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Pineal Gland and Ocular Influences on Turkey Breeder Hens.
Pineal Gland and Ocular Influences on Turkey Breeder Hens. 1. Reproductive Performance 1 ' 2 T. D. SIOPES and H. A. UNDERWOOD Department of Poultry Science and Department of Zoology, North Carolina State University, Raleigh, North Carolina 27695-7608 (Received for publication May 19, 1986)
1987 Poultry Science 66:521-527 INTRODUCTION
The pineal gland and its putative hormone, melatonin, are clearly involved in daily and seasonal reproductive processes in mammals. For instance, short-day-induced gonadal regression in hamsters is blocked by pinealectomy (Reiter, 1981). However, a well-defined role of the avian pineal in reproduction remains to be established. In reviews of the subject, Ralph (1970, 1981) has compiled evidence for both antigonadotropic and progonadotropic functions of the avian pineal gland as well as a lack of function depending on species, age, lighting, sex, and other factors. Pineal gland metabolism of both mammals and birds can be controlled by light. Lightentrainable melatonin levels vary diurnally with greater amounts being produced during darkness than during light (Ralph, 1976). Thus, the pineal
'Paper Number 10577 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695. 2 The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the product named nor criticism of similar ones not mentioned.
gland seems to be a logical candidate as a transducer for lighting effects on the avian reproductive system. However, support for this hypothesis in the scientific literature is sparse. Pinealectomy has no (or a transient) effect on photoinduced gonadal development in a variety of species including sparrows (Donham and Wilson, 1969; Menaker et al., 1970), quail (Sayler and Wolfson, 1968a; Arrington et al., 1969; Siopes and Wilson, 1974), chickens (Harrison, 1972; Cogburn and Harrison, 1977; Johnson and Van Tienhoven, 1984), and ducks (Cuello et al., 1972). In a few cases, such as the Indian Weaver bird and male ducks, however, substantial effects of pinealectomy have been noted (Cardinali et al, 1971; Saxena et al, 1979). Although extraretinal photoreceptors can mediate photoperiodic responses in birds (Benoit, 1964; Menaker, and Keatts, 1968; Homma etal., 1972; McMillan ef a/., 1975; Siopes and Wilson, 1974, 1980a), some studies indicate a possible involvement of the eyes as well in the photosexual response (Benoit, 1964; Homma et al., 1972; Oishi and Lauber, 1973; Siopes and Wilson, 1974, 1980a,b; Yokoyama and Farner, 1976). It is, therefore, of considerable interest
521
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ABSTRACT The influence of the pineal gland and the eyes on reproductive performance of turkey hens was examined. Photosensitive, yearling Large White turkey breeder hens underwent pinealectomy (PX) or bilateral ocular enucleation (EX) or both while held on 8 hr of light per day (8L:16D) and were then photoinduced into a typical 20-week egg laying period by exposing the birds to 16 hr of light per day (16L:8D). Data were obtained for the time to first egg (sexual maturation), rate of egg laying, percent fertility, percent hatchability, weight of poults at hatching, and plasma melatonin levels. A significant interaction between PX and EX treatments occurred in the sexual maturation data only. Pinealectomy significantly delayed (P<.05) the onset of egg laying (by 4.1 to 7.4 days) compared with the other treatment groups. No other significant differences in onset of lay occurred. Pinealectomy significantly depressed egg production during weeks 11 to 20 of lay and this resulted in fewer eggs per PX hen over the 20-week study (85.4 vs. 93.3 eggs in the PX and pineal intact groups, respectively). Enucleation did not significantly affect egg production. Neither the PX nor the EX treatment significantly affected fertility or hatchability determined at 4-week intervals over the 20-week study. However, poult weights were significantly greater as a result of either PX (P<.01) or EX (P<.05) treatment. Nocturnal elevation of plasma melatonin was significantly reduced by PX but not by EX. It was concluded that an extraretinal, extrapineal photoreceptive mechanism is operative in turkey breeder hens but both the pineal gland and the eyes can influence certain reproductive parameters. (Key words: pineal gland, eye, turkeys, egg production, fertility, hatchability)
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SIOPES AND UNDERWOOD
MATERIALS AND METHODS
Fifty Large White turkey breeder hens, which were good egg layers during their first breeding season, were selected for the present study. These yearling hens were placed in light-controlled floor pens and exposed to 8 hr of incandescent light per day to ensure that all hens would be photosensitive when subsequently photostimulated. The regimen consisted of 8L:16D, lights on at 0600 hr; illumination of 60 lx. Twenty hens were pinealectomized and 10 were sham pinealectomized after 6 weeks of the
short day light exposure. The sham operation consisted of exposure of the pineal as well as all other aspects of the pinealectomy procedure except pineal removal. All surgical procedures were performed while the hens were under general anesthesia induced by ketamine (10 mg/kg) and xylazine (2 mg/kg). Verification of the completeness of pineal removal was done by microscopic examination of the intact, whole pineal at the time of removal and examination of the brain tissue at the end of the test. In addition, plasma melatonin levels were measured at the midpoints of a daily photophase and scotophase at the end of the study. After 8 weeks of short day exposure all hens were moved from floor pens to individual wire cages (46 cm x 61 cm x 56 cm, width X height x depth) in an adjacent light-controlled room. The photoperiod remained at 8L:16D. After 2 weeks in the cages, 10 intact (unoperated) hens and 10 previously pinealectomized hens were surgically blinded by bilateral ocular enucleation while under general anesthesia induced with ketamine and xylazine. Thus, the experimental treatments consisted of 10 hens in each of the following groups: Intact (I), sham pinealectomized (S), pinealectomized (PX), bilaterally enucleated (EX), and a group both pinealectomized and enucleated (PXEX). Two weeks later (after a total of 12 weeks exposure to 8L:16D), hens in all treatments were photostimulated (December) into a 20-week egg laying cycle with 16 hr of incandescent light per day (16L:8D, light on at 0600 hr) at an intensity of 60 lx. Temperature was not controlled in the test room, but the building was insulated and the room was mechanically ventilated. The range of mean weekly room temperatures was 8 to 31 C during the study period. Feed and fresh water were provided ad libitum throughout the entire study. The feed was a breeder ration calculated to contain 16% protein, 3.05% calcium, and 2970 kcal metabolizable energy/kg of feed. During the 20-week experimental laying period, the following data were obtained for each hen: rate of sexual development, number of eggs laid per hen, percent fertility, percent hatchability, and body weights of poults on day of hatching. Rate of sexual development was the time required to lay the first egg following photostimulation. All hens were artifically inseminated with pooled semen within 30 min of semen collection from toms. Semen was diluted 1:1 with a commercial extender and .025 ml of
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that significant amounts of melatonin are present in the eyes of some birds and that melatonin levels fluctuate on a daily basis (Underwood et al., 1984; Underwood and Siopes, 1985). Underwood et al. (1984) reported that 54 and 33% of nighttime blood melatonin levels in adult quail originated in the pineal gland and eyes, respectively. In both the pineal gland and the eyes the diurnal melatonin rhythm was regulated by photoperiod, and separate circadian pacemakers in the eyes and pineal may be involved in regulating the daily rhythms in melatonin production (Underwood and Siopes, 1985). It seems possible that the pineal gland and the eyes of at least some birds are integral components of the neuroendocrine apparatus mediating the effects of photoperiod on reproduction; the inconsistent effects of pinealectomy on avian reproduction previously reported may have been due to an ocular contribution of melatonin which masked the effects of pinealectomy. A few studies of avian reproduction have utilized both pinealectomized and blinded birds. An inhibitory influence of pinealectomy and blinding on photostimulated gonadal development has been noted in ducks (Cuello et al., 1972) and quail (Sayler and Wolfson, 1968b). Little or no effect on egg laying occurred over short periods (4 to 8 weeks) in chickens (Harrison, 1972), but in quail either blinding or blinding plus pinealectomy blocked short-day-induced cessation of egg laying or testicular regression (Siopes and Wilson, 1974). To what extent the pineal gland and eyes, combined and alone, participate in regulating avian reproductive performance over a seasonal breeding period has not been reported. Thus, the purpose of this study was to determine the influence of the pineal gland and eyes on the reproductive performance of turkey breeder hens during a typical 20-week, photo-induced breeding period.
