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ENVIRONMENT, WELL-BEING, AND BEHAVIOR |
Department of Poultry Science, Auburn University, AL 36849
1 Corresponding author: lienrog{at}auburn.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Key Words: broiler • light intensity • photoperiod • breast meat yield • stress
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Awareness of lighting programs has recently increased as governmental (Commission of the European Communities, 2005), poultry industry (National Chicken Council, 2005), and industry customer groups (Food Marketing Institute and National Council of Chain Restaurants, 2003) have established guidelines that define minimum light intensities and amounts and durations of darkness that must be provided to broilers daily. These guidelines have increased interest in the efficacy of restricted photoperiods (16 to 20 h) of different intensities [0.1 to 2 footcandles (FC); 1 FC = 10.76 lx], because all of them restrict the use of continuous or near-continuous photoperiods and the Commission of the European Communities (2005) restricts the use of low intensities (<2.0 FC), which are still commonly used in the United States.
Results of the few studies on the influence of either photoperiod or light intensity on physiological stress responses of chickens are inconsistent, although there is a widely held assumption that long photoperiods and very high or low light intensities compromise their welfare (Gordon, 1994; Buyse et al., 1996b; Bessei, 2005). Heterophil:lymphocyte (H:L) ratios of broilers were observed to be unaffected by photoperiod (Blair et al., 1993). Similarly, H:L ratios of layers were unaffected by photoperiod; however, exposure to 23L:1D increased their duration of tonic immobility (a measure of psychological stress) relative to 14L:10D (Campo and Davila, 2002). Plasma corticosterone levels of broilers were elevated by exposure to continuous as opposed to intermittent photoperiods or higher light intensity in 1 of 2 trials testing each parameter but unaffected in the other (Buckland et al., 1976). Renden et al. (1994a) also observed no effect of photoperiod on broiler corticosterone levels.
Only a small percentage of reports focusing on the influence of photoperiod and light intensity on broiler production continue data collection past slaughter. Renden et al. (1992b, 1993b, 1994b, 1996) observed that relative to those of broilers exposed to 23L:1D, restricted, intermittent, and increasing photoperiod programs can influence the yields of different parts and cuts even though transient BW reductions were overcome by the time of slaughter. Recently, it has also been observed that breast meat yield increased linearly as rearing photoperiod treatments were increased in 3-h increments from 14L:10D to 23L:1D (Schwean-Lardner et al., 2006) and that reducing light intensity from 2 to 0.25 FC resulted in a slightly greater amount of wing at the expense of breast (Downs et al., 2006). The purpose of the present study was to compare effects of relatively low light intensities (1.0 vs. 0.1 FC) and long photoperiods (18L:6D vs. 23L:1D), both within ranges commonly used in commercial production and mentioned in recent guidelines, on the live performance, a physiological stress response, and carcass and breast meat yields of broilers.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Experimental Treatments
Photoperiod and light intensity were the 2 factors varied by the experimental treatments. All rooms were provided 23L:1D with an intensity of 3 FC until d 8. Three replicate rooms were then subjected to the following photoperiod and intensity treatments in a 2 x 2 factorial arrangement: either 1 FC (1FC) or 0.1 FC (0.1FC) from 8 to 49 d and either 23L:1D from 8 to 49 d (23L) or 18L:6D from 8 to 42 d followed by 23L:1D from 42 to 49 d (18L). It should be noted that the 18L treatment was returned to 23L for the last 6 d before slaughter, so the 18L and 23L treatments only differed in duration from 8 to 43 d. This was done, because it is common industry practice to maximize photo-period for 3 to 7 d before slaughter, and it is provided for by recent guidelines (Food Marketing Institute and National Council of Chain Restaurants, 2003; Commission of the European Communities, 2005; National Chicken Council, 2005). Light intensity treatments differed from 8 to 49 d.
