984). Extended periods of dim lighting or darkness can also cause decreased corneal thickness in chickens (Harrison et al., 1968; Jenkins et al., 1979).

Kirby and Froman (1991) compared the immune responses of White Leghorn cockerels reared with constant light or with a 12L:12D regimen (both at a photophase intensity of 40 to 45 lx). Chickens in the constant light group had significantly less anti-SRBC antibody titers and a less delayed hypersensitivity response in the wattle than the 12L:12D group, which indicates a potential impairment of immune system response. Similar results have been observed in Japanese quail (Moore and Siopes, 2000) reared with constant light or on short (8L:16D) or long (16L:8D) days, with photophase intensities of 700 to 800 lx. The 2 groups on a light:dark schedule showed greater humoral and cellular immune responses than the group on the constant light regimen. The intensity of the lighting used in these studies is greater than that used by the broiler industry; the effect of light intensity alone on immune function has not been systematically studied.

The aim of this study was to examine the effect of different photophase light intensities (5, 50, and 200 lx) on the activity patterns and health of broilers. These illumination levels were chosen to provide low, medium, and high intensity contrasts between the photophase and the scotophase (1 lx for all treatments) and for comparison with previous published studies of the effects of different illumination levels on poultry. Broilers reared with greater light intensities were predicted to be more active during daylight periods, with the potential for better leg, eye, and immune system health.

	MATERIALS AND METHODS

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Birds and Husbandry

Cobb 500 broilers (n = 753) were obtained from a commercial hatchery as day-old straight run chicks from 3 separate hatches. The hatches were used as intime trials. All chicks were vaccinated against Marek’s disease at the hatchery. Upon arrival approximately the same numbers of chicks were randomly allocated to each of 6 pens. The birds were given access to feed and water ad libitum throughout the study. They were fed a prestarter mash (23.21% CP, 3.10 kcal of ME/g) for the first 3 wk and then Purina Mills Flock Raiser Sunfresh Crumble (St. Louis, MO; 20% CP, 3.00 kcal of ME/g) for the remainder of the 6-wk growout period.

The broilers were housed in 6 environmental chambers and managed according to the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999). Each chamber contained a 5.0-m² pen bedded with wood shavings (approximately 10 cm deep). The stocking density was 7.7 birds/m². Temperature was set at 29°C for the first week and decreased by 2°C each week until reaching 21°C. Relative humidity was set at 50% throughout the study.

During the first 3 d all broilers were housed under a 23L:1D regimen (provided by incandescent lights) with intensities of 200 and 1 lx during the photophase and scotophase, respectively. Light intensity was measured along a horizontal plane at 25 cm above the litter with the photoreceptor sensor of a light meter (LT Lutron, model LX-100; Das Distribution Inc., East Granby, CT) pointed toward the light sources. There were no dawn-dusk transitions between the photophase and the scotophase. On d 4, each chamber was assigned a lighting regimen of 16L:8D and 1 of 3 photophase light intensities: 5, 50, or 200 lx (as measured at broiler head height). Scotophase intensity remained at 1 lx. Light spectra in the chambers ranged from 400 to 660 nm, with all colors represented in all treatments. These treatments continued for the remainder of the grow-out period. Due to facility constraints, assignment of treatments to chambers could not be completely randomized. The 5 and 50 lx treatments were rotated through different chambers, but the 200 lx treatment was not. However, environmental variables, except for light intensity, were kept constant for all chambers.

Behavioral Measures

General activity patterns were measured using passive infrared detection (PID) devices (Brinks, model 7295b, Foothill Ranch, CA) as described in Pedersen and Pedersen (1995) and Nielsen et al. (2003). Starting at 3 wk of age, activity was recorded over a 48-h period once a week. The PID were placed 0.3 m from the front of each pen and at a height of approximately 20 cm from the floor. The infrared beam of the device was horizontal and spanned the entire width and depth of the pen. If at least one broiler was moving, the beam was broken and the device was turned on. If no movement was occurring in the pen, the device remained off. Every 10 s a Dickson Pro Series data logger (Dickson, Addison, IL) recorded whether the device was on or off. These values were then averaged (adjusting for the number of broilers in each pen) for each hour of the 24-h period. Each hourly mean was then divided by the overall mean activity of the broilers in all pens over that 24-h period to correct for any differences in individual PID devices. The resulting value represented the general activity for that pen during that hour on a scale from 0 to 1 (although the maximum value was actually higher than 1 due to correction for the number of birds in the pen). Thus, a relative activity value of 0 indicated no activity and of 1.27 indicated constant activity.

