J APPL POULT RES 2006. 15:406-416
© 2006 Poultry Science Association
The Effects of Photoperiod Length, Light Intensity, and Feed Energy on Growth Responses and Meat Yield of Broilers
K. M. Downs*,1,
R. J. Lien
,
J. B. Hess,
S. F. Bilgili and
W. A. Dozier, III
* School of Agribusiness & Agriscience, Middle Tennessee State University, Murfreesboro 37132; Department of Poultry Science, Auburn University, AL 36849; and USDA-ARS Poultry Research Unit, Mississippi State 39762
1 Corresponding author: kdowns{at}mtsu.edu
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SUMMARY
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A study was conducted to assess the effects of photoperiod length (constant 23L:1D vs. a photoperiod program going from decreasing to increasing quantity of light), light intensity (bright vs. a dim, reducing intensity), and feed ME levels (low vs. high) on performance and carcass characteristics of female broilers grown to 56 d. Use of a treatment with early decreasing photoperiod followed by an increasing photoperiod reduced feed consumption and subsequent BW early. However, growth compensation occurred and feed consumption and BW were similar across photoperiod treatments by study end. Likewise, reducing light intensity (from 1 to 0.25 fc) stimulated feed consumption and a subsequent BW improvement early, as compared with high-intensity (2 fc) lighting maintained at a constant level. However, the disparity in feed consumption and BW, as influenced by light intensity, did not persist throughout the growing period. Feed conversion was not noticeably affected by photoperiod or light intensity treatments. Minimal effects of lighting were observed for carcass or part yields; however, there appeared to be a subtle substitution effect between leg, wing, and breast yield influenced by lighting program. Birds exposed to the decreasing–increasing photoperiod and dim, reducing light treatments yielded more leg and wing at the expense of breast. Feeding a low ME diet resulted in increased feed consumption and feed conversion. However, birds consuming a low ME diet were more uniform. No effects of treatment on mortality were measured. These data indicate that a decreasing–increasing photoperiod can be used effectively to reduce early growth, yet allow birds to compensate as they approach market age. Low intensity lighting, however, appears to stimulate early feed consumption and growth, although this effect is transitory. Furthermore, the increased feed conversion of birds grown on the low energy diet may make its use less desirable.
Key Words: lighting • photoperiod • light intensity • feed energy • broiler • carcass characteristic
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DESCRIPTION OF PROBLEM
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Broiler producers continually balance genetic improvements dictating a rapidly growing, heavy BW broiler with the logistics of managing these birds to market age with a high rate of livability. Traditionally, to maximize growth potential, broilers have been subjected to continuous (24L:0D) or near continuous (23L:1D) lighting (and feed access) from placement to market age. However, relatively recent work has focused on the effect of alternative lighting protocols and their application in the commercial broiler growout. Use of alternative lighting programs during growout is relatively commonplace.
Programs with decreasing followed by increasing photoperiod have reduced the incidence of ascites [1, 2], sudden death syndrome [1], leg disorders [3, 4], and total mortality [1, 2, 3, 4, 5] in broilers. It has been suggested that this improvement in health may result from early feed restriction, enhanced bird activity level, increased androgenic hormone production, changes in metabolism, or a combination of these factors [3]. Most work has shown that a decreasing-increasing photoperiod produces an early restriction of BW, initiated by the early decreasing photoperiod, which is ameliorated by market age [1, 2, 3, 5, 6, 7, 8, 9]. Riddel and Classen [4] did not demonstrate this attenuation of BW when roasters were grown using a decreasing–increasing photoperiod. Furthermore, feed conversion has been shown to be unresponsive to this type of photoperiod [1, 2, 3, 4, 5, 6, 7, 8, 9].
Carcass yield and body composition of broilers can be affected by photoperiod, but conflicting results have been reported. Fillet (pectoralis major) yield was reduced 1.1% when the photo-period was progressively increased from 8 to 23 h of light during a 49-d growth period [7]. Two other studies by Renden and coworkers [6, 8] demonstrated no effect of a decreasing–increasing or only an increasing photoperiod regimen on carcass yield. Similarly, Newcombe et al. [9] showed that increasing photoperiod encourages greater abdominal fat deposition; however, others [5, 6, 7, 8] have reported no effect of photoperiod on body composition.