Measurements
Individual BW were determined, and BW uniformity (% within ± 10% of BW mean) was calculated at 8, 15, and 49 d. Pen group BW was determined at 29 and 43 d. Feed consumption by each room was determined at 8, 15, 22, 29, 36, 43, and 49 d. Feed conversion by each room was calculated at 8, 15, 29, 43, and 49 d. Mortalities were recorded daily, necropsied, and the cause of death was classified as either metabolic (ascites, skeletal disorders, or sudden death syndrome) or nonmetabolic (other causes) based on position and posture when found as well as internal and external abnormalities.
At 40 d, a blood sample was drawn from each of 3 birds per pen without regard to sex by venipuncture with heparinized syringes. Immediately, 2 thin smears were prepared from each blood sample on clean microscope slides and allowed to air-dry. Smears were stained with a modified Wright’s stain, then cover-slipped, and a total of 100 heterophils and lymphocytes were identified and counted under 100x oil immersion. Other types of leukocytes were not counted or used in calculations. The H:L ratios were calculated by dividing the number of heterophils by the number of lymphocytes.
At 49 d, following a 10-h feed withdrawal period, 8 males and 8 females per room were randomly selected for processing at the Auburn University Poultry Processing Unit and placed in transport coops. Birds were weighed, hung on shackles, and electrically stunned (50 V, 20 mA, 400 Hz). Killing was by a single cut severing the right carotid artery and jugular vein. Following a 95-s bleed-out, birds were subscalded in a 2.44-m-long single pass steam-injected scalder at 56.6°C for 90 s, defeathered in a 1.22-m-long picker for 42 s, eviscerated using an automatic eviscerator, and chilled in a 2°C ice-slush of static tap water for 2 h. Carcasses were then drained, weighed, and deboned to obtain skinless, boneless breast fillet (pectoralis major muscle) and breast tender (pectoralis minor muscle) weights. Carcass yields are expressed as a percentage of live weight, and carcass part yields are expressed as a percentage of chilled carcass weights.
Statistical Analysis
A randomized complete block design with a 2 x 2 factorial arrangement of the light intensities and photoperiods tested was used for this study. Data for group BW, feed consumption, feed conversion, uniformity, mortality, and H:L ratio parameters were analyzed for intensity and photoperiod effects and their interaction in 1 statistical model using PROC GLM (2004 version, SAS Institute Inc., Cary, NC). Individual BW and carcass and parts weights and yields were analyzed for sex effects (nested within rooms) and all possible interactions among sex, intensity, and photoperiod treatments. However, because there were no significant interactions involving sex, data were combined across sex. All data were analyzed independently at each age with rooms serving as experimental units. Percentage data were arc sine-transformed before analysis. Statistical significance was reported at P 
0.05.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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). At 29 d, both 18L and 0.1FC treatments reduced BW. These effects were not additive, so BW reduction relative to that of the 1FC-23L treatment was similar in the 1FC-18L (66 g), 0.1FC-23L (48 g), and 0.1FC-18L (59 g) treatments. At 43 d, the 0.1FC-18L treatment was intermediate to but not different from the 1FC-23L and both the 1FC-18L and 0.1FC-23L treatments, which were significantly reduced (74 and 55 g) relative to the 1FC-23L treatment, respectively. This was before the photoperiod being increased to 23L:1D for last 6 d before slaughter in the 18L treatment. At 49 d, the BW of the 1FC-23L and 0.1FC-18L treatments were similar and an average of 49 g greater than those of the 1FC-18L and 0.1FC-23L treatments. Complete compensatory growth occurred in the 0.1FC-18L treatment; however, this was not the case in the 1FC-23L and 0.1FC-23L treatments. This effect was not only due to the increase in photoperiod from 18L:6D to 23L:1D during the last 6 d in the 18L treatment, because it was already underway at 43 d and occurred in the 0.1FC-18L but not the 1FC-18L treatment. Several previous reports have indicated that BW of broilers provided photoperiods between 20L:4D and 16L:8D did not differ from those provided 23L:1D, particularly at later