Feeding activity was measured over a continuous 24-h period each week in each pen, starting at 3 wk of age. Each feeder was placed on a digital scale (Ohaus, Pinebrook, NJ) that recorded the feeder’s weight every 30 s using WinWedge Pro Version 3.0 (TAL Technologies Inc., Philadelphia, PA). The average difference in feed consumed per hour (adjusted for the number of broilers in each pen) was used as the measure of feeding activity. Feeding activity was measured and analyzed over the total 24-h period, and also partitioned into photophase and scotophase periods for analysis. Chickens in each chamber were weighed at 7, 14, 21, 28, and 39 d of age.

Health and Immune Measures

At 21 d of age, broilers from trials I and II (3 per pen, n = 36) were injected with keyhole limpet hemocyanin (KLH) conjugated to dinitrophenol, s.c. (0.1 mg in 0.5 mL of PBS). Seven days later blood was taken from the brachial vein and the chicks were boosted with the same dose of KLH. Chicks were bled 3 d later to determine the secondary IgG response. Also at 21 d of age, a second group of chicks from trials I and II (3 per pen; n = 36) was injected with Escherichia coli lipopolysaccharide (LPS) into the abdominal cavity (3 mg in 3 mL of PBS) and bled 16 h later to determine concentrations of NO and acute phase proteins, lysozyme, and haptoglobin. Blood was also taken at the time of LPS injection to determine mitogen-induced lymphocyte proliferation and the bactericidal capacity toward E. coli and Staphylococcus aureus.

Bactericidal activity of whole blood and concentrations of lysozyme and haptoglobin were determined as described by Millet et al. (2007). Proliferation of B and T lymphocytes in response to the mitogens LPS and phytohemagglutinin) was determined as described by Leshchinsky and Klasing (2001). Antibody levels against KLH were determined by ELISA using the technique of Hangalapura et al. (2004).

At 39 d of age, all chickens were assessed for lameness using the 0 to 5 modified gait scoring system of Garner et al. (2002), where a score of 0 represents a perfect gait and a score of 5 represents an inability to stand. Broilers were also informally assessed for lameness throughout the study, and any chickens scoring 4 or 5 were killed for ethical reasons. At 40 d of age all chickens were killed via argon gas with less than 2% residual oxygen and assessed for the following leg abnormalities by postmortem examination: occurrence of leg rotation (valgus-varus); bruises, calluses, and erosions of the hocks; pododermatitis; and incidences of tibial dyschondroplasia and femoral head-neck necrosis.

At the time of necropsy, 10 broilers from each pen were randomly selected to have their left and right eyes removed. The eyes were fixed in a 10% neutral buffered formalin solution for histopathological analysis. They were then hardened by fixing them in a series of alcohols at 50, 70, and 90% concentration for 24 h each, and then trimmed 2 to 3 mm thick making sure that the cornea, lens, posterior and anterior uvea, pecten, and optic nerve were included. The trimmed eyes were transferred to a decalcifying solution containing formic acid-sodium citrate and fixed for 1 to 2 d. They were then processed overnight, embedded in paraffin, sectioned at 4 µm, stained with hematoxylin and eosin, and examined by bright-field microscopy. The right and left eyes were also removed at necropsy from an additional 10 randomly selected broilers per pen from trial III (n = 60) to take eye measurements. Extraocular tissue was trimmed from the eyes and gross measures were made of eye weight, back-to-front and side-to side diameters, and corneal radii.

Statistical Analysis

A split plot design (with pen as a blocking variable to control for any variation across trials) was used, with treatment as the main plot and age as the subplot. To analyze behavioral differences (general activity and feeding activity) among the treatments, an unbalanced mixed GLM was used, with treatment and age as fixed variables and pen as a random variable. When significant differences were found, Tukey post hoc tests were performed. All the assumptions of the GLM were tested (Shapiro-Wilk test for normality, Levene’s test for homogeneity of variance) and data were transformed as necessary to meet those assumptions. All analyses were performed using SAS 9.1 for Windows (SAS Institute Inc., Cary, NC).

Body weight was also analyzed using the unbalanced mixed GLM described above. Because gait score and leg abnormality data were ordinal, they were each analyzed using the Kruskal-Wallis test on the equality of the medians, adjusted for ties. When significant differences were found, Wilcoxon 2-sample post hoc tests were performed. Immunological data were analyzed by 2-way ANOVA for the main effects of light treatment and replication and for the interaction between treatment and time. Differences in eye measurements were compared using a 1-way ANOVA.

