Third Of Incubation Research Articles

Efficiency of Thermoregulatory Control Elements in Precocial Poultry Embryos

Toexplainallaspectsof theefficiencyof thethermoregulatorysysteminpoultryembryos,theactivityandthedynamicsofdifferent control elements have to be investigated systematically during the prenatal period.The relevant methodology and results, citedinthispaperaremainly fromourowngroupbutarecomparedwithrelatedexperimentsdescribedinthescientificliterature. They may be summarised: Thermoregulatory behaviour is developed early in poultry embryos. Temperature of allantoic fluid (Taf) represents the internal body temperature in the last third of incubation because Taf and Tc are much the same at normal (37.5C) and low incubation temperatures (34.5C) after internal pipping. Fowl embryos show endothermic reactions from day14 and Muscovy duck embryos from day 22. In precocial avian embryos, body core temperature increases in accordance with heat production. In contrast to heat production the efficiency of heat loss is high in precocial avian embryos. Development of physiologicalcontrol systems starts withnon-co-ordinatedandproximate (immediate) non-adaptive reactions. In summary, endothermic reactions occur very early during embryonic development but their efficiency is limited. Due to the van’t Hoff rule, low temperatures decrease the net heat production but the trajectories of endothermy are stimulated and related epigenetic adaptation mechanisms are activated. Using behavioural mechanisms the embryo is protected against super-cooling during the natural incubation process. The heat loss mechanisms are most efficient against heat stress, which may occur for only very short time during incubation, protect the embryo against disturbances caused by hyperthermia.

Chronic hypoxia alters the physiological and morphological trajectories of developing chicken embryos

Chicken embryos were chronically exposed to hypoxia ( P O 2 ∼110 mmHg) during development, and assessed for detrimental metabolic and morphological effects. Eggs were incubated in one of four groups: control (i.e. 151 mmHg), or treated with continuous 110 mmHg (15% O 2) during days 1–6 (H1–6), 6–12 (H6–12), or 12–18 (H12–18) with normoxia during the remaining incubation. Metabolism ( V O 2 ), body mass, hemoglobin (Hb) and hematocrit (Hct) were measured in embryos on days 12 and 18 of incubation and in day-old hatchlings. Ability to maintain V O 2 was acutely measured during a step-wise decrease in P O 2 from normoxia to hypoxia (55 mmHg). On day 12, V O 2 of H1–6 eggs were significantly lower than in the control and H6–12 eggs. P crit in H6–12 eggs was lower than in control and H1–6 eggs. Body mass of H1–6 and H6–12 embryos on day 12 was significantly lower than in control embryos, while in H6–12 embryos, Hct and Hb were higher. On day 18, H6–12 embryos had significantly lower V O 2 than control eggs. Body mass of H6–12 and H12–18 embryos was significantly lower than control embryos. Hct and Hb did not differ between treatments. In hatchlings, mass, Hb and Hct had returned to values statistically identical to controls. However, H6–12 embryos had significantly lower V O 2 . Long-term hypoxia altered V O 2 when hypoxic incubation occurred during the middle third of incubation, but not during earlier or later incubation. Thus, chronic hypoxic exposure during critical periods in development altered the developmental physiological trajectories and modified the phenotypes of the developing embryos.

Efficiency of thermoregulation in precocial avian species during the prenatal period

Eggs of Muscovy duck and domestic fowl were incubated at 37.5°C and relative air humidity of 70%. After 60 min the influence of lowered (31.5°C, 34.5°C and 28.5°C) T a on heat production (HP) and temperature of the allantoic fluid (T af) as a measure of core temperature was estimated for 3 h. The Q 10 was calculated using the relationships between T af and HP. HP dropped with decreasing T af. The Q 10 crossed the 2.0 threshold mostly between 34°C and 36°C T af in dependence of T a. Precocial birds are endothermic in the last third of incubation but these reactions have only an ultimate but not a proximate influence on efficiency of thermoregulation.

Thermal conditions in nests of loggerhead turtles: further evidence suggesting female skewed sex ratios of hatchling production in the Mediterranean

Temperature was recorded in 23 nests of the loggerhead turtle ( Caretta caretta) and control sites of nest depth at Alagadi (35°33′N, 33°47′E), Northern Cyprus, eastern Mediterranean. Control site sand temperature was found to be highly correlated with mean daily air temperature and mean nest temperature. Mean temperature in nests ranged from 29.5°C to 33.2°C, with mean temperature in the middle third of incubation ranging from 29.3°C to 33.7°C. Hatching success was significantly correlated with incubation temperature, with nests experiencing very high temperatures exhibiting low hatching success. All nests demonstrated regular diel variation in temperature with mean daily fluctuations ranging from 0.3°C to 1.4°C. Increase in temperature above that of the prevailing sand temperature attributed to metabolic heating was clearly demonstrated in 14 of 15 clutches, with the mean level of metabolic heating of all nests being 0.4°C. However, the level of metabolic heating varied markedly throughout the incubation period with levels being significantly higher in the final third of incubation. Incubation duration was found to be significantly correlated to both the mean temperature of nests throughout the incubation period and during the middle third of incubation. The relationship between incubation duration and mean incubation temperature was used to estimate mean incubation temperatures at most major nesting sites throughout the Mediterranean from available data on incubation durations, showing that mean incubation temperature is likely to be above 29.0°C at most sites in most seasons.

Growth hormone in neural tissues of the chick embryo.