ages (Renden et al., 1992b, 1993, 1994b, 1996; Laster et al., 1999; Schwean-Lardner et al., 2006). Robbins et al. (1984) observed decreased 49-d BW in broilers provided 16L:8D relative to 23L:1D. Renden et al. (1992b, 1993b, 1994b, 1996) generally saw a transitory reduction in BW by 16L:8D and 14L:10D relative to 23L:1D, with similar BW attained at 48 or 49 d; however, sometimes the BW of those provided 14L:10D did not catch up (Renden et al., 1994b). Photoperiods less than 14L:10D decrease BW relative to that of broilers provided continuous or near-continuous light (Barott and Pringle, 1951; Beane et al., 1962; Skoglund et al., 1966; Deaton et al., 1970; Ingram et al., 2000; Schwean-Lardner et al., 2006). With respect to light intensity, we recently reported (Downs et al., 2006) a transient increase in the BW of broilers provided 0.25 FC, in either increasing or 23L:1D lighting programs, when compared with those provided 2 FC. However, BW were similar at 56 d. A similar transient BW increase in response to providing 0.5 FC instead of 15 FC in both increasing and 23L:1D lighting programs was also observed in an earlier report (Charles et al., 1992). Several much earlier publications report increased (Barott and Pringle, 1951; Skoglund and Palmer, 1962) or similar (Deaton et al., 1970; Buckland et al., 1976; Dorminey and Nakaue, 1977; Newberry et al., 1986, 1988; Deaton et al., 1988) BW in broilers provided lower light intensities when comparing intensities ranging from 0.1 to 120 FC. However, although broilers were grown to similar or greater ages in many of these earlier studies, BW were only 30 to 50% of those in the present study. No previous reports have observed an interaction between photoperiod and light intensity, as was the case in this study in which BW were greater in near-continuous light at a higher intensity, whereas with a shorter photoperiod, BW were greater at a lower intensity.
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). The significance of these effects gradually diminished as the birds aged. The intensity effect only approached significance (P = 0.0591) at 22 d (an average of 48 g or 3.7%) and was nonsignificant thereafter. The photoperiod effect persisted through 29 d, only approached significance (P = 0.0910) at 36 d (an average of 98 g or 2.8%), and was nonsignificant thereafter. Different photoperiods have generally been accepted to influence growth rates via their effect on feeding behavior and consumption (Renden et al., 1992a,b, 1993). Photoperiods of less than 18 h have been observed to decrease feed consumption (Skoglund et al., 1966; Robbins et al., 1984; Schwean-Lardner et al., 2006). It appears that at earlier ages, broilers are more sensitive to shorter photoperiods in terms of feed consumption. Either they learn to consume feed in shorter photoperiods after a period of exposure or they are able to catch up in feed consumption, because its age-related increase slows as they approach slaughter age. The transient reduction in consumption observed in the 0.1FC treatment in the present study was likely due to the abrupt change in intensity from 3 to 0.1 FC at 8 d. In previous studies in which intensity was gradually reduced (Newberry et al., 1986; Downs et al., 2006), consumption was not decreased following the decrease in intensity. Abrupt changes in lighting programs, such as from long to intermittent, have also been observed to result in short-term decreases in feed consumption (Buyse et al., 1996a).
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). Previous reports on the influence of photoperiods of 18 h or less on feed conversion have been inconsistent. Some have observed a decrease (Beane et al., 1962; Ingram et al., 2000; Schwean-Lardner et al., 2006), whereas in others, it was unaffected (Skoglund et al., 1966; Deaton et al., 1970; Robbins et al., 1984; Renden et al., 1992b, 1993, 1994b, 1996; Laster et al., 1999) or increased (Renden et al., 1994b). Feed conversion has consistently been reported to be unaffected by light intensity (Dorminey and Nakaue, 1977; Newberry et al., 1986, 1988; Deaton et al., 1988; Charles et al., 1992; Downs et al., 2006). The lack of an effect on feed conversion and the parallel effects on BW and feed consumption observed in the present study support the contention that lighting program effects on BW are due to their influence on feed consumption.