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PINEAL, EYES, AND REPRODUCTION
significant interaction between PX and EX treatments occurred only in the sexual development data, thus, individual treatment results are presented for the sexual maturation data only. All of the remaining results will be presented in terms of main treatment factors (P vs. PX and E vs. EX). RESULTS
Table 1 shows the days to onset of egg laying following photostimulation. Pinealectomy significantly delayed the onset of egg production from all other treatments by as little as 4.6 and as much as 7.4 days. The PX hens had significantly depressed egg production (Table 2) in comparison with P hens, expressed as eggs per hen, during weeks 11 to 20 of lay; this resulted in fewer eggs per PX hen over the 20-week study (85.4 vs. 93.3 in the PX and P groups, respectively). The EX did not significantly affect the number of eggs produced per hen during the study. After 20 weeks of egg laying, the E hens laid 86.3 eggs/hen, whereas the EX hens laid 92.8 eggs/hen. The temporal pattern of biweekly percent egg production over the 20-week period was typical for turkey breeder hens in all treatment groups, and no significant treatment differences occurred at any biweekly period (Fig. 1). Mean percent production over the 20-week study period was 64.2, 58.8, 58.9, and 64.3 for the P, PX, E, and EX treatments, respectively. Neither the PX treatment nor the EX treatment significantly affected fertility or hatchability determined at 4-week intervals over the 20week study. Mean percentage fertility was 90.4 and 91.1% for the PX and P treatments, respectively, and 90.8 in the EX treatment vs. 90.9% in the E group. Mean percentage hatchability was 66.1 vs. 70.3% and 65.3 vs. 71.5% for the PX vs. P and EX vs. E groups, respectively. Poult weights were significantly larger as a result of either PX or EX treatment (Table 2). The effect was highly significant (P<.01) for PX vs. P; mean poult weights were 66.0 vs. 62.7 g, respectively. The EX treatment resulted in a mean poult weight of 65.2 g over the five measurement periods as compared with 63.3 g for poults from the E group. A significant elevation of plasma melatonin during the dark phase of the daily photoperiod occurred in the P hens. This peak was essentially eliminated by PX (Table 3). Nocturnal levels of melatonin were similar and elevated in the E
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semen was inseminated per hen. Starting 2 weeks after photostimulation hens were inseminated weekly for 3 consecutive weeks and then biweekly for the remainder of the study. Percent fertility was determined by candling of eggs after 7 days of incubation. In addition, all eggs judged infertile by candling were visually examined for embryos to establish true fertility. Percent hatchability is the percentage hatch of all fertile eggs. Both fertility and hatchability were determined from five collection periods ending after 4, 8, 12, 16, and 20 weeks of egg laying. All eggs were placed in incubators within 7 days of collection. Poults hatched from eggs collected during weeks 2 to 4, 10 to 12, 14 to 16, and 18 to 20 weeks of the breeding season were weighed immediately upon removal from the incubator. Plasma melatonin levels were estimated by radioimmunoassay as described by Underwood et al. (1984). Blood plasma was obtained from a 2-ml blood sample taken by venipuncture at 1400 hr (midday) and 0200 hr (middark) of the same 24-hr period. A dim point-source light was confined to the venipuncture site for dark period blood sampling. All plasma samples were stored frozen until assayed for melatonin. Melatonin was quantitatively recovered by adding 625, 312, 156, 78, and 39 pg of melatonin/ml of pooled turkey plasma collected during midphotophase. Recoveries ranged from 81 to 104%. The correlation coefficient for recovery was .99 and the slope was .84. The Y-intercept value, which represents the endogenous melatonin concentration, was 30 pg/ml. Assay precision measures, determined by calculating within and between assay coefficients of variation from daytime pooled turkey plasma samples, were 7.6 and 13.0%, respectively. Corresponding coefficients of variation from darktime pooled turkey plasma were 10.9 and 14.6%. The sensitivity of the assay averaged 13 pg/ml. Analysis of variance was used to evaluate the treatment effects using the general linear model procedure of the Statistical Analysis System (Barr et al., 1979). Comparisons of treatment effects were estimated by orthogonal contrasts (Steel and Torrie, 1980). This experiment was based on a 2 x 2 factorial design evaluating reproductive performance in the presence or absence of the pineal gland (P vs. PX, respectively) and the eyes (E vs. EX, respectively). For all parameters measured in this study there were no significant differences observed between the I and S hens and, therefore, data from the S group were used in the statistical analyses. A
SIOPES AND UNDERWOOD
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TABLE 1. Effects of pinealectomy (PX) and enucleation (EX) on the onset of egg laying, livability, and reproductive condition of turkey hens during the study period
Treatment Sham PX EX PXEX PX X EX
No. hens
Number of nonlaying hens
Days to first egg1
Start
End
0 - 7 wk
8-12 wk
13-17 wk
1 8 - 2 2 wk
18.1 a 22.7 b 17.1 a 15.3 a
10 10 10 10
10 10 9 10
0 0 0 0
0 0 0 0
0 1 0 0
2 2 1 2
*
ab ' Means in a column with different letters are significantly different (P<.05). 1
Days following photostimulation.
and EX hens. Daytime plasma melatonin levels were similar among all treatments. DISCUSSION
The results of our study indicate that an extraretinal and extrapineal photoreceptive mechanism is operative in turkey hens. Neither pinealectomy (PX) nor bilateral enucleation (EX) prevented the typical 20-week photo-induced egg laying cycle of turkeys, although these treatments did affect certain reproductive parameters. Pineal Effects. In the present study PX affected both the rate of photoinduced sexual development and the number of eggs produced per
hen. Pinealectomy delayed the onset of egg laying from the other treatment groups by as much as 7.4 days, which suggests a progonadal function for the pineal in the sexually developing turkey hen. A similar response has been reported for female quail (Sayler and Wolfson, 1968a) and chickens (Sharp et al., 1981). The PX-induced delay in onset of lay did not occur if PX was combined with EX. This is somewhat contrary to the report by Sayler and Wolfson (1968b) in which the inhibitory effects of PX on ovary weights of 7 week-old quail were similar when alone or in combination with EX. In both quail and chickens the inhibitory effect of PX has been reported to be transient, as normal rates of egg laying were subsequently
TABLE 2. Effect of pinealectomy and enucleation on egg production during 20 weeks of egg laying and on mean poult weight from eggs laid during weeks 4 to 22 after photoinduction of egg production
Main treatment factor
Poult weight by weeks from photostimulation
Eggs per hen during weeks of egg production 0-10
11-20
0-20
4-6
8-10
12-14
16-18
20-22
Mean
•(g)Pineal Intact pineal Pinealectomized 1 Eyes Intact eyes Enucleated 1
52.0 a 49.5 a
41.3 a 35.9b
93.3 a 85.4 b
62.1/ 65.9E
63.5^ 66.1 E
62.7^ 66.2E
62.2-° 64.9E
63.6^ 67.4E
62.7^ 66.0 E
49.4 a 52.3 a
36.9 a 40.5 a
92.8 a
63.1a 64.4 b
64.0 a 65.5 b
63.3a 64.9b
62.7 a 64.6 b
64.2 a 67.0 b
63.3A 65.2E
a ' b Within main treatments, means within a column with different superscripts are significantly different (P<.05). AR
' Within main treatments, means within a column with different superscripts are significantly different (P<.01). 1
Significant interaction between pinealectomized and enucleated treatments (P>.05).
