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Lighting for Summer Egg Production by Turkeys: Day Length and Light Intensity

Department of Poultry Science, North Carolina State University, Raleigh 27695

¹ Corresponding author: tom_siopes{at}ncsu.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
This experiment tested the hypothesis that typical poor egg production during the summer is a consequence of insufficient lighting and reduced photoperiodic drive. Large White turkey breeder hens were photostimulated at 30 wk of age with incandescent light on May 12 for summer (off-season) egg production and continued for 28 wk. The lighting treatments were given in a 2 x 2 factorial arrangement with day length and light intensity as main effects. Day lengths used were 15L:9D and 18L:6D, whereas the intensities were 567 ± 67 and 22 ± 2 lx. All the treatments were within a light-controlled building, and there were 8 replicate pens of 4 hens for each treatment. Data were collected, by pen, for onset and the rate of lay; BW and feed consumption at 4-wk intervals; and egg weight (EW) at 4-wk intervals including the weight of the first 14 eggs laid, livability, and plasma thyroid hormones for 8 wk postlighting. The rate of egg production through 28 wk of photostimulation was better in the hens receiving 18 than 15 h of light per day (14 eggs/hen difference) but was similar between the 2 intensity treatments. The lower number of eggs in the 15-h group was associated with a greater number of photorefractory hens than in the 18 h of light per day group (39 vs. 14%, respectively). Egg weights were similar between the 18 and 15 h of light/day treatment groups but was significantly greater in the low intensity treatment as compared with the high intensity treatment. We may conclude that by increasing photoperiodic drive by increased day length, but not light intensity, there results an improved summer egg production by turkeys and reduced incidence of photorefractoriness. Egg weight was best at a reduced light intensity.

Key Words: photoperiod • light intensity • turkey • egg production • photorefractoriness • egg weight • thyroid hormone

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The year-round production of turkeys is not possible without proper lighting management, especially with regard to day length. There is no one lighting program that surpasses all others, and a basic requirement is that sufficiently long days are provided to induce egg production. A sufficiently long day means a day length that exceeds the critical day length (CDL), which is the minimum hours of light per day to induce egg production. Add to this the fact that sufficient light intensity must be present so that there is a distinct contrast between day and night periods.

It is well known that reproductive performance of turkeys is poor in summer as compared with winter, but this was thought to be mostly effects of heat per se and broodiness. We now know that lighting requirements for turkey hens change drastically during the year due to changes in the CDL and that this has significant effects on egg production (Siopes, 1994, 1998). The CDL is longest in summer (>14 h) and shortest in winter (11 to 11.5 h). Because more light (h per day) is required to induce and maintain egg production in summer than winter seasons, it is possible we are still not providing sufficient light in the form of hours per day, intensity, or both to promote maximum egg production in the summer. There is no available scientific literature that specifically addresses lighting requirements for turkey breeder hens during the summer, certainly not for a combination of day length and intensity. The present study addresses this situation.

A day length of 14 to 16 h per d is required to bring turkey hens into normal production (Marsden et al., 1962; Ogasawara et al., 1962) and is the general standard used today. Giving more light than 16 h per d does not appear to result in better production. Egg production of hens given 24 h or 22 h of light per day was not different from hens lit with 15 h of light per day (Leighton and Shoffner, 1961; McCartney et al., 1961), and Ogasawara et al. (1962) found that 20 h of light decreased egg production as compared with 14 h of light per day. None of these reports considered seasonal effects on the results.

The minimum light intensity necessary for normal egg production is in the range of 4.3 to 22 lx (Asmundson et al., 1946; Thomason et al., 1972; Siopes, 1991a) but this value was determined without regard to season of the year. Most light intensity research suggests that once some certain minimum photostimulatory light intensity level is exceeded, there is little benefit from additional levels of light intensity (Siopes, 1991b).