Growth hormone (GH) gene expression predominantly occurs in the pituitary gland, although it also occurs in many extrapituitary sites, including the brain. The cellular location and ontogeny of neural GH production is, however, largely unknown. This has therefore been determined during chick embryogenesis. In chicks, the brain develops from the neural tube at embryonic day (ED) 3. At this age, the divisions of the brain (the telencephalon, diencephalon, mesencephalon, metencephalon and myelencephalon) have intense GH immunoreactivity (GH-IR) (detected by two polyclonal antibodies and a monoclonal antibody for chicken GH). The otic and optic vesicles were also strongly GH immunoreactive, as were the Vth (semi-lunar), VIIth (facial), VIIIth (acoustic) and IXth (glossopharyngeal) nerve ganglia. This GH-IR was specific for GH and was lost when the antibodies were preabsorbed with recombinant chicken GH. The widespread distribution of GH-IR in the neural tissues of ED 3 embryos was mirrored by the distribution of GH receptor (GHR) immunoreactivity, detected by an antibody raised against the chicken GHR. In ED 6/ED 7 embryos, the neural retina of the eye and the epithelial and lens fiber cells were intensely stained for GH-IR, as was Rathke's pouch and the wall of the diencephalon. In contrast, only a few scattered cells were immunoreactive in the surrounding mesoderm. At ED 14, the GH-IR in the brain was restricted to specific tissues and cells. For instance, immunoreactive cells were present in the molecular and pyramidal layers of the cerebral cortex, in the gray matter of the cerebellum, in the choroid plexus, and in the walls of the ventricles. In summary, GH- and GHR-like proteins are abundant in neural tissues of the chick during the first third of incubation, becoming discretely localized to specific tissues and cells during later incubation. The localization of GH and GHR in these tissues, prior to the ontogeny of plasma GH, suggests autocrine or paracrine roles for GH during early embryogenesis.

Metabolic heating and the prediction of sex ratios for green turtles (Chelonia mydas).

We compared incubation temperatures in nests (n=32) of the green turtle (Chelonia mydas) on Ascension Island in relation to sand temperatures of control sites at nest depth. Intrabeach thermal variation was low, whereas interbeach thermal variation was high in both control and nest sites. A marked rise in temperature was recorded in nests from 30% to 40% of the way through the incubation period and attributed to metabolic heating. Over the entire incubation period, metabolic heating accounted for a mean rise in temperature of between 0.07 degrees and 2.86 degrees C within nests. During the middle third of incubation, when sex is thought to be determined, this rise in temperature ranged between 0.07 degrees and 2.61 degrees C. Metabolic heating was related to both the number of eggs laid and the total number of hatchlings/embryos produced in a clutch. For 32 clutches in which temperature was recorded, we estimate that metabolic heating accounted for a rise of up to 30% in the proportion of females produced within different clutches. Previous studies have dismissed any effect of metabolic heating on the sex ratio of marine turtle hatchlings. Our results imply that metabolic heating needs to be considered when estimating green turtle hatchling sex ratios.

Temperature variation within and between nests of the green sea turtle, Chelonia mydas (Chelonia: Cheloniidae) on Heron Island, Great Barrier Reef

Four temperature data-loggers were placed in each of five green sea turtle nests on Heron Island in the 1998–99 nesting season. Temperatures in all nests increased as incubation progressed due to general sand heating and increased metabolic heat production of the developing embryos. Even at the top of nests no daily diurnal fluctuation in temperature was evident. The temperature of eggs in the middle of the nest increased above those in the nest periphery during the last third of incubation. However, this metabolic nest heating would have little effect on hatchling sex ratio because it occurred after the sex-determining period. Small differences in temperature between regions of a nest persisted throughout incubation and may be important in ensuring the production of at least some individuals of the opposite sex in nests that have temperatures close to either the all-male or all-female determining temperatures. Location and degree of shading of nests had little effect on mean nest temperature, but deeper nests were generally cooler and therefore were predicted to produce a higher proportion of males than were shallower nests. Nest temperature profile data indicated that the 1998–99 nesting season on Heron Island would have produced a strongly female-biased sex ratio amongst hatchlings.

The ontogenesis of reproductive hormones in the female embryo of the domestic fowl

The ontogenesis of sexual hormones and the responsiveness of both ovaries to LH were studied during the last third of incubation of chick embryos. Pituitary LH and FSH and serum 17β-estradiol increase through development to reach a plateau near hatching. Serum LH and the ovarian progesterone content show maxima on Day 19 of incubation. Serum progesterone levels are highly variable, with apparently unchanged values during development. Ovine LH was able to stimulate progesterone secretion in vitro in the left ovary at all times during development. LH stimulation of 17β-estradiol secretion in vitro is high on Day 13 in both ovaries but lower at later stages.

Immunoreactive neuropeptide systems in avian embryos (domestic mallard, domestic fowl, Japanese quail).

In embryos of the domestic mallard, domestic fowl, and Japanese quail vasotocin-, mesotocin-, luliberin (LHRH)-, met-enkephalin-, corticotropin-, and somatostatin-immunoreactive perikarya and fiber formations were visualized at different incubation stages by means of the PAP technique (Sternberger 1979). The most striking results were: (1) Vasotocin-, mesotocin-, and luliberin-immunoreactive systems display, up to the late embryonic period, morphological features most probably related to a neurohormonal function. (2) Met-enkephalin immunoreactivity appears very late during embryonic life; it is restricted to fiber networks and not found in perikarya. (3) Corticotropin immunoreactivity is observed in the tuberal region temporarily at the end of the second and the beginning of the last third of the incubation period. (4) Somatostatin-immunoreactive material is present (i) at the end of the first third of incubation, in association with the olfactory system; (ii) during the same period, adjacent to thin-layered portions of the roof of the brain; (iii) shortly thereafter, in cells of both pancreatic primordia and thyroid gland; and (iv) onward from the middle of the incubation period, in a mesencephalic cell group. The striking difference, in the early embryo, between the mature somatostatin plays a role in the development of the brain, as well as the pancreas, and the thyroid gland.