Thermal treatments prior to and during the beginning of incubation affects development of the broiler embryo and yolk sac membranes, and live performance and carcass characteristics.

This study evaluated temperature during preincubation and embryonic day 0 (E0) E0 to E5 of incubation on broiler embryo development and subsequent live performance. Freshly laid eggs from a single 41-wk-old Ross 708 broiler breeder flock produced on a single day were weighed individually for weight matching purposes, stored overnight, and assigned to 4 treatment combinations of 2 preincubation temperatures (23.9 or 29.4°C) × 2 E0 to E5 temperatures (38.1 or 37.5°C). The 29.4°C preincubation temperature decreased (P ≤ 0.05) yolk sac membrane (YSM) vasculature at E6 and E7, and increased (P ≤ 0.05) embryo weight and length but decreased (P ≤ 0.05) yolk sac weight (YSW) at E15. No subsequent main effects were observed. The 38.1°C incubation temperature increased YSM vasculature at E7, chorioallantoic membrane (CAM) vasculature at E8 and E10, and egg weight loss, embryo weight, and embryo length at E15 and chick length at E21 in the presence of reduced BW and YSW (P ≤ 0.05). This was followed by greater male BW at 35 d, as well as improved FCR in females 0 to 14 d and in males 15 to 35 d (P ≤ 0.05). Pectoralis major and minor yields were increased (P ≤ 0.05) at 50 d of age in males and females, respectively. There were no interactions observed with regards to broiler live performance and carcass yield, which probably negated the importance of the interactions observed for preincubation temperature by E0 to E5 incubation temperature that affected YSM vasculature, CAM vasculature area, egg weight loss, embryo weight, yolk sac weight, and chick length.

Thermal manipulations of turkey embryos: The effect on thermoregulation and development during embryogenesis.

Previous studies conducted on meat-type chickens in our laboratory showed that thermal manipulations (TMS:) of the embryo during the time window of the hypothalamus-hypophysis-thyroid axis development and maturation significantly reduced the metabolic rates of the embryo and the chicken, improving the posthatch feed conversion rate (FCR:). The aim of the present study was to investigate the effect of intermittent TMs during turkey embryogenesis on embryo development. Fertile turkey eggs were divided into three treatments: control; 6H--with TM by elevation of temperature and RH by 1.7°C and 9%, respectively, above the control conditions for 6 h/d, from E10 through E22, i.e., 240 through 552 h of incubation; and 12H--with TM as above, for 12 h/d, during the same time period. From E0 through E10 and from E23 onward all eggs were incubated under control conditions. The embryo growth rate was not negatively affected by TM. During TM eggshell temperature, the embryonic heart rate and oxygen consumption were elevated by the manipulation while the embryos were in their ectothermic phase. However, by the end of the TM period and until hatch (the endothermic phase) these parameters were significantly lower in both TM treatments than in the control, indicating a lower metabolic rate and heat production. The TM embryos hatched approximately 10 h earlier than the controls, without any negative effects on chick body weight or hatchability. Nevertheless, TM treatments resulted in a higher proportion of chicks with unhealed navels. Body temperature at hatch was significantly lower in the TM chicks than in the controls, suggesting lower heat production and metabolic rate, which might affect the energy requirements for posthatch maintenance. It was concluded that TM during turkey embryogenesis might have altered the thermoregulatory set point, and thus lowered the embryo metabolic rate, which might have a long-lasting posthatch effect.

Cyclic variations in incubation conditions induce adaptive responses to later heat exposure in chickens: a review.

