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Effect of Light Regime and Age on Reproduction of Turkeys1,2
Effect of Light Regime and Age on Reproduction of Turkeys1'2 2. RESTRICTED vs. UNRESTRICTED LIGHT A. T. LEIGHTON, JR., 3 AND R. N. SHOFFNER Department of Poultry Husbandry. University of Minnesota, St. Paul (Received for publication July 25, 1960)
I
1 Minnesota Agricultural Experiment Station Scientific Journal Series Paper #4444. 2 A portion of a thesis submitted by the senior author to the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 3 Present address: Department of Poultry Husbandry, Virginia Agricultural Experiment Station, Blacksburg, Virginia.
871
Parker (1957). The results of a pilot study undertaken during the 1956-57 breeding season by Leighton and Shoffner (1961) have also shown that if light was restricted to 8 hours per day for a 4 week period and then supplemented to provide 15 hours per day for the remainder of a 6 to 7 month breeding season, a production response followed which simulated that observed in flocks of turkeys lighted in January. In contrast, females already under essentially optimum light levels (13 or more hours) responded more slowly to 15 hour lights and laid at a lower rate during the fall production period than did the restricted group. This study reports on the utilization of various light regimes for improvement of reproductive performance in turkeys. Particular reference is made to the following: (1) The alteration of sexual maturity by various light regimes as measured by age at first egg; (2) The minimum age at which turkeys can be induced to lay; (3) The light treatment which produces optimum egg production in the fall and the effect age has on this response; (4) The relative importance of light treatment and age interaction on reproductive response; (5) Seasonal variation of egg production through the fall, winter, and spring. MATERIALS AND METHODS
The experimental stock used during the fall of 1957 through the spring of 1959 was obtained from a heterozygous gene pool derived from crosses in all possible combina-
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NFORMATION on the effect of date of hatch on age at sexual maturity for the turkey is meager. Asmundson (1939a, b, 1941) stated that date at first egg, as determined by the number of days after January 1 was a better measure of sexual maturity than age at first egg for females which start their breeding season during the spring. Investigations by Whitson et al. (1944), Dearstyne et al. (1945), Harper (1949), and Asmundson and Moses (1950), all appeared to be measuring the rapidity with which turkeys responded to light rather than sexual maturity per se. Date at first egg during the spring breeding season varied little among physically mature turkeys under similar environmental conditions, and its effect on spring egg production was negligible except in those cases where supplemental artificial light was not used. Siegel and Howes (1959) showed that days to first egg after lighting increased and egg production decreased in birds placed under lights at less than 29 weeks of age. The possibility of utilizing restricted light to induce out of season egg production was demonstrated by Harper and
872
A. T. LEIGHTON, JR. AND R. N. SHOFFNER
ment of birds between pens within the same house. Fall, Winter, and Spring 1958-59. A group of 368 spring hatched female offspring from the first 4 hatches of the "Long Term" line were removed from range August 21, 1958. Females within each hatch were then assigned at random to 1 of 3 possible treatments: (1) Treatment 1—Light restricted to 6 hours per day for 2 weeks followed by 15 hours of continuous light throughout the remainder of the season. (2) Treatment 2—Light restricted to 6 hours per day for 4 weeks followed by 15 hours of continuous light throughout the remainder of the season. (3) Treatment 4—No restricted light. Females were maintained under 14 hours of natural daylight during the period when the other 2 groups were under restricted light. Females which were to receive 4 weeks of restricted light were placed under treatment on August 22, 1958. Those to receive 2 weeks of restricted light were placed under treatment on September 5. On September 19, 1958, all females of all treatments were assigned to pens by hatches so that a proportionate number of birds from each treatment was represented in each pen. Only females of the same age group were placed in the same pen. All birds received 15 hours of daily illumination on the date they were assigned to pens. Individual trap nest records were obtained on each female throughout the season. On December 19,1958, selection of superior producers was made. Birds which were considered as culls in the fall were maintained along with selected birds tiuouguout tuc ureeding season in order to obtain performance data for the flock as a whole. The "Short Term" egg production line consisting of 192 selected females was
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tions of 4 turkey varieties maintained at the Rosemont Agricultural Experiment Station in Southern Minnesota. The original varieties used in the initial cross consisted of Standard Bronze, Broad Breasted Bronze, Broad Breasted White, and Jersey Buffs. Three lines have been developed from the base population. Two lines have been selected for egg production and the third is maintained as a random mating line. These will be referred to as: (1) "Long Term" production line, consisting of females brought into production during the fall and maintained until mid-April each year; (2) "Short Term" production line, consisting of females brought into production during January and maintained until mid-April each year; (3) "Control" line, a random mating population derived from the same base population and maintained each year. Fall, Winter, and Spring 1957-58. A group of 178 "Long Term" females, two to three full sibs from each of 79 dam families were used to provide a cross section of all genotypes present in the base population. Females hatched March 7 and 21, 1957, representing the first and second hatches were used in the comparisons. The females were removed from range on September 9 and placed in a house modified to prevent the entrance of extraneous light. Eight hours of artificial illumination were provided daily. On October 7, 1957, all females received 15 hours of light. Individual egg production records were obtained throughout. Selection took place on December 25, 1957, when the higher producing individuals were placed in breeding pens. However, the cull birds were maintained through April 14, 1958 in order to obtain additional information on egg production. The test pens of the fall period and the breeding pens and test pens of the winter and spring were the same series of pens, so that the selection meant only a rearrange-
873
LIGHT, AGE AND REPRODUCTION
maintained on range until December 30, 19S8, at which time they were housed and placed under 15 hours of artificial light. The "Control" population was handled in exactly the same manner as the "Short Term" line and housed at the same time. Complete egg production records were also obtained for all "Short Term" and "Control" females. The study terminated on April 13, 1959. RESULTS AND DISCUSSION
Treatment Light restricted to 8 h r s . / d a y on 9/9—15hrs. 70 / d a y on 10/7 89 Total
Hatch number
Mean fall prod.
Mean winter prod.
Mean total prod.
1 2
32 33
43 39
75 72
159 Weighted
Production started to decline as broodiness commenced and continued to decline throughout the production period even though the incidence of broodiness fluctuated considerably. This trend in production was comparable to that obtained by Leighton and Shoffner (1960) for restricted light groups during the 1956-57 breeding season. Fall, Winter, and Spring 1958-59. Age at first egg and days to first egg. The effect of hatch and treatment on age at first egg and days to first egg after lighting are summarized in Table 3. There was a 14 day difference in age between each successive hatch. Females in Treatment 1 showed a gradual decrease in age at first egg corresponding to the age when exposed to 15 hour lights. The first 3 hatches took an average of 31 to 34 days to respond. This essentially constant response was reflected in the gradual decrease in age at
TABLE 1.—Effect of a four week restricted light program on mean age at first egg (in days) and mean number of days to first egg in turkeys by hatch {1957-1958) H„, . number
Treatment Light restricted to 8 h r s . / d a y on 9/9—15hrs. 69 / d a y on 10/7. 88 Total
1 2
157 Weighted
Mean age Mean age Mean days at fct t0 fat * * ? . lighted egg egg
214 200 206
244 228
30 28
JAN FEB MONTH
FIG. 1. Seasonal variation in egg production and broodiness at 15 day intervals. (1957-1958)
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Fall, Winter and Spring 1957-58. Age at first egg and days to first egg. The effect of 4 weeks of restricted light on age at first egg and days to first egg are summarized in Table 1. The difference of 14 days in age when lighted was altered slightly as shown by the difference in mean age at first egg. The mean difference in days to first egg of 2 days between the two hatches was in favor of the younger birds (Hatch 2). Fall, winter and total egg production. Mean fall, winter and total egg production is summarized in Table 2. The total production was somewhat higher for the older birds (Hatch 1). However, observed differences between hatches for fall and total production were statistically nonsignificant. Seasonal variation in egg production. Figure 1 shows percentage egg production at 15 day intervals of the combined hatches. Almost all of the restricted light females responded to supplementary light by peaking in production within 3 weeks.
