Intermittent Light Stimuli in Egg Production of Chickens

532

C. C. BRTJNSON, G. F. GODFREY AND B. L. GOODMAN

Poultry Sci. 32:248-259. Goodman, B. L., and G. F. Godfrey, 1956. Heritability of body weight in the domestic fowl. Poultry Sci. 35: 50-53. Hazel, L. N., M. L. Baker and C. F. Reinmiller, 1943. Genetic and environmental correlations between the growth rates of pigs at different ages. J. Animal Sci. 2: 118-128. Lerner, I. M., 1950. Population Genetics and Animal

Improvement. Cambridge University Press, Cambridge. Lerner, I. M., V. S. Asmundson and D. M. Cruden, 1947. The improvement of New Hampshire fryers. Poultry Sci. 26: 515-524. Wright, S., 1939. Genetic principles governing the rate of progress in livestock breeding. Amer. Soc. Anim. Prod. Proa, Thirty-second Ann. Meet. pp. 18-26.

Intermittent Light Stimuli in Egg Production of Chickens (Received for publication September 22, 1955)

T

HE stimulation of egg production by the use of artificial lights is well known to poultrymen. However, the minimum quantity of light that will sustain egg production in birds once it is initiated has not been determined. The successful use by Staffe (1951) of light shocks to increase winter egg production in chickens suggested that the total amount of light could be less than 12 hours in 24. Earlier work by Dobie et al. (1946) showed that chicken hens with 3 hours of intermittent light per day would produce at a low rate. A test by Rider (1938) indicated that raising pullets in darkness does not prevent their coming into production. I t has been suggested by Farner et al. (1953) that the light-sensitive gonadotropic mechanism becomes active almost immediately after the photoperiod begins and has a persistent carry-over period of activity after the end of the photoperiod. If this were true, light given intermittently would perhaps be more effective than the same amount of light given continuously. This paper reports the results of experiments designed to study this theory and to dePresented at the 44th annual meeting of the Poultry Science Association, East Lansing, Michigan, August 11, 1955.

termine the minimum photoperiod necessary to maintain egg production. The present study consisted of four experiments which varied somewhat in procedure because of their preliminary nature. As a consequence, greater confidence may be placed in the final experiment. The first three tests provide a comparison of the effect of intermittent vs. continuous lighting. The fourth test was to determine the minimum quantity of light necessary to sustain egg production. The stock consisted of pullets of the University of California strain of S.C. White Leghorns. The 19 pullets used in the first experiment were in production for 2-1/2 months before being placed under experimental conditions. The second experiment involved 38 pullets just starting production; 34 of these birds were regrouped for the third experiment. The fourth experiment included 18 birds used in the second and third, plus 20 pullets just starting egg production. The hatching dates of the stock were December 4, 1953, for the first test; May 6, 1954, for the second, third, and a portion of the fourth test; and October 21, 1954, for the pullets of the fourth test. In the fourth test, since birds of different ages were involved, it was possible

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WILBOR O. WILSON AND HANS ABPLANALP Department of Poultry Husbandry, University of California, Davis

INTERMITTENT LIGHT STIMULATION AND EGG PRODUCTION

TABLE 1.— Plan

Expt. No.

Age of hens at start (days)

1

248

Total hrs. light in 24 hrs.

lighting is given in Table 1. In all experiments with intermittent lighting, the 24hour day was divided into six cycles of four hours each. Within every cycle a photoperiod was followed by darkness. Continuous lighting, on the other hand, represented but one sequence of one light and one dark period within the 24-hour day. In experiment 1, the total daily amount of light was set at 6 and at 9 hours for each of two treatments. Six hours of light was given continuously to one group of hens, while another one obtained the same amount in 6 exposures of one hour each. Similarly, 9 hours of light was provided continuously and intermittently to two groups of hens. In experiment 2 the treatments were set at four and a half hours of total light per day as compared with 14 hours for a control group. Again, the reduced amount of light was given continuously to one group of hens and intermittently to another. In the third experiment total daily

of lighting schedules for 4 experiments

No. cycles in 24 hrs.