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*P>.05.
PINEAL, EYES, AND REPRODUCTION 90
z- 8 0 o
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70
3o
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40
s« I
2
I
I
I
I
I
I
I
4 6 8 10 12 14 16 WEEKS OF EGG PRODUCTION
I
I
18
20
achieved. In the present study an initial transient delay in the onset of lay in the PX birds was observed, followed by 10 weeks in which the rate of egg production in the PX group was similar to that of P hens. However, during the last 10 weeks of the 20-week egg laying period, PX hens layed fewer eggs per hen than P hens. Thus, over the 20 weeks of egg laying in this study, PX hens laid about 8 fewer eggs per hen than the hens in the P group. Other reports of PX effects on late season egg laying do not exist but PX of chickens (Harrison, 1972) or quail (Siopes and Wilson, 1974) did not significantly affect photo-induced or photo-inhibited egg production during relatively short (4 to 9 week) egg laying periods. There do not appear to be any published studies of the influence of the avian pineal gland on fertility and hatchability. In the present study fertility and hatchability evaluated after 4, 8, 12, 16, and 20 weeks of egg laying did not indicate any significant effects of PX. Mean fertility for the five periods was 90.4 and 91.1% for the PX and P treatments, respectively, whereas mean hatchability for the five periods was 66.1 and 70.3%, for the PX and P treatments, respectively. In the turkey industry poult quality is of utmost importance and poult weight is commonly used as an indicator of quality. The PX hens in the present study produced poults considerably heavier than poults from the P hens (Table 2). The overall mean difference was 3.3 g, a 5.3% higher poult weight compared with that of poults from PX hens. It is highly likely that the large
poults from PX hens were a consequence of the increased egg size observed in these hens (Siopes, 1986). It has been amply demonstrated in long-day breeding mammals that the pineal gland plays a role in regulating seasonal reproduction (Reiter, 1974; Reiter et al., 1981). For example, pinealectomized hamsters remain reproductively competent even during the short daylengths of the winter months (Reiter, 1973). Similar studies in birds are sparse and most suggest that the pineal does not have a seasonal transducing role. However, male ducks held under natural photoperiodic conditions and pinealectomized at the beginning of spring exhibited an inhibition of reproductive function as compared with controls during the first annual cycle. However, no differences were noted in the subsequent annual cycle (Cardinali et al., 1971). Male Indian weaver birds that were held under natural conditions and pinealectomized during the nonbreeding phase showed premature recrudescence of the testes, and pinealectomy during the breeding phase inhibited gonadal regression (Saxena et al., 1979). If the pineal gland regulates the duration of the breeding period, this could be of considerable value to economically important avian species. Although PX significantly delayed onset of egg production in the present study, once production had commenced neither PX nor EX qualitatively altered the temporal profile of a typical turkey breeding season: onset of egg laying occurred within 3 weeks of photostimulation, and peak production levels occurred
TABLE 3. Effect of pinealectomy (PX) and enucleation (EX) on day and night mean plasma melatonin levels (pg/ml) after 20 weeks of egg production1
Treatment
Pineal Intact PX Eyes Intact EX
Number hens
Sample time Midday Middark (1400 hr)
(0200 hr)
10 10
40.4 a 34.9 a
148.5 a 41.0 b
10 10
38.5 a 37.0 a
114.8 a 94.9 a
' Within main treatments, means within a column with different letters are significantly different (P<.01). 1 Significant interaction treatments (P>.05).
between
PX and EX
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FIG. 1. Percent hen-day egg production (total number eggs/number hens x number days) at biweekly intervals during the 20-week egg laying period. P = intact pineal, PX = pinealectomy,E = intact eyes, EX = enucleated.
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SIOPES AND UNDERWOOD
Underwood et al. (1984) reported that both the pineal and eyes of quail contribute to this nocturnal elevation in plasma melatonin with the pineal gland being the primary source. Based on the scotophase plasma sampling at the end of the present study, however, the pineal gland seems to be the sole source of plasma melatonin, because PX eliminated the nocturnal increase in plasma melatonin and the melatonin levels in EX birds were not significantly different from levels seen in intact birds (Table 3). There appears, therefore, to be significant species-specific differences in whether or not melatonin synthesized in the eyes can be secreted into the blood. It is clear from our results that a compensatory mechanism for maintaining circulating levels of melatonin in the absence of the pineal (Osol et al., 1985) did not occur. The function of melatonin in the control of reproduction in the turkey hen is still unclear. Elimination of the plasma melatonin rhythm by PX clearly does not abolish the photoperiodic response in turkey hens, although certain parameters, such as rate of sexual maturation, are affected. Whether or not these effects are mediated by melatonin is unknown. REFERENCES Arlington, L. C , R. K. Ringer, and J. H. Wolford, 1969. Effect of pinealectomy of coturnix quail reared under non-stimulatory photoperiods. Poultry Sci. 48:454— 459. Barr, A. J., H. H. Goodnight, J. P. Sail, W. H. Blair, and D. M. Chilko, 1979. Statistical Analysis Systems. 9th ed. SAS Inst., Inc., Raleigh, NC. Benoit, J., 1964. The role of the eye and ofthe hypothalamus in photostimulation of gonads in the duck. Ann. N.Y. Acad. Sci. 117:204-217. Cardinali, D. P., A. E. Cuello, J, H. Tramezzani, and J. M. Rozner, 1971. Effect of pinealectomy on the testicular function of the adult male duck. Endocrinology 89:1082-1093. Cogburn, L. A., and P. C. Harrison, 1977. Retardation of sexual development in pinealectomized Single Comb White Leghorn Cockerels. Poultry Sci. 56:876-882. Cuello, A. C , N. Hisano, and J. H. Tramezzani, 1972. The pineal gland and the photosexual reflex in female ducks. Gen. Comp. Endocrinol. 18:162-168. Donham, R. S., and F. E. Wilson, 1969. Pinealectomy in Harris' sparrow. Auk 86:553-554. Harrison, P. C , 1972. Extraretinal photocontrol of reproductive responses of leghorn hens to photoperiods of different length and spectrum. Poultry Sci. 51:20602064. Harrison, P. C , and W. C. Becker, 1969. Extraretinal photocontrol of oviposition in pinealectomized domestic fowl. Proc. Soc. Exp. Biol. Med. 132:161-164. Homma, K., W. O. Wilson, and T. D. Siopes, 1972. Eyes have a role in photoperiodic control of sexual activity of coturnix. Science 178:421^123.
