I. Yıldırım, A. Aygün and V. Sariyel. Manuskript eingegangen am 8. Mai 2003, angenommen am 30. August Introduction. Materials and methods

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1 Arch.Geflügelk., 69 (1). S , 2005, ISSN Verlag Eugen Ulmer GmbH & Co. Stuttgart Responses of embryos produced by young and old parents to different cabinet temperatures at the plateau stage of incubation in Japanese Quails (Coturnix coturnix japonica) Reaktion von Embryonen junger und alter Eltern auf unterschiedliche Temperaturen in der Plateauphase der Brut bei japanischen Wachteln (Coturnix coturnix japonica) I. Yıldırım, A. Aygün and V. Sariyel Manuskript eingegangen am 8. Mai 2003, angenommen am 30. August 2003 Introduction Hatchability and chick quality decreases, hatching time changes and more anomalies occur when incubator temperature is too low or too high (ROMANOFF 1960). The metabolic rate of precocial bird eggs reaches a plateau when about 80 % of the incubation period has passed (DIETZ et al. 1998). During this period the needs of the embryo are greatest and the ability of the incubator environment to provide respiratory gas levels prove to be most difficult (WINELAND 1996). It has been established that parental age of the breeder bird has a considerable effect upon embryonic hatchability and subsequent chick survival (SHANAWA- NY 1984; YILDIRIM and YETISIR 1996). Although, the interaction between breeder age and incubation humidity has been well cited in some papers (TULLETT and BURTON 1982; TULLETT 1990; SHANAWANY 1984), the relations of incubation temperature and parental age effects on hatching traits at the plateau stage of incubation has not well been investigated. In the early 50 s and 60 s, numerous studies have been conducted to quantify the metabolic heat production of eggs, and this data are still used to a large extend. The question is whether the modern breeds produce the same amount of heat as 40 years ago, especially the broiler side. Due to increased genetic growth potential of the birds, the heat production may be increased (MEIJERHOF 1999). Few studies have investigated the effects of temperature and parental age on hatching results at plateau stage of incubation The objective of the present study was to investigate the responses of eggs produced by 2 and 8 moths old quail to different incubator cabinet temperatures at the plateau stage of incubation and its residual effects on hatching results. Materials and methods Hatching eggs were produced from two Japanese quail (Coturnix coturnix japonica) flocks at different parental ages. The fist one termed as young group (YG) was 2 months old and the second one termed as old group (OG) was 8 months old. The parent quails were placed in batteries. They were exposed to 16 h of light / d. Birds were fed Selcuk Üniversitesi, Ziraat Fakültesi, Kampus, Konya, Turkey a basal diet (maize and soy bean based; 240 g kg -1 crude protein; 12.1 MJ ME kg -1 ) formulated to contain the NATION- AL RESEARCH COUNCIL (1994) requirements of all nutrients; without added antibiotics, coccidiostats or growth promoters. Diet and water were available, ad libutum. Hatching eggs were collected twice daily, sanitized and held at 18 C and at 70 % relative humidity (RH) for 1 to 7 days before setting. In present study, to eliminate egg weight effect, the eggs were chosen around the same weighs for each parent age group and mean egg weights were around g for both groups. After storage, the eggs were allowed to acclimatize to room temperature (24 C) overnight. The eggs were incubated in forced draft (the capacity of it is 1020 broiler eggs) laboratory incubator until the end of 13 days (335 hours) of incubation at 37.4 C and at 58 % relative humidity. The machine was monitored twice daily for proper operation. At the completion of 13 days (at the start 14 d of incubation) of incubation, the eggs were transferred to three hatchers (the capacity of each one is 280 broiler eggs) operated at different temperature degrees. The first group was placed into the incubator cabinet (IC) that operated at 36.4 C (Low-L), the other two groups were placed in two identical incubator cabinets that operated at 37.4 C (Control-CON) and 38.4 C (High-H), respectively. During the plateau stage of incubation, humidity (RH) was kept as 58 % in all groups. Four identical replicate trials of about 200 eggs of each age group for each IC were conducted. In other words, within each age group, 200 eggs were set per IC. Totally, 400 eggs were set for each IC for both of 2 age groups. In total, 1,200 quail hatching eggs were used in the experiment. At the completion of 15 days (383 hours) of incubation, the temperature and RH were kept as 37.2 C and 75 % in all three IC. The embryo temperature measurements were taken indirectly from the eggshell surface in the study and eggshell surface temperature (T es ) was monitored every 8 hour between 14 th (336 h) and 17 th (424 h) day of incubation using an ear thermometer (Braun, Thermoscan type; IRT 3020, Germany). Measuring internal egg temperature is problematic, but only a small difference between internal and eggshell surface temperature exists (FRENCH 1997). In total, 12 measurements have been taken from the eggs (10 random eggs for each age group in a single IC and totally, 20 eggs for each IC) during experiment. At hatch time, all unhatched eggs were opened and examined macroscopically to determine percentages of prenatal period deaths (before pip) and piped deaths (after pip to hatch - perinatal period) classified as described by YETISIR and YILDIRIM (1998).