TABLE 2.—Effect of the four week restricted : on mean fall, winter, and total e production (egg number) by hatch (1957-1958)
874
A. T. LEIGHTON, JR. AND R. N. SHOFFNER TABLE 3.—Mean age {in days) at first egg and mean number of days to first egg by hatch and treatment. (1958-1959) Hatch number
(1) Light restricted to 6 hrs. / day on 9/5 —15 hrs. / day on 9/19 Treatment total
24 29 24 25 102 22 29 26 20
Treatment total
97
(4) Natural daylight (14 hrs.) on 8/22 —15 hrs. / day on 9/19
20 35 20 26
Treatment total
101
Hatch totals and weighted hatch means
66 93 70 71
Grand total
300
1 2 3 4
Mean age at first egg
Mean days tofirstegg
196 182 168 154
227 216 200 201
31 34 32 47
175
211
36
196 182 168 154
228 216 205 198
32 34 37 44
176
212
36
196 182 168 154
252 235 228 205
56 53 60 51
175
229
54
1 2 3 4
196 182 168 154
235 223 210 201
39 41 42 47
Population mean
175
217
42
Weighted mean 1 2 3 4 Weighted mean 1 2 3 4 Weighted mean
first egg. Undoubtedly the most interesting response was obtained with Hatch 4 where it took, on the average, 47 days before the first egg was laid. Very nearly identical results were obtained with females in Treatment 2. The weighted mean of age at first egg for Treatment 1 and 2 was 211 and 212 days, respectively. The weighted mean for days to first egg was 36 for the both treatments. In contrast, females under Treatment 4 (nonrestricted) did not show any particular trends relative to mean number of days to first egg. In all cases, it took longer for them to respond to IS hour lights than it did for the same ase errouDS in the restricted light treatments. Further examination of the weighted hatch means show that, on the average, the younger the birds were when exposed to IS hour lights, the longer it took them to respond to light
stimulus. Similar results were obtained by Siegel and Howes (1959) with females lighted in January. The analysis of the data on age at first egg is presented in Table 4. The model for the analysis was given by Leighton and Shoffner (1961). The analysis of variance utilized the Method of Fitting Constants, and when interaction was significant the method of TABLE 4.—A nalysis of variance of age at first egg
Tt.i-
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J. X.
Between treatments Between hatches (ages) TreatmentXhatch Within Subclasses
2 3 6 288
**P<.01. NS = No significant difference.
AAQA 1 * * U T U T . l
10,957.2** 15,409.9** 710.5 NS 427.3
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(2) Light restricted to 6 hrs. / day on 8/22 —15 hrs. / day on 9/19
Mean age when lighted
LIGHT, AGE AND REPRODUCTION
light. Of that group, over 20 percent did not lay during the fall production period but most of them did commence laying sometime during the winter and early spring. In contrast only 2 to 3 percent of the restricted light females did not lay at any time during the year. With the exception of two restricted females, those which did not lay during the fall also failed to lay during the rest of the year. One possible explanation for the slow response of the females which did not receive restricted light is that the hypothalamic-hypophyseal system may have been partially refractory and that the presence of 15 hours of daily illumination did not produce adequate levels of gonadotrophins necessary for gonadal response. However, as the females became older with continued lighting the gonadal threshold may have become lower so that even if the level of gonadotrophins remained the same or was even lower, egg production commenced. Support for this possibility was reported by Phillips (1942) who showed that the gonadotrophic potency of unfractionated pituitary extracts was highest in birds prior to sexual maturity. In the case of mature birds, the ranks in potency of the pituitary extracts from the highest to the lowest was: pullets (approaching sexual maturity), fowl (medium to poor layers), and fowl (good layers). Another possibility also exists whereby refractiveness of the hypothalamic-hypophyseal system was lost during the latter part of the breeding season. This would permit the release of adequate levels of gonadotrophins for gonadal response. The results of the present study indicate that restricted light apparently helped abolish refractoriness of the hypothalamichypophyseal system. Similar conclusions were obtained by Burger (1947), Damste (1947), Wolfson (1952), and Callenbach et al. (1944) regarding the response in other species of birds. They are also in
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Weighted Squares of Means as presented by Snedecor and Cox (1935) and Goulden (1952) was used. No significant interaction was obtained. Since there was a highly significant difference between hatches as well as between treatments, this suggests that certain inherent mechanisms determined only the minimum age at which the young females could lay their first egg. The environment peculiar to the hatch from which they came and the previous light regime determined when production would commence after the minimum age was reached. These results are in agreement with those obtained by Margolf et al. (1947). It seems likely that although the pituitary can be stimulated to produce FSH in immature birds, macroscopic follicular response is unable to occur until females reach physical maturity. Support for this hypothesis was presented by Nalbandov and Card (1946) who found that injection of immature chickens with mammalian FSH resulted in only microscopic follicular proliferation. It was not until the birds were 100 to 120 days old that any macroscopic development (up to .95 mm.) was observed. Such small follicles could not be forced to ovulate even with heavy doses of mammalian LH. Since follicles of birds do not reach preovulatory size until a large amount of yolk material has been deposited, the above workers stated that mammalian gonadotrophins alone in the immature bird were incapable of bringing about maturation of the ovum. They also hypothesized that it is possible that in the chick, unlike the mammal, the ability of the gametogenic portion of the ovary to respond to gonadotrophins may lie in the ability to mobilize and deposit yolk material. Further investigation is necessary to validate this hypothesis. A very interesting phenomenon, rather difficult to explain, occurred in the group of females which did not receive restricted
875
876
A. T. LEIGHTON, JR. AND R. N. SHOFFNER TABLE S.—Mean fall egg production (egg number) to December 20, 1958 by hatch and treatment Weighted
Hatch
Light treatment
1
2
3
4
means
(1)
n Production
24 34
32 29
24 32
28 23
29
(2)
n Production
25 32
29 33
2728
22 23
29
(4)
n Production
23 20
35 24
25 18
27 23
22
29
28
26
23
27
Weighted hatch means
TABLE 6.—Analysis of variance of fall egg production (egg number) Source of variation Between subclasses Between treatments Between hatches (ages) TreatmentXhatch Within subclasses **P<.01. *P<.05.
Degrees of freedom 11 2 3 6 309
Mean square 745.3** 2,274.3** 581. 5* 375.4* 171.9
to constant levels of light. This would result in subthreshold levels of gonadotrophins being released. Fall, winter and total egg production. The effect of the various light regimes on fall egg production measured to December 20, 1958 is presented in Table 5. The first 3 hatches in Treatment 1 and 2 laid approximately the same number of eggs on the average but the production of the fourth hatch in both treatments was considerably lower. This occurred because fall production was determined to the fixed date of December 20 and response time of that hatch group to light stimulus was greater. The slower response of Treatment 4 females also resulted in fewer eggs being produced when compared with corresponding hatches in the restricted light groups. An important contribution to the variation between hatches within the Treatment 4 group was the presence of 24 birds which did not lay during the fall period. The nonproducers appeared at random throughout the hatches. The analysis of fall egg production in Table 6 shows a significant hatch-treatment interaction. This indicates that the number of eggs laid by females from the different hatches and treatments was somewhat dependent on the hatch-treatment combination, even though there were differences in treatments and ages (hatches).