There are a few older reports suggestive of a day length and intensity interaction in turkeys. On photoperiods of 14L:10D increasing light intensity increased egg production (Garland et al., 1961; Nestor and Brown, 1972), but with 16L:8D or 15L:9D photoperiods egg production remained unchanged as light intensity increased (McCartney, 1971; Thomason et al., 1972; Siopes, 1984, 1991b). Siopes (1991b) addressed the possibility of a day length and intensity interaction for turkey hens photostimulated in March and given 16 or 14 h of light per day at 54 or 324 lx. There was no photoperiod x light intensity interaction, and the season of lighting was similar to the objectives proposed herein. None of these studies considered seasonal effects on the results, but Siopes (1992) reported a significant improvement in egg production by hens photostimulated in April, but not February, with 270 lx as compared with 22 lx light intensity.

In the present study we widened the range for day length and light intensity and designed the experiment specifically for summer egg production by photostimulating the hens in May.

Photoperiodic drive (PD) is a term that refers to the combined effects of light (duration and intensity) in stimulating reproductive activity. We know that more hours of light are required to maximize PD in summer than winter because the CDL has increased, but there is no comparable information for light intensity (Siopes, 1994). Light intensity cannot substitute for long day effects on PD, but it can supplement the effects of long days (Bentley et al., 1998). It appears that the supplemental effects of light intensity are mediated by an effect on thyroid hormones. As light intensity increases, thyroid hormones increase (Bentley et al., 1998). Interestingly, summer heat depresses thyroid hormones and thyroid hormones are required for the initiation and maintenance of egg production in turkeys (Lien and Siopes, 1989). So, it appears likely that the increased CDL in summer could be overcome by increasing the day length. Any benefits of increased light intensity may be to boost PD by some improvement in thyroid hormone level. Our objective was to maximize PD to improve summer egg production with proper day lengths and light intensity. The present project was designed to determine whether day length or light intensity or a combination of the 2 would best address this objective.

	MATERIALS AND METHODS

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An experiment was conducted to determine if the poor reproductive performance typical of turkey breeder hens during the summer involves photoresponsiveness, in particular a lack of PD. The hens (Large White Nicholas parent stock) were obtained as poults from a commercial breeder during the winter and brooded and reared in a curtain-sided grow-out house on site. To ensure photosensitivity, all birds were light restricted in a solid-walled, light-controlled building (closed-confinement) and exposed to 8 h of light/d (8L:16D) from 20 wk of age until photostimulation (start of treatments).

The mean light intensity in each pen during this time was 43 to 54 lx. Photostimulation occurred at 30 wk of age on May 12 for summer (off-season) egg production and continued for 28 wk. All hens were given identical housing and management during the study. The lighting treatments used only incandescent light and were given in a 2 x 2 factorial arrangement with day length and light intensity as main effects. Day length was controlled by mechanical clocks and provided 15 h or 18 h of light per day (15L:9D and 18L:6D, respectively). Day length was validated by use of photocells and an electronic recorder. The light intensities were 567 ± 67 and 22 ± 2 lx. Thus, the 4 light treatments were 18L, 567 lx; 18L, 22 lx; 15L, 567 lx; and 15L, 22 lx, and there were 32 hens in each treatment.

Light intensity was measured at turkey head height at 5 locations within each pen to establish a mean pen light intensity. Different intensities were achieved by masking of incandescent lamps at the same wattage and by adjusting the distance of the lamps to the birds. All the treatments were within a light-controlled building, and there were 8 replicate pens of 4 hens for each treatment. The pens were 2.9 x 4.6 m and contained 4 nest boxes and 1 feeder and waterer. The building was not temperature controlled but was insulated, and the rooms were mechanically ventilated. Ambient temperature within pens was recorded daily.

Feed and fresh water were provided for ad libitum intake throughout the study. During the prelay light restriction period, the feed was formulated to contain 12% CP, 0.85% calcium, and 3,084 kcal of ME/kg of feed. At the onset of photostimulation (and treatments), and to the end of the experiment, a pelleted breeder ration was fed that was formulated to contain 16% CP, 3.05% calcium, and 2,970 kcal of ME/kg of feed.

