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Secondary Heating of Chicken Eggs Exposed to Light During Incubation
Secondary Heating of Chicken Eggs Exposed to Light During Incubation P. S. GOLD AND J. KALB
Division of Biology, State University of New York at Buffalo, Buffalo, New York 14214 (Received for publication January 3, 1975)
ABSTRACT An increased rate of development of chick embryos caused by light could be explained by uncontrolled heating. Single eggs were fitted with thermistor probes for monitoring temperature in the air cell and at the location of the germinal disc (upon the yolk). Incandescent and, to a lesser extent, fluorescent lighting heated both regions of the egg more than the air temperature of the incubator. With incandescent lighting preferential heating of the superficial yolk occurred dependent upon the orientation of the egg to the light. Methods for controlling egg heating are evaluated. POULTRY SCIENCE 55: 34-39, 1976
W
ITHIN the avian egg, the developing embryo is intimately connected to, though buffered from the external environment. Normal development is affected by: light (see below for references); x-rays, (Strobel et al., 1968); heat, humidity and gas exchange (Romanoff, 1960); mechanical vibration, gravity (Landauer, 1967); egg turning (Gold, 1972). We investigated extraneous heat variables associated with the use of light as an independent variable. Topics of developmental studies in which light is an independent variable include (1) behavior (see Gottlieb, 1968, for review; Dimond, 1968; Oppenheim, 1968; Bursian, 1964; and Gold, 1972); (2) teratogeny (Tamimie and Fox, 1967; and Kallen and Rudeberg, 1964), and (3) the photoacceleration effect (Lauber and Shutze, 1964; and Siegel et al, 1969). Lauber and Shutze (1964) and Siegel et al. (1969) have demonstrated that embryonic development is accelerated and hatching time is reduced when eggs are incubated under continuous incandescent light and to a lesser extent under fluorescent light (Lauber and Shutze, 1964), as compared with control eggs incubated in the dark. Unlike incandescent light however, fluorescent light did not accelerate development if used only during the 34
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first, second, or third week even when used at three times the intensity of the incandescent. The differences in photoacceleration between incandescent and fluorescent light may be the result of spectral differences or the result of extraneous heat differences. A variety of techniques have been used to mitigate the effect of heating in light stimulation experiments with chick embryos. For example in behavioral studies, Bursian (1964) and Oppenheim (1968) used a copper sulfate heat filter to absorb infrared from the light source. In the Lauber and Shutze (1964) demonstration of the photoacceleration effect, zero radiant energy was recorded at egg level, and continuous temperature recordings showed no heat differential between light and dark incubators. In a more sophisticated approach, Siegel et al. (1969) adjusted incubation temperature to equalize the air cell temperatures of selected eggs in the dark and incandescent light. To compensate for an increase in the air cell temperature in the incandescent treatment, the dark incubator was kept 0.2° C. warmer, and after as little as 10 hrs. embryos under incandescent light showed significantly accelerated development. Siegel et al. (1969) concurring with Lauber and Shutze concluded that since the incubator with light was significantly cooler than the dark incubator and the air cell
INTRODUCTION
LIGHT AND HEATING DURING INCUBATION
METHODS AND INSTRUMENTATION In each experiment single eggs were fitted with thermistor probes both in the air cell and at the yolk surface. Temperature was recorded with eggs in different orientations under both incandescent and fluorescent lighting. Normally shaped, infertile, White Leghorn eggs were used. In pilot investigations there were no differences in egg temperatures and temperature differentials between 24 hr. or 48 hr. fertile and infertile eggs. Coleman et al. (1964) reported temperature differences at the germinal disc in fertile and infertile White Leghorn eggs with a different temperature sensor placement and recording procedure than described below. The egg compartment of a "GQF-400" forced air incubator (75 cm. deep, 37 cm. wide and 24 cm. high) was fitted with an overhead lighting panel containing two 25
watt-frosted Sylvania incandescent lamps and two 15 watt Sylvania "delux warm white" fluorescent lamps. For the experiments reported here, only one incandescent or fluorescent lamp was used and lamp voltage was reduced by 40% to reduce the heating to previously reported levels (Siegel etal., 1969). Light availability at egg positions varied from 140 to 350 lux (incandescent) and 700 to 1100 lux (fluorescent) as measured with a "Lunasix" exposure meter. In the experiment the eggs were displaced from a point directly beneath the light source. The minimum vertical distance from eggs to light was 10 cm. Temperature in the incubator was controlled by a YSI (Yellow Springs Instrument) Model 71 Thermistemp Temperature Controller, and the light intensity was varied as required by a Sorvall Powerstat. The YSI #402 thermistor probes were inserted into the egg through small holes in the shell to a depth just beyond their 4 mm. sensitive capped tips and sealed with a minimum of paraffin. One probe was inserted through the middle of the blunt end of the egg into the air cell. The superficial yolk probe was inserted above the middle of the long axis. Care was taken to insure the integrity of both air space and vitelline membrane, and the egg was examined before and after experimentation for irregularities. The egg was always oriented on its side (parallel with the long axis) with air cell facing either the front or back of the incubator and the yolk probe was at the top of the yolk. A YSI #405 air probe monitored the temperature of the incubator above the egg compartment, in the direct flow of heated air. A matched probe at the same location controlled incubator temperature. Calibration studies showed that the difference in air temperature in the dark between the recording location above the egg compartment and the varied egg displacements ranged from -0.12° C. to -0.16° C , indicating a small temperature gradient within