Uniformity was reduced in the 0.1FC treatment at 15 d (Table 3). This was due to the lack of an increase in uniformity from 8 to 15 d in the 0.1FC treatment as it did in the 1FC treatment and is normal in broilers of this age. This adverse effect is likely related to the concurrent transient decrease in feed consumption in the 0.1 FC treatment and due to the previously mentioned abrupt change in light intensity. Although uniformity is a serious concern of the industry, only 1 previous report has documented the influence of lighting programs on uniformity, and it also noted few significant effects (Downs et al., 2006).
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). This may be due to recent increased selection against metabolic disorders by breeding companies. However, broiler mortality was recently observed to increase linearly as photoperiod was increased from 14 to 23 h (Schwean-Lardner et al., 2006). Other reports have failed to note an improvement in mortality when comparing shorter photoperiods to 23L:1D (Renden et al., 1992b, 1994b, 1996). Renden et al. (1996) indicated that restricted lighting programs generally have beneficial effects when mortality approaches 10%, as was the case in several previous reports (Charles et al., 1992; Blair et al., 1993; Renden et al., 1993). Most previous reports indicate no effect of lower light intensities on mortality (Newberry et al., 1986; Deaton et al., 1988; Charles et al., 1992; Downs et al., 2006), although Newberry et al. (1988) observed an increase in mortality in 1 of 2 trials in which light intensity was reduced from 18 to 0.6 FC.
Physiological Stress
Percentages of heterophils and lymphocytes and the H:L ratio at 40 d were unaffected by treatments (Table 3). Relative to ratios reported in response to specific stressors by Gross and Siegel (1983), the average H:L ratio of 0.44 observed in the present study indicates a low level of stress. The H:L ratios of 3 Spanish breeds of laying hens housed in floor pens averaged 0.61 at 40 wk and were unaffected by photoperiods ranging from 14L:10D to 23L:1D (Campo and Davila, 2002). Similarly, H:L ratios averaged 0.43 at 2 wk and 0.60 at 5 wk of age and did not differ in commercial broilers exposed to either 23L:1D or an increasing photoperiod program (Blair et al., 1993). These results are correlated with the observation of Renden et al. (1994a) that photoperiod does not affect plasma corticosterone levels of broilers. However, in 1 of 2 trials, broilers exposed to continuous light had significantly higher plasma corticosterone levels than those on intermittent lighting programs, and in 1 of 2 trials, corticosterone was greater in broilers exposed to a light intensity of 0.75 FC than in those provided 0.1 FC (Buckland et al., 1976). Additionally, Campo and Davila (2002) did observe that tonic immobility durations were elevated in hens exposed to 23L:1D instead of 14L:10D. Therefore, it appears that although H:L ratios in the present study indicated that longer photoperiods and brighter intensities did not induce physiological stress, there is evidence in the literature that different lighting programs may influence either physiological or psychological stress responses.
Processing Performance
The statistical relationship of the treatment liveweights (Table 4) from the sample of birds processed was slightly different than that for the BW of all birds (Table 1) in the present trial. Similar to the BW results, the sample liveweights of the 0.1FC-18L and 1FC-23L treatments were greatest. However, the sample liveweight of the 0.1FC-18L treatment was not greater than that of the 1FC-18L treatment, as was the case with BW. Also, the 1FC-18L sample liveweight was greater than that of the 0.1FC-23L treatment, whereas these treatments had similar BW. An interaction effect on chilled carcass weight (Table 4) resulted in the 0.1FC-23L treatment carcass weight being reduced an average of 78 g relative to the other 3 treatments, which were similar. Chilled carcass yield averaged 0.5% greater in the 23L than in the 18L treatment. An interaction effect resulted in the 1FC-23L treatment having greater whole breast weights (average + 45 g), fillet weights (average + 40 g), and fillet yields (average + 1.1%) than the other 3 treatments, which were similar (Table 4). The whole breast yield of 23L averaged 1.0% greater than that of the 18L treatment. Tender weights of the 1FC treatment averaged 5 g more than those of the 0.1FC treatment. There were no significant effects on tender yield.
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ACKNOWLEDGMENTS |
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Received for publication October 12, 2006. Accepted for publication March 23, 2007.
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REFERENCES |
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