Eggs were collected twice daily throughout the study, recorded by pen, placed in a refrigerated room at 12.8 C, and weighed to the nearest 0.1 g on alternate days. Time to onset of lay was defined as days to reach 50% hen-day egg production from the start of the light treatments. Egg production was evaluated as cumulative eggs produced per hen or as a weekly hen-day percentage. At the end of the lay period (28 wk of photostimulation) all hens were palpated daily in the morning for 7 consecutive days to identify nonlayers. Any hens during the lay period that lost body and primary feathers (molted) were recorded. Hens that had stopped lay and had molted were considered to be photorefractory (PR).

Individual egg weights (EW) were obtained for the first 14 d of lay in each pen. In addition, EW were obtained in 7-d periods immediately preceding 8, 12, 16, and 20 wk of photostimulation. Body weight and feed consumption were recorded at 4 wk intervals during the study, and weekly blood samples were obtained at the same time of day (0900 to 1100) during the first 8 wk of photostimulation for plasma thyroid hormone evaluation. Thyroxine (T4) and triiodothyronine (T3) were measured using commercial kits (Diagnostic Products Corp., Los Angeles, CA) with modifications for turkey plasma (Siopes, 1997).

A 2-way ANOVA was used to evaluate the treatment effects using the GLM procedure of SAS software (SAS Institute, 1990). Main effects were day length (18 vs. 15 h), and light intensity (567 vs. 22 lx). Where no significant treatment interaction occurred, results are presented as main effects only. The arc sine transformation was applied to all percentage data before analysis. In addition, repeated measures ANOVA was used to evaluate rate of lay occurring from postpeak production. Where treatment or treatment x time effects were found, differences between means of the groups within times were assessed using the GLM procedure. The least squares means option was used to estimate significant differences among treatment means. Statements of statistical significance are based on P 0.05 unless specified otherwise.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
No significant interactions occurred between photoperiod and intensity for any of the results of this study, and therefore results are presented as main treatment effect means for photoperiod (18L:6D vs. 15L:9D) and light intensity (567 vs. 22 lx).

Livability

Livability was 92.2 and 96.9% for the main treatment effects of 18L:6D and 15L:9D, respectively and 92.2 and 96.9% for 567 and 22 lx, respectively. There was no difference in livability between day lengths (P = 0.21) or light intensities (P = 0.21). Notably, the highest livability occurred in the shorter day length and lower light intensity.

Egg Production

Day length and light intensity effects on cumulative eggs per hen and the days required to reach 50% hens-day production are given in Table 1. Neither day length nor light intensity altered the onset of egg production, and the time to 50% production ranged from 17.7 to 19.7 d. Cumulative eggs per hen was similar between light intensity treatments, whereas an 18-h day improved egg production as compared with the egg production of hens receiving 15L:9D. This amounted to 11 eggs per hen after 24 wk of photostimulation and 14 eggs per hen after 28 wk of photostimulation. Likewise, mean percentage hen-day production during the experiment was similar between intensity treatments but differed by day length treatment. The longer day length improved mean production by 8.4 and 8.7% after 24 and 28 wk of photostimulation, respectively. At 28 wk of photostimulation 13.6% (8/59) of the hens on 18L:6D were PR, whereas 38.7% (24/62) were PR in the hens receiving 15L:9D. There were 25.8% (16/62) and 27.1% (16/59) PR hens in the low and high intensity groups, respectively.

View larger version (16K): [in this window] [in a new window]   Figure 1. Mean hen-day percentage summer egg production for turkeys photostimulated in May with photoperiods of 18L:6D and 15L:9D and light intensities of 567 and 22 lx. No significant interactions occurred among photoperiod, light intensity, and time. Repeated measures AN-OVA P > F for photoperiod = 0.04; for light intensity = 0.28; and for time = 0.0001. Pooled SEM = 3.8.

Body weight at the time of photostimulation was similar among all treatment groups and ranged from 13.3 to 13.8 kg (Figure 2, top). During 28 wk of photostimulation, BW was not different in either of the main treatments, and there were no significant interactions between treatments or with treatment x time interactions. There was a significant time effect as expected. Body weight declined from that at the start of photostimulation by 15 to 18% to 12 wk of photostimulation among all treatments and then gradually increased during the rest of the experiment as the seasonal temperatures decreased.