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temperatures of eggs were the same for both environments, the observed effect resulted from light per se rather than elevated temperature . Despite these conclusions we feel that the effect of heat from the light source in photoacceleration merits further study. In an egg the yolk floats with the blastodisc on its upper surface and hence the embryo is the closest part of the egg to an overhead light source. It is reasonable to assume that the temperature at this immediate location is a more crucial determinant of embryonic development than either air cell temperature or incubator air temperature. Therefore, we hypothesized that certain lighting conditions, incandescent in particular, may preferentially heat the egg in the blastodisc region. In order to test this hypothesis, we have simultaneously recorded the superficial yolk temperature, the air cell temperature, and the incubator air temperature in darkness, and under fluorescent and incandescent lighting conditions.
35
P. S. GOLD AND J. KALB
36
FIG. 1. Temperature of air cell and superficial yolk measured at different horizontal displacements from a 25 watt incandescent lamp (voltage reduced by 40%), with reversed air cell orientations. Incubator temperature was regulated at 36.50° C.
RESULTS Figure 1 shows the increased air cell and yolk temperatures while incubator temperature remained unchanged when an egg was lighted with an incandescent lamp. These data are typical of all eggs tested. Temperatures, with the egg at increasing distances from the lamp and the air cell oriented towards or away from the direct flow of heated air, indicate expected effects in an experiment ultilizing one to three incandescent sources above a tray containing many eggs. In the dark incubator, the temperature of the air cell was slightly elevated with respect to the yolk, when the air cell faced toward the flow of fan forced air. The two forward positions did not maintain this relationship because of turbulence associated with a change in direction when air moving downward from the
upper incubator compartment moved toward the rear of the incubator. When the air cell was oriented away from the direct flow of heated air the air cell temperature was lower with respect to the yolk at all positions. When the incubator was lighted by the incandescent source, the air cell and yolk were heated above incubator temperature. The maximal increase in temperature did not occur directly under the incandescent source but rather at a variable distance from the source specific to each air cell orientation. When the air cell was oriented away from the light source the yolk was heated from +0.16° C. to +0.28° C. above air cell temperature at every position. When the air cell was oriented toward the light source the yolk
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the incubator. Incandescent lighting heated a shaded YSI #405 at the position of the egg (+0.16° C. to +0.24° C.) while the incubator temperature setting of 36.50° C. was unchanged. Thus, incubator air temperature is changed by local effects of convected and radiated heat. Temperatures were taken approximately 100 minutes following a shift in egg position or lighting condition and always after the egg temperature had stabilized. This procedure controlled the effects of radiant heating of the thermistor stems ("stem effect"). At equilibrium the "stem effect" was found to be negligible. Temperatures were registered on a YSI Tele-thermometer, Model #46 TUC, and recorded on a Grass 7B polygraph according to the manufacturer's instructions. Probes were calibrated with each other and with a fractional-degree mercury thermometer. The calibration curves obtained were rechecked at regular intervals. Temperature readings were within 0.02° C.
37
LIGHT AND HEATING DURING INCUBATION
gradients noted in the Methods. Fluorescent lighting heated yolk and air cell less than did the incandescent light. The parallel egg orientation resulted in equal heating of egg components. Table lb shows egg heating when the air cell was oriented away from the incandescent source. The yolk was warmer than the air cell (+0.21° C ) , and the temperature of both yolk and air cell were greater than with fluorescent lighting. The mean change in yolk temperature was +0.50° C. Air cell temperatures increased only +0.29° C. Table lc shows the heating that occurred when the air cell was oriented towards the incandescent source. In dark or light, mean yolk and air cell temperatures were similar. The yolk was heated equivalently to the away condition (+36.77° C. towards and +36.82° C. away) but the mean air cell temperature was now +0.16° C. warmer than in the away condition. In sum any lighting treatment significantly heated eggs and in addition the yolk was heated more than the air cell when the air cell was oriented away from the incandescent light source with at least a 5 cm. displacement or with any air cell orientation when closer to the incandescent light source.
