Avian embryonic thermoregulation: role of Q10 in interpretation of endothermic reactions

Glucose Supplementation Improves Performance and Alters Glucose Transporters' Expression in Pectoralis major of Heat-Stressed Chickens

Glucose level in birds' tissue decreases due to heat stress (HS)-induced reduction in feed intake (FI); impairing metabolism and growth. The effect of glucose supplementation on the performance of broiler chickens was evaluated under thermoneutral (TN) and HS conditions. Glucose was supplemented at 0 and 6% under TN-(25 °C) and HS-(25 °C-35 °C-25 °C) conditions. The treatments were TN + 0%-glucose (TN0); TN + 6%-glucose (TN6), HS + 0%-glucose (HS0) and HS + 6%-glucose (HS6). There were 6 replicates (19 birds each)/treatment. Heat and glucose supplementation were applied from d28-35. At d35, Pectoralis (P.) major was sampled from one bird/replicate to determine glucose transporters' mRNA expression. Heat application lowered (p < 0.05) FI, body weight gain, and increased feed and water conversion ratios. Glucose supplementation increased total energy intake by 4.9 and 3.2% in TN and HS groups, respectively but reduced FI under TN and HS conditions. The P. major- and drumstick-yield reduced (p < 0.05) in HS0 compared to TN0, TN6 and HS6. Under HS, glucose supplementation improved eviscerated carcass weight by 9% and P. major yield by 14%. Glucose supplementation increased SGLT1 expression with/without heat treatment while HS independently increased the expression of GLUT 1, 5 and 10. Glucose supplementation under HS could improve performance of broilers.

Facultative hypothermia as a survival strategy during snowstorm induced food shortages in Antarctic storm-petrel chicks

Wilson's storm-petrels (Oceanites oceanicus) are the smallest marine birds breeding in Antarctica, where events like snowstorms often prevent parents from providing food daily for their offspring. To minimize energy expenses, Wilson's storm-petrel chicks can reduce their metabolism and body temperature by entering hypothermia. Hypothermia is reported to impact development, hence we hypothesized that hypothermia will be majorly used after long fasting periods. Chick development in a breeding colony of Wilson's storm-petrels on the South Shetland Islands was monitored daily during three consecutive summers by recording chicks' body mass and temperature, as well as environmental parameters. Provisioning, and body conditions were highest in 2017, and chicks became hypothermic most frequently in 2016. Body temperature was influenced by age, mass, body condition, and minimal nocturnal temperatures. While most chicks were able to maintain stable body temperatures when not fed for one day, some chicks' body temperatures decreased by up to 21 °C. Age did not differ between those two groups, but chicks maintaining their active body temperatures had higher body conditions. Snowstorms were typically followed by several days of unreliable food provisioning and continuous days of fasting. Most chicks were hypothermic during this time, and were hence able to survive periods of food shortages, reverse their low body temperatures after the next feeding event, and regain body mass. We conclude that hypothermia is a strong survival strategy to endure times of fasting, which might be necessary for Antarctic storm-petrel chicks to reach adulthood. However, in future scenarios, which may include more frequent snowstorms due to climate change, malnourishment could lead to more frequent use of hypothermia, which could affect chicks' development.

Aerobic scope in chicken embryos

We investigated the aerobic scope of chicken embryos, that is, the margin of increase of oxygen consumption ( [Formula: see text] ) above its normal value. [Formula: see text] was measured by an open-flow methodology at embryonic ages E3, E7, E11, E15, E19 and at E20 at the internal (IP) and external pipping (EP) phases, at the normal incubation temperature (Ta=38°C), in hypothermia (Ta=30°C) and in hyperthermia (Ta=41 and 44°C). In the cold, Q₁₀ averaged ~2 at all ages, except in IP and EP when lower values (~1.5) indicated some degree of thermogenesis. In hyperthermia (38-44°C) Q₁₀ was between 1 and 1.4. Hyperthermia had no significant effects on [Formula: see text] whether the results combined all ages or considered individual age groups, except in IP (in which [Formula: see text] increased 8% with 44°C) and EP embryos (+13%). After opening the air cell, which exposed the embryo to a higher O₂ pressure, hyperthermic [Formula: see text] was significantly higher than in normothermia in E19 (+13%), IP (+22%) and EP embryos (+22%). We conclude that in chicken embryos throughout most of incubation neither heat nor oxygen availability limits the normal (normoxic-normothermic) values of [Formula: see text] . Only close to hatching O₂-diffusion represents a limiting factor to the embryo's [Formula: see text] . Hence, embryos differ from postnatal animals for a nearly absent aerobic scope, presumably because their major sources of energy expenditure (growth and tissue maintenance) are constantly maximized.