View larger version (15K): [in this window] [in a new window]   Figure 2. Mean BW (top) and feed intake (bottom) of Large White turkey hens in response to photoperiods of 18L:6D or 15L:9D and to light intensities of 567 or 22 lx. No significant interactions occurred among photoperiod, light intensity, and time. Repeated measures AN-OVA P > F for BW: photoperiod = 0.69; intensity = 0.15; and time = 0.0001. For feed intake P > F: photoperiod = 0.81; intensity = 0.44; and time = 0.0001. Pooled SEM BW = 0.09; feed intake = 1.95.

Thyroid Hormones

The plasma T4, T3, and T3/T4 ratio (latter not presented) was similar during the first 7 wk of photostimulation of hens in the 18L:6D and 15L:9D treatment groups as well as the high and low intensity groups (Figure 3).

View larger version (17K): [in this window] [in a new window]   Figure 3. Photoperiod (A,B) and light intensity (C,D) effects on mean plasma thyroid hormones during the first 7 wk of photostimulation for summer egg production. Hens photostimulated in the month of May. No significant interactions occurred among photoperiod, light intensity, and time. Repeated measures ANOVA for P > F, Photoperiod effects: thyroxine (T4) = 0.23; triiodothyronine (T3) = 0.72; and for time in each case = 0.001. Intensity effects: T4 = 0.52; T3 = 0.49; and for time in each case = 0.001. The pooled SEM was 0.59 and 0.13 for T4 and T3, respectively.

Treatment main effects on EW are given in Figure 4. Hens on low intensity light treatment had consistently larger eggs (mean difference of 2.5 g) than the eggs from hens on the high intensity treatment. This difference first appeared on d 8 to 14 of egg laying and persisted throughout lay. Egg weights were similar between the day length treatments, and in all treatments EW increased as time in lay progressed. The increased EW in the low intensity treatment group was associated with proportional increases in shell, yolk, and albumin as determined over a 7-d period ending at 18 wk of photostimulation (data not included).

View larger version (17K): [in this window] [in a new window]   Figure 4. Photoperiod (18L:6D and 15L:9D) and light intensity (567 and 22 lx) effects on turkey egg weights during summer production. Hens were photostimulated in the month of May. No significant interactions occurred among photoperiod, light intensity, and time. Repeated measures ANOVA P > F for photoperiod = 0.77; for light intensity = 0.03; and for time = 0.001. Pooled SEM = 0.57.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

Light intensity in the ranges used not only did not provide different photoinduced egg production during summer, it also did not alter (interact with) the photoperiod (day length) effects. We consider the improved production by day length to have occurred as a result of increased PD (photostimulation) because the 18 h of light provided more hours of light above the increased summer CDL than did the 15L:9D photoperiod.

The initial photostimulation by increasing the day length from 8 h per day during prelay light restriction to 18L:6D was abrupt rather than incremental. This is likely a necessity considering the low photoresponsiveness of breeder hens at this time of year. Note that 18 h of light per day is most effective for summer egg production, and similar results should not be expected for winter season production and associated lower CDL (unpublished results, this laboratory).

It is notable that ambient temperature in the high intensity treatment groups was slightly higher than that for the low intensity treatment. This was not unexpected when using incandescent lighting and the differences were most prominent early in lay in the months of June through August with a maximum difference being 1.9°C. This clearly had no significant effect on egg production, and because neither BW nor feed intake were different between the 2 light intensity treatment groups of hens, we consider any temperature effects on egg production to be trivial. In fact, BW and feed intake were similar among all treatments and thus did not seem to be involved with the variations in egg production among the treatments.