	RESULTS

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There was no effect of light intensity on overall activity patterns throughout the entire photoperiod (F_2,14 = 1.75, P = 0.21) or during the scotophase (F_2,14 = 0.43, P = 0.66). However, broilers reared with 5 lx of light were less likely to be active (F_2,14 = 4.94, P = 0.02) during the photophase than broilers reared with 50 or 200 lx (P = 0.001 and 0.01, respectively; Figure 1). Broilers reared with 5 lx of light also showed less (F_2,14 = 17.70, P < 0.0001) change in activity (0.14 ± 0.01) between the photophase and scotophase across all weeks than broilers reared with 50 (0.34 ± 0.02) or 200 lx (0.35 ± 0.02; Figure 2). Light intensity did not have an effect on feeding activity during the total photoperiod (F_2,14 = 0.01, P = 0.10), the photophase (F_2,14 = 0.12, P = 0.89), or the scotophase (F_2,14 = 0.54, P = 0.60).

View larger version (26K): [in this window] [in a new window]   Figure 1. The least squares mean (±SEM) levels of general activity of broilers reared under 5, 50, or 200 lx illumination; values are shown for the photoperiod, photophase, and scotophase. a,bBars with different letters indicate significant differences (P < 0.01).

View larger version (16K): [in this window] [in a new window]   Figure 2. The changes in least squares mean relative activity over a 48-h period for broilers reared under 5, 50, or 200 lx. The least squares means are averaged across all weeks. Dark bars on hour axis indicate the scotophase.

View larger version (9K): [in this window] [in a new window]   Figure 3. The mean (±SEM) BW of broilers reared under 5, 50, or 200 lx illumination on d 7, 14, 21, 28, and 39.

Eye measurements are shown in Figure 4. There was no effect of light intensity on back-to-front (F_2,55 = 0.61, P = 0.55) or side-to-side (F_2,55 = 0.51, P = 0.61) diameter of the eyes, or corneal radii (F_2,55 = 1.27, P = 0.29). However, broilers reared with 5 lx had heavier eyes (F_2,55 = 6.81, P = 0.002) than broilers reared with 50 or 200 lx. There were no obvious systematic abnormalities seen in the stained sections, although inflammation of the choroid (choroiditis) was evident in 12 of the 60 broilers from the 5 lx treatment; there was no evidence of inflammation in the eyes of broilers from the other 2 treatments.

View larger version (21K): [in this window] [in a new window]   Figure 4. The least squares mean (±SEM) of gross back to front (BF) and side to side (SS) eye diameters, corneal radii (CR), and eye weight (EW) measurements of 40-d-old broilers reared with 1 of 3 light intensities: 5, 50, or 200 lx. The BF, SS, and CR are measured in centimeters, whereas eye weight is measured in grams. a,bBars with different letters indicate significant differences (P < 0.01).

	DISCUSSION

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The activity of the broilers during the scotophase is not surprising given that they were not in complete darkness. In fact, Nielsen et al. (2003), also using passive infrared detection, reported that broilers were active during the scotophase even in complete darkness. Although Nielsen et al. (2003) did not record behavior directly, based on indirect evidence they speculated that the nocturnal activity consisted primarily of feeding and drinking. Alvino (2008) video-recorded broilers during the scotophase, and found that they did engage in active behaviors such as feeding, drinking, and foraging when in 1 lx of light.

Feeding behavior was not affected by the different light intensities, a finding that is consistent with other studies (Weaver and Siegel, 1968; Charles et al., 1992; Downs et al., 2006; Kristensen et al., 2006b). Although broiler feeding behavior has been demonstrated to be closely linked with lighting regimens (Gordon, 1994), it is likely that feeding patterns are more influenced by day length rather than light intensity per se (Morris, 1968; Savory, 1976).

Light intensity also had no effect on the weight gain of the broilers. Final BW met the mean values outlined by Cobb-Vantress Inc. for Cobb 500 broilers (http://www.cobb-vantress.com/Products/ProductProfile/Cobb_500_PP.Pdf) across all treatments. This lack of difference between intensity treatments is similar to that found in other studies examining light intensity effects on final BW (Newberry et al., 1988; Downs et al., 2006; Kristensen et al., 2006b) and is consistent with the lack of treatment effects on feeding activity. However, greater light intensities did not result in a transitory decrease in weight gain, as found by Charles et al. (1992) and Downs et al. (2006). The increasing and decreasing photoperiods used in these studies were different from the constant photoperiod in the present study, which could have contributed to the difference in findings.