2 Yıldırım et al.: Responses of embryos to different cabinet temperatures at the plateau stage of incubation 41 Infertile, cracked or contaminated, eggs containing early and mid dead embryos were excluded from data analysis. At hatch, the chicks were weighed and decapitated. The heart, liver and yolk sac with yolk material (YSwY) (their weights based on percentage of whole body mass) were dissected, trimmed, blotted and weighed to the nearest 0.01 mg on an analytical balance. All external vessels were trimmed from the heart using surgical scissors prior to weighing. All data in table 3 were calculated as percentage of chick weight at hatch. The data were examined using an analysis based on a 3 by 2 factorial arrangement of treatments with three levels of temperature and two age groups. Statements of statistical significance were based on P < 0.05 unless otherwise cited. The statistical analyses were conducted using the General Linear Models procedure of MINITAB (1998). All percentage data in Table 2 were transformed to arc sin to normalize them prior to analysis. Means were compared using least significant differences (LSD). Results Eggshell Surface Temperature The eggshell temperatures (T es ) of the three trials are summarized in Table 1. Significant interaction effects were observed for measurement at T es3 (P < 0.05), T es8 (P < 0.01), T es11 (P < 0.01), and T es12 (P < 0.05). Significant T es differences were observed in the time of measurement at T es1, T es2, T es4, T es5, T es6 (P < 0.01) and T es9 (P < 0.05) groups for temperature main effects. Besides, significant effects of parent age were observed for T es2, T es4, T es6 (P < 0.05), T es5, T es7 and T es10 (P < 0.01). The mean T es increased with increasing IC temperature regardless of parent age. T es increased significantly with increasing cabinet temperature in YF and OF groups to and 37.27, respectively. In general, YF exhibited lower T es values than OF. Hatching Results The effects of trial on hatchability of fertile eggs, late mortality stages and dead in tray values are shown in table 2. A significant interaction occurred between IC temperature and flock age at 38.4 C (P < 0.05) for the percentage of chicks hatched. The eggs produced by YF ( x = 87.94%) at 38.4 C gave the best hatchability results compared with OF eggs ( x =77.48%). Conversely, there were not found any interaction effects in the other groups for hatchability of fertile eggs. At prenatal stage, a significant interaction effect was detected at 38.4 C (age * temperature), and the mean values amounted to 0.58 % and 4.63 % for YF and OF groups, respectively. Nearly, eight-fold more embryos died in OF than in YF group. Embryo deaths at perinatal stage were not statistically different for the interaction effect among groups. Contrary, significant differences were found between age groups at 38.4 C IC in perinatal stage. The mean values for 2 and 8 months of age were 1.20 % and 4.02 %, respectively. No significant differences were observed for any main or interactions effects for dead in tray values at hatch. Embryonic Growth The effects of trial on selected supply organs and yolk sac weights (YswY) are shown in table 3. A significant interaction occurred between temperature and age group for YSwY both at 37.4 and 38.4 C IC temperatures (P < 0.10). The chicks at hatch produced by OF had heavier YSwY (for The hatching results indicate that fertile eggs from OF have a reduced hatching potential when compared with that of YF exposed to 38.4 C IC temperature. The hatchery manager doesn t allow temperature increases in hatchers for old flock eggs at the plateau stage of