Light intensity can dramatically influence the activity level of growing broilers; however, its effects on live performance (BW, feed consumption, feed conversion) are limited. A field study by Scheideler [10] using 8 commercial broiler houses (170,000 birds grown to 48 d) revealed that a 75 and 80% reduction in light intensity did not influence BW, feed conversion, or mortality rate. Others have confirmed the absence of significant performance effects from light intensity [11, 12]. Increased activity levels associated with higher light intensity do promote greater walking and standing behaviors [12], which may reduce leg abnormalities [13]. Furthermore, the extent of fat deposition in broilers exposed to high intensity lighting is limited; however, it is unlikely that this response would realize substantial economic effects for the processor [5]. Clearly, potential negative effects of lighting protocols on bird performance and final product yield must also be considered.
Feed ME level can produce dramatic effects on feed consumption and resulting growth and feed conversion; however, data on the interaction of lighting with dietary energy are limited. Manipulation of dietary energy level and lighting protocol may produce a synergistic effect on early growth rate and the incidence of metabolic disorders. Therefore, the objective of this study was to determine if a photoperiod program going from decreasing to increasing quantity of light ("step-down, step-up"), in conjunction with variations in light intensity and dietary energy levels, could be used in female broilers grown to 56 d to achieve acceptable performance and carcass yield while reducing early rapid growth and its associated mortality.
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MATERIALS AND METHODS
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Experimental Treatments
Experimental treatments were evaluated as 3 factors (photoperiod length, light intensity, and feed energy), with 2 levels per treatment factor. Table 1
summarizes specific details of each treatment level. Photoperiod lengths were either constant (CONS) or decreasing–increasing (DEIN), light intensities were either bright (BRI) or dim, reducing (DIR), and diets had either high (HIE) or low (LOE) energy levels. Birds on the BRI treatment were exposed to 2 fc from d 0 to 56 and those on DIR were exposed to 1 fc from d 0 to 7, 0.5 fc from d 8 to 14, and 0.25 fc from d 15 to 56.
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Table 1. Summary of 56-d experimental design as a 2 x 2 x 2 factorial arrangement of lighting program, light intensity, and feed energy
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Bird Management
A 56-d growout was conducted using 1,680 1-d-old female broiler chicks (Ross 344 x Ross 508) [14] assigned to 1 of 8 treatments (2 x 2 x 2 factorial arrangement) with 3 replicate pens per treatment. Twelve light-tight environmentally controlled experimental rooms (3.66 x 3.05 m) were subdivided into 2 pens per room for a total of 24 experimental pens (1.83 x 3.05 m). One treatment was assigned to each pen. Seventy chicks were placed in each pen to achieve a density of 797 cm2/bird. Placement density, feeder and drinker space, and daily bird management were consistent with established guidelines [15]. Room temperatures were maintained at 31 to 33°C from d 1 to 7; 27 to 29°C from d 8 to 14; 24 to 29°C from d 15 to 21; and 18 to 29°C from d 22 to 56. Birds were provided ad libitum access to water through an automatic bell-type drinker system. Birds were provided feed ad libitum using a typical broiler starter (fed d 0 to 17), grower (fed d 17 to 28), finisher (fed d 28 to 42), and withdrawal (fed d 42 to 56) feeding program at 1 of 2 dietary energy levels (LOE or HIE). Nutrient compositions of experimental feeds are presented in Table 2. Nutrient analysis of diets (finisher diets not analyzed) for CP, fat, Ca, and P was conducted at 2 independent laboratories [16, 17]. Crude protein, Ca, and P levels were consistent across diets. Analyzed fat levels averaged 70% of calculated values.