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agreement with those obtained by Harper and Parker (1957) with Beltsville Small White turkeys. The critical factor in determining days to first egg appeared to be the age when females received 15 hour lights following the restricted light period. Although conclusive evidence is lacking, one might speculate that for the restricted females, sensitivity of the gametogenic portion of the gonads to increased output of gonadtrophins was the primary determiner of response. The stimulus for increased gonadotrophins production was undoubtedly the relative change in light from 6 or 8 hours to 15 hours. Two factors might possibly be involved in the response of the unrestricted birds. One factor may involve the sensitivity of the gonads to gonadotrophins. The second factor (and one of major importance) probably involves refractiveness of the hypothalamic-hypophyseal system
877
LIGHT, AGE AND REPRODUCTION TABLE 7 .—Mean
fall, winter,, and total production i[egg number) by hatch and treatment (1958-1959)
(1) Light restricted to 6 hrs. / day on 9/5 —15 hrs. / day on 9/19 Treatment total
23 30 24 27 104 22 28 24 19
Treatment total
93
(4) Natural daylight (14 hrs.) on 8/22 —15 hrs. / day on 9/19
21 33 22 26
Hatch totals and weighted hatch means Grand total
102
Weighted mean
Weighted mean 1 2 3 4 Weighted mean
Fall
Winter
Total
35 30 32 24
37 34 27 21
72 64 59 45
30
30
60
34 32 29 25
36 37 28 30
70 69
30
33
63
21 24 21 23
37 41 35 36
60 65 56 59
22
38
60
57 55
66 91 70 72
1 2 3 4
30 29 27 24
37 37 30 29
67 66 57 53
299
Population mean
28
33
61
The fall and winter records along with total production shown in Table 7 point out the relationship between fall and winter production and the relative contribution of the two periods to total egg production. Even though females in Treatments 1 and 2 were higher in egg production in the fall than those in Treatment 4, the production trends were consistently reversed for winter production. Treatment 4 females, even though they laid fewer eggs in the fall, laid more eggs in the winter so that by April 15, their total production averaged 60 eggs as compared to 60 and 63 for Treatment 1 and 2 respectively. The analysis of total egg production presented in Table 8 shows that interaction between light treatment and hatch was statistically nonsignificant. There was also a nonsignificant difference between treatment groups in total egg pro-
duction. This indicates that even though different light regimes altered time at which egg production response took place, it apparently did not affect the genetic potential of the flock in regard to total number of eggs laid during the period of time covered by this study. Similar results were obtained by Leigh ton and Shoffner (1961). Differences between means of hatches were TABLE 8.—Analysis of variance of total egg production (egg number) Source of variation Between subclasses Between treatments Between hatches (ages) Treatment Xhatch Within subclasses
Degrees of freedom 11 2 3 6 287
**P<.01. NS = No significant
Mean square 1,467.5 NS 319.8 NS 3,557.6** 772.1 NS 891.1
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(2) Light restricted to 6 hrs. / day on 8/22 —15 hrs. / day on 9/19
Treatment total
Mean production
Hatch number
:ment
878
A. T. LEIGHTON, JR. AND R.
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months in duration. In the present study and earlier ones, it was during the last two months of production that the unrestricted females were laying at an appreciably higher rate than the restricted birds. This
SHOFFNER
resulted in a narrowing of the differences between treatment groups to the point where there was no real difference between light treatment groups by the time they had laid for a 6 to 7 month period. If our experiments had been terminated at 4 to 5 months, the conclusions would have been comparable to those of the forementioned investigators. Seasonal variation in egg production of the Long Term production line. Figure 2 shows graphically the percentage egg production by 15 day intervals for hatches within each treatment. Females of Treatment 1 and 2 have about the same trends in egg production. Egg production started by October 15 and following an initial peak, there was a gradual decline through the remainder of the laying period. This decline was characteristic of all hatches. However, the first 2 hatches (the older birds) had a higher initial production and maintained this level throughout most of the breeding season. In contrast the Treatment 4 females came into production more slowly showed no pronounced peak, laid at a lower rate, and did not show any appreciable decline in production until about March 1. The graphs of Figure 3 shows percentage egg production by 15-day intervals for treatment within each hatch. Treatment 1 and 2 females were superior in production to those under Treatment 4 during approximately the first 3 months of production except for hatch 4. Throughout the remainder of the breeding season, the Treatment 4 females were superior in production to the other 2 treatments. The graph for Hatch 4 illustrates that turkeys placed under 15 hour lights at 154 days of age during the fall have the same general distribution of egg production regardless of previous light treatment. An interesting phenomenon of considerable importance was observed in regard to
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highly significant. Referring again to Table 7, it is evident that there was a gradual decrease in total number of eggs laid as age when exposed to IS hour lights decreased. This decrease by hatches was particularly evident in Treatment 1 and 2 but not in Treatment 4. These results add support to the results obtained by Siegel and Howes (1959) with turkeys lighted in January who showed that egg production was lowest in birds exposed to 14 hour lights at 29 weeks of age or younger. The results also support the conclusions of Asmundson (1939a), Harper (1949), and Asmundson and Moses (1950) who showed that hens which respond most rapidly to light laid the most eggs. In general this study was in agreement with the observations of Piatt (1955) in regard to chickens and with those of Marr et al. (1956) and Harper and Parker (1957) in regard to turkeys, who indicated that initial egg production was higher in birds which were preconditioned to restricted light followed by 14 or more hours of continuous daily light. However, the results are not in agreement with the latter two investigations in regard to total egg production. Those investigators found that restricted light groups were higher in total number of eggs laid than were the unrestricted controls. The present study and those by Leighton and Shoffner (1961) could demonstrate no real difference in total egg production between light treatment groups. A probable reason for the lack of agreement lies in the length of the laying period used to measure the response. The study of Marr et al. (1956) encompassed a 19 week period and that of Har-
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FIG. 3. Seasonal variation in egg production at 15 day intervals by treatment within Hatches 1, 2, 3, and 4. (1958-1959)
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FIG. 4. Seasonal variation in egg production and broodiness at IS days intervals within Short Term egg production line and Control line and by treatment over all hatches within the Long Term egg production line. (1958-1959)
non-laying females of the fall production period. Females in Treatment 4 were superior in production to both Treatments 1 and 2 during the latter part of the breeding season. A major reason for this was that females in Treatment 4 which did not lay during the fall period did lay at sometime during the winter production period (one individual exception). In contrast, females which received restricted light and did not lay in the fall, failed to lay at anytime during the period of time covered by this study (two individual exceptions). When these fall nonproducers were removed from the comparison and rough graphs plotted, the production curves for all treatments were slightly higher, but most noticeable was that characteristic curve for Treatment 4 changed its form to coincide with that of the other two treatments. It thus became evident that regardless of prelaying light treatment, egg production trends of birds which actually started laying during the fall were for all practical purposes the same. The use of preliminary restricted light treatment thus provides a technique where-
by nearly all individuals can be stimulated into production at the same time. Seasonal variation in egg production of the Long Term, Short Term and Control lines. Figure 4 illustrates graphically the results shown in Table 7. Treatment 1 and Treatment 2 females show the same general trends in production as was obtained by Leighton and Shoffner (1961) and that shown in Figure 1 for the 1957-58 study. The unrestricted females (Treatment 4) show trends similar to that obtained by Leighton and Shoffner (1961). Two additional production curves are plotted in Figure 4. The Short Term group had one generation of selection for egg production and the Control group had none. The most interesting point in regard to these two populations is that the response to light was the same. The only difference was that the controls did not reach as high a level of production as did the Short Term selected group. The similarity of the curves of the Short Term and Control group compared with the fall restricted light birds shows that the initial trends in production
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882
A. T. LEIGHTON, JR. AND R. N. SHOFFNER
younger than 26 weeks of age when subsequently exposed to 15 hour lights. Unrestricted females should start receiving 15 hour lights at 22 weeks of age. The data presented also suggests that a restricted light program must be used on females during the late summer and early fall if out-of-season poult production is to be a profitable venture for the turkey breeder. This is particularly true if the flock is maintained for less than a five month production period. SUMMARY AND CONCLUSIONS
The study presented was designed to ascertain the effect of restricted and unrestricted light on reproduction in the turkey. A segregating population of turkeys was used during the 1957-58 and 1958-59 breeding seasons. All birds were hatched during late winter and early spring each year. Light regime studies began early in the fall and were terminated in mid-April each year. Restricting light to 6 or 8 hours per day for a 2 or 4-week period during the fall and subsequently exposing females to 15 hour lights for the remainder of the breeding season resulted in significantly earlier age at first egg when compared with unrestricted females. Restricted females, within the range of age groups studied, required a greater number of days to respond to light stimulus, as age when exposed to 15 hour lights decreased; however, age at first egg decreased as age at lighting decreased. Unrestricted females maintained on 14 hours of light and subsequently exposed to 15 hour lights showed essentially the same degree of refractoriness to light between the ages of 154 and 196 days of age as measured by days to first egg after lighting. True age at sexual maturity as determined by the minimum age at which females could be induced to lay was approxi-
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are the same and provides additional evidence that restricted light in the fall simulates the light environment to which turkeys are exposed prior to being placed under lights early in January. Another interesting point shown in Figure 4 is the relationship between broodiness and egg production of the three populations. The Control line and the Short Term production line show the characteristic decline in egg production commonly observed in turkey flocks as broodiness increases during the late winter production period. However, in the Long Term production line, broodiness reached a peak of only 3 percent by December 1 and remained at less than 2 percent for the remainder of the breeding season. Egg production did show a slight decline when broodiness started in the fall but since broodiness was at such low levels throughout the fall and winter breeding season, it apparently was not an important factor in declining egg production as the season progressed. The incidence of broodiness for the 1957-58 flock shown in Figure 1 is somewhat higher than for 1958-59. The experiments discussed were designed to obtain information on the minimum age at which turkeys could be induced to lay. Unfortunately, the range in ages used, as far the authors are concerned, was not adequate to determine the maximum age at which turkeys should be lighted in order to lay at the most efficient rate. However, Siegel and Howes (1959) presented evidence which suggested that turkeys brought into production in January should be placed under lights at 29 to 30 weeks of age for most economical production. Based upon the results it appears that within the range of age groups studied, medium to large type female turkeys should have light restricted from 6 to 8 hours per day for a 4-week period at approximately 22 weeks of age during the fall and they should be no
LIGHT, AGE AND REPRODUCTION
no longer than a 5-month period.