incubation for best hatchability results. Hatchability of fertile eggs was not influenced by the temperature main effect. This result suggests that eggs can be incubated at the temperature of 36.4 and 37.4 C at IC during plateau stage of incubation regardless of parent age. Our findings are in agreement with WIL- SON (1991), who stated that the optimum incubation temperature is between 37 and 38 C but disagrees with YILDI- YF; x = 1.51% and x = 2.56% OF) compared with the chicks obtained from YF at 37.4 C IC temperature. Conversely, chicks of OF hens exhibited less YSwY weight compared with chicks of YF hens at 38.4 C. Relative heart and liver weights were not affected by IC temperature and age group or by their interaction. Discussion Eggshell Surface Temperature Temperature Main Effect. The results from current study show that the response of fertile eggs to temperature effects mainly depends on the IC temperature and age of parents. In other words, there is a linear relationship between IC temperature and T es, and additionally, parent age and T es, independently, at the plateau stage of incubation. The results agree with that of ROMIJN and LOKHOEST (1955) who stated that in embryo s (for chicken) younger than 18 days the egg temperature follows the environmental temperature exactly during cooling and warming. YILDIRIM and YETISIR (unpublished data) demonstrated that the embryo temperature depends on the cabinet air temperature from transfer until hatch in broiler eggs. HOLLAND et al. (1998) stated that during embryonic development, the chick embryo is poikilotherm and also MEIJERHOF (1999) and TAZAWA et al. (2001) stated that the embryo is not able to regulate its own body temperature. Therefore, the embryo reacts as a cold-blooded animal on temperature fluctuations. On the other hand, the high T es value at OF eggs could not be explained. It was speculated that the differences between groups might be due to relative distribution of egg components. But, it needs reinforcement with other comprehensive studies. Main Effect. The eggs from OF group followed more close the mean IC temperature than that of YF. LOWE and GARWOOD (1977) stated that eggs from older birds are known to hatch earlier than those from younger birds. FRENCH (1997) stated that as temperature changes, the oxygen consumption of the embryo and by this its heat production changes as well. As mentioned previously in the paper, in order to eliminate the egg weight effect hatching eggs were selected to have around the same weights for both groups. Thus, it is not entirely clear what mechanisms may be responsible for the lower response of eggs produced by hens of YF to IC temperature compared to those from hens of OF group. It was assumed that the difference might be due to relative distribution of egg components. The results from current study are in agreement with WEYTJENS et al. (1999) who indicated that parent age influences the regulation of heat production during the first days of life. As a result, breeder flock age should be considered as an additional factor in thermoregulatory experiments. Hatching Results