Lighting treatments did not have a differential effect on mortality. Of the 18 mortalities, 10 occurred before 7 d of age, mostly among chicks that seemed weak when they arrived from the hatchery. The remaining 8 mortalities occurred approximately equally across treatments (3 in 5 lx, 3 in 50 lx, and 2 in 200 lx).

All but one of the broilers examined had a gait score greater than zero. The majority (96%) were scored 1 or 2, which signifies that their gait abnormalities had little to no impact on their overall function. Only 4% of the broilers were scored 3 or greater, signifying impairment of function (Garner et al., 2002). It is noteworthy that there were no gait scores greater than 2 in the broilers reared with 200 lx, whereas approximately 5% of both 5 and 50 lx birds had greater scores, although there were no significant treatment differences. Thus, increased activity was not clearly associated with an improvement in gait.

There was no difference between the treatments in occurrence of calluses, torsion, pododermatitis, tibial dyschondroplasia, or femoral erosions. However, the 200 lx birds had more bruising, but fewer erosions on their hocks and footpads, than those reared with 5 or 50 lx. Several studies have suggested that an increase in exercise could lead to better overall leg health (Haye and Simmons, 1978; Newberry et al., 1988; Weeks et al., 1994; Su et al., 2000; Mench et al., 2001). However, even though broilers reared under the greater intensities were more active than broilers reared under dim light, there were few differences in leg health. The greater occurrence of bruising in the 200 lx broilers could be related to their greater activity, but no formal measures were made to assess this link. The greater occurrence of erosions in the 5 lx group may be due to their lessened activity, creating longer contact time with the litter (Hester, 1994), but is harder to explain in the 50 lx group, as they had activity levels similar to those of the 200 lx group. Further investigation is needed to determine the cause of this difference.

Light treatments had little effect on indices of immunity in this experiment, with the exception of a tendency for 50 lx to increase the primary IgM response to the novel antigen, KLH. Melatonin secretion is sensitive to day length and influences immune responses (reviewed by Nelson and Demas, 1997). Receptors for melatonin are present on the spleen, thymus, and bursa (Skwarlo-Sonta, 1999) and are presumably present on lymphocytes because melatonin stimulates cytokine production by lymphocytes (Poon et al., 1994). Injection of newly hatched turkey poults with melatonin accelerates development of cellular and humoral immune responses (Moore and Siopes, 2005). Melatonin treatment can also ameliorate negative affects of glucocorti-coids on the immune system (Nelson and Demas, 1997). It is possible that the range of light intensities used in this experiment did not influence melatonin levels sufficiently to result in measurable changes in immunity.

Broilers exposed to 5 lx had increased eye weight compared with those reared with 50 or 200 lx. This could have been related to the inflammation of the choroid evident in 20% of the 5 lx birds, although what might have initiated this is difficult to determine. It is possible that it was caused by degeneration of photo-receptors, but this was not evident using light microscopy. Another possible explanation could be systemic viral or bacterial infection, or both, such as with E. coli or mycoplasma, although this would need to be verified by gross or histological examination of other organs. Although difficult to explain, the enlarged eyes of the broilers raised in low intensity light are similar to the studies of Harrison et al. (1968) and Jenkins et al. (1979), except that in those studies increased eye weight was also associated with a corresponding difference in one or more gross measures of the eye, which was not found in the current study.

In this study, varying light intensity with a photope-riod of 16L:8D had minimal effects on broiler health, with the possible exception of eye health. However, a light intensity of at least 50 lx did stimulate higher diurnal activity levels in broilers without negatively affecting weight gain. Further investigation of intensities between 5 and 50 lx, which are more typical of commercial production, are needed to determine the minimum intensity that increases activity. Finally, to help elucidate the potential effects of increased activity on leg health and production parameters, it would be valuable to examine the effects of light intensity and the interactions between light intensity and photoperiod using larger numbers of birds under conditions that are more similar to the commercial production environment.

	ACKNOWLEDGMENTS

 
This research was funded by USDA-Cooperative State Research and Extension Service, National Research Initiative grant no. 2005-35204-16110. We thank Gina Alvino, Giuseppe Vezzoli, and Gena Fagerberg (University of California, Davis) for their assistance with the care of the broilers and data collection and Rose-line Holt (University of California, Davis) for help in conducting immunological assessments. We also thank Foster Farms (Livingston, CA) and Cobb-Vantress Inc. (Siloam Springs, AR) for supplying the broilers used in this study.

Received for publication April 29, 2008. Accepted for publication August 24, 2008.

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