Selection programs have enabled broiler chickens to gain muscle mass without similar enlargement of the cardiovascular and respiratory systems that are essential for thermoregulatory efficiency. Meat-type chickens cope with high ambient temperature by reducing feed intake and growth during chronic and moderate heat exposure. In case of acute heat exposure, a dramatic increase in morbidity and mortality can occur. In order to alleviate heat stress in the long term, research has recently focused on early thermal manipulation. Aimed at stimulation of long-term thermotolerance, the thermal manipulation of embryos is a method based on fine tuning of incubation conditions, taking into account the level and duration of increases in temperature and relative humidity during a critical period of embryogenesis. The consequences of thermal manipulation on the performance and meat quality of broiler chickens have been explored to ensure the potential application of this strategy. The physiological basis of the method is the induction of epigenetic and metabolic mechanisms that control body temperature in the long term. Early thermal manipulation can enhance poultry resistance to environmental changes without much effect on growth performance. This review presents the main strategies of early heat exposure and the physiological concepts on which these methods were based. The cellular mechanisms potentially underlying the adaptive response are discussed as well as the potential interest of thermal manipulation of embryos for poultry production.

Chick embryogenesis: a unique platform to study the effects of environmental factors on embryo development.

Bird embryogenesis takes place in a relatively protected environment that can be manipulated especially well in domestic fowl (chickens) where incubation has long been a commercial process. The embryonic developmental process has been shown to begin in the oviduct such that the embryo has attained either the blastodermal and/or gastrulation stage of development at oviposition. Bird embryos can be affected by "maternal effects," and by environmental conditions during the pre-incubation and incubation periods. "Maternal effects" has been described as an evolutionary mechanism that has provided the mother, by hormonal deposition into the yolk, with the potential to proactively influence the development of her progeny by exposing them to her particular hormonal pattern in such a manner as to influence their ability to cope with the expected wide range of environmental conditions that may occur post-hatching. Another important aspect of "maternal effects" is the effect of the maternal nutrient intake on progeny traits. From a commercial broiler chicken production perspective, it has been established that greater cumulative nutrient intake by the hen during her pullet rearing phase prior to photostimulation resulted in faster growing broiler progeny. Generally, maternal effects on progeny, which have both a genetic and an environmental component represented by yolk hormones deposition and embryo nutrient utilization, have an important effect on the development of a wide range of progeny traits. Furthermore, commercial embryo development during pre-incubation storage and incubation, as well as during incubation per se has been shown to largely depend upon temperature, while other environmental factors that include egg position during storage, and the amount of H2O and CO2 lost by the egg and the subsequent effect on albumen pH and height during storage have become important environmental factors to be considered for successful embryogenesis under commercial conditions. Manipulating environmental temperature during the period of egg storage, during the intermediate pre-incubation period, and incubation period per se has been found to significantly affect embryo development, hatching progress, chick quality at hatching, and chick development post-hatching. These temperature manipulations have also been shown to affect the acquisition of thermotolerance to subsequent post-hatching thermal challenge. This chapter will focus on: a. "maternal effects" on embryo and post-hatching development; b. environmental effects during the post-ovipositional period of egg storage, the intermediate pre-incubation period, and incubation period per se on chick embryogenesis and subsequent post-hatching growth and development; and c. effects of temperature manipulations during the pre-incubation and incubation periods on acquisition of thermotolerance and development of secondary sexual characteristics in broiler chickens.

Thermal manipulation of the embryo modifies the physiology and body composition of broiler chickens reared in floor pens without affecting breast meat processing quality.