TABLE 1.—Superficial yolk and air cell temperature (°C.) in different lighting conditions measured at 5 cm. from the light source. Incubator air temperature was 36.50° C. and any slight variations were normalized to 36.50° C. in both light and dark. N = 5. Abbreviations: Incub—Incubator air temperature. Yolk—Y—superficial yolk temperature. AC—air cell. L—lighted. D—dark. AL_D—temperature difference between light and dark a. FLUORESCENT:
Long axis of egg parallel with bulb.
Yolk X
a
36.37 .08
b. INCANDESCENT: X
C. X
rr
36.82 .07 INCANDESCENT: 36.77 .06
n = 4.
Dark
Light AC
Yolk
AC
36.42 .06
36.29 .02
36.34 .06
Air cell oriented away from bulb. 36.60 .07
36.32 .07
36.76 .06
36.30 .07
AAC L _ D
+ .10 .02
+ .08 .02
+ .21 .07
+ .50 .10
+ .29 .09
+ .01 .09
+ .47 .11
+ .42 .05
n == 5.
36.32 .06
Air cell oriented towards bulb,
AY L _ D
Y L - ACL -.03 .04
n == 5.
36.34 .04
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was warmer than the air cell at displacements 2.5 cm. in front of and at 2.5 cm. and 5.0 cm. behind the lamp. Yolk temperatures were equal to or cooler (-0.10° C.) than air cell temperature only when the air cell was oriented towards the lamp and the egg was at least 5 cm. in front of or 10 cm. behind the lamp. The frontal asymmetry in differential heating of yolk and air cell indicates that egg orientation and incubator position were interacting with the airflow and the lighting. The location at which the maximum warming of yolk or air cell occurred varied with each egg, but it always occurred between 0 cm. and 15 cm. (back). A possible explanation for this was the difference in the angle of incident light striking the shell with differently shaped eggs. Table 1 shows temperature differentials with different egg orientation and lighting at a horizontal displacement of 5 cm. from the lamp. In the fluorescent condition (Table la) with the egg oriented parallel to the lamp, the yolk and air cell are not different in dark or light, but both are heated with light (+0.10° C. and +0.08° C. respectively). The dark and light egg temperatures are lower than the incubator temperature of 36.50° C , but this is consistent with the temperature
38
P. S. GOLD AND J. KALB
DISCUSSION
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The information gained from this model incubation system allows us to re-examine the actual procedures and results of several studies using light stimulation. It seems apparent that under certain conditions the use of incandescent light will produce a heating effect difficult to separate from a photic effect. In this study a single low intensity incandescent source raised yolk surface temperature as much as 0.5° C , while incubator temperature remained relatively constant. In a study of the effect of heat on development Romanoff (1960, p. 203) showed that after 42 hours of incubation (to the 15 somite stage), an increase of 0.2° C. would result in an additional pair of somites. The heating effect observed in our study was of sufficient magnitude to produce a measurable acceleration in early embryonic development. The lack of a photoacceleration effect with fluorescent light during the first week of incubation (Lauber and Shutze, 1964) is confirmed by a study done in our laboratory (Tenser, 1974) which compared somite number after 48 or 72 hours in darkness or under fluorescent light. This lack of photoacceleration under fluorescent lighting is in accord with our present findings and with Romanoff's data, that a 0.1° C. increase in temperature would not produce a measurable increase in somite number. The short term photoacceleration effect using incandescent light (produced by one week or less of lighting) reported by Lauber and Shutze (1964) and Siegel et al. (1969) may have included an uncontrolled heating effect. However our data are not a direct replication of the above studies because the long axis of the eggs was vertical or inclined at 45 ° and multiple incandescent sources were used. Differential heating of yolk and air cell would still occur at several points on the egg trays. The measurement of air temperatures within culture dishes containing explanted
embryos on a glucose medium (Isakson et al., 1970) also may not accurately indicate the temperature of the embryo or the medium. Since our data shows yolk surface temperature to have increased more than both air cell and incubator temperatures, we conclude that a photoacceleration effect in early chick embryogeny has not yet been unambiguously demonstrated. A full-term photoacceleration (lighting during entire three-week incubation period) unconfounded by heat is likewise in question, although positive results obtained with fluorescent light (Lauber and Shutze, 1964; Gold, 1972) may reflect a qualitatively different photic effect during late embryogeny. Our results are not directly applicable to studies of later embryogeny when the embryo occupies a significant portion of the egg and becomes a significant producer of heat. It seems clear, as Gottlieb (1968) has suggested, that the abnormalities in development produced by a single high intensity incandescent source as used by Tamimie and Fox (1967) and by Kallen and Rudeberg (1964) would have, at least in part, resulted from overheating and not lighting per se. The possibility also exists that