3 42 Yıldırım et al.: Responses of embryos to different cabinet temperatures at the plateau stage of incubation Table 1. Effects of different temperature levels and age groups on eggshell surface temperature at plateau stage of incubation in Japanese quail hatching eggs. (n = 10 for temp. age interaction; n = 20 for temperature and n = 30 for age) Einfluss unterschiedlicher Bruttemperaturen und Hennenalter auf die Oberflächentemperatur der Eischale während der Plateauphase der Brut bei Wachtelbruteiern (n = 10 für Temperatur x Alter Interaktion; n = 20 für die Temperatur und n = 30 für das Alter) Temperature 1 C (weeks) Tes1 ( C) (336 h) Tes2 ( C) (344 h) Tes3 ( C) (352 h) Tes4 ( C) (360 h) Tes5 ( C) (368 h) Tes6 ( C) (376 h) Tes7 ( C) (384 h) Tes8 ( C) (392 h) Tes9 ( C) (400 h) Tes10( C) (408 h) Tes11 ( C) (416 h) Tes12 ( C) (424 h) Means Tes ( C) ± ± a ± ± ± ± ± a ± ± ± a ± a ± ± ± ± a ± ± ± ± ± a ± ± ± b ± a ± ± ± ± a ± ± ± ± ± a ± ± ± a ± b ± ± ± ± a ± ± ± ± ± a ± ± ± b ± a ± ± ± ± a ± ± ± ± ± a ± ± ± a ± a ± ± ± ± b ± ± ± ± ± b ± ± ± a ± a ± ±0.07 P< NS NS 0.05 NS NS NS NS 0.01 NS NS NS Temp. Tes1 ( C) Tes2 ( C) Tes3 ( C) Tes4 ( C) Tes5 ( C) Tes6 ( C) Tes7 ( C) Tes8 ( C) Tes9 ( C) Tes10( C) Tes11 ( C) Tes12 ( C) Tes ( C) b ± c ± ± b ± c ± c ± ± ± b ± ± ± ± c ± a ± b ± ± a ± b ± b ± ± ± a ± ± ± ± b ± a ± a ± ± a ± a ± a ± ± ± a ± ± ± ± a ±0.04 P< NS NS NS 0.05 NS NS NS ± b ± ± a ± b ± b ± b ± ± ± a ± ± ± b ± ± a ± ± b ± a ± a ± a ± ± ± b ± ± ± a ±0.1 P< NS 0.05 NS NS NS 0.01 NS NS 1; Dry-bulb temperature from 14 days of incubation to the end of 15 days of incubation. NS: Not Significant

4 Yıldırım et al.: Responses of embryos to different cabinet temperatures at the plateau stage of incubation 43 Table 2. Effects of different temperature levels and age groups on hatchability, late embryo mortality and dead in tray (expressed as percentage of fertile eggs set) at the plateau stage of incubation in Japanese Quail (Coturnix coturnix japonica) ( x ± SEM) Einfluss von Bruttemperatur und Hennenalter auf Schlupfrate, späte Embryonalsterblichkeit und tote Küken beim Schlupf (in Prozent der eingelegten Eier) während der Plateauphase der Brut bei der japanischen Wachtel (Coturnix coturnix japonica) ( x ± SEM) Temperature 1 C (months) Hatchability of fertile eggs Late deaths Prenatal Perinatal Dead in Tray (at hatch) Interactions a (129) ± a (9) ± (2) ± (10) ± a (142) ± a (6) ± (5) ± (8) ± a (121) ± a (7) ± (2) ± (11) ± a (131) ± a (3) ± (8) ± (10) ± a (151) ± b (1) ± (2) ± (8) ± b (134) ± a (8) ± (8) ± (5) ± 1.5 Main effects * * NS NS Temperature ± ± ± ± ± ± ± ± ± ± ± ± 0.9 (Month) NS NS NS NS ± ± a ± ± ± ± b ± ± 0.6 NS NS * NS *; a.b; Means within each main effect within each age treatment groups differ significantly (P < 0.05); The actual numbers of chicks and dead embryos are shown in parentheses. 1; Dry-bulb temperature from 14 days of incubation to the end of 15 days of incubation. NS: Not Significant RIM and YETISIR (unpublished data), who stated that the temperature of IC for last five days of incubation might be increased to 38.3 C for broiler eggs. The current study shows that the IC temperature of 38.4 C was not detrimental to hatchability of YF eggs. The temperature tolerance of eggs varies depending on their parent ages. The high level of mortality at prenatal stage of incubation in the OF group might be a reason for decreased hatchability in the group at 38.4 C IC temperature. TAZAWA et al. (2001) stated that in birds during incubation thermoregulatory capacity is not provided yet or is very feeble, if any. It was assumed that embryos from YF were prepared better than that of OF to pass this paradox stage in present study. WINELAND (1996) stated that in the third week of incubation the needs of embryo are greatest and yolk is a primary nutrient source. FLETCHER et al. (1981) stated that hen age may influence the proportion of yolk, albumen and shell present in eggs of chickens. Unfortunately, the egg component weights were not taken in present study. Further studies should take it into account for precise justifications. The percentage of perinatal dead embryos was significantly increased for the OF eggs as compared