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about 3 weeks later, followed by a spontaneous but gradual and persistent decline in egg production (Figure 1). To what extent holding birds on a constant lighting regimen (16L:8D) throughout the breeding period affected this study is not known. This point needs to be considered, because it has been suggested that the pineal receives information about changing daylengths and transduces this information into a hormonal (melatonin) output to induce appropriate responses (Tamarkin et al., 1985; Underwood and Siopes, 1985). Ocular Effects. In the present study the rate of photoinduced sexual development was not significantly altered by EX. Bilateral ocular EX of quail also did not alter the rate of sexual development on long daylengths (Sayler and Wolfson, 1968b; Siopes and Wilson, 1980a) or short daylengths (Siopes and Wilson, 1974). Enucleated chickens (Harrison, 1972; Siopes and Wilson, 1980b), ducks (Cuello etal., 1972), and sparrows (Menaker and Keatts, 1968; McMillan et al., 1975) also mature normally following photostimulation. These data imply that the eyes play no role in mediating photostimulated sexual development in birds. However, Siopes and Wilson (1980a,b) reported that although the eyes may not be essential for photostimulated sexual development in quail and chickens they can function to modify (inhibit) the photosexual response. Rate of egg production was also not signficantly altered by EX in the present study. This is consistent with reports of studies with quail (Sayler and Wolfson, 1968b; Siopes and Wilson, 1974) and chickens (Harrison, 1972). However, it should be noted that egg production of hens in the EX treatment consistently exceded that of hens in the E group and over the 20-week egg laying period EX hens produced about 6.5 more eggs (P= .08) per hen than E hens. Fertility and subsequent hatchability of eggs from EX birds has not been previously reported. In the present study neither fertility nor hatchability were significantly affected by EX. However, poults from EX hens were heavier than those from E hens. The mean difference was 1.9 g, a 3.0% increase. As with PX hens, this was likely the result of larger eggs layed by EX hens (Siopes, 1986). Plasma Melatonin. The plasma melatonin level of the turkey is apparently similar to that of many other vertebrates in that melatonin is regulated by photoperiod and scotophase levels are significantly greater than photophase levels.
PINEAL, EYES, AND REPRODUCTION
Saxena, R. N., L. Malhotra, R. Kant, and P. K. Baweja, 1979. Effect of pinealectomy and seasonal changes on pineal antigonadotropic activity of male Indian weaver bird Ploceus phillipinus. Ind. J. Exp. Biol. 17:732737. Sayler, A., and A. Wolfson, 1968a. Influence of the pineal gland on gonadal maturation in the Japanese quail. Endocrinology 83:1237-1246. Sayler, A., and A. Wolfson, 1968b. Role of the eyes and superior cervical ganglia on the effects of light on the pineal and gonads of the Japanese quail. Arch. Anat. Histol. Embryol. 51:615-626. Sharp, P. J., O.F.X. Almeida, H. Klandorf, and R. W. Lea, 1981. The effect of pinealectomy on daily rhythms in plasma concentrations of melatonin and on onset of puberty in the domestic hen. Proc. Soc. Endocr., London, UK 64:32. (Abstr.) Siopes, T. D., 1987. Pineal gland and ocular influences in turkey breeder hens. II. Body weight, feed intake and egg characteristics. Poultry Sci. 66:528-534. Siopes, T. D., and W. O. Wilson, 1974. Extraocular modification of photoreception in intact and pinealectomized coturnix. Poultry Sci. 53:2035-2041. Siopes, T. D., and W. O. Wilson, 1980a. Participation of the eyes in the photosexual response of Japanese quail (Coturnix coturnix japonica). Biol. Reprod. 23:352357. Siopes, T. D., and W. O. Wilson, 1980b. Participation of the eyes in the photostimulation of chickens. Poultry Sci. 59:1122-1125. Steel, R.C.D., and J. H. Torrie, 1980. Principles and Procedures of statistics. A Biomedical Approach. 2nd ed. McGraw-Hill Book Co., New York, NY. Tamarkin, L., C. J. Baird, and O.F.X. Almeida, 1985. Melatonin: a coordinating signal for mammalian reproduction. Science 227:714-720. Underwood, H., S. Binkley, T. Siopes, and K. Mosher, 1984. Melatonin rhythms in the eyes, pineal, and blood of Japanese quail (Coturnix coturnix japonica). Gen. Comp. Endocrinol. 56:70-81. Underwood, H. A., and T. D. Siopes, 1985. Melatonin rhythms in quail: Regulation by photoperiod and circadian pacemakers. J. Pineal Res. 2:133-143. Yokoyama, K., and D. S. Farner, 1976. Photoperiodic responses in bilaterally enucleated female whitecrowned sparrows, Zonotrichia leucophrys gambeli. Gen. Comp. Endocrinol. 30:528-533.
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Johnson, P. A., and A. van Tienhoven, 1984. Plasma luteinizing hormone levels throughout development and relative to ovulation in pinealectomized hens (Callus domesticus). Gen. Comp. Endocrinol. 54:450456. McMillan, J. P., H. A. Underwood, J. A. Elliott, M. H. Stetson, andM. Menaker, 1975. Extraretinal light perception in the sparrow. IV. Further evidence that the eyes do not participate in photoperiodic photoreception. J. Comp. Physiol. 97:205-213. Menaker, M., and H. Keatts, 1968. Extraretinal light perception in the sparrow. II. Photoperiodic stimulation of testis growth. Proc. Natl. Acad. Sci. 67:320-325. Menaker, M., R. Roberts, J. Elliott, and H. Underwood, 1970. Extraretinal light perception in the sparrow, III: the eyes do not participate in photoperiodic photoreception. Proc. Natl. Acad. Sci. USA 67:320-325. Oishi, T., and J. K. Lauber, 1973. Photoreception in the photosexual response of quail. I. Site of the photoreceptor. Am. J. Physiol. 225:155-158. Osol, G., B. Schwartz, and D. C. Foss, 1985. Effects of time, photoperiod, and pinealectomy on ocular and plasma melatonin concentrations in the chick. Gen. Comp. Endocrinol. 58:415-420. Ralph, C. L., 1970. Structure and alleged functions of avian pineals. Am. Zool. 10:217-235. Ralph, C. L., 1976. Correlation of melatonin content in pineal gland, blood, and brain of some birds and mammals. Am. Zool. 16:35—41. Ralph, C. L., 1981. The pineal and reproduction in birds. Pages 31-40 in: The Pineal Gland. Vol. II: Reproductive Effects. R. J. Reiter, ed. CRC Press, Inc., Boco Raton, FL. Reiter, R. J., 1973. Pineal control of a seasonal reproductive rhythm in male golden hamsters exposed to natural daylight and temperature. Endocrinology 92:423-426. Reiter, R. J., 1974. Circannual reproductive rhythms in mammals related to photoperiod and pineal function: A review. Chronobiologia 1:365-381. Reiter, R. J., 1981. Reproductive effects of the pineal gland and pineal indoles in the Syrian hamster and the albino rat. Pages 46-73 in: R. J. Reiter, ed. CRC Press, Inc., Boca Raton, FL. Reiter, R. J., B. A. Richardson, M. K. Vaughn, and L. Y. Johnson, 1981. Pineal actions and mechanisms in reproductive physiology. Jikeikai Med. J. 28 (Suppl. 1):35^16.