An insight into the heat and mass transfer mechanisms of eggshells hatching broiler chicks and its effects to the hatcher environment

Thermodynamic study of incubated eggs is an important component in the optimisation of incubation processes. However, research on the interaction of heat and moisture transfer mechanisms in eggs is rather limited and does not focus on the hatching stage of incubation. During hatch, both the recently hatched chick and the broken eggshell add extra heat and moisture contents to the hatcher environment. In this study, we have proposed a novel way to estimate thermodynamically the amount of water evaporated from a broken eggshell during hatch. The hypothesis of this study considers that previously reported drops in eggshell temperature during hatching of chicks is the result remaining water content evaporating from the eggshell, released on the inner membrane by the recently hatched wet chick, just before hatch. To reproduce this process, water was sprayed on eggshells to mimic the water-fluid from the wet body of a chick. For each sample of eggshell, the shell geometry and weight, surface area and eggshell temperature were measured. Water evaporation losses and convection coefficient were calculated using a novel model approach considering the simultaneous heat and mass transfer profiles in an eggshell. The calculated average convective coefficient was 23.9 ± 7.5 W/m(2) °C, similar to previously reported coefficients in literature as a function of 0.5-1m/s air speed range. Comparison between measured and calculated values for the water evaporation showed 68% probability accuracy, associated to the use of an experimentally derived single heat transfer coefficient. The results support our proposed modelling approach of heat and mass transfer mechanisms. Furthermore, by estimating the amount of evaporated water in an eggshell post-hatch, air humidity levels inside the hatcher can be optimised to ensure wet chicks dry properly while not dehydrating early hatching chicks.

Impact of environmental thermal stimulation on activation of hypothalamic neuronal nitric oxide synthase during the prenatal ontogenesis in Muscovy ducks

The aim of the study is to investigate the influence of prenatal temperature stimulation on neuronal NO synthase (nNOS) expression in the anterior hypothalamus of Muscovy duck embryos. Experiments were performed on embryonic day (E) E20, E23, E28, and E33 using histochemistry for identification of the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) as marker of NOS-containing neurons. Until the experiments, all duck embryos were incubated under standard temperature conditions (37.5°C). During 3 hours before the start of the experiments, one group was incubated at 37.5°C (control group), the second was warm-experienced at 39°C, and the third was cold-experienced at 34°C. In normal and warm-incubated duck embryos, nNOS activity could be first detected on E23. Particularly, after cold stimulation, a significant increase in nNOS activity was found in all embryos investigated even on day 20. Warm stimulation obviously induces the opposite effect, but at later embryonic age (E33). It can be concluded that probably in late-term bird embryos NO acts as a mediator of the neuronal cold pathway in the anterior hypothalamus, which might be improved by prenatal cold stimulation.

Thermal manipulations of broiler embryos--the effect on thermoregulation and development during embryogenesis

This study aimed to elucidate the effects of thermal manipulations (TM) of broiler embryos, during the development of the thyroid and adrenal axis, on embryo development and metabolism. Cobb eggs were divided into 3 treatments: control, 24H-continuous TM at 39.5 degrees C and 65% RH from embryonic day 7 to 16 inclusive, and 12H-intermittent TM for 12 h/d in the same period. Only the 24H treatment negatively affected embryo growth and development, with lower relative weights of embryo, liver, and pipping muscle. During TM, eggshell temperature, heart rate, and oxygen consumption were elevated as embryos were in their ectothermic phase, but from the end of the TM until hatch, these parameters were significantly lower in both treatments than in the control. Moreover, plasma concentrations of the thyroid hormones were significantly lower in the 2 treatments during and after TM, until hatch. Plasma corticosterone concentration of the TM-treated embryos was significantly lower after the TM but significantly higher at hatch. It was concluded that TM during the development of the thyroid and adrenal axis lowered their functional set point, thus lowering metabolic rate during embryogenesis and at hatch.