to that of YF. The findings are supported by the findings of CHRIS- TENSEN et al. (1996) who stated that as the hen aged the embryonic survival rates declined. On the other hand, the data from current study do not agree with BRUZAL et al. (2000), who stated no changes in the number of late dead embryos as hen age increased in broiler chicks. The difference between studies might be related to late mortality in OF possibly due to parent age and strain differences. Embryonic Growth The selected supply organ weights did not reveal any significant difference. The findings from present study don t support that of CHRISTENSEN et al. (1996), who stated that both liver and heart weights were greatest in embryos from eggs produced by hens of the youngest age compared to those from hens of the oldest age. The possible reason for the difference between studies might be due to the egg weights or to the effects of experimental temperatures chosen, or to the combination of both. At 37.4 C IC temperature the YSwY was greater in chicks from eggs produced by hens of the OF group than those from hens of the YF group (P<0.10). But, the weight of YSwY reflected just the opposite trend at 38.4 C IC temperature, and it was heavier in chicks produced by YF than by OF parents. The lower weight of YSwY in OF group at 38.4 C IC temperature than of YF group is a contradiction. This paradox might possibly be due to hatch of time. SHANAWANY (1984) stated that eggs from older birds hatch earlier than those from younger birds. And, it is well known that the high incubation temperature would accelerate the hatch of time of embryos (WILSON 1991). This might imply that chicks produced by old flock would stay longer in incubator than that of YF. And possibly, the consumption of residual yolk material in yolk sac would be faster than for YF. STIKELEATHER and BRAKE (1990) stated that the time of hatch is important, because chick held in incubator trays for 14 to 32 h post hatch weighed 5 to 12 % less than chicks removed promptly. The study suggests that the response of quail embryos to the IC temperature at the plateau stage of incubation varies when viewed at different ages. The data may suggest that different temperature levels may be required at the plateau stage of incubation with eggs of each age for the optimization of hatching results. Many physiological events are integrated during hatching (RAHN 1981) and synchronization of these events may be more important than any isolated mechanism. The use of different hatcher temperatures for old and young parent hatching eggs at

5 44 Yıldırım et al.: Responses of embryos to different cabinet temperatures at the plateau stage of incubation Table 3. Effects of different temperature levels and age groups on organ wet mass (expressed as percentage of chick weight) at the plateau stage of incubation in Japanese Quail (Coturnix japonica) (n=5; x ± SEM) Einfluss von Bruttemperatur und Hennenalter auf die Organfrischsubstanz (in Prozent des Kükengewichts) während der Plateauphase der Brut bei der japanischen Wachtel (Coturnix coturnix japonica) (n=5; x ± SEM) Temp. 1 C (months) Mean egg weights (g) Chick Wt (g) Heart Wt Liver Wt Yolk Sac Wt Interactions ± ± ± ± a ± ± ± ± ± a ± ± ± ± ± b ± ± ± ± ± a ± ± ± ± ± a ± ± ± ± ± b ± 0.12 Main effects NS NS NS NS * Temp. Mean egg weights Chick Wt (g) Heart Wt Liver Wt Yolk Sac Wt (g) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.25 Main effects NS NS NS NS NS (Month) Mean egg weights Chick Wt (g) Heart Wt Liver Wt Yolk Sac Wt (g) ± ± ± ± ± ± ± ± ± ± 0.14 NS NS NS NS *; a,b; Means within each main effect within each age treatment groups differ significantly (P < 0.10); The mean for each main effect represents 4 replicate trays. 