heating effects may have determined results obtained in other embryological studies involving light responsivity. Bursian (1965) reported changes in motility of 4 to 9 day chick embryos following intense non-visual light stimulation and Oppenheim (1968) reported increased bill clapping following intense visual stimulation one to two days before hatching in chick and duck embryos. In both experiments the stimulating beam of light was passed through a saturated solution of copper sulfate, which filters infrared, and was expected to eliminate radiant heating. However, we focused a high intensity (1500 Lux) light beam through 7 cm. of saturated copper sulfate solution onto a probe (painted black) immersed in egg white, and observed a 0.2° C. increase in temperature within 10 minutes. In the experi-
LIGHT AND HEATING DURING INCUBATION
merits discussed above, significant heating effects may not have been introduced because the light stimulation was one minute or less in duration. However, the adequacy of a copper sulphate filter in chronic stimulation studies is doubtful. REFERENCES
of electric light on early chick embryos. Acta Morphol. Neerl-Scand. 6: 95-99. Landauer, W., 1967. The hatchability of chicken eggs as influenced by environment and heredity. Bull. Storrs (Connecticut) Agric. Exp. Sta. Monog. 1 (Revised). Lauber, J. K., and J. V. Shutze, 1964. Accelerated growth of embryo chicks under the influence of light. Growth, 28: 179-190. Oppenheim, R. W., 1968. Light responsivity in chick and duck embryos just prior to hatching. Anim. Behav. 16: 276-281. Romanoff, A. L., 1960. The Avian Embryo. Macmillan, New York. Siegel, P. B., S. T. Isakson, F. N. Coleman and B. J. Huffman, 1969. Photoacceleration of development in chick embryos. Comp. Biochem. Physiol. 28: 753-758. Strobel, M. G., G. M. Clark and G. E. MacDonald, 1968. Ontogeny of the following response: A radiosensitive period during embryological development of the domestic chick. J. Comp. Physiol. Psychol. 65: 314-319. Tamimie, H. S., and M. W. Fox, 1967. Effect of continuous and intermittent light exposure on the embryonic development of chicken eggs. Comp. Biochem. Physiol. 20: 793-799. Tenser, P. J., 1974. Photoacceleration of early chick embryo development: a replication. M.S. Nat. Sci., S.U.N.Y. at Buffalo. Unpubl.
NEWS AND NOTES (Continued from page 13) purpose is to help encourage the education and professional development of college students pursuing careers in agricultural communications. This scholarship will be administered by the Office of Agricultural Communications at the University as part of its career program. U.S.D.A. NOTES The U.S. Department of Agriculture has proposed new disease surveillance measures to protect U.S. poultry from diseases that could be introduced into the country through the importation of live poultry and hatching eggs. Changes in the federal import regulations proposed by the Animal and Plant Health Inspection Service, U.S.D.A., include: Eggs imported for hatching purposes, when shipped
from countries in which exotic Newcastle disease exists, must be found free of disease under an A.P.H.I.S.-approved surveillance system or they must be hatched and brooded in the U.S. at A.P.H.I.S.-approved quarantine facilities under prescribed conditions. Imported poultry and hatching eggs must originate from flocks that have been tested and found free of pullorum disease and fowl typhoid. All hatching eggs must be fumigated with formaldehyde and shipped directly to the U.S. from the country of origin, in new containers. ALABAMA NOTES Dr. Rex D. Bushong, former Director of Technical Services and Nutrition, Herider Farms, Inc., has been appointed to the state staff of the Alabama Co-opera-
(Continued on page 84)
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Bursian, A. V., 1964. The influence of light on the spontaneous movements of chick embryos. Bull. Exper. Biol. Med. 7: 7-11. (In Russian.) Coleman, J. W., H. S. Siegel and G. F. Krause, 1964. Initial internal temperature changes of incubating eggs. Poultry Sci. 43: 205-208. Dimond, S. J., 1968. Effects of photic stimulation before hatching on the development of fear in chicks. J. Comp. Physiol. Psychol. 65: 320-324. Gold, P. S., 1972. The effects of sensory stimulation during embryogeny on growth, hatching, and imprinting in domestic chicks. Dissert. Abstr. Int. 32: 6074B. Gottlieb, G., 1968. Prenatal behavior of birds. Quart. Rev. Biol. 43: 148-174. Isakson, S. T., B. J. Huffman and P. B. Siegel, 1970. Intensities of incandescent light and the development of chick embryos in ovo and in vitro. Comp. Biochem. Physiol. 34: 299-305. Kallen, B., and S. Rudeberg, 1964. Teratogenic effects
39
Division of Biology, State University of New York at Buffalo, Buffalo, New York 14214 (Received for publication January 3, 1975)
ABSTRACT An increased rate of development of chick embryos caused by light could be explained by uncontrolled heating. Single eggs were fitted with thermistor probes for monitoring temperature in the air cell and at the location of the germinal disc (upon the yolk). Incandescent and, to a lesser extent, fluorescent lighting heated both regions of the egg more than the air temperature of the incubator. With incandescent lighting preferential heating of the superficial yolk occurred dependent upon the orientation of the egg to the light. Methods for controlling egg heating are evaluated. POULTRY SCIENCE 55: 34-39, 1976