Data Collection
Individual BW and feed consumption were determined on d 8, 15, 36, 50, and 56 and were used to calculate average bird weight, BW uniformity (±10% of BW mean), and feed conversions (cumulative). The occurrence of dead birds was monitored daily and these data were used to determine cumulative (d 0 to 56) percentage mortality. Mortalities were necropsied and classified as metabolic (sudden death syndrome, ascites, and skeletal disorders) or nonmetabolic (other causes) based on their position and posture when found, as well as internal and external anatomical abnormalities. On d 56, 10 birds within ±91 g of pen BW mean were selected from each pen, wing-banded, and processed at the Auburn University Poultry Processing Plant. Carcasses (without giblets or necks) were placed in static slush ice (4°C) and allowed to chill for 4 h. Following chilling, carcasses were allowed to drain for approximately 3 min, abdominal fat was removed, and chilled carcasses weighed to determine chilled carcass yield (as a percentage of preslaughter live weight). Abdominal fat weight was used to determine fat yield (as a percentage of preslaughter live weight). Fillets (pectoralis major), tenders (pectoralis minor), wings, and whole legs (thigh and drum) were removed from each carcass and weighed to determine carcass parts yield.
Statistical Analysis
Data were analyzed as a 2 x 2 x 2 factorial design with pen representing the experimental unit. The significance of treatment main effects and interactions for BW, feed consumption, feed conversion, mortality, and carcass parameters were determined using the GLM procedure of the SAS statistical package [18]. Significance was evaluated at the P < 0.05 level. All percentage data were transformed using the arc sine procedure.
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RESULTS AND DISCUSSION
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Lighting Program
A decreasing photoperiod during the early phases (up to d 14) of the DEIN treatment resulted in suppression of BW. On d 15 and 36, average BW was 36.3 g (7.9%) and 68.1 g (3.4%) less (P < 0.05), respectively, for birds exposed to the DEIN protocol (Table 3). This effect is a result of the concomitant suppression of feed consumption for birds treated with DEIN light (Table 4). Feed consumption monitored between d 0 and 15 was 41 g (7.3%) less for birds in the DEIN treatment (P < 0.05). Likewise, d 0 to 36 feed consumption for DEIN birds was 73 g (2.2%) less than for those exposed to the CONS treatment (P < 0.05). Light-restricted birds consumed less feed, which resulted in reduced BW. Within the DEIN treatment, suppression of BW was a result of mild feed restriction (through early light restriction), not a direct light effect. Even though BW and feed consumption did differ among photoperiod length treatments on d 15 and 36, no differences were detected subsequently through market age (d 56; P = 0.250 and P = 0.224, respectively), indicating that growth compensation occurred during the convergence of available light between treatments (23L:1D from d 43 to 56 for both lighting treatments). In fact, by d 56 DEIN birds were numerically heavier (+31.8 g) and had consumed more feed (+86.3 g) than birds exposed to the CONS treatment. Reduction of early BW in birds exposed to a decreasing–increasing photo-period system has been documented by others [1, 2, 3, 5, 6, 7, 8, 19]. Each of these studies, however, did report growth compensation as birds approached market age (between 42 and 56 d). Although feed conversion tended (P = 0.085) to be different at d 36 with a 2-point spread (CONS = 1.65; DEIN = 1.67) among photoperiod length treatments, this response was not noted at any other time (Table 3). In previous studies, photoperiod did not dramatically affect feed conversion [1, 2, 3, 4, 5, 6, 7, 8, 9]. In some, early light restriction (resulting in indirect feed restriction) improved feed conversion ratio during the early phases of the growout [1, 2, 3, 5, 7]. These studies utilized a decreasing–increasing photoperiod system more restrictive than that of the current study, resulting in greater indirect feed restriction early, with birds compensating by improving their feed use potential.
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Table 3. The influence of photoperiod length, light intensity, and feed energy level on BW and feed conversion of female broilers grown to 56 d1
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Table 4. The influence of photoperiod length, light intensity, and feed energy level on feed consumption and BW uniformity of female broilers grown to 56 d1
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A reduction in the daily photoperiod early in the production period followed by an increase in the daily photoperiod has been shown to reduce the incidence of ascites [1, 2], sudden death syndrome [1], and leg disorders [3, 4] in broilers. Metabolic and nonmetabolic mortalities in the present study, however, were not different between photoperiod length treatments (P > 0.05; Table 5). This lack of expected response may be due to the overall low cumulative mortality rate in the current study, which is substantially less than that reported by others (6 to 8%) and is also likely due to lower metabolic and nonmetabolic mortality rates in females. This low mortality effect was also demonstrated by Renden et al. [8].