Attainment of thermoregulation as affected by environmental factors

The review addresses the development of thermoregulation in poultry embryos as well as the effect of acute and chronic changes of environmental factors on this process and the incubation temperature being the foremost. In poultry, the early development of adaptive body functions, like the thermoregulatory system, is characterized by the following peculiarities. First, the development of peripheral as well as central nervous thermoregulatory mechanisms start during the prenatal ontogeny. However, their maturity is attained during early postnatal development. In the perinatal period, environmental factors have a high effect on development of temperature regulation. Second, acute changes in the environmental conditions induce as a rule first uncoordinated and immediately nonadaptive reactions. Later, the uncoordinated nonadaptive reactions change into coordinated (adaptive) reactions. Prenatal environmental influences may have a training effect on the postnatal efficiency of the thermo-regulatory system. Third, functional systems of the organism develop from an open loop system without feedback control into a closed system controlled by a feedback mechanism. During this critical period, the actual environment modulates the development of the respective physiological control systems for the entire life period, especially by changes in neuroorganization and expression of related effector genes. Knowledge on these mechanisms might be specifically used to generate long-term adaptation of the organism to the postnatal climatic conditions (perinatal epigenetic temperature adaptation). In poultry, perinatal epigenetic temperature adaptation was developed by changes in the incubation temperature. When a comparison is made in birds, which were incubated at 37.5 degrees C, a low incubation temperature induced postnatal cold adaptation, and warm incubation temperature induced postnatal heat adaptation. Perinatal epigenetic temperature adaptation exhibited changes in the neuronal thermosensitivity in the hypothalamus as well as in the peripheral thermoregulatory mechanisms. These alterations could be already found at the end of incubation. Further, temperature-experienced embryos have a lower c-fos expression than in the control after acute heat stress.

Ontogeny of vocalizations and movements in response to cooling in chickens fetuses

Bird incubation demands a balance between parental needs for foraging with fetal needs for heat provision and protection so that any means of communication between the fetus and the parents would have an adaptive value. The aim of the study was to investigate whether putative avenues of feto-maternal communication would correlate to physiological changes caused by environmental alterations. Oxygen consumption was used as an indicator of fetal well being. The frequency, duration, intensity and composition of fetal vocalizations and the frequency and intensity of movements were used to evaluate the potential for communicating fetal status quo. Fetuses of broiler chickens (Gallus gallus domesticus) at three developmental stages (day 18, internally pipped and externally pipped) were challenged by a stepwise reduction in ambient temperature down to 30 degrees C. A drop in oxygen consumption in response to lowered temperatures was found in all stages. No differences correlating with temperature variations were found in any of the variables associated with fetal vocalization, even if externally pipped fetuses vocalized more than internally pipped fetuses. Movement occurrence and movement intensity, however, increased initially and decreased at temperatures below 35.0-35.5 degrees C. Considering that the lower limit of optimal development is between 35 and 36 degrees C, the results suggest that fetal movements can be of potential use to the incubating parent to assess and protect the well-being of the fetus.

Metabolic responses of chick embryos to short-term temperature fluctuations

Two experiments were carried out to study embryonic metabolic responses to short-term temperature fluctuations in order to explore the possibilities of using embryonic metabolic responses as a tool to control the incubation process. In the first experiment, eggshell temperature (ET) in the control group was kept constant at 37.8 degrees C, and embryos in the experimental group were exposed to varying ET within the range of 36.8 to 38.8 degrees C using ET steps of 0.2 degrees C and time steps of 3 h. This was repeated in 3 periods between 6.5 and 9.5 d, 10.5 and 13.5 d, and 14.5 and 17.5 d. In the studied ET range, heat production (HP) increased linearly at 4.9% per 1 degrees C ET. In the second experiment, a standard machine temperature (MT) was used for the control group, and eggs in the experimental group were exposed to low (MT - 0.3 degrees C) or high (MT + 0.3 degrees C) temperatures for 1 h of time at d 8, 9, and 11 to 16. When MT was decreased, CO2 production initially increased at 0.5% and decreased thereafter. When MT was increased, CO2 production initially decreased at 0.4% and increased thereafter. It was concluded that embryonic HP responded linearly with short-term ET changes in the studied ET range of 36.8 to 38.8 degrees C. Changes in CO2 concentration due to short-term MT changes could not be explained by embryonic HP only. It can be speculated that blood flow through the chorio-allantoic membrane changes with MT, affecting heat transfer and diffusion of CO2. A second, delayed response to MT changes was in accordance with the findings in Experiment 1. Within the studied temperature range it will be difficult to use embryonic metabolic responses as a tool to control the incubation process. Because HP is linearly related to ET as in the studied temperature range, other factors such as O2 availability or CO2 release may limit embryo development at higher ET. At this moment, research on the effects of gas exchange at different temperatures on embryo development and survival is lacking.