We measured thyroid hormone levels because it has been reported that the supplemental effects of light intensity on long day induced gonad responses are mediated by thyroid hormones. As light intensity increased, thyroid hormones increased (Bentley et al., 1998). Also, summer heat depresses thyroid hormones and thyroid hormones are required for the initiation and maintenance of egg production in turkeys (Lien and Siopes, 1989). In the present study plasma thyroid hormones did not vary among the treatment groups and this was consistent with the absence of a light intensity effect on egg production. So, it appears that the increased CDL in summer may be overcome by increasing the day length but not by increasing the light intensity, at least not within a range up to 567 lx. In addition, it seems clear from the results that the poor egg production of summer is not a consequence of altered thyroid function and the same applies for improved egg production associated with increased hours of light per day.

Even though the light intensity treatments had no effect on egg production, hens in the lower light intensity treatment produced EW consistently heavier (about 2.5 g) than in the high intensity treatment after the first week of lay. There was no interaction between day length and light intensity; that is, light intensity effects on EW were not altered by day length. So, a combination of long day lengths (18L:6D) and low light intensity light (22 lx) resulted in not only more eggs than controls, but bigger eggs.

Increased EW associated with turkeys in dim light has been reported as early as 1946 (Asmundson et al., 1946). We have reported that light intensity in the range of 22 to 220 lx did not affect turkey egg size (Siopes, 1984, 1992). To reconcile the different reports (including the present study), it seems reasonable to conclude that there exists a wide range of light intensities over which turkey egg size is not altered. At an upper range >220 and 567 lx, EW becomes smaller as compared with 22 lx (low) treatments. We cannot say for sure why EW is larger in low as compared with high light intensity. In fact, it remains unclear whether altered EW is a consequence of a positive effect of low light intensity or a negative effect of the high intensity, and each of these likely involves different mechanisms. We can say from the results of the present study that age, time in lay, season, BW, feed composition, and feed intake were not involved.

In addition, altered time between eggs in a sequence is an important factor influencing EW, with longer times resulting in larger eggs and vice versa. But this is not applicable to our results. For example, for low intensity to increase EW the time between eggs must increase and consequently the number of eggs produced in a set period of time must decrease. The converse would be expected for smaller EW in bright light. In our results egg production was not only not different between the light intensity treatments, but also the numerical values for hen-day production were opposite to what would be expected. So, increased EW occurred with no loss in the number of eggs produced.

Among some speculative possibilities for low EW in high light intensities, increased ambient temperature levels seems a good candidate. However, because neither BW nor feed intake were altered between intensity treatments any adverse effects of elevated temperature would require mechanisms without effect on BW or feed intake. Possibly low light intensity increased egg size as a result of a reduction in maintenance energy requirements as a consequence of reduced general activity and social interactions. More energy resources could then be diverted to egg size.

From the results of this study we may conclude that by increasing PD by increased day length, but not light intensity, there results an improved summer egg production by turkeys and reduced incidence of PR. Egg weight was enhanced by reduced light intensity.

	ACKNOWLEDGMENTS

 
This work was supported by a grant from the US Poultry & Egg Association and is part of the USDA Multi-State Research Project S-1020, Enhancing Reproductive Efficiency of Poultry. The author gratefully acknowledges the excellent technical assistance of Vickie Hedgpeth.

Received for publication June 13, 2007. Accepted for publication July 23, 2007.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
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Garland, F. W., R. C. Easton, D. E. Greene, H. L. Wilke, and R. M. Bethke. 1961. Duration and intensity of light for out of season egg production in turkeys. Poult. Sci. 40:1406–1407.

Leighton, A. T., and R. N. Shoffner. 1989. Effect of light regime and age on reproduction of turkeys. 1. Effect of 15, 24 hour and restricted light treatment. Poult. Sci. 40:861–870.

Lien, R. J., and T. D. Siopes. 1984. Effects of thyroidectomy on egg reduction, molt, and plasma thyroid hormone concentrations of turkey hens. Poult. Sci. 68:1126–1132.

Marsden, S. J., N. S. Cowen, and L. M. Lucas. 1962. Effect of gradual and abrupt lengthening of photoperiod on reproductive responses of turkeys. Poult. Sci. 41:1864–1868.[Web of Science]

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SAS Institute. 1990. SAS/Stat^® User’s Guide. Version 6. Fourth Edition. Vol. 2. SAS Inst. Inc., Cary, NC.

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