No. hrs. of of light per

period

No. hrs. darkness per period

6 6 9 9

1 6 1 6

6 1 9 1.5

18 3 15 2.5

Type of light

p* F

Footcandles

I

6 6 6 6

to to to to

98 98 14 14

to to to to

98 98 14 98

It

2

170

4.5 4.5 4.5 14

1 6 6 1

4.5 .75 .75 14

19.5 3.25 3.25 10

F F I F

6 6 6 6

3

245

1.5 1.5 14

1 6 1

1.5 .25 14

22.5 3.75 10

F F F

6 to 98 6 to 98 6 to 98

4

349 and 168

0.1 0.5 1.5 24.00

6 6 6 1

0.017 0.083 0.25 24.00

I I I I

0 0 0 0

* Fluorescent light, t Incandescent light.

3.983 3.917 3.75 0.00

to to to to

6.6 6.6 6.6 6.6

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to study the effect of age on the amount of light required to maintain egg production. Each experimental group had a replication in a different experimental room. Four climatic chambers (16'X16') were used to provide controlled lighting. The hens were kept in individual 10" cages which were arranged in step fashion to provide, among other things, a uniform exposure to light. Forty cages were located in the center of each room. The four chambers were windowless and opened into a hallway which was never open to natural lighting. Artificial light from the hallway was not permitted to interrupt the experimental dark periods; this was achieved by coordinating the care and feeding of birds with the light intervals of the experiments. Exceptions to this rule occurred on rare occasions, but are not considered a major source of error in the outcome of different trials. An outline of the experimental procedures designed to provide various sequences of continuous and intermittent

533

534

W. 0. WILSON AND H. ABPLANALP

In the first three experiments the birds were brought into the chambers 28 to 30 days ahead of the scheduled experiment to allow a period of adaptation to the new environment under a normal schedule of 14 continuous hours daily light, with a light intensity of 6 to 96 foot-candles. The pullets of the fourth test had no pretreatment period; instead, they were brought into their new quarters from floor pens where they had received a daily amount of about 13 hours of natural light. Test periods were set at four weeks in the first, third, and fourth experiments, while the test in the second experiment extended over six weeks. After these treatment periods were over, the birds were left in their cages for another four weeks during which 14 hours of continuous lighting was provided. The recovery period of the fourth experiment differed in that light of low intensity was provided for 24 instead of 14 hours per day. Changes in the hours of light exposure were made abruptly at the beginning of the test and recovery periods. Controlled environmental temperatures ranged between 80° and 90°F. except for a few instances in the fourth test when a high of 95° was reached. A laying ration now used for the laying flocks of the University of California at Davis was fed throughout the experiment. The feed was pelleted for convenience of handling. Daily egg records were taken in order to evaluate responses to the different experimental light regimes. Also, for a limited number of hens in the fourth test the exact hour of oviposition was determined by means of an automatic timing device. (This apparatus consisted of a microswitch coupled with an electric time clock.) RESULTS AND DISCUSSION