Effect of egg size on heat production and the transition of energy from egg to hatchling

An experiment was conducted to study the effect of egg size on embryo development, heat production, and energy partitioning between egg and hatchling. Small (56.1 +/- 0.12 g SEM) and large (70.0 +/- 0.11 g SEM) hatching eggs were incubated in climate respiration chambers, and eggshell temperature was maintained constant at 37.8 degrees C in both egg weight classes by adjusting machine temperature. Dry matter, ash, protein, and fat contents were determined in albumen, yolk, yolk-free body (YFB), and residual yolk (RY), and carbohydrate contents and caloric values were calculated. To achieve a constant eggshell temperature, machine temperature needed to be set lower from d 15 onward, coinciding with increased heat production in large eggs compared with small eggs. Selective nutrient uptake resulted in higher fat content and lower protein content in RY in chicks that hatched from small eggs compared with large eggs. The respiration quotient in small and large eggs was the same, and embryos in small and large eggs were equally efficient in the transfer of energy from egg to YFB. The surplus availability of nutrients in large eggs was therefore held responsible for the absolute and relative higher weight of RY in chicks that hatched from large eggs compared with small eggs.

The Effects of Suboptimal Eggshell Temperature During Incubation on Broiler Chick Quality, Live Performance, and Further Processing Yield

Different incubation conditions can cause eggshell temperature (EST) to deviate from optimum. Two experiments were performed to determine the effect of low EST at the start of incubation and high EST at the end of incubation on hatchability, chick quality, 6-wk live performance, and breast meat yield of broiler chickens. In each experiment, 1,800 eggs from a single flock were divided and set into 2 setters. From 0 to 10 d of incubation, one setter was set to attain an EST of 36.6 degrees C (considered low), whereas the other was set to 37.8 degrees C (the control temperature). Using an infrared thermometer, EST was measured daily on a sample of eggs to ensure treatment intentions. On d 11 of incubation, the temperature of the low EST setter was increased to 37.8 degrees C in synchrony with the other setter until transfer. On d 18 of incubation, eggs from both setters were combined into 2 equal groups and transferred to hatchers. The EST in one hatcher was set to 37.8 degrees C (control) and in the other to 39.5 degrees C (considered high) until 21 d of incubation. Hatched males were placed in battery cages (Experiment 1) or floor pens (Experiment 2) and reared on common feeds to 1 or 6 wk of age, respectively. Low EST in the first 10 d of incubation reduced hatchability, increased BW and chick yield, and reduced 1-wk gain compared with the control EST. Throughout rearing, BW was reduced for low EST chicks compared with control EST chicks; consequently, carcass, fillet, and tender weights were also reduced. High EST in the hatcher increased hatchability, and reduced BW, chick yield, and 1-wk gain compared with control EST in the hatcher. By 3 wk of age, there was no difference in BW between chicks in high EST and control EST treatments. Subsequent carcass and processing yields were also similar. Incubation at the control EST of 37.8 degrees C, particularly from 0 to 10 d, resulted in the best performance overall.

Effect of eggshell temperature during incubation on embryo development, hatchability, and posthatch development