Selection in broiler chickens has increased muscle mass without similar development of the cardiovascular and respiratory systems, resulting in limited ability to sustain high ambient temperatures. The aim of this study was to determine the long-lasting effects of heat manipulation of the embryo on the physiology, body temperature (Tb), growth rate and meat processing quality of broiler chickens reared in floor pens. Broiler chicken eggs were incubated in control conditions (37.8°C, 56% relative humidity; RH) or exposed to thermal manipulation (TM; 12 h/d, 39.5°C, 65% RH) from d 7 to 16 of embryogenesis. This study was planned in a pedigree design to identify possible heritable characters for further selection of broiler chickens to improve thermotolerance. Thermal manipulation did not affect hatchability but resulted in lower Tb at hatching and until d 28 post-hatch, with associated changes in plasma thyroid hormone concentrations. At d 34, chickens were exposed to a moderate heat challenge (5 h, 32°C). Greater O2 saturation and reduced CO2 partial pressure were observed (P < 0.05) in the venous blood of TM than in that of control chickens, suggesting long-term respiratory adaptation. At slaughter age, TM chickens were 1.4% lighter and exhibited 8% less relative abdominal fat pad than controls. Breast muscle yield was enhanced by TM, especially in females, but without significant change in breast meat characteristics (pH, color, drip loss). Plasma glucose/insulin balance was affected (P < 0.05) by thermal treatments. The heat challenge increased the heterophil/lymphocyte ratio in controls (P < 0.05) but not in TM birds, possibly reflecting a lower stress status in TM chickens. Interestingly, broiler chickens had moderate heritability estimates for the plasma triiodothyronine/thyroxine concentration ratio at d 28 and comb temperature during the heat challenge on d 34 (h(2) > 0.17). In conclusion, TM of the embryo modified the physiology of broilers in the long term as a possible adaptation for heat tolerance, without affecting breast meat quality. This study highlights the value of 2 new heritable characters involved in thermoregulation for further broiler selection.

Thermal manipulations during broiler incubation alter performance of broilers to 70 days of age.

Recent decades have seen significant progress in the genetic selection of fast-growing broiler chickens. Whereas in many countries the average marketing age is 5 to 6 wk, the US, French, and other markets demand heavier broilers (~4 kg) that require a longer posthatching growing period. With greater age and greater BW, the ability to cope with hot weather conditions deteriorates, which can result in increased economic losses during periods of hot weather. Recent studies have demonstrated a long-lasting effect of intermittent thermal manipulation (TM) during embryogenesis, when it was applied for 12 h/d between embryonic (E) days E7 and E16, which was shown by improved thermotolerance during acute posthatching heat stress as well as improved feed conversion ratio (FCR) and breast muscle yield. The present study was designed to elucidate the effect of TM during embryogenesis on Cobb 500 broiler performance up to 70 d of age. Hatchability and male BW were not affected by TM, but TM females demonstrated a lower (P = 0.024) BW during the entire 70-d posthatching study. However, following embryonic TM, both sexes exhibited lower (P = 0.028 and P = 0.018 for males and females, respectively) feed intake and body temperature accompanied by improved FCR and greater breast muscle weight. In light of the present and previous studies, it was concluded that intermittent TM during broiler embryonic development had a long-lasting effect on energy balance that led to improved FCR and breast muscle yield.

Thermal treatments prior to and during the beginning of incubation affect phenotypic characteristics of broiler chickens posthatching.

The significance and importance of the preincubation and incubation temperatures for broiler chickens has been elucidated by altering normal incubation conditions to study the effects on embryo development. Furthermore, only recently has convincing evidence that temperature could influence the sex ratio of avian offspring become available. The objective of this study was to elucidate the effects of temperature before or during (or both) the sex determination period of incubation on hatchability, apparent sex ratio, growth and development posthatching, and secondary sexual phenotypic characteristics. Two experiments were conducted in winter and summer using Cobb 500 fertile eggs that had been stored for 4 and 9 d, respectively. Four treatments of 180 eggs each were applied: control, preheating (Pre) 30.2°C for 12 h before incubation, heating (38.1°C) the embryos between embryonic d 0 (E0) and E5 (M) of incubation, and a combination of both (Pre+M). All 3 thermal treatments increased early embryonic deaths, but improved hatchability in both experiments. The point of 50% hatchability was achieved more rapidly in the treated eggs. The BW of males and females at 35 d of age in both experiments was numerically or significantly greater in the broilers that had been exposed to thermal treatments, which was coincident with a similar trend for increased relative breast muscle weight. Secondary sexual characteristics (comb, wattles, testes in males) were also affected by thermal treatments, being heavier in most cases, which may be attributed to the finding that the 3 thermal treatments resulted in numerically or significantly increased plasma testosterone concentration in both sexes and experiments. Differences in the level of significance