W
ITHIN the avian egg, the developing embryo is intimately connected to, though buffered from the external environment. Normal development is affected by: light (see below for references); x-rays, (Strobel et al., 1968); heat, humidity and gas exchange (Romanoff, 1960); mechanical vibration, gravity (Landauer, 1967); egg turning (Gold, 1972). We investigated extraneous heat variables associated with the use of light as an independent variable. Topics of developmental studies in which light is an independent variable include (1) behavior (see Gottlieb, 1968, for review; Dimond, 1968; Oppenheim, 1968; Bursian, 1964; and Gold, 1972); (2) teratogeny (Tamimie and Fox, 1967; and Kallen and Rudeberg, 1964), and (3) the photoacceleration effect (Lauber and Shutze, 1964; and Siegel et al, 1969). Lauber and Shutze (1964) and Siegel et al. (1969) have demonstrated that embryonic development is accelerated and hatching time is reduced when eggs are incubated under continuous incandescent light and to a lesser extent under fluorescent light (Lauber and Shutze, 1964), as compared with control eggs incubated in the dark. Unlike incandescent light however, fluorescent light did not accelerate development if used only during the 34
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 14, 2015
first, second, or third week even when used at three times the intensity of the incandescent. The differences in photoacceleration between incandescent and fluorescent light may be the result of spectral differences or the result of extraneous heat differences. A variety of techniques have been used to mitigate the effect of heating in light stimulation experiments with chick embryos. For example in behavioral studies, Bursian (1964) and Oppenheim (1968) used a copper sulfate heat filter to absorb infrared from the light source. In the Lauber and Shutze (1964) demonstration of the photoacceleration effect, zero radiant energy was recorded at egg level, and continuous temperature recordings showed no heat differential between light and dark incubators. In a more sophisticated approach, Siegel et al. (1969) adjusted incubation temperature to equalize the air cell temperatures of selected eggs in the dark and incandescent light. To compensate for an increase in the air cell temperature in the incandescent treatment, the dark incubator was kept 0.2° C. warmer, and after as little as 10 hrs. embryos under incandescent light showed significantly accelerated development. Siegel et al. (1969) concurring with Lauber and Shutze concluded that since the incubator with light was significantly cooler than the dark incubator and the air cell
INTRODUCTION
LIGHT AND HEATING DURING INCUBATION
METHODS AND INSTRUMENTATION In each experiment single eggs were fitted with thermistor probes both in the air cell and at the yolk surface. Temperature was recorded with eggs in different orientations under both incandescent and fluorescent lighting. Normally shaped, infertile, White Leghorn eggs were used. In pilot investigations there were no differences in egg temperatures and temperature differentials between 24 hr. or 48 hr. fertile and infertile eggs. Coleman et al. (1964) reported temperature differences at the germinal disc in fertile and infertile White Leghorn eggs with a different temperature sensor placement and recording procedure than described below. The egg compartment of a "GQF-400" forced air incubator (75 cm. deep, 37 cm. wide and 24 cm. high) was fitted with an overhead lighting panel containing two 25
watt-frosted Sylvania incandescent lamps and two 15 watt Sylvania "delux warm white" fluorescent lamps. For the experiments reported here, only one incandescent or fluorescent lamp was used and lamp voltage was reduced by 40% to reduce the heating to previously reported levels (Siegel etal., 1969). Light availability at egg positions varied from 140 to 350 lux (incandescent) and 700 to 1100 lux (fluorescent) as measured with a "Lunasix" exposure meter. In the experiment the eggs were displaced from a point directly beneath the light source. The minimum vertical distance from eggs to light was 10 cm. Temperature in the incubator was controlled by a YSI (Yellow Springs Instrument) Model 71 Thermistemp Temperature Controller, and the light intensity was varied as required by a Sorvall Powerstat. The YSI #402 thermistor probes were inserted into the egg through small holes in the shell to a depth just beyond their 4 mm. sensitive capped tips and sealed with a minimum of paraffin. One probe was inserted through the middle of the blunt end of the egg into the air cell. The superficial yolk probe was inserted above the middle of the long axis. Care was taken to insure the integrity of both air space and vitelline membrane, and the egg was examined before and after experimentation for irregularities. The egg was always oriented on its side (parallel with the long axis) with air cell facing either the front or back of the incubator and the yolk probe was at the top of the yolk. A YSI #405 air probe monitored the temperature of the incubator above the egg compartment, in the direct flow of heated air. A matched probe at the same location controlled incubator temperature. Calibration studies showed that the difference in air temperature in the dark between the recording location above the egg compartment and the varied egg displacements ranged from -0.12° C. to -0.16° C , indicating a small temperature gradient within