1; Dry-bulb temperature from 14 days of incubation to the end of 15 days of incubation. NS: Not Significant the plateau stage of incubation may alter the sequence of physiological events that affect embryonic survival. Summary The quail eggs produced by young and old flock hens (2 and 8 months old) were incubated at three different hatchers for two days at the plateau stage of incubation. The hatcher temperatures were adjusted to 36.4 C (Low-L), 37.4 C (Control-CON) and 38.4 C (High-H), respectively. Mean eggshell temperatures have shown different trends among groups, both for temperature and age main effects (P < 0.01). A significant interaction occurred between IC temperature and flock age at 38.4 C (P < 0.05) for the percentage of chicks hatched. At prenatal stage, a significant interaction effect was detected between groups at 38.4 C (P < 0.05). A significant interaction occurred between temperature and age group for yolk sac weight both at 37.4 and 38.4 C IC temperatures (P < 0.10). The study suggests that the response of quail embryos to the IC temperature at the plateau stage of incubation varies when viewed at different ages. The information may suggest that different temperature levels may be required at the plateau stage of incubation with eggs of each age for the optimization of hatching results. The application of 36.4 and 37.4 C IC temperatures at plateau stage of incubation seems to be more convenient for both of age groups than 38.4 C IC temperature. Although, the plateau stage is around between days of incubation in quails, the plateau stage should be reinvestigated depending on the age of parent. It might be recommended that the old and young parent eggs should be set at different temperature levels for plateau stage of incubation. Particularly, temperature increases should not be allowed for eggs of old parent hens at the plateau stage of incubation. Key words Incubation, temperature, plateau stage, Quail Zusammenfassung Reaktion von Embryonen junger und alter Eltern auf unterschiedliche Temperaturen in der Plateauphase der Brut bei japanischen Wachteln (Coturnix coturnix japonica) Die Eier von jungen und alten Wachtelhennen (2 und 8 Monate) wurden während der Plateauphase der Brut für zwei Tage in drei verschiedenen Brutapparaten bebrütet. Die Bruttemperaturen wurden auf 36,4 C (Low = L), 37,4 C (Control = Con) und 38,4 C (High = H) eingestellt. Die mittleren Temperaturen auf der Eischale wurden sowohl durch die Bruttemperaturen als auch durch das Alter der Hennen beeinflusst (p < 0,01). Für folgende Merkmale wurden signifikante Interaktionen ermittelt: für die Schlupfrate zwischen der Bruttemperatur von 38,4 C und dem Herdenalter (P < 0,05), vor dem Schlupf bei einer Bruttemperatur von 38,4 C zwischen den Altersgruppen

6 Yıldırım et al.: Responses of embryos to different cabinet temperatures at the plateau stage of incubation 45 (P < 0,05) und für das Dottersackgewicht zwischen der Bruttemperatur (37,4 und 38,4 C) und der Altersgruppe (P < 0,10). Die Ergebnisse der Untersuchung deuten darauf hin, dass die Wachtelembryonen in Abhängigkeit vom Alter der Hennen unterschiedlich auf die Bruttemperaturen während der Plateauphase reagieren. Hieraus kann der Schluss gezogen werden, dass in Abhängigkeit vom Alter der Hennen unterschiedliche Bruttemperaturen zur Optimierung des Schlupferfolges verwendet werden sollten. Die Verwendung von 36,4 oder 37,4 C liefert bessere Ergebnisse als eine Temperatur von 38,4 C. Obwohl allgemein davon ausgegangen wird, dass die Plateauphase in der Wachtelbrut zwischen dem 