The results of the three preliminary tests are shown in Table 2. Limiting the

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light was reduced to one and a half hours, given continuously to one group, intermittently to another. Results were compared with those of a control group given 14 hours of continuous lighting. The fourth experiment was restricted to comparisons of reduced intermittent light stimuli with continuous lighting of 24 hours per day. A series of three intermittent light periods provided the following total daily amounts of light: 90, 30, and 6 minutes. In the first experiment differences of light quality were confounded with hours of experimental treatments; both fluorescent and incandescent lights were used. Light intensity, as measured with a General Electric light meter, ranged from 6 to 98 foot-candles for fluorescent lights and from 6 to 14 foot-candles for incandescent. The seemingly great variation in readings results from the light meter's being aimed at the light source as well as at reflecting surfaces. A zero measurement does not mean total darkness but the limitation imposed by the meter, which had 0.2-foot-candle graduations. Fluorescent light was the principal source of illumination used in the second experiment and was used exclusively in experiment 3, as shown in Table 1. In the fourth experiment only incandescent light of reduced intensity was used. Under this regime the old hens were placed in the upper-deck cages where the light, provided by a 10-watt bulb, varied between 0.4 and 6.6 foot-candles, while pullets were kept in the lower decks with light intensities between 0 and 0.4 foot-candles. Thus, it must be assumed that the older birds had all the advantages of higher light intensity, if such advantages exist. In order to provide replication of treatments, each chamber was subdivided into two separate parts by means of a light trap. Each treatment could thus be given in two different chambers.

535

INTERMITTENT LIGHT STIMULATION AND EGG PRODUCTION TABLE 2.—Average percentage egg production and clutch size for conditioning test and recovery periods First three lighting experiments Conditioning Lighting regime total/24 hrs.

Recovery

Test

egg prod.

Av. clutch size

Hens with 6 day pauses

egg prod.

Av. clutch size

61.8 66.5 58.1 61.2

3.37 3.67 3.19 2.54

42.7 43.6 46.1 57.4

2.12 1.82 1.95 1.84

7 12 10 7

39.6 48.5 41.7 50.5

2.80 2.53 2.82 2.39

Expt. 2 4J hrs. cont. 4 i hrs. int. 4J hrs. int. I* 14 hrs. control

60.0 59.2 62.0 64.0

4.67 4.56 3.56 4.61

54.8 52.7 66.0 76.9

2.43 2.50 3.37 5.15

17 15 16 4

45.9 49.0 43.7 73.8

3.23 2.66 2.76 3.70

Expt. 3 1 | hrs. cont. 1J hrs. int. 14 hrs. control

70.7 72.9 70.0

2.80 2.62 3.07

44.1 64.0 70.2

1.64 2.61 2.87

24 8 3

45.6 49.1 59.6

2.38 2.18 2.00

Expt. 1 6 hrs. 6 hrs. 9 hrs. 9 hrs.

:

continuous intermittent cont. I* int. I*

%

I=incandescent light. All others fluorescent light.

hours of lighting to less than 14 apparently reduced egg production regardless of the lighting method. In four out of five comparisons egg production of the group with intermittent light exceeded that of the comparable group with continuous light during both test and recovery periods. Egg production was initially higher in the intermittent groups, which also

gave an especially favorable response during recovery. Since there were only 19 birds per group in the first test, this experiment showed more variation than the second and third. Intermittent light slightly increased the average clutch size, with the exception of the hens in the first test. The older birds generally had smaller clutches

TABLE 3.—Fourth experiment's average percentage egg production and clutch size for two trial periods and recovery 1st trial Lighting regime cycles (period)/24 hrs.

Expt. 4 Hens

2nd trial

Recovery 1st test period

egg prod.

%

Av. clutch size

egg prod.

Av. clutch size

Hens with 6 day pauses

egg prod.

Av. clutch size

%

%

6 6 6 24

(1 min.) (5 min.) (15 min.) hours

56.2 54.3 50.8 65.4

2.25 2.00 1.71 3.72

46.4 33.1 39.2 48.9

1.88 2.31 1.94 3.12

4 6 6 0

36.6 26.2 24.1 44.6

1.64 1.74 1.19 2.67

Pullets 6 6 6 24 14

(1 min.) (5 min.) (15 min.) hours hours

57.7 63.0 69.2 67.7 54.1

3.90 4.23 5.05 5.57

76.4 76.7 76.1 76.1 70.7

4.09 4.00 4.26 4.24

1 1 0 1

69.8 63.0 72.0 66.9

2.85 2.69 3.35 3.29

All pens had incandescent light.

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%

egg prod.