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temperatures of eggs were the same for both environments, the observed effect resulted from light per se rather than elevated temperature . Despite these conclusions we feel that the effect of heat from the light source in photoacceleration merits further study. In an egg the yolk floats with the blastodisc on its upper surface and hence the embryo is the closest part of the egg to an overhead light source. It is reasonable to assume that the temperature at this immediate location is a more crucial determinant of embryonic development than either air cell temperature or incubator air temperature. Therefore, we hypothesized that certain lighting conditions, incandescent in particular, may preferentially heat the egg in the blastodisc region. In order to test this hypothesis, we have simultaneously recorded the superficial yolk temperature, the air cell temperature, and the incubator air temperature in darkness, and under fluorescent and incandescent lighting conditions.
35
P. S. GOLD AND J. KALB
36
FIG. 1. Temperature of air cell and superficial yolk measured at different horizontal displacements from a 25 watt incandescent lamp (voltage reduced by 40%), with reversed air cell orientations. Incubator temperature was regulated at 36.50° C.
RESULTS Figure 1 shows the increased air cell and yolk temperatures while incubator temperature remained unchanged when an egg was lighted with an incandescent lamp. These data are typical of all eggs tested. Temperatures, with the egg at increasing distances from the lamp and the air cell oriented towards or away from the direct flow of heated air, indicate expected effects in an experiment ultilizing one to three incandescent sources above a tray containing many eggs. In the dark incubator, the temperature of the air cell was slightly elevated with respect to the yolk, when the air cell faced toward the flow of fan forced air. The two forward positions did not maintain this relationship because of turbulence associated with a change in direction when air moving downward from the
upper incubator compartment moved toward the rear of the incubator. When the air cell was oriented away from the direct flow of heated air the air cell temperature was lower with respect to the yolk at all positions. When the incubator was lighted by the incandescent source, the air cell and yolk were heated above incubator temperature. The maximal increase in temperature did not occur directly under the incandescent source but rather at a variable distance from the source specific to each air cell orientation. When the air cell was oriented away from the light source the yolk was heated from +0.16° C. to +0.28° C. above air cell temperature at every position. When the air cell was oriented toward the light source the yolk
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the incubator. Incandescent lighting heated a shaded YSI #405 at the position of the egg (+0.16° C. to +0.24° C.) while the incubator temperature setting of 36.50° C. was unchanged. Thus, incubator air temperature is changed by local effects of convected and radiated heat. Temperatures were taken approximately 100 minutes following a shift in egg position or lighting condition and always after the egg temperature had stabilized. This procedure controlled the effects of radiant heating of the thermistor stems ("stem effect"). At equilibrium the "stem effect" was found to be negligible. Temperatures were registered on a YSI Tele-thermometer, Model #46 TUC, and recorded on a Grass 7B polygraph according to the manufacturer's instructions. Probes were calibrated with each other and with a fractional-degree mercury thermometer. The calibration curves obtained were rechecked at regular intervals. Temperature readings were within 0.02° C.
37
LIGHT AND HEATING DURING INCUBATION
gradients noted in the Methods. Fluorescent lighting heated yolk and air cell less than did the incandescent light. The parallel egg orientation resulted in equal heating of egg components. Table lb shows egg heating when the air cell was oriented away from the incandescent source. The yolk was warmer than the air cell (+0.21° C ) , and the temperature of both yolk and air cell were greater than with fluorescent lighting. The mean change in yolk temperature was +0.50° C. Air cell temperatures increased only +0.29° C. Table lc shows the heating that occurred when the air cell was oriented towards the incandescent source. In dark or light, mean yolk and air cell temperatures were similar. The yolk was heated equivalently to the away condition (+36.77° C. towards and +36.82° C. away) but the mean air cell temperature was now +0.16° C. warmer than in the away condition. In sum any lighting treatment significantly heated eggs and in addition the yolk was heated more than the air cell when the air cell was oriented away from the incandescent light source with at least a 5 cm. displacement or with any air cell orientation when closer to the incandescent light source.