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1987 Poultry Science 66:521-527 INTRODUCTION
The pineal gland and its putative hormone, melatonin, are clearly involved in daily and seasonal reproductive processes in mammals. For instance, short-day-induced gonadal regression in hamsters is blocked by pinealectomy (Reiter, 1981). However, a well-defined role of the avian pineal in reproduction remains to be established. In reviews of the subject, Ralph (1970, 1981) has compiled evidence for both antigonadotropic and progonadotropic functions of the avian pineal gland as well as a lack of function depending on species, age, lighting, sex, and other factors. Pineal gland metabolism of both mammals and birds can be controlled by light. Lightentrainable melatonin levels vary diurnally with greater amounts being produced during darkness than during light (Ralph, 1976). Thus, the pineal
'Paper Number 10577 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695. 2 The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the product named nor criticism of similar ones not mentioned.
gland seems to be a logical candidate as a transducer for lighting effects on the avian reproductive system. However, support for this hypothesis in the scientific literature is sparse. Pinealectomy has no (or a transient) effect on photoinduced gonadal development in a variety of species including sparrows (Donham and Wilson, 1969; Menaker et al., 1970), quail (Sayler and Wolfson, 1968a; Arrington et al., 1969; Siopes and Wilson, 1974), chickens (Harrison, 1972; Cogburn and Harrison, 1977; Johnson and Van Tienhoven, 1984), and ducks (Cuello et al., 1972). In a few cases, such as the Indian Weaver bird and male ducks, however, substantial effects of pinealectomy have been noted (Cardinali et al, 1971; Saxena et al, 1979). Although extraretinal photoreceptors can mediate photoperiodic responses in birds (Benoit, 1964; Menaker, and Keatts, 1968; Homma etal., 1972; McMillan ef a/., 1975; Siopes and Wilson, 1974, 1980a), some studies indicate a possible involvement of the eyes as well in the photosexual response (Benoit, 1964; Homma et al., 1972; Oishi and Lauber, 1973; Siopes and Wilson, 1974, 1980a,b; Yokoyama and Farner, 1976). It is, therefore, of considerable interest
521
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ABSTRACT The influence of the pineal gland and the eyes on reproductive performance of turkey hens was examined. Photosensitive, yearling Large White turkey breeder hens underwent pinealectomy (PX) or bilateral ocular enucleation (EX) or both while held on 8 hr of light per day (8L:16D) and were then photoinduced into a typical 20-week egg laying period by exposing the birds to 16 hr of light per day (16L:8D). Data were obtained for the time to first egg (sexual maturation), rate of egg laying, percent fertility, percent hatchability, weight of poults at hatching, and plasma melatonin levels. A significant interaction between PX and EX treatments occurred in the sexual maturation data only. Pinealectomy significantly delayed (P<.05) the onset of egg laying (by 4.1 to 7.4 days) compared with the other treatment groups. No other significant differences in onset of lay occurred. Pinealectomy significantly depressed egg production during weeks 11 to 20 of lay and this resulted in fewer eggs per PX hen over the 20-week study (85.4 vs. 93.3 eggs in the PX and pineal intact groups, respectively). Enucleation did not significantly affect egg production. Neither the PX nor the EX treatment significantly affected fertility or hatchability determined at 4-week intervals over the 20-week study. However, poult weights were significantly greater as a result of either PX (P<.01) or EX (P<.05) treatment. Nocturnal elevation of plasma melatonin was significantly reduced by PX but not by EX. It was concluded that an extraretinal, extrapineal photoreceptive mechanism is operative in turkey breeder hens but both the pineal gland and the eyes can influence certain reproductive parameters. (Key words: pineal gland, eye, turkeys, egg production, fertility, hatchability)
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SIOPES AND UNDERWOOD
MATERIALS AND METHODS
Fifty Large White turkey breeder hens, which were good egg layers during their first breeding season, were selected for the present study. These yearling hens were placed in light-controlled floor pens and exposed to 8 hr of incandescent light per day to ensure that all hens would be photosensitive when subsequently photostimulated. The regimen consisted of 8L:16D, lights on at 0600 hr; illumination of 60 lx. Twenty hens were pinealectomized and 10 were sham pinealectomized after 6 weeks of the
short day light exposure. The sham operation consisted of exposure of the pineal as well as all other aspects of the pinealectomy procedure except pineal removal. All surgical procedures were performed while the hens were under general anesthesia induced by ketamine (10 mg/kg) and xylazine (2 mg/kg). Verification of the completeness of pineal removal was done by microscopic examination of the intact, whole pineal at the time of removal and examination of the brain tissue at the end of the test. In addition, plasma melatonin levels were measured at the midpoints of a daily photophase and scotophase at the end of the study. After 8 weeks of short day exposure all hens were moved from floor pens to individual wire cages (46 cm x 61 cm x 56 cm, width X height x depth) in an adjacent light-controlled room. The photoperiod remained at 8L:16D. After 2 weeks in the cages, 10 intact (unoperated) hens and 10 previously pinealectomized hens were surgically blinded by bilateral ocular enucleation while under general anesthesia induced with ketamine and xylazine. Thus, the experimental treatments consisted of 10 hens in each of the following groups: Intact (I), sham pinealectomized (S), pinealectomized (PX), bilaterally enucleated (EX), and a group both pinealectomized and enucleated (PXEX). Two weeks later (after a total of 12 weeks exposure to 8L:16D), hens in all treatments were photostimulated (December) into a 20-week egg laying cycle with 16 hr of incandescent light per day (16L:8D, light on at 0600 hr) at an intensity of 60 lx. Temperature was not controlled in the test room, but the building was insulated and the room was mechanically ventilated. The range of mean weekly room temperatures was 8 to 31 C during the study period. Feed and fresh water were provided ad libitum throughout the entire study. The feed was a breeder ration calculated to contain 16% protein, 3.05% calcium, and 2970 kcal metabolizable energy/kg of feed. During the 20-week experimental laying period, the following data were obtained for each hen: rate of sexual development, number of eggs laid per hen, percent fertility, percent hatchability, and body weights of poults on day of hatching. Rate of sexual development was the time required to lay the first egg following photostimulation. All hens were artifically inseminated with pooled semen within 30 min of semen collection from toms. Semen was diluted 1:1 with a commercial extender and .025 ml of
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that significant amounts of melatonin are present in the eyes of some birds and that melatonin levels fluctuate on a daily basis (Underwood et al., 1984; Underwood and Siopes, 1985). Underwood et al. (1984) reported that 54 and 33% of nighttime blood melatonin levels in adult quail originated in the pineal gland and eyes, respectively. In both the pineal gland and the eyes the diurnal melatonin rhythm was regulated by photoperiod, and separate circadian pacemakers in the eyes and pineal may be involved in regulating the daily rhythms in melatonin production (Underwood and Siopes, 1985). It seems possible that the pineal gland and the eyes of at least some birds are integral components of the neuroendocrine apparatus mediating the effects of photoperiod on reproduction; the inconsistent effects of pinealectomy on avian reproduction previously reported may have been due to an ocular contribution of melatonin which masked the effects of pinealectomy. A few studies of avian reproduction have utilized both pinealectomized and blinded birds. An inhibitory influence of pinealectomy and blinding on photostimulated gonadal development has been noted in ducks (Cuello et al., 1972) and quail (Sayler and Wolfson, 1968b). Little or no effect on egg laying occurred over short periods (4 to 8 weeks) in chickens (Harrison, 1972), but in quail either blinding or blinding plus pinealectomy blocked short-day-induced cessation of egg laying or testicular regression (Siopes and Wilson, 1974). To what extent the pineal gland and eyes, combined and alone, participate in regulating avian reproductive performance over a seasonal breeding period has not been reported. Thus, the purpose of this study was to determine the influence of the pineal gland and eyes on the reproductive performance of turkey breeder hens during a typical 20-week, photo-induced breeding period.