Av. clutch size

%

536

W. 0 . WILSON AND H. ABPLANALP

^=K 6/5min.^^^ >

5

NUMBER

6 OF

7

±

8

2nd. Test 10

^

_1_ II

12

WEEKS

FIG. 1. Percent of egg production by weeks, of Pullets given 6, 30 and 90 minutes of light in 24 hrs. Continuous light given the control and to all groups in the recovery period. Expt. No. 4.

as shown in Table 3. Many more birds paused longer than 6 days in the group given one and a half hours of continuous light than in the comparable group with intermittent light. This did not seem to be the case when more light was given per day. The light requirement of chickens was studied in greater detail in the fourth experiment. On the basis of the three previous experiments, intermittent lighting seemed to be more effective than continuous light in maintaining egg production. Also, it was concluded from this earlier work that age seemed to influence the response of hens to a reduced amount of light. The results of experiment 4 support these preliminary observations, as shown in Figures 1 and 2. Changes in light regime decreased the old hen's production re-

4

5

NUMBER

6 OF

7

8

WEEKS

FIG. 2. Percent of egg production by weeks, of Bens given 6, 30 and 90 minutes of light in 24 hrs. Continuous light given the control and to all groups in the recovery period. Expt. No. 4.

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4

gardless of the amount of light given. Production decreased even in the 24-hour continuous-light group where no change was made. The pullets which were coming into production when the first trial started, responded quite differently to changes in lighting. Their rate of lay increased in the recovery period. Only the second trial of experiment 4 showed a decline in production in all groups regardless of lighting regime. Pullet egg production tended to show a graded response to lighting in the first trial period. The difference however is not great and the (15-minute) group laid as well as the group with 24-hour continuous light. By the end of the first ten days all groups were laying at approximately the same rate. Clutch size decreased as the hens aged. In the groups with intermittent light it did not appear to be related to the quan-

INTERMITTENT LIGHT STIMULATION AND EGG PRODUCTION TABLE 4.—Regressions of egg production for two successive ;

Expts. 1, 2 and 3 combined data Intermittent groups Continuous groups

Test and recovery

.188 .394

.299 .491

1st trial and recovery

Recovery and 2nd trial

.533 .983 .959 .745

.943 .754 .819 .704

1 min. period 5 min. period 15 min. period 24 hours

tity of light received. Clutch size was largest in the 24-hour light group. The evidence based on pauses is consistent with this observation. As would be expected, the pullets experienced fewer pauses than the hens. For the pullets, clutch size was greatest in the first trial, with the exception of the group with the least amount of light, which did not mature sexually as early as the other groups. The results derived from pullets indicate that the light requirement for maintaining egg production is less than 6 minutes when divided in to 6 one-minute periods in 24 hours. This finding is similar to Burger's (1953) observation in starlings which suggests that down to 8.5 hours of continuous light there is no all-or-none threshold for maintaining egg production. Hens that laid at a high rate previously were more capable of laying after the environmental change, as shown by means of regressions in Table 4. This is in agree-

ment with observations by Rothchild and Fraps (1945) that hens with a high rate of ovulation frequency were less likely to show follicular atresia following surgery than hens with lower rates. The egg-laying pattern of hens subjected to intermittent lighting is shown in Table 5. All of the data for these groups were combined. There was a tendency for more eggs to be laid during the hour in which light was given and the following hour than were laid during the two subsequent hours of the 4-hour cycle. When hens were given 24 hours of continuous light more eggs were laid in the afternoon and evening than in the morning. This distribution of oviposition is a reversal of the pattern under conditions of natural daylight intervals. A possible explanation for such periodicity must be sought in regularly recurring environmental events other than light, such as feeding and management practices. Under the conditions of the present experiments the birds were fed regularly at 09:00 hours, and eggs were collected at 13:00 hours. These practices may have established an ovulatory rhythm similar to the one reported by Fraps et al. (1947), where egg production of hens was closely coincident with feeding times. The birds with short light intervals and long dark periods would eat in the dark. They also became trained to eat large amounts of feed during the light periods. This feature was most noticeable early during the recovery period when the birds' crops would be so distended as to appear pendulous. The data presented here are by no

TABLE 5.—Distribution of oppositions under continuous and under intermittent lighting

(Number of eggs laid each hour) 2

Hours starting a t

0

1*

Combined intermittent groups Continuous light

4 7

14 10 8 6

* Indicates hour of exposure to light.