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Table 5. Mortality of female broilers associated with variation in photoperiod length, light intensity, and feed energy level between d 0 and 561
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Carcass characteristics were only mildly affected by photoperiod length. Chilled carcass weight, chilled carcass yield, and abdominal fat yield were unaffected by photoperiod (Table 6). Likewise, absolute weight and yield of wings, fillets (pectoralis major), and tenders (pectoralis minor) were not significantly different (P > 0.05) between the CONS and DEIN treatments (Table 7). Whole leg weight and yield, however, did differ, with birds exposed to DEIN having 2.9% (P = 0.003) and 0.43% (P = 0.046) greater whole leg weight and yield, respectively, than those birds receiving the constant photoperiod treatment. A substitution effect may be indicated by the tendency (P = 0.107) for whole breast yield to be less (0.44%) in birds on the DEIN treatment. It appears that birds exposed to DEIN photoperiod yielded more leg in exchange for a reduction in breast yield. A reduction (0.2%) in breast yield under an increasing photoperiod program was confirmed by Newcombe et al. [9]; however, no additional carcass part yields were measured. They also demonstrated that yield of abdominal fat was increased when birds were exposed to photoperiod increases from 6 to 23 h. Conversely, Renden and coworkers [6, 8], in 2 separate studies, reported that neither an increasing photoperiod nor a decreasing–increasing photoperiod significantly affected carcass yield or abdominal fat pad weight when birds were processed at 42 and 56 d.
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Table 6. Live weight and carcass parameters of female broilers exposed to different photoperiod lengths, light intensities, and feed energy levels from d 0 to 561
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Table 7. Carcass parts of female broilers exposed to different photoperiod lengths, light intensities, and feed energy levels from d 0 to 561
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Light Intensity
Between d 0 and 8 of the study, average BW was not influenced by light intensity (2 fc for BRI treatment and 1 fc for DIR treatment). However, as the intensity provided to the DIR treatment was reduced, feed consumption and BW effects were significant (Tables 3
and 4). Birds on the DIR treatment consumed more feed from d 9 to 50 resulting in heavier BW on d 15 and 36 (P < 0.05; Tables 3 and 4). The DIR treatment may have encouraged less bird distraction (less time scratching and more time eating) and thus less activity. These behavioral influences likely contributed to the transitory elevation of feed consumption. However, overall feed consumption (d 0 to 56) was not different between light intensity treatments (P = 0.150). Average BW of DIR birds was 4.0 and 3.2% greater on d 15 and 36, respectively. By d 56, however, this BW effect had disappeared (nonsignificant 1.0% difference between treatments). Body weight differences due to light intensity may reflect greater activity levels in birds exposed to bright light [12], whereby more energy is expended for activity and less partitioned to growth. The convergence of BW and feed consumption between light intensity treatments by market age may be due to either a progressive reduction in activity of BRI birds due to physical space and bird size limitations or growth compensation occurring once growth rate began to decline. Feed conversions were generally unaffected by light intensity treatments (Table 3). Much like the effects observed for photoperiod treatments, light intensity treatments did not influence BW uniformity or bird mortality rates (P > 0.05; Tables 4 and 5).
Light intensity has not been conclusively shown by others to affect performance of broilers. Effects on performance are highly dependent on the levels of intensity used. Charles and coworkers [5] observed a 3% improvement in 56-d BW when male broilers were exposed to a light intensity of 0.5 fc, as opposed to 14 fc, throughout the growout, with no influence on feed conversion or mortality rate. On the other hand, a field study conducted by Scheideler [10] observed no effects on live production or processing variables in broilers exposed to light intensities ranging from 0.4 to 2 fc. Moreover, light intensities from 0.9 to 2.8 fc did not appreciably affect BW, feed conversion, mortality, or incidence of sudden death syndrome in roasters grown to 63 d [12]. These and the present study support the view that birds exposed to higher light intensities expend more energy on activities unrelated to feed intake, thus creating BW differentials between high and low light intensity. The results of the current study, however, could indicate that birds exposed to light intensities of 2 fc or more may become less active (activity level not measured) as they reach market age, resulting in less activity-associated energy expenditure and the amelioration of the BW differential between light intensities (Table 3). There is some evidence to suggest light intensity effects differ between sexes. In an older study, Wathes et al. [20] observed a depression of BW in female broilers exposed to light intensities above 0.3 fc. This effect was not confirmed in the present study.