523
PINEAL, EYES, AND REPRODUCTION
significant interaction between PX and EX treatments occurred only in the sexual development data, thus, individual treatment results are presented for the sexual maturation data only. All of the remaining results will be presented in terms of main treatment factors (P vs. PX and E vs. EX). RESULTS
Table 1 shows the days to onset of egg laying following photostimulation. Pinealectomy significantly delayed the onset of egg production from all other treatments by as little as 4.6 and as much as 7.4 days. The PX hens had significantly depressed egg production (Table 2) in comparison with P hens, expressed as eggs per hen, during weeks 11 to 20 of lay; this resulted in fewer eggs per PX hen over the 20-week study (85.4 vs. 93.3 in the PX and P groups, respectively). The EX did not significantly affect the number of eggs produced per hen during the study. After 20 weeks of egg laying, the E hens laid 86.3 eggs/hen, whereas the EX hens laid 92.8 eggs/hen. The temporal pattern of biweekly percent egg production over the 20-week period was typical for turkey breeder hens in all treatment groups, and no significant treatment differences occurred at any biweekly period (Fig. 1). Mean percent production over the 20-week study period was 64.2, 58.8, 58.9, and 64.3 for the P, PX, E, and EX treatments, respectively. Neither the PX treatment nor the EX treatment significantly affected fertility or hatchability determined at 4-week intervals over the 20week study. Mean percentage fertility was 90.4 and 91.1% for the PX and P treatments, respectively, and 90.8 in the EX treatment vs. 90.9% in the E group. Mean percentage hatchability was 66.1 vs. 70.3% and 65.3 vs. 71.5% for the PX vs. P and EX vs. E groups, respectively. Poult weights were significantly larger as a result of either PX or EX treatment (Table 2). The effect was highly significant (P<.01) for PX vs. P; mean poult weights were 66.0 vs. 62.7 g, respectively. The EX treatment resulted in a mean poult weight of 65.2 g over the five measurement periods as compared with 63.3 g for poults from the E group. A significant elevation of plasma melatonin during the dark phase of the daily photoperiod occurred in the P hens. This peak was essentially eliminated by PX (Table 3). Nocturnal levels of melatonin were similar and elevated in the E
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semen was inseminated per hen. Starting 2 weeks after photostimulation hens were inseminated weekly for 3 consecutive weeks and then biweekly for the remainder of the study. Percent fertility was determined by candling of eggs after 7 days of incubation. In addition, all eggs judged infertile by candling were visually examined for embryos to establish true fertility. Percent hatchability is the percentage hatch of all fertile eggs. Both fertility and hatchability were determined from five collection periods ending after 4, 8, 12, 16, and 20 weeks of egg laying. All eggs were placed in incubators within 7 days of collection. Poults hatched from eggs collected during weeks 2 to 4, 10 to 12, 14 to 16, and 18 to 20 weeks of the breeding season were weighed immediately upon removal from the incubator. Plasma melatonin levels were estimated by radioimmunoassay as described by Underwood et al. (1984). Blood plasma was obtained from a 2-ml blood sample taken by venipuncture at 1400 hr (midday) and 0200 hr (middark) of the same 24-hr period. A dim point-source light was confined to the venipuncture site for dark period blood sampling. All plasma samples were stored frozen until assayed for melatonin. Melatonin was quantitatively recovered by adding 625, 312, 156, 78, and 39 pg of melatonin/ml of pooled turkey plasma collected during midphotophase. Recoveries ranged from 81 to 104%. The correlation coefficient for recovery was .99 and the slope was .84. The Y-intercept value, which represents the endogenous melatonin concentration, was 30 pg/ml. Assay precision measures, determined by calculating within and between assay coefficients of variation from daytime pooled turkey plasma samples, were 7.6 and 13.0%, respectively. Corresponding coefficients of variation from darktime pooled turkey plasma were 10.9 and 14.6%. The sensitivity of the assay averaged 13 pg/ml. Analysis of variance was used to evaluate the treatment effects using the general linear model procedure of the Statistical Analysis System (Barr et al., 1979). Comparisons of treatment effects were estimated by orthogonal contrasts (Steel and Torrie, 1980). This experiment was based on a 2 x 2 factorial design evaluating reproductive performance in the presence or absence of the pineal gland (P vs. PX, respectively) and the eyes (E vs. EX, respectively). For all parameters measured in this study there were no significant differences observed between the I and S hens and, therefore, data from the S group were used in the statistical analyses. A
SIOPES AND UNDERWOOD
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TABLE 1. Effects of pinealectomy (PX) and enucleation (EX) on the onset of egg laying, livability, and reproductive condition of turkey hens during the study period
Treatment Sham PX EX PXEX PX X EX
No. hens
Number of nonlaying hens
Days to first egg1
Start
End
0 - 7 wk
8-12 wk
13-17 wk
1 8 - 2 2 wk
18.1 a 22.7 b 17.1 a 15.3 a
10 10 10 10
10 10 9 10
0 0 0 0
0 0 0 0
0 1 0 0
2 2 1 2
*
ab ' Means in a column with different letters are significantly different (P<.05). 1
Days following photostimulation.
and EX hens. Daytime plasma melatonin levels were similar among all treatments. DISCUSSION
The results of our study indicate that an extraretinal and extrapineal photoreceptive mechanism is operative in turkey hens. Neither pinealectomy (PX) nor bilateral enucleation (EX) prevented the typical 20-week photo-induced egg laying cycle of turkeys, although these treatments did affect certain reproductive parameters. Pineal Effects. In the present study PX affected both the rate of photoinduced sexual development and the number of eggs produced per
hen. Pinealectomy delayed the onset of egg laying from the other treatment groups by as much as 7.4 days, which suggests a progonadal function for the pineal in the sexually developing turkey hen. A similar response has been reported for female quail (Sayler and Wolfson, 1968a) and chickens (Sharp et al., 1981). The PX-induced delay in onset of lay did not occur if PX was combined with EX. This is somewhat contrary to the report by Sayler and Wolfson (1968b) in which the inhibitory effects of PX on ovary weights of 7 week-old quail were similar when alone or in combination with EX. In both quail and chickens the inhibitory effect of PX has been reported to be transient, as normal rates of egg laying were subsequently
TABLE 2. Effect of pinealectomy and enucleation on egg production during 20 weeks of egg laying and on mean poult weight from eggs laid during weeks 4 to 22 after photoinduction of egg production
Main treatment factor
Poult weight by weeks from photostimulation
Eggs per hen during weeks of egg production 0-10
11-20
0-20
4-6
8-10
12-14
16-18
20-22
Mean
•(g)Pineal Intact pineal Pinealectomized 1 Eyes Intact eyes Enucleated 1
52.0 a 49.5 a
41.3 a 35.9b
93.3 a 85.4 b
62.1/ 65.9E
63.5^ 66.1 E
62.7^ 66.2E
62.2-° 64.9E
63.6^ 67.4E
62.7^ 66.0 E
49.4 a 52.3 a
36.9 a 40.5 a
92.8 a
63.1a 64.4 b
64.0 a 65.5 b
63.3a 64.9b
62.7 a 64.6 b
64.2 a 67.0 b
63.3A 65.2E
a ' b Within main treatments, means within a column with different superscripts are significantly different (P<.05). AR
' Within main treatments, means within a column with different superscripts are significantly different (P<.01). 1
Significant interaction between pinealectomized and enucleated treatments (P>.05).