An experiment was conducted to study the effects of different eggshell temperature (EST) profiles during incubation on embryo mortality, hatchability, and embryo development. Furthermore, chicks from different EST profiles were reared under low and high housing temperatures to investigate subsequent posthatch growth and rectal temperature. Two batches of eggs were used in this experiment. Hatching eggs were subjected to 36.7 or 37.8 degrees C EST during the first week, to 37.8 degrees C EST during the second week, and to 37.8 or 38.9 degrees C EST during the third week of incubation. Posthatch housing temperature decreased from 35 degrees C at d 1 to 30 degrees C at d 7 (high) or decreased from 30 degrees C at d 1 to 25 degrees C at d 7 (low). The difference between machine temperature and EST (DT) was used to illustrate the effect of EST on heat production during incubation. DT differed per batch, and was smallest when eggs were incubated at 36.7 degrees C instead of 37.8 degrees C during wk 1. High EST during wk 3 of incubation (38.9 degrees C instead of 37.8 degrees C) reduced DT only in batch 2. Embryo development was most retarded in eggs incubated at 36.7 degrees C EST compared with at 37.8 degrees C during the first week of incubation. However, highest hatchability and embryo development were always found when EST was maintained at 37.8 degrees C constantly throughout incubation. Chicks that hatched from eggs incubated at low EST during wk 1 of incubation had lower rectal temperature after hatching, especially under low housing temperatures, and this effect lasted until 7 d posthatch in batch 1. The highest rectal temperatures were always found in chicks incubated at 37.8 degrees C EST constantly throughout incubation. Eggs and chicks from different batches require different environmental conditions for optimal embryo development, hatchability, and posthatch growth. Rearing temperature and incubation conditions affect the ability of young chicks to maintain their rectal temperature during the first week posthatch.

Metabolic responses of chicken and muscovy duck embryos to high incubation temperatures

Oxygen consumption, heat production (HP) and core temperature (T(af)) were measured over 3 h in 20-34-day-old Muscovy duck and 12-21-day-old chicken embryos at ambient temperature (T(a)) of 37.5 degrees C and thereafter for 3 h at T(a) of 39.0 degrees C. At 37.5 degrees C T(a), HP increased with age in avian embryos of both species, following an exponential function. In muscovy duck embryos, a plateau phase occurred between D29 and D32; in chicken embryos, a similar plateau occurred between D19 and D21. T(af) rose in accordance with HP, and the relationships between T(af) and HP could be described by significant linear regressions in both species. Mostly, HP increased in embryos of both species during heat load, but by less than calculated by the van't Hoff rule; however, there was often also a decrease in HP under these conditions. Obviously, in avian embryos high T(a) causes a down-regulation of HP mediated by active thermoregulatory mechanisms. This is in agreement with data describing the influence of hyperthermia on HP in the postnatal period of birds and mammals. Because of this, the term 'second chemical thermoregulation' defined by Gelineo [C. R. Soc. Biol. (1936) 122 337] for birds and mammals should also be used for avian embryos.

Ontogeny of thermoregulation in precocial birds

The aim of this paper is to summarise the results of earlier experiments on thermoregulation and heat balance in birds, to present new results concerning thermoregulation during the perinatal period in precocial embryos and to develop a model of the ontogeny of thermoregulation over the whole lifespan of birds. The ontogeny of thermoregulation in precocial birds is characterised by three phases with different efficiency of the system. In the prenatal phase, all control elements of the thermoregulatory system can function, but the efficiency of the system is low. It is postulated that endothermic reactions during the prenatal period do not have a proximate (immediate), but rather an ultimate influence on the efficiency of thermoregulation. They may support adaptivity to expected environmental conditions and may be involved in epigenetic adaptation processes. During the early postnatal phase, the thermoregulatory system develops and matures. Summit metabolism and resting metabolic rate and their thermoregulatory set points increase. Preferred temperature is significantly different during different behavioural activities. The phase of full-blown homeothermy starts at approximately the 10th day of life. It is characterised by an activation order of thermoregulatory control elements and by secondary chemical thermoregulation. The influence of thermal and non-thermal climatic factors on heat production and heat loss may be described by mathematical models.

Biological rhythms in birds--development, insights and perspectives

The aim of this review is to show that probably the internal clock of precocial birds is imprinted in the prenatal period by exogenous factors (zeitgeber). The activity of organ functions occurs early during embryonic development, before this function is ultimately necessary to ensure the survival of the embryo. Prenatal activation of some functional systems may have a training effect on the postnatal efficiency. The development of physiological control systems is influenced by endogenous and exogenous factors during the late prenatal and early postnatal period: epigenetic adaptation processes play an important role in the development of animals; they have acquired characteristics which are innated but not genetically fixed. As a rule, the actual value during the determination period has a very strong influence on the set-point of the system. This will be explained using the example of thermoregulation. It is shown in detail that it seems to be possible to imprint the prenatal development of circadian rhythms by periodic changes of the light-dark cycle but not by rhythmic influence of acoustic signals. Altogether, there are more questions open than solved concerning the perinatal genesis of circadian rhythms in birds. Topics are given for the future research.