Similar to the responses seen among lighting programs, carcass parameters were not dramatically influenced by light intensity (Tables 6 and 7). Carcass and fat yields were not different between treatments (P > 0.05). Among deboned parts, wing weight was the only parameter statistically different between light intensity treatments (P = 0.040), with birds exposed to DIR lighting producing more yield as wing. Wing yield tended to exhibit a similar trend between treatments (+0.15% for DIR birds; P = 0.083). Conversely, fillet yield tended to be lower (0.39%) for birds on the DIR treatment (P = 0.081). When evaluating the numeric trends between wing, leg, and fillet yields, a pattern emerges. Wing and leg yield were 0.15 and 0.24% numerically higher, respectively, in birds on the DIR treatment; however, fillet yield was 0.39% numerically lower in birds on the DIR treatment. Although not statistically significant, there might be a carcass parts yield substitution effect. Low light intensity that is reduced throughout the growing period may result in a shift from breast to wings and legs. Although fat pad yield in the current study was not influenced by light intensity, an increase of abdominal fat in birds exposed to low light intensity has been indicated by others [5]. The differential between bright and dim in that study, however, was much higher than in the present, which may explain this discrepancy.
Feed Energy
As might be expected, adjustments to dietary energy density did influence some aspects of bird live performance. Although feed consumption through 50 d was not influenced by dietary energy, feed consumption through 56 d did differ (P = 0.034) between treatments, with birds receiving LOE consuming 2.3% more feed than HIE (Table 4). However, birds receiving the LOE diet actually consumed 1.2% less metabolizable energy during the growth period from d 0 to 56. Average BW was unaffected by dietary energy; however, feed conversion through 50 d (P = 0.028) and 56 d (P = 0.012) was significantly lowered (P < 0.05) by the high-energy treatment (Table 3). This response is not unexpected due to increased feed consumption of birds on the LOE to match BW gains and energy requirements. Birds on the HIE diet were more efficient at converting feed to BW gain. It has been suggested that dietary fat use is affected by bird age, with older broilers utilizing fat ME more efficiently [21, 22]. This could explain the results of improved feed consumption and feed conversion for only the 0 to 50 and 0 to 56 d periods. Late BW uniformity (d 50), however, was improved (+3.9%) for birds consuming the LOE diet, indicating that the slowed growth rate response of these birds increased BW uniformity. Likewise, LOE birds consumed approximately 1.5% more dietary protein from d 0 to 56, further contributing to increased uniformity. Dietary energy density did not influence (P > 0.05) mortality rate or carcass characteristics (carcass, fat, or parts yield; Tables 5, 6, and 7). Hidalgo and coworkers [23] reported similar performance, mortality, and carcass yield responses to increasing ME concentration in the diets of straight-run broilers. Within the range of 2,750 to 3,250 kcal of ME/kg of diet, Holsheimer and Ruesink [24] showed BW and carcass yields to be unresponsive to dietary ME level. Increased feed conversion, however, was observed at lower ME levels. Another study demonstrated that high ME levels (3,200 or 3,400 kcal/kg) in broiler grower diets could produce improvements in breast and thigh yield, but with a concomitant increase in fat pad yield [25].
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CONCLUSIONS AND APPLICATIONS
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- The decreasing–increasing photoperiod treatment used in this study did limit early feed consumption and slowed early growth rate, but no resulting differences in final BW were measured.
- Female broilers exposed to a dim, reducing light intensity showed a reduced early feed consumption and BW. Body weights rebounded by d 56 to weights similar to those for birds on bright light intensity. Exposure to dim, reducing light intensity tended to increase wing yield at the expense of the breast fillet.
- Increasing dietary ME concentration improved 0 to 56 d feed consumption and 0 to 50 and 0 to 56 d feed conversion, but other variables were not affected by the dietary treatments.
- According to these results, a decreasing–increasing photoperiod program used with a dim, reducing light intensity regimen would appear to produce the greatest BW benefits for the broiler producer. However, some less than optimum carcass parts yield substitution may be expected.
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REFERENCES AND NOTES
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TOP
SUMMARY
DESCRIPTION OF PROBLEM