production
REFERENCES Asmundson, V. S., 1939a. The relative influence of various factors on the egg production of turkeys during different parts of the first laying year. J. Agr. Res. 58: 747-754. Asmundson, V. S., 1939b. On the measurement and inheritance of sexual maturity in turkeys. (Meleagris gallapovo). Am. Nat. 73: 365-374. Asmundson, V. S., 1941. Differences in sexual maturity and egg production in turkeys. Poultry Sci. 20: 51-56. Asmundson, V. S., and B. D. Moses, 1950. Influence of length of day on reproduction in turkey hens. Poultry Sci. 29: 34-41. Burger, J. W., 1947. On the relation of day length to the phases of testicular involution and inactivity of the spermatogenetic cycle of the starling. J. Exp. Zool. 105: 259-267. Callenbach, E. W., J. E. Nicholus and R. R. Murphy, 1944. Influence of light on age at sexual maturity and ovulation rate of pullets. Pennsylvania Agr. Expt. Sta. Bui. No. 461. Damste, P. H., 1947. Experimental modification of the sexual cycle of the Green Finch. J. Exp. Biol. 24 : 20-35. Dearstyne, R. S., C. H. Bostian and W. B. Nesbit, 1945. Improving turkey production. North Carolina Agr. Expt. Sta. Bui. No. 350. Goulden, C. H., 1952. Methods of Statistical Analysis. Second Ed. John Wiley and Sons Inc. New York. Harper, J. A., 1949. The rate of response of turkey hens to artificial light as related to reproduction. Poultry Sci. 28: 312-314. Harper, J. A., and J. E. Parker, 1957. Changes in seasonal egg production of turkeys induced through controlled light exposure and forced moulting. Poultry Sci. 36: 967-973. Leighton, A. T., Jr., and R. N. Shoffner, 1961. Effect of light regime and age on reproduction of turkeys. 1. Effect of 15, 24 hour and restricted light treatment. Poultry Sci.: 40: 861-870. Margolf, P. H., J. A. Harper and E. W. Callenbach, 1947. Response of turkeys to artificial illumination. Pennsylvania Agr. Expt. Sta. Bui. No. 486. Marr, J. E., F. W. Garland, Jr., J. L. Milligan and H. L. Wilcke, 1956. Effect of controlled light during the growing period upon subsequent performance of breeder turkeys. Poultry Sci. 35: 1156.
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mately 200 days of age for the turkeys utilized in this study. Light environment appeared to have little effect on minimum age at which turkeys could be induced to lay. No significant hatch-treatment interactions were obtained in regard to age at first eggThe use of restricted light for a 2 to 4-week period in the fall increased fall egg production significantly over that of unrestricted females. No significant difference in total egg production was obtained between the light treatment groups utilized in this study. It appears therefore, that the genetic potential of the female turkeys for total number of eggs produced, was not altered by the various light regimes. The major effect of changing the light environment appeared to be alteration in time and rapidity of response. Over 20 percent of the females which had not received restricted light were non-layers during the fall. However, in almost every case such non-layers did start laying during the winter or spring. In contrast, only 2 to 3 percent of the females which had received preliminary restricted light treatment did not lay in the fall. This resulted in higher egg production for the restricted birds for fall production. The fact that new females were coming into production in the spring resulted in higher egg production during that period for the unrestricted birds. Hatch-treatment interactions in regard to fall egg production were small. As a consequence of this, the relative importance of such interactions is questionable. No significant-hatch treatment interactions were obtained for total egg production. Under the conditions of this study, the use of restricted light to increase the efficiency of producing out-of-season turkey poults showed considerable promise, particularly when turkey breeders are kept for
883
884
A. T. LEIGHTON, JE. AND R. N. SHOFFNER
Nalbandov, A., and L. E. Card, 1946. Effect of FSH and LH upon ovaries of immature chicks and low producing hens. Endocrinol. 38: 7178. Phillips, R. E., 1942. Comparative gonadotropic potency of unfractionated extracts of poultry pituitaries. Poultry Sci. 2 1 : 161-172. Piatt, C. S., 19SS. A study of the effect of restricted lighting on January hatched pullets. Poultry Sci. 34: 1045-1047. Siegel, P. B., and C. E. Howes, 1959. Age at lighting and egg production of Bronze and Large White turkeys. Virginia Agr. Expt. Sta.
Bull. No. 503. Snedecor, G. W., and G. W. Cox, 1935. Disproportionate subclass numbers in tables of multiple classification. Iowa Agr. Exp. Sta. Bui. No. 180. Whitson, D., S. J. Marsden and H. W. Titus, 1944. A comparison of the performance of four varieties of turkeys during the breeding season. Poultry Sci. 23:314-320. Wolfson, A., 1952. The occurrence and regulation of the refractory period in the gonadal and fat cycles of the Junco. J. Exp. Zool. 121: 311326.
ALLEN E. WOODARD, H. ABPLANALP AND F. X. OGASAWARA Poultry Husbandry Department, University of California, Davis (Received for publication August 17, 1960)
T
HERE are many advantages of housing of turkey breeding flocks in individual cages. One of the most important is positive identification of the hen that laid the egg. Cage confinement of turkeys reduces the need for large acreage and provides protection from winter storms and predators; dust can be eliminated in areas where air pollution may be a problem; and light restriction programs are possible when hens are kept in laying houses. The Poultry Department of the University of California since 1953 has kept turkey hens in individual wire floor cages and a few trials with caged males have been in progress since 1957. Three difficulties with cage management have appeared so far: high incidence of egg breakage, larger numbers of soft shelled eggs than found with floor management and foot contusions. Some commercial turkey growers have experienced similar difficulties. The effects of cage confinement on turkey males and females have not been investigated systematically so far. The present
study was made in order to determine the influence of cage confinement of turkeys on egg production, egg breakage, semen volume and incidence of swollen feet. METHODS AND MATERIALS In earlier trials it was found here that large Broad Breasted Bronze males could not be confined to sloping floor cages, that had originally been designed for females.* Within two weeks such males were showing severe foot damage and had to be removed from cages. In order to alleviate this situation, the authors designed a larger flat bottomed cage (24" X 24") and secured a 1" X 6" board to the bottom and near the center of the cage. This correction greatly reduced the incidence of foot contusion in Bronze males. * The dimensions of the turkey female cages are 16" wide, 24" deep and approximately 18" high. The roll-away-floor is constructed of 1" X 2"welded 12 gauge wire with a %" cold rolled steel rod supporting the center floor of the cage. The cage is a commercially manufactured type.