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*P>.05.
PINEAL, EYES, AND REPRODUCTION 90
z- 8 0 o
^-
70
3o
o o 60 or a. 5 0 w C3 UJ
40
s« I
2
I
I
I
I
I
I
I
4 6 8 10 12 14 16 WEEKS OF EGG PRODUCTION
I
I
18
20
achieved. In the present study an initial transient delay in the onset of lay in the PX birds was observed, followed by 10 weeks in which the rate of egg production in the PX group was similar to that of P hens. However, during the last 10 weeks of the 20-week egg laying period, PX hens layed fewer eggs per hen than P hens. Thus, over the 20 weeks of egg laying in this study, PX hens laid about 8 fewer eggs per hen than the hens in the P group. Other reports of PX effects on late season egg laying do not exist but PX of chickens (Harrison, 1972) or quail (Siopes and Wilson, 1974) did not significantly affect photo-induced or photo-inhibited egg production during relatively short (4 to 9 week) egg laying periods. There do not appear to be any published studies of the influence of the avian pineal gland on fertility and hatchability. In the present study fertility and hatchability evaluated after 4, 8, 12, 16, and 20 weeks of egg laying did not indicate any significant effects of PX. Mean fertility for the five periods was 90.4 and 91.1% for the PX and P treatments, respectively, whereas mean hatchability for the five periods was 66.1 and 70.3%, for the PX and P treatments, respectively. In the turkey industry poult quality is of utmost importance and poult weight is commonly used as an indicator of quality. The PX hens in the present study produced poults considerably heavier than poults from the P hens (Table 2). The overall mean difference was 3.3 g, a 5.3% higher poult weight compared with that of poults from PX hens. It is highly likely that the large
poults from PX hens were a consequence of the increased egg size observed in these hens (Siopes, 1986). It has been amply demonstrated in long-day breeding mammals that the pineal gland plays a role in regulating seasonal reproduction (Reiter, 1974; Reiter et al., 1981). For example, pinealectomized hamsters remain reproductively competent even during the short daylengths of the winter months (Reiter, 1973). Similar studies in birds are sparse and most suggest that the pineal does not have a seasonal transducing role. However, male ducks held under natural photoperiodic conditions and pinealectomized at the beginning of spring exhibited an inhibition of reproductive function as compared with controls during the first annual cycle. However, no differences were noted in the subsequent annual cycle (Cardinali et al., 1971). Male Indian weaver birds that were held under natural conditions and pinealectomized during the nonbreeding phase showed premature recrudescence of the testes, and pinealectomy during the breeding phase inhibited gonadal regression (Saxena et al., 1979). If the pineal gland regulates the duration of the breeding period, this could be of considerable value to economically important avian species. Although PX significantly delayed onset of egg production in the present study, once production had commenced neither PX nor EX qualitatively altered the temporal profile of a typical turkey breeding season: onset of egg laying occurred within 3 weeks of photostimulation, and peak production levels occurred
TABLE 3. Effect of pinealectomy (PX) and enucleation (EX) on day and night mean plasma melatonin levels (pg/ml) after 20 weeks of egg production1
Treatment
Pineal Intact PX Eyes Intact EX
Number hens
Sample time Midday Middark (1400 hr)
(0200 hr)
10 10
40.4 a 34.9 a
148.5 a 41.0 b
10 10
38.5 a 37.0 a
114.8 a 94.9 a
' Within main treatments, means within a column with different letters are significantly different (P<.01). 1 Significant interaction treatments (P>.05).
between
PX and EX
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FIG. 1. Percent hen-day egg production (total number eggs/number hens x number days) at biweekly intervals during the 20-week egg laying period. P = intact pineal, PX = pinealectomy,E = intact eyes, EX = enucleated.
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Underwood et al. (1984) reported that both the pineal and eyes of quail contribute to this nocturnal elevation in plasma melatonin with the pineal gland being the primary source. Based on the scotophase plasma sampling at the end of the present study, however, the pineal gland seems to be the sole source of plasma melatonin, because PX eliminated the nocturnal increase in plasma melatonin and the melatonin levels in EX birds were not significantly different from levels seen in intact birds (Table 3). There appears, therefore, to be significant species-specific differences in whether or not melatonin synthesized in the eyes can be secreted into the blood. It is clear from our results that a compensatory mechanism for maintaining circulating levels of melatonin in the absence of the pineal (Osol et al., 1985) did not occur. The function of melatonin in the control of reproduction in the turkey hen is still unclear. Elimination of the plasma melatonin rhythm by PX clearly does not abolish the photoperiodic response in turkey hens, although certain parameters, such as rate of sexual maturation, are affected. Whether or not these effects are mediated by melatonin is unknown. REFERENCES Arlington, L. C , R. K. Ringer, and J. H. Wolford, 1969. Effect of pinealectomy of coturnix quail reared under non-stimulatory photoperiods. Poultry Sci. 48:454— 459. Barr, A. J., H. H. Goodnight, J. P. Sail, W. H. Blair, and D. M. Chilko, 1979. Statistical Analysis Systems. 9th ed. SAS Inst., Inc., Raleigh, NC. Benoit, J., 1964. The role of the eye and ofthe hypothalamus in photostimulation of gonads in the duck. Ann. N.Y. Acad. Sci. 117:204-217. Cardinali, D. P., A. E. Cuello, J, H. Tramezzani, and J. M. Rozner, 1971. Effect of pinealectomy on the testicular function of the adult male duck. Endocrinology 89:1082-1093. Cogburn, L. A., and P. C. Harrison, 1977. Retardation of sexual development in pinealectomized Single Comb White Leghorn Cockerels. Poultry Sci. 56:876-882. Cuello, A. C , N. Hisano, and J. H. Tramezzani, 1972. The pineal gland and the photosexual reflex in female ducks. Gen. Comp. Endocrinol. 18:162-168. Donham, R. S., and F. E. Wilson, 1969. Pinealectomy in Harris' sparrow. Auk 86:553-554. Harrison, P. C , 1972. Extraretinal photocontrol of reproductive responses of leghorn hens to photoperiods of different length and spectrum. Poultry Sci. 51:20602064. Harrison, P. C , and W. C. Becker, 1969. Extraretinal photocontrol of oviposition in pinealectomized domestic fowl. Proc. Soc. Exp. Biol. Med. 132:161-164. Homma, K., W. O. Wilson, and T. D. Siopes, 1972. Eyes have a role in photoperiodic control of sexual activity of coturnix. Science 178:421^123.