TABLE 1.—Superficial yolk and air cell temperature (°C.) in different lighting conditions measured at 5 cm. from the light source. Incubator air temperature was 36.50° C. and any slight variations were normalized to 36.50° C. in both light and dark. N = 5. Abbreviations: Incub—Incubator air temperature. Yolk—Y—superficial yolk temperature. AC—air cell. L—lighted. D—dark. AL_D—temperature difference between light and dark a. FLUORESCENT:
Long axis of egg parallel with bulb.
Yolk X
a
36.37 .08
b. INCANDESCENT: X
C. X
rr
36.82 .07 INCANDESCENT: 36.77 .06
n = 4.
Dark
Light AC
Yolk
AC
36.42 .06
36.29 .02
36.34 .06
Air cell oriented away from bulb. 36.60 .07
36.32 .07
36.76 .06
36.30 .07
AAC L _ D
+ .10 .02
+ .08 .02
+ .21 .07
+ .50 .10
+ .29 .09
+ .01 .09
+ .47 .11
+ .42 .05
n == 5.
36.32 .06
Air cell oriented towards bulb,
AY L _ D
Y L - ACL -.03 .04
n == 5.
36.34 .04
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was warmer than the air cell at displacements 2.5 cm. in front of and at 2.5 cm. and 5.0 cm. behind the lamp. Yolk temperatures were equal to or cooler (-0.10° C.) than air cell temperature only when the air cell was oriented towards the lamp and the egg was at least 5 cm. in front of or 10 cm. behind the lamp. The frontal asymmetry in differential heating of yolk and air cell indicates that egg orientation and incubator position were interacting with the airflow and the lighting. The location at which the maximum warming of yolk or air cell occurred varied with each egg, but it always occurred between 0 cm. and 15 cm. (back). A possible explanation for this was the difference in the angle of incident light striking the shell with differently shaped eggs. Table 1 shows temperature differentials with different egg orientation and lighting at a horizontal displacement of 5 cm. from the lamp. In the fluorescent condition (Table la) with the egg oriented parallel to the lamp, the yolk and air cell are not different in dark or light, but both are heated with light (+0.10° C. and +0.08° C. respectively). The dark and light egg temperatures are lower than the incubator temperature of 36.50° C , but this is consistent with the temperature
38
P. S. GOLD AND J. KALB
DISCUSSION
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The information gained from this model incubation system allows us to re-examine the actual procedures and results of several studies using light stimulation. It seems apparent that under certain conditions the use of incandescent light will produce a heating effect difficult to separate from a photic effect. In this study a single low intensity incandescent source raised yolk surface temperature as much as 0.5° C , while incubator temperature remained relatively constant. In a study of the effect of heat on development Romanoff (1960, p. 203) showed that after 42 hours of incubation (to the 15 somite stage), an increase of 0.2° C. would result in an additional pair of somites. The heating effect observed in our study was of sufficient magnitude to produce a measurable acceleration in early embryonic development. The lack of a photoacceleration effect with fluorescent light during the first week of incubation (Lauber and Shutze, 1964) is confirmed by a study done in our laboratory (Tenser, 1974) which compared somite number after 48 or 72 hours in darkness or under fluorescent light. This lack of photoacceleration under fluorescent lighting is in accord with our present findings and with Romanoff's data, that a 0.1° C. increase in temperature would not produce a measurable increase in somite number. The short term photoacceleration effect using incandescent light (produced by one week or less of lighting) reported by Lauber and Shutze (1964) and Siegel et al. (1969) may have included an uncontrolled heating effect. However our data are not a direct replication of the above studies because the long axis of the eggs was vertical or inclined at 45 ° and multiple incandescent sources were used. Differential heating of yolk and air cell would still occur at several points on the egg trays. The measurement of air temperatures within culture dishes containing explanted
embryos on a glucose medium (Isakson et al., 1970) also may not accurately indicate the temperature of the embryo or the medium. Since our data shows yolk surface temperature to have increased more than both air cell and incubator temperatures, we conclude that a photoacceleration effect in early chick embryogeny has not yet been unambiguously demonstrated. A full-term photoacceleration (lighting during entire three-week incubation period) unconfounded by heat is likewise in question, although positive results obtained with fluorescent light (Lauber and Shutze, 1964; Gold, 1972) may reflect a qualitatively different photic effect during late embryogeny. Our results are not directly applicable to studies of later embryogeny when the embryo occupies a significant portion of the egg and becomes a significant producer of heat. It seems clear, as Gottlieb (1968) has suggested, that the abnormalities in development produced by a single high intensity incandescent source as used by Tamimie and Fox (1967) and by Kallen and Rudeberg (1964) would have, at least in part, resulted from overheating and not lighting per se. The possibility also exists that heating effects may have determined results obtained in other embryological studies involving light responsivity. Bursian (1965) reported changes in motility of 4 to 9 day chick embryos following intense non-visual light stimulation and Oppenheim (1968) reported increased bill clapping following intense visual stimulation one to two days before hatching in chick and duck embryos. In both experiments the stimulating beam of light was passed through a saturated solution of copper sulfate, which filters infrared, and was expected to eliminate radiant heating. However, we focused a high intensity (1500 Lux) light beam through 7 cm. of saturated copper sulfate solution onto a probe (painted black) immersed in egg white, and observed a 0.2° C. increase in temperature within 10 minutes. In the experi-
LIGHT AND HEATING DURING INCUBATION
merits discussed above, significant heating effects may not have been introduced because the light stimulation was one minute or less in duration. However, the adequacy of a copper sulphate filter in chronic stimulation studies is doubtful. REFERENCES
of electric light on early chick embryos. Acta Morphol. Neerl-Scand. 6: 95-99. Landauer, W., 1967. The hatchability of chicken eggs as influenced by environment and heredity. Bull. Storrs (Connecticut) Agric. Exp. Sta. Monog. 1 (Revised). Lauber, J. K., and J. V. Shutze, 1964. Accelerated growth of embryo chicks under the influence of light. Growth, 28: 179-190. Oppenheim, R. W., 1968. Light responsivity in chick and duck embryos just prior to hatching. Anim. Behav. 16: 276-281. Romanoff, A. L., 1960. The Avian Embryo. Macmillan, New York. Siegel, P. B., S. T. Isakson, F. N. Coleman and B. J. Huffman, 1969. Photoacceleration of development in chick embryos. Comp. Biochem. Physiol. 28: 753-758. Strobel, M. G., G. M. Clark and G. E. MacDonald, 1968. Ontogeny of the following response: A radiosensitive period during embryological development of the domestic chick. J. Comp. Physiol. Psychol. 65: 314-319. Tamimie, H. S., and M. W. Fox, 1967. Effect of continuous and intermittent light exposure on the embryonic development of chicken eggs. Comp. Biochem. Physiol. 20: 793-799. Tenser, P. J., 1974. Photoacceleration of early chick embryo development: a replication. M.S. Nat. Sci., S.U.N.Y. at Buffalo. Unpubl.
NEWS AND NOTES (Continued from page 13) purpose is to help encourage the education and professional development of college students pursuing careers in agricultural communications. This scholarship will be administered by the Office of Agricultural Communications at the University as part of its career program. U.S.D.A. NOTES The U.S. Department of Agriculture has proposed new disease surveillance measures to protect U.S. poultry from diseases that could be introduced into the country through the importation of live poultry and hatching eggs. Changes in the federal import regulations proposed by the Animal and Plant Health Inspection Service, U.S.D.A., include: Eggs imported for hatching purposes, when shipped
from countries in which exotic Newcastle disease exists, must be found free of disease under an A.P.H.I.S.-approved surveillance system or they must be hatched and brooded in the U.S. at A.P.H.I.S.-approved quarantine facilities under prescribed conditions. Imported poultry and hatching eggs must originate from flocks that have been tested and found free of pullorum disease and fowl typhoid. All hatching eggs must be fumigated with formaldehyde and shipped directly to the U.S. from the country of origin, in new containers. ALABAMA NOTES Dr. Rex D. Bushong, former Director of Technical Services and Nutrition, Herider Farms, Inc., has been appointed to the state staff of the Alabama Co-opera-
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Bursian, A. V., 1964. The influence of light on the spontaneous movements of chick embryos. Bull. Exper. Biol. Med. 7: 7-11. (In Russian.) Coleman, J. W., H. S. Siegel and G. F. Krause, 1964. Initial internal temperature changes of incubating eggs. Poultry Sci. 43: 205-208. Dimond, S. J., 1968. Effects of photic stimulation before hatching on the development of fear in chicks. J. Comp. Physiol. Psychol. 65: 320-324. Gold, P. S., 1972. The effects of sensory stimulation during embryogeny on growth, hatching, and imprinting in domestic chicks. Dissert. Abstr. Int. 32: 6074B. Gottlieb, G., 1968. Prenatal behavior of birds. Quart. Rev. Biol. 43: 148-174. Isakson, S. T., B. J. Huffman and P. B. Siegel, 1970. Intensities of incandescent light and the development of chick embryos in ovo and in vitro. Comp. Biochem. Physiol. 34: 299-305. Kallen, B., and S. Rudeberg, 1964. Teratogenic effects
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