3

4

5*

s

6 8

13 10 8 9 10 6 6 10 12 9

8

6

7

8

9* 10 11 12 13* 14 IS 16 17* 18 19 20 21» 22 23 7 9

7 9 14 3 6 7 13 11 2 13 10 10 18 15 13 14 13 13 10 15 11 7

9 6

8 10

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Pretreatment and test

537

538

W. 0 . WILSON AND H. ABPLANALP

SUMMARY

S. C. White Leghorn pullets and hens were kept in windowless climatic chambers at relatively stable temperatures. These birds were used to compare intermittent versus continuous lighting at levels thought to be suboptimum for egg production. Intermittent light was provided at regular cycles of 4 hours. In a series of tests the quantity of light during the four-hour cycles was set at 90, 60, 45, 15, 5 and 1 minutes. From these experiments the following conclusions may be drawn: 1. Intermittent lighting generally gave higher egg production than the same amount of continuous lighting. 2. Egg production obtained under short photoperiods was not proportionate to the amount of light given.

3. The minimum amount of light needed for an all-or-none response for maintaining egg production in pullets is probably less than 6 evenly spaced oneminute photoperiods in 24 hours. 4. Hens were more susceptible than pullets to light changes and possibly to other environmental factors. 5. Good layers were more resistant to shocks from light changes than poor layers. 6. The time of oviposition is influenced by light and management factors. REFERENCES Burger, J. W., 1953. The effect of photic and physic stimuli on the reproductive cycle of the male starling, Sturnus vulgaris. J. Exp. Zool. 124: 227— 239. Dobie, J. B., J. S. Carver and J. Roberts, 1946. Poultry lighting for egg production. Washington Agr. Exp. Sta. Bui. 471. Farner, D. S., L. R. Mewaldt and S. D. Irving, 1953. The role of darkness and light in the activation of avian gonads. Science, 118: 351-352. Fraps, R. M., B. H. Neher and I. Rothchild, 1947. The imposition of diurnal ovulatory and temperature rhythms by periodic feeding of hens maintained under continuous light. Endocrinology, 40: 241-250. Rider, P. L., 1938. The influence of light on growth and reproduction of the domestic fowl. Unpublished Master's Thesis, Ohio State University. Rothchild, I., and R. M. Fraps, 1945. The relation between ovulation frequency and the incidence of follicular atresia following surgical operations in the domestic hen. Endocrinology, 37: 415-430. Staffe, A., 1951. Belichtung and Legeleistung beim Huhn. Experientia, 7: 399-400. Wolfson, A., 1954. Production of repeated gonadal, fat and molt cycles within one year in the junco and white-crowned sparrow by manipulation of day length. J. Exp. Zool. 125: 353-376.

POULTRY SCIENCE INDEX A subject matter index of volumes 1 to 20 inclusive, is available from C. B. Ryan, Secretary-Treasurer, Poultry Science Association, Texas A and M

College System, College Station, Texas, at $1.00 per copy.

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means clear-cut as to the importance of total hours of light needed for maximum rate of egg production or the relationship of maximum egg production to total production, nor was a minimum amount of light reached below which all hens would cease laying. Evidence in the literature shows that the conditioning of birds for molting seems to require relatively long days (Wolfson, 1954). In starlings the refractory state seems to be reinforced by long days and weakened by short daylight periods (Burger, 1953). It may be that hens can be kept under short light intervals and maintain higher egg production for a longer time than was formerly thought possible