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Egg and Semen Production Performance of Turkeys Under Cage Management
I
1 Minnesota Agricultural Experiment Station Scientific Journal Series Paper #4444. 2 A portion of a thesis submitted by the senior author to the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 3 Present address: Department of Poultry Husbandry, Virginia Agricultural Experiment Station, Blacksburg, Virginia.
871
Parker (1957). The results of a pilot study undertaken during the 1956-57 breeding season by Leighton and Shoffner (1961) have also shown that if light was restricted to 8 hours per day for a 4 week period and then supplemented to provide 15 hours per day for the remainder of a 6 to 7 month breeding season, a production response followed which simulated that observed in flocks of turkeys lighted in January. In contrast, females already under essentially optimum light levels (13 or more hours) responded more slowly to 15 hour lights and laid at a lower rate during the fall production period than did the restricted group. This study reports on the utilization of various light regimes for improvement of reproductive performance in turkeys. Particular reference is made to the following: (1) The alteration of sexual maturity by various light regimes as measured by age at first egg; (2) The minimum age at which turkeys can be induced to lay; (3) The light treatment which produces optimum egg production in the fall and the effect age has on this response; (4) The relative importance of light treatment and age interaction on reproductive response; (5) Seasonal variation of egg production through the fall, winter, and spring. MATERIALS AND METHODS
The experimental stock used during the fall of 1957 through the spring of 1959 was obtained from a heterozygous gene pool derived from crosses in all possible combina-
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NFORMATION on the effect of date of hatch on age at sexual maturity for the turkey is meager. Asmundson (1939a, b, 1941) stated that date at first egg, as determined by the number of days after January 1 was a better measure of sexual maturity than age at first egg for females which start their breeding season during the spring. Investigations by Whitson et al. (1944), Dearstyne et al. (1945), Harper (1949), and Asmundson and Moses (1950), all appeared to be measuring the rapidity with which turkeys responded to light rather than sexual maturity per se. Date at first egg during the spring breeding season varied little among physically mature turkeys under similar environmental conditions, and its effect on spring egg production was negligible except in those cases where supplemental artificial light was not used. Siegel and Howes (1959) showed that days to first egg after lighting increased and egg production decreased in birds placed under lights at less than 29 weeks of age. The possibility of utilizing restricted light to induce out of season egg production was demonstrated by Harper and
872
A. T. LEIGHTON, JR. AND R. N. SHOFFNER
ment of birds between pens within the same house. Fall, Winter, and Spring 1958-59. A group of 368 spring hatched female offspring from the first 4 hatches of the "Long Term" line were removed from range August 21, 1958. Females within each hatch were then assigned at random to 1 of 3 possible treatments: (1) Treatment 1—Light restricted to 6 hours per day for 2 weeks followed by 15 hours of continuous light throughout the remainder of the season. (2) Treatment 2—Light restricted to 6 hours per day for 4 weeks followed by 15 hours of continuous light throughout the remainder of the season. (3) Treatment 4—No restricted light. Females were maintained under 14 hours of natural daylight during the period when the other 2 groups were under restricted light. Females which were to receive 4 weeks of restricted light were placed under treatment on August 22, 1958. Those to receive 2 weeks of restricted light were placed under treatment on September 5. On September 19, 1958, all females of all treatments were assigned to pens by hatches so that a proportionate number of birds from each treatment was represented in each pen. Only females of the same age group were placed in the same pen. All birds received 15 hours of daily illumination on the date they were assigned to pens. Individual trap nest records were obtained on each female throughout the season. On December 19,1958, selection of superior producers was made. Birds which were considered as culls in the fall were maintained along with selected birds tiuouguout tuc ureeding season in order to obtain performance data for the flock as a whole. The "Short Term" egg production line consisting of 192 selected females was
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tions of 4 turkey varieties maintained at the Rosemont Agricultural Experiment Station in Southern Minnesota. The original varieties used in the initial cross consisted of Standard Bronze, Broad Breasted Bronze, Broad Breasted White, and Jersey Buffs. Three lines have been developed from the base population. Two lines have been selected for egg production and the third is maintained as a random mating line. These will be referred to as: (1) "Long Term" production line, consisting of females brought into production during the fall and maintained until mid-April each year; (2) "Short Term" production line, consisting of females brought into production during January and maintained until mid-April each year; (3) "Control" line, a random mating population derived from the same base population and maintained each year. Fall, Winter, and Spring 1957-58. A group of 178 "Long Term" females, two to three full sibs from each of 79 dam families were used to provide a cross section of all genotypes present in the base population. Females hatched March 7 and 21, 1957, representing the first and second hatches were used in the comparisons. The females were removed from range on September 9 and placed in a house modified to prevent the entrance of extraneous light. Eight hours of artificial illumination were provided daily. On October 7, 1957, all females received 15 hours of light. Individual egg production records were obtained throughout. Selection took place on December 25, 1957, when the higher producing individuals were placed in breeding pens. However, the cull birds were maintained through April 14, 1958 in order to obtain additional information on egg production. The test pens of the fall period and the breeding pens and test pens of the winter and spring were the same series of pens, so that the selection meant only a rearrange-
873
LIGHT, AGE AND REPRODUCTION
maintained on range until December 30, 19S8, at which time they were housed and placed under 15 hours of artificial light. The "Control" population was handled in exactly the same manner as the "Short Term" line and housed at the same time. Complete egg production records were also obtained for all "Short Term" and "Control" females. The study terminated on April 13, 1959. RESULTS AND DISCUSSION
Treatment Light restricted to 8 h r s . / d a y on 9/9—15hrs. 70 / d a y on 10/7 89 Total
Hatch number
Mean fall prod.
Mean winter prod.
Mean total prod.
1 2
32 33
43 39
75 72
159 Weighted
Production started to decline as broodiness commenced and continued to decline throughout the production period even though the incidence of broodiness fluctuated considerably. This trend in production was comparable to that obtained by Leighton and Shoffner (1960) for restricted light groups during the 1956-57 breeding season. Fall, Winter, and Spring 1958-59. Age at first egg and days to first egg. The effect of hatch and treatment on age at first egg and days to first egg after lighting are summarized in Table 3. There was a 14 day difference in age between each successive hatch. Females in Treatment 1 showed a gradual decrease in age at first egg corresponding to the age when exposed to 15 hour lights. The first 3 hatches took an average of 31 to 34 days to respond. This essentially constant response was reflected in the gradual decrease in age at
TABLE 1.—Effect of a four week restricted light program on mean age at first egg (in days) and mean number of days to first egg in turkeys by hatch {1957-1958) H„, . number
Treatment Light restricted to 8 h r s . / d a y on 9/9—15hrs. 69 / d a y on 10/7. 88 Total
1 2
157 Weighted
Mean age Mean age Mean days at fct t0 fat * * ? . lighted egg egg
214 200 206
244 228
30 28
JAN FEB MONTH
FIG. 1. Seasonal variation in egg production and broodiness at 15 day intervals. (1957-1958)
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Fall, Winter and Spring 1957-58. Age at first egg and days to first egg. The effect of 4 weeks of restricted light on age at first egg and days to first egg are summarized in Table 1. The difference of 14 days in age when lighted was altered slightly as shown by the difference in mean age at first egg. The mean difference in days to first egg of 2 days between the two hatches was in favor of the younger birds (Hatch 2). Fall, winter and total egg production. Mean fall, winter and total egg production is summarized in Table 2. The total production was somewhat higher for the older birds (Hatch 1). However, observed differences between hatches for fall and total production were statistically nonsignificant. Seasonal variation in egg production. Figure 1 shows percentage egg production at 15 day intervals of the combined hatches. Almost all of the restricted light females responded to supplementary light by peaking in production within 3 weeks.
TABLE 2.—Effect of the four week restricted : on mean fall, winter, and total e production (egg number) by hatch (1957-1958)
874
A. T. LEIGHTON, JR. AND R. N. SHOFFNER TABLE 3.—Mean age {in days) at first egg and mean number of days to first egg by hatch and treatment. (1958-1959) Hatch number
(1) Light restricted to 6 hrs. / day on 9/5 —15 hrs. / day on 9/19 Treatment total
24 29 24 25 102 22 29 26 20
Treatment total
97
(4) Natural daylight (14 hrs.) on 8/22 —15 hrs. / day on 9/19
20 35 20 26
Treatment total
101
Hatch totals and weighted hatch means
66 93 70 71
Grand total
300
1 2 3 4
Mean age at first egg
Mean days tofirstegg
196 182 168 154
227 216 200 201
31 34 32 47
175
211
36
196 182 168 154
228 216 205 198
32 34 37 44
176
212
36
196 182 168 154
252 235 228 205
56 53 60 51
175
229
54
1 2 3 4
196 182 168 154
235 223 210 201
39 41 42 47
Population mean
175
217
42
Weighted mean 1 2 3 4 Weighted mean 1 2 3 4 Weighted mean
first egg. Undoubtedly the most interesting response was obtained with Hatch 4 where it took, on the average, 47 days before the first egg was laid. Very nearly identical results were obtained with females in Treatment 2. The weighted mean of age at first egg for Treatment 1 and 2 was 211 and 212 days, respectively. The weighted mean for days to first egg was 36 for the both treatments. In contrast, females under Treatment 4 (nonrestricted) did not show any particular trends relative to mean number of days to first egg. In all cases, it took longer for them to respond to IS hour lights than it did for the same ase errouDS in the restricted light treatments. Further examination of the weighted hatch means show that, on the average, the younger the birds were when exposed to IS hour lights, the longer it took them to respond to light
stimulus. Similar results were obtained by Siegel and Howes (1959) with females lighted in January. The analysis of the data on age at first egg is presented in Table 4. The model for the analysis was given by Leighton and Shoffner (1961). The analysis of variance utilized the Method of Fitting Constants, and when interaction was significant the method of TABLE 4.—A nalysis of variance of age at first egg
Tt.i-
.,..T,„1„,.„„„
11
UCLWCCH
SUtJUdSSCS
J. X.
Between treatments Between hatches (ages) TreatmentXhatch Within Subclasses
2 3 6 288
**P<.01. NS = No significant difference.
AAQA 1 * * U T U T . l
10,957.2** 15,409.9** 710.5 NS 427.3
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(2) Light restricted to 6 hrs. / day on 8/22 —15 hrs. / day on 9/19
Mean age when lighted
LIGHT, AGE AND REPRODUCTION
light. Of that group, over 20 percent did not lay during the fall production period but most of them did commence laying sometime during the winter and early spring. In contrast only 2 to 3 percent of the restricted light females did not lay at any time during the year. With the exception of two restricted females, those which did not lay during the fall also failed to lay during the rest of the year. One possible explanation for the slow response of the females which did not receive restricted light is that the hypothalamic-hypophyseal system may have been partially refractory and that the presence of 15 hours of daily illumination did not produce adequate levels of gonadotrophins necessary for gonadal response. However, as the females became older with continued lighting the gonadal threshold may have become lower so that even if the level of gonadotrophins remained the same or was even lower, egg production commenced. Support for this possibility was reported by Phillips (1942) who showed that the gonadotrophic potency of unfractionated pituitary extracts was highest in birds prior to sexual maturity. In the case of mature birds, the ranks in potency of the pituitary extracts from the highest to the lowest was: pullets (approaching sexual maturity), fowl (medium to poor layers), and fowl (good layers). Another possibility also exists whereby refractiveness of the hypothalamic-hypophyseal system was lost during the latter part of the breeding season. This would permit the release of adequate levels of gonadotrophins for gonadal response. The results of the present study indicate that restricted light apparently helped abolish refractoriness of the hypothalamichypophyseal system. Similar conclusions were obtained by Burger (1947), Damste (1947), Wolfson (1952), and Callenbach et al. (1944) regarding the response in other species of birds. They are also in
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Weighted Squares of Means as presented by Snedecor and Cox (1935) and Goulden (1952) was used. No significant interaction was obtained. Since there was a highly significant difference between hatches as well as between treatments, this suggests that certain inherent mechanisms determined only the minimum age at which the young females could lay their first egg. The environment peculiar to the hatch from which they came and the previous light regime determined when production would commence after the minimum age was reached. These results are in agreement with those obtained by Margolf et al. (1947). It seems likely that although the pituitary can be stimulated to produce FSH in immature birds, macroscopic follicular response is unable to occur until females reach physical maturity. Support for this hypothesis was presented by Nalbandov and Card (1946) who found that injection of immature chickens with mammalian FSH resulted in only microscopic follicular proliferation. It was not until the birds were 100 to 120 days old that any macroscopic development (up to .95 mm.) was observed. Such small follicles could not be forced to ovulate even with heavy doses of mammalian LH. Since follicles of birds do not reach preovulatory size until a large amount of yolk material has been deposited, the above workers stated that mammalian gonadotrophins alone in the immature bird were incapable of bringing about maturation of the ovum. They also hypothesized that it is possible that in the chick, unlike the mammal, the ability of the gametogenic portion of the ovary to respond to gonadotrophins may lie in the ability to mobilize and deposit yolk material. Further investigation is necessary to validate this hypothesis. A very interesting phenomenon, rather difficult to explain, occurred in the group of females which did not receive restricted
875
876
A. T. LEIGHTON, JR. AND R. N. SHOFFNER TABLE S.—Mean fall egg production (egg number) to December 20, 1958 by hatch and treatment Weighted
Hatch
Light treatment
1
2
3
4
means
(1)
n Production
24 34
32 29
24 32
28 23
29
(2)
n Production
25 32
29 33
2728
22 23
29
(4)
n Production
23 20
35 24
25 18
27 23
22
29
28
26
23
27
Weighted hatch means
TABLE 6.—Analysis of variance of fall egg production (egg number) Source of variation Between subclasses Between treatments Between hatches (ages) TreatmentXhatch Within subclasses **P<.01. *P<.05.
Degrees of freedom 11 2 3 6 309
Mean square 745.3** 2,274.3** 581. 5* 375.4* 171.9
to constant levels of light. This would result in subthreshold levels of gonadotrophins being released. Fall, winter and total egg production. The effect of the various light regimes on fall egg production measured to December 20, 1958 is presented in Table 5. The first 3 hatches in Treatment 1 and 2 laid approximately the same number of eggs on the average but the production of the fourth hatch in both treatments was considerably lower. This occurred because fall production was determined to the fixed date of December 20 and response time of that hatch group to light stimulus was greater. The slower response of Treatment 4 females also resulted in fewer eggs being produced when compared with corresponding hatches in the restricted light groups. An important contribution to the variation between hatches within the Treatment 4 group was the presence of 24 birds which did not lay during the fall period. The nonproducers appeared at random throughout the hatches. The analysis of fall egg production in Table 6 shows a significant hatch-treatment interaction. This indicates that the number of eggs laid by females from the different hatches and treatments was somewhat dependent on the hatch-treatment combination, even though there were differences in treatments and ages (hatches).
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agreement with those obtained by Harper and Parker (1957) with Beltsville Small White turkeys. The critical factor in determining days to first egg appeared to be the age when females received 15 hour lights following the restricted light period. Although conclusive evidence is lacking, one might speculate that for the restricted females, sensitivity of the gametogenic portion of the gonads to increased output of gonadtrophins was the primary determiner of response. The stimulus for increased gonadotrophins production was undoubtedly the relative change in light from 6 or 8 hours to 15 hours. Two factors might possibly be involved in the response of the unrestricted birds. One factor may involve the sensitivity of the gonads to gonadotrophins. The second factor (and one of major importance) probably involves refractiveness of the hypothalamic-hypophyseal system
877
LIGHT, AGE AND REPRODUCTION TABLE 7 .—Mean
fall, winter,, and total production i[egg number) by hatch and treatment (1958-1959)
(1) Light restricted to 6 hrs. / day on 9/5 —15 hrs. / day on 9/19 Treatment total
23 30 24 27 104 22 28 24 19
Treatment total
93
(4) Natural daylight (14 hrs.) on 8/22 —15 hrs. / day on 9/19
21 33 22 26
Hatch totals and weighted hatch means Grand total
102
Weighted mean
Weighted mean 1 2 3 4 Weighted mean
Fall
Winter
Total
35 30 32 24
37 34 27 21
72 64 59 45
30
30
60
34 32 29 25
36 37 28 30
70 69
30
33
63
21 24 21 23
37 41 35 36
60 65 56 59
22
38
60
57 55
66 91 70 72
1 2 3 4
30 29 27 24
37 37 30 29
67 66 57 53
299
Population mean
28
33
61
The fall and winter records along with total production shown in Table 7 point out the relationship between fall and winter production and the relative contribution of the two periods to total egg production. Even though females in Treatments 1 and 2 were higher in egg production in the fall than those in Treatment 4, the production trends were consistently reversed for winter production. Treatment 4 females, even though they laid fewer eggs in the fall, laid more eggs in the winter so that by April 15, their total production averaged 60 eggs as compared to 60 and 63 for Treatment 1 and 2 respectively. The analysis of total egg production presented in Table 8 shows that interaction between light treatment and hatch was statistically nonsignificant. There was also a nonsignificant difference between treatment groups in total egg pro-
duction. This indicates that even though different light regimes altered time at which egg production response took place, it apparently did not affect the genetic potential of the flock in regard to total number of eggs laid during the period of time covered by this study. Similar results were obtained by Leigh ton and Shoffner (1961). Differences between means of hatches were TABLE 8.—Analysis of variance of total egg production (egg number) Source of variation Between subclasses Between treatments Between hatches (ages) Treatment Xhatch Within subclasses
Degrees of freedom 11 2 3 6 287
**P<.01. NS = No significant
Mean square 1,467.5 NS 319.8 NS 3,557.6** 772.1 NS 891.1
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(2) Light restricted to 6 hrs. / day on 8/22 —15 hrs. / day on 9/19
Treatment total
Mean production
Hatch number
:ment
878
A. T. LEIGHTON, JR. AND R.
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months in duration. In the present study and earlier ones, it was during the last two months of production that the unrestricted females were laying at an appreciably higher rate than the restricted birds. This
SHOFFNER
resulted in a narrowing of the differences between treatment groups to the point where there was no real difference between light treatment groups by the time they had laid for a 6 to 7 month period. If our experiments had been terminated at 4 to 5 months, the conclusions would have been comparable to those of the forementioned investigators. Seasonal variation in egg production of the Long Term production line. Figure 2 shows graphically the percentage egg production by 15 day intervals for hatches within each treatment. Females of Treatment 1 and 2 have about the same trends in egg production. Egg production started by October 15 and following an initial peak, there was a gradual decline through the remainder of the laying period. This decline was characteristic of all hatches. However, the first 2 hatches (the older birds) had a higher initial production and maintained this level throughout most of the breeding season. In contrast the Treatment 4 females came into production more slowly showed no pronounced peak, laid at a lower rate, and did not show any appreciable decline in production until about March 1. The graphs of Figure 3 shows percentage egg production by 15-day intervals for treatment within each hatch. Treatment 1 and 2 females were superior in production to those under Treatment 4 during approximately the first 3 months of production except for hatch 4. Throughout the remainder of the breeding season, the Treatment 4 females were superior in production to the other 2 treatments. The graph for Hatch 4 illustrates that turkeys placed under 15 hour lights at 154 days of age during the fall have the same general distribution of egg production regardless of previous light treatment. An interesting phenomenon of considerable importance was observed in regard to
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highly significant. Referring again to Table 7, it is evident that there was a gradual decrease in total number of eggs laid as age when exposed to IS hour lights decreased. This decrease by hatches was particularly evident in Treatment 1 and 2 but not in Treatment 4. These results add support to the results obtained by Siegel and Howes (1959) with turkeys lighted in January who showed that egg production was lowest in birds exposed to 14 hour lights at 29 weeks of age or younger. The results also support the conclusions of Asmundson (1939a), Harper (1949), and Asmundson and Moses (1950) who showed that hens which respond most rapidly to light laid the most eggs. In general this study was in agreement with the observations of Piatt (1955) in regard to chickens and with those of Marr et al. (1956) and Harper and Parker (1957) in regard to turkeys, who indicated that initial egg production was higher in birds which were preconditioned to restricted light followed by 14 or more hours of continuous daily light. However, the results are not in agreement with the latter two investigations in regard to total egg production. Those investigators found that restricted light groups were higher in total number of eggs laid than were the unrestricted controls. The present study and those by Leighton and Shoffner (1961) could demonstrate no real difference in total egg production between light treatment groups. A probable reason for the lack of agreement lies in the length of the laying period used to measure the response. The study of Marr et al. (1956) encompassed a 19 week period and that of Har-
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PER CENT PRODUCTION
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FIG. 3. Seasonal variation in egg production at 15 day intervals by treatment within Hatches 1, 2, 3, and 4. (1958-1959)
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FIG. 4. Seasonal variation in egg production and broodiness at IS days intervals within Short Term egg production line and Control line and by treatment over all hatches within the Long Term egg production line. (1958-1959)
non-laying females of the fall production period. Females in Treatment 4 were superior in production to both Treatments 1 and 2 during the latter part of the breeding season. A major reason for this was that females in Treatment 4 which did not lay during the fall period did lay at sometime during the winter production period (one individual exception). In contrast, females which received restricted light and did not lay in the fall, failed to lay at anytime during the period of time covered by this study (two individual exceptions). When these fall nonproducers were removed from the comparison and rough graphs plotted, the production curves for all treatments were slightly higher, but most noticeable was that characteristic curve for Treatment 4 changed its form to coincide with that of the other two treatments. It thus became evident that regardless of prelaying light treatment, egg production trends of birds which actually started laying during the fall were for all practical purposes the same. The use of preliminary restricted light treatment thus provides a technique where-
by nearly all individuals can be stimulated into production at the same time. Seasonal variation in egg production of the Long Term, Short Term and Control lines. Figure 4 illustrates graphically the results shown in Table 7. Treatment 1 and Treatment 2 females show the same general trends in production as was obtained by Leighton and Shoffner (1961) and that shown in Figure 1 for the 1957-58 study. The unrestricted females (Treatment 4) show trends similar to that obtained by Leighton and Shoffner (1961). Two additional production curves are plotted in Figure 4. The Short Term group had one generation of selection for egg production and the Control group had none. The most interesting point in regard to these two populations is that the response to light was the same. The only difference was that the controls did not reach as high a level of production as did the Short Term selected group. The similarity of the curves of the Short Term and Control group compared with the fall restricted light birds shows that the initial trends in production
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A. T. LEIGHTON, JR. AND R. N. SHOFFNER
younger than 26 weeks of age when subsequently exposed to 15 hour lights. Unrestricted females should start receiving 15 hour lights at 22 weeks of age. The data presented also suggests that a restricted light program must be used on females during the late summer and early fall if out-of-season poult production is to be a profitable venture for the turkey breeder. This is particularly true if the flock is maintained for less than a five month production period. SUMMARY AND CONCLUSIONS
The study presented was designed to ascertain the effect of restricted and unrestricted light on reproduction in the turkey. A segregating population of turkeys was used during the 1957-58 and 1958-59 breeding seasons. All birds were hatched during late winter and early spring each year. Light regime studies began early in the fall and were terminated in mid-April each year. Restricting light to 6 or 8 hours per day for a 2 or 4-week period during the fall and subsequently exposing females to 15 hour lights for the remainder of the breeding season resulted in significantly earlier age at first egg when compared with unrestricted females. Restricted females, within the range of age groups studied, required a greater number of days to respond to light stimulus, as age when exposed to 15 hour lights decreased; however, age at first egg decreased as age at lighting decreased. Unrestricted females maintained on 14 hours of light and subsequently exposed to 15 hour lights showed essentially the same degree of refractoriness to light between the ages of 154 and 196 days of age as measured by days to first egg after lighting. True age at sexual maturity as determined by the minimum age at which females could be induced to lay was approxi-
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are the same and provides additional evidence that restricted light in the fall simulates the light environment to which turkeys are exposed prior to being placed under lights early in January. Another interesting point shown in Figure 4 is the relationship between broodiness and egg production of the three populations. The Control line and the Short Term production line show the characteristic decline in egg production commonly observed in turkey flocks as broodiness increases during the late winter production period. However, in the Long Term production line, broodiness reached a peak of only 3 percent by December 1 and remained at less than 2 percent for the remainder of the breeding season. Egg production did show a slight decline when broodiness started in the fall but since broodiness was at such low levels throughout the fall and winter breeding season, it apparently was not an important factor in declining egg production as the season progressed. The incidence of broodiness for the 1957-58 flock shown in Figure 1 is somewhat higher than for 1958-59. The experiments discussed were designed to obtain information on the minimum age at which turkeys could be induced to lay. Unfortunately, the range in ages used, as far the authors are concerned, was not adequate to determine the maximum age at which turkeys should be lighted in order to lay at the most efficient rate. However, Siegel and Howes (1959) presented evidence which suggested that turkeys brought into production in January should be placed under lights at 29 to 30 weeks of age for most economical production. Based upon the results it appears that within the range of age groups studied, medium to large type female turkeys should have light restricted from 6 to 8 hours per day for a 4-week period at approximately 22 weeks of age during the fall and they should be no
LIGHT, AGE AND REPRODUCTION
no longer than a 5-month period.
production
REFERENCES Asmundson, V. S., 1939a. The relative influence of various factors on the egg production of turkeys during different parts of the first laying year. J. Agr. Res. 58: 747-754. Asmundson, V. S., 1939b. On the measurement and inheritance of sexual maturity in turkeys. (Meleagris gallapovo). Am. Nat. 73: 365-374. Asmundson, V. S., 1941. Differences in sexual maturity and egg production in turkeys. Poultry Sci. 20: 51-56. Asmundson, V. S., and B. D. Moses, 1950. Influence of length of day on reproduction in turkey hens. Poultry Sci. 29: 34-41. Burger, J. W., 1947. On the relation of day length to the phases of testicular involution and inactivity of the spermatogenetic cycle of the starling. J. Exp. Zool. 105: 259-267. Callenbach, E. W., J. E. Nicholus and R. R. Murphy, 1944. Influence of light on age at sexual maturity and ovulation rate of pullets. Pennsylvania Agr. Expt. Sta. Bui. No. 461. Damste, P. H., 1947. Experimental modification of the sexual cycle of the Green Finch. J. Exp. Biol. 24 : 20-35. Dearstyne, R. S., C. H. Bostian and W. B. Nesbit, 1945. Improving turkey production. North Carolina Agr. Expt. Sta. Bui. No. 350. Goulden, C. H., 1952. Methods of Statistical Analysis. Second Ed. John Wiley and Sons Inc. New York. Harper, J. A., 1949. The rate of response of turkey hens to artificial light as related to reproduction. Poultry Sci. 28: 312-314. Harper, J. A., and J. E. Parker, 1957. Changes in seasonal egg production of turkeys induced through controlled light exposure and forced moulting. Poultry Sci. 36: 967-973. Leighton, A. T., Jr., and R. N. Shoffner, 1961. Effect of light regime and age on reproduction of turkeys. 1. Effect of 15, 24 hour and restricted light treatment. Poultry Sci.: 40: 861-870. Margolf, P. H., J. A. Harper and E. W. Callenbach, 1947. Response of turkeys to artificial illumination. Pennsylvania Agr. Expt. Sta. Bui. No. 486. Marr, J. E., F. W. Garland, Jr., J. L. Milligan and H. L. Wilcke, 1956. Effect of controlled light during the growing period upon subsequent performance of breeder turkeys. Poultry Sci. 35: 1156.
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mately 200 days of age for the turkeys utilized in this study. Light environment appeared to have little effect on minimum age at which turkeys could be induced to lay. No significant hatch-treatment interactions were obtained in regard to age at first eggThe use of restricted light for a 2 to 4-week period in the fall increased fall egg production significantly over that of unrestricted females. No significant difference in total egg production was obtained between the light treatment groups utilized in this study. It appears therefore, that the genetic potential of the female turkeys for total number of eggs produced, was not altered by the various light regimes. The major effect of changing the light environment appeared to be alteration in time and rapidity of response. Over 20 percent of the females which had not received restricted light were non-layers during the fall. However, in almost every case such non-layers did start laying during the winter or spring. In contrast, only 2 to 3 percent of the females which had received preliminary restricted light treatment did not lay in the fall. This resulted in higher egg production for the restricted birds for fall production. The fact that new females were coming into production in the spring resulted in higher egg production during that period for the unrestricted birds. Hatch-treatment interactions in regard to fall egg production were small. As a consequence of this, the relative importance of such interactions is questionable. No significant-hatch treatment interactions were obtained for total egg production. Under the conditions of this study, the use of restricted light to increase the efficiency of producing out-of-season turkey poults showed considerable promise, particularly when turkey breeders are kept for
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A. T. LEIGHTON, JE. AND R. N. SHOFFNER
Nalbandov, A., and L. E. Card, 1946. Effect of FSH and LH upon ovaries of immature chicks and low producing hens. Endocrinol. 38: 7178. Phillips, R. E., 1942. Comparative gonadotropic potency of unfractionated extracts of poultry pituitaries. Poultry Sci. 2 1 : 161-172. Piatt, C. S., 19SS. A study of the effect of restricted lighting on January hatched pullets. Poultry Sci. 34: 1045-1047. Siegel, P. B., and C. E. Howes, 1959. Age at lighting and egg production of Bronze and Large White turkeys. Virginia Agr. Expt. Sta.
Bull. No. 503. Snedecor, G. W., and G. W. Cox, 1935. Disproportionate subclass numbers in tables of multiple classification. Iowa Agr. Exp. Sta. Bui. No. 180. Whitson, D., S. J. Marsden and H. W. Titus, 1944. A comparison of the performance of four varieties of turkeys during the breeding season. Poultry Sci. 23:314-320. Wolfson, A., 1952. The occurrence and regulation of the refractory period in the gonadal and fat cycles of the Junco. J. Exp. Zool. 121: 311326.
ALLEN E. WOODARD, H. ABPLANALP AND F. X. OGASAWARA Poultry Husbandry Department, University of California, Davis (Received for publication August 17, 1960)
T
HERE are many advantages of housing of turkey breeding flocks in individual cages. One of the most important is positive identification of the hen that laid the egg. Cage confinement of turkeys reduces the need for large acreage and provides protection from winter storms and predators; dust can be eliminated in areas where air pollution may be a problem; and light restriction programs are possible when hens are kept in laying houses. The Poultry Department of the University of California since 1953 has kept turkey hens in individual wire floor cages and a few trials with caged males have been in progress since 1957. Three difficulties with cage management have appeared so far: high incidence of egg breakage, larger numbers of soft shelled eggs than found with floor management and foot contusions. Some commercial turkey growers have experienced similar difficulties. The effects of cage confinement on turkey males and females have not been investigated systematically so far. The present
study was made in order to determine the influence of cage confinement of turkeys on egg production, egg breakage, semen volume and incidence of swollen feet. METHODS AND MATERIALS In earlier trials it was found here that large Broad Breasted Bronze males could not be confined to sloping floor cages, that had originally been designed for females.* Within two weeks such males were showing severe foot damage and had to be removed from cages. In order to alleviate this situation, the authors designed a larger flat bottomed cage (24" X 24") and secured a 1" X 6" board to the bottom and near the center of the cage. This correction greatly reduced the incidence of foot contusion in Bronze males. * The dimensions of the turkey female cages are 16" wide, 24" deep and approximately 18" high. The roll-away-floor is constructed of 1" X 2"welded 12 gauge wire with a %" cold rolled steel rod supporting the center floor of the cage. The cage is a commercially manufactured type.
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Egg and Semen Production Performance of Turkeys Under Cage Management