14. und 15. Bruttag liegt, sollte dieser Brutabschnitt noch einmal eingehender unter Berücksichtigung des Alters der Hennen untersucht werden. Generell kann aber empfohlen werden, dass die Eier junger und alter Wachtelhennen bei unterschiedlichen Temperaturen in der Plateauphase bebrütet werden sollten. Insbesondere sollte aber eine Temperaturerhöhung bei den Eiern älterer Wachteln vermieden werden. Stichworte Japanische Wachtel, Brut, Bruttemperatur, Plateau References BRUZAL, J.J., S.D. PEAK, J. BRAKE and E.D. PEEBLES 2000: Effects of relative humidity during incubation on hatchability and body weight of broiler chicks from young breeder flocks. Poultry Sci. 79: CHRISTENSEN, V. L., W.E. DONALDSON and J.P. MCMURTRY 1996: Physiological differences in late embryos from Turkey breeders at different ages. Poultry Sci. 75: DIETZ, M.W., M.P. KAMPEN, J.M.M. GRIENSVEN and S. MOURIK 1998: Daily energy budgets of avian embryos: the paradox of the plateau phase in egg metabolic rate. Physiological Zoology 71(2): FLETCHER, D., W. BRITTON, A. RAHN and S. SAVAGE 1981: The influenceof layer flockage on egg component yields and solid contents. Poultry Sci. 60: FRENCH, N.A. 1997: Modeling incubation temperature: The effects of incubator design, embryonic development, and egg size. Poultry Sci. 76: HOLLAND, S., J. HÖCHEL, A. BURMEISTER, O. JANKE and M. NICH- ELMANN 1998: A method for measuring deep body temperature in avian embryos. J.Therm. Biol. 23 (2): LOWE, P.C. and V.A. GARWOOD 1977: Chick embryo development rate in response to light stimulus. Poultry Sci. 56: MEIJERHOF, R. 1999: Embryo temperature is the key factor in incubation. World Poultry- Elsevier 15: MINITAB 1998: Minitab for Windows. Minitab inc., USA NATIONAL RESEARCH COUNCIL 1994: Nutrient requirements of poultry, 9 th Edn, pp (Washington DC., National Academy Press) RAHN, H. 1981: Gas exchange of avian eggs with special reference to turkey eggs. Poultry Sci. 60: ROMANOFF, A.L. 1960: The Avian Embryo. New York: Macmillan. ROMIJN, C. and W. LOKHOEST 1955: Chemical heat regulation in the chick embryo. Poultry Sci. 34: SHANAWANY, M. 1984: Interrelationship between egg weight, parental age and embryonic development. Br. Poultry Sci. 25: STIKELEATHER, G. S. and J. BRAKE 1990: Effect of incubation dry-bulb and wet bulb temperatures on time of hatch and chick weight at hatch. Poultry Sci. 69: TAZAWA, H., K. MORIYA, A. TAMURA, T. KOMORO and R. AKIYAMA 2001: Ontogenetic study of thermoregulation in birds. J. therm. Biol. 26: TULLET, S.G. 1990: Science and art of incubation. Poultry Sci. 69: TULLET, S.G. and F.G. BURTON 1982: Factors affecting the weight and water status of the chick at hatch. Br. Poultry Sci. 23: YETIŞIR, R. and İ. YILDIRIM 1998: Data Base Applications in Hatching, Technical Knowledge, Hatching Abnormalities, Record Keeping and Evaluations. 2. National Symposium on Computer Science in Agriculture YILDIRIM, İ. and R. YETIŞIR 1996: Effects of Hatching Egg Weight and Parental on the Hatching Weight and 6 th Week Live weight in Japanese Quail (Coturnix coturnix japonica). Tr.J. of Veterinary and Animal Sciences 22(4): WEYTJENS, S., R. MEIJERHOF, J. BUYSE and E. DECUYPERE 1999: Thermoregulation in chicks origanating from breeder flocks of two different ages. J.Appl. Poultry Res. 8: WILSON, H.R. 1991: Physiological requirements of the developing embryo: temperature and turning. Avian Incubation. Tullet,S.G., (ed.), pp Butterworth- Heinemann Ltd. WINELAND, M.J. 1996: Factors influencing embryo respiration. Poultry Digest, September; pp: Correspondence: Dr. I. Yildirim, Selcuk Üniversitesi, Ziraat Fakültesi, Kampus, Konya, Turkey; iyildir@selcuk.edu.tr