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about 3 weeks later, followed by a spontaneous but gradual and persistent decline in egg production (Figure 1). To what extent holding birds on a constant lighting regimen (16L:8D) throughout the breeding period affected this study is not known. This point needs to be considered, because it has been suggested that the pineal receives information about changing daylengths and transduces this information into a hormonal (melatonin) output to induce appropriate responses (Tamarkin et al., 1985; Underwood and Siopes, 1985). Ocular Effects. In the present study the rate of photoinduced sexual development was not significantly altered by EX. Bilateral ocular EX of quail also did not alter the rate of sexual development on long daylengths (Sayler and Wolfson, 1968b; Siopes and Wilson, 1980a) or short daylengths (Siopes and Wilson, 1974). Enucleated chickens (Harrison, 1972; Siopes and Wilson, 1980b), ducks (Cuello etal., 1972), and sparrows (Menaker and Keatts, 1968; McMillan et al., 1975) also mature normally following photostimulation. These data imply that the eyes play no role in mediating photostimulated sexual development in birds. However, Siopes and Wilson (1980a,b) reported that although the eyes may not be essential for photostimulated sexual development in quail and chickens they can function to modify (inhibit) the photosexual response. Rate of egg production was also not signficantly altered by EX in the present study. This is consistent with reports of studies with quail (Sayler and Wolfson, 1968b; Siopes and Wilson, 1974) and chickens (Harrison, 1972). However, it should be noted that egg production of hens in the EX treatment consistently exceded that of hens in the E group and over the 20-week egg laying period EX hens produced about 6.5 more eggs (P= .08) per hen than E hens. Fertility and subsequent hatchability of eggs from EX birds has not been previously reported. In the present study neither fertility nor hatchability were significantly affected by EX. However, poults from EX hens were heavier than those from E hens. The mean difference was 1.9 g, a 3.0% increase. As with PX hens, this was likely the result of larger eggs layed by EX hens (Siopes, 1986). Plasma Melatonin. The plasma melatonin level of the turkey is apparently similar to that of many other vertebrates in that melatonin is regulated by photoperiod and scotophase levels are significantly greater than photophase levels.
PINEAL, EYES, AND REPRODUCTION
Saxena, R. N., L. Malhotra, R. Kant, and P. K. Baweja, 1979. Effect of pinealectomy and seasonal changes on pineal antigonadotropic activity of male Indian weaver bird Ploceus phillipinus. Ind. J. Exp. Biol. 17:732737. Sayler, A., and A. Wolfson, 1968a. Influence of the pineal gland on gonadal maturation in the Japanese quail. Endocrinology 83:1237-1246. Sayler, A., and A. Wolfson, 1968b. Role of the eyes and superior cervical ganglia on the effects of light on the pineal and gonads of the Japanese quail. Arch. Anat. Histol. Embryol. 51:615-626. Sharp, P. J., O.F.X. Almeida, H. Klandorf, and R. W. Lea, 1981. The effect of pinealectomy on daily rhythms in plasma concentrations of melatonin and on onset of puberty in the domestic hen. Proc. Soc. Endocr., London, UK 64:32. (Abstr.) Siopes, T. D., 1987. Pineal gland and ocular influences in turkey breeder hens. II. Body weight, feed intake and egg characteristics. Poultry Sci. 66:528-534. Siopes, T. D., and W. O. Wilson, 1974. Extraocular modification of photoreception in intact and pinealectomized coturnix. Poultry Sci. 53:2035-2041. Siopes, T. D., and W. O. Wilson, 1980a. Participation of the eyes in the photosexual response of Japanese quail (Coturnix coturnix japonica). Biol. Reprod. 23:352357. Siopes, T. D., and W. O. Wilson, 1980b. Participation of the eyes in the photostimulation of chickens. Poultry Sci. 59:1122-1125. Steel, R.C.D., and J. H. Torrie, 1980. Principles and Procedures of statistics. A Biomedical Approach. 2nd ed. McGraw-Hill Book Co., New York, NY. Tamarkin, L., C. J. Baird, and O.F.X. Almeida, 1985. Melatonin: a coordinating signal for mammalian reproduction. Science 227:714-720. Underwood, H., S. Binkley, T. Siopes, and K. Mosher, 1984. Melatonin rhythms in the eyes, pineal, and blood of Japanese quail (Coturnix coturnix japonica). Gen. Comp. Endocrinol. 56:70-81. Underwood, H. A., and T. D. Siopes, 1985. Melatonin rhythms in quail: Regulation by photoperiod and circadian pacemakers. J. Pineal Res. 2:133-143. Yokoyama, K., and D. S. Farner, 1976. Photoperiodic responses in bilaterally enucleated female whitecrowned sparrows, Zonotrichia leucophrys gambeli. Gen. Comp. Endocrinol. 30:528-533.
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Johnson, P. A., and A. van Tienhoven, 1984. Plasma luteinizing hormone levels throughout development and relative to ovulation in pinealectomized hens (Callus domesticus). Gen. Comp. Endocrinol. 54:450456. McMillan, J. P., H. A. Underwood, J. A. Elliott, M. H. Stetson, andM. Menaker, 1975. Extraretinal light perception in the sparrow. IV. Further evidence that the eyes do not participate in photoperiodic photoreception. J. Comp. Physiol. 97:205-213. Menaker, M., and H. Keatts, 1968. Extraretinal light perception in the sparrow. II. Photoperiodic stimulation of testis growth. Proc. Natl. Acad. Sci. 67:320-325. Menaker, M., R. Roberts, J. Elliott, and H. Underwood, 1970. Extraretinal light perception in the sparrow, III: the eyes do not participate in photoperiodic photoreception. Proc. Natl. Acad. Sci. USA 67:320-325. Oishi, T., and J. K. Lauber, 1973. Photoreception in the photosexual response of quail. I. Site of the photoreceptor. Am. J. Physiol. 225:155-158. Osol, G., B. Schwartz, and D. C. Foss, 1985. Effects of time, photoperiod, and pinealectomy on ocular and plasma melatonin concentrations in the chick. Gen. Comp. Endocrinol. 58:415-420. Ralph, C. L., 1970. Structure and alleged functions of avian pineals. Am. Zool. 10:217-235. Ralph, C. L., 1976. Correlation of melatonin content in pineal gland, blood, and brain of some birds and mammals. Am. Zool. 16:35—41. Ralph, C. L., 1981. The pineal and reproduction in birds. Pages 31-40 in: The Pineal Gland. Vol. II: Reproductive Effects. R. J. Reiter, ed. CRC Press, Inc., Boco Raton, FL. Reiter, R. J., 1973. Pineal control of a seasonal reproductive rhythm in male golden hamsters exposed to natural daylight and temperature. Endocrinology 92:423-426. Reiter, R. J., 1974. Circannual reproductive rhythms in mammals related to photoperiod and pineal function: A review. Chronobiologia 1:365-381. Reiter, R. J., 1981. Reproductive effects of the pineal gland and pineal indoles in the Syrian hamster and the albino rat. Pages 46-73 in: R. J. Reiter, ed. CRC Press, Inc., Boca Raton, FL. Reiter, R. J., B. A. Richardson, M. K. Vaughn, and L. Y. Johnson, 1981. Pineal actions and mechanisms in reproductive physiology. Jikeikai Med. J. 28 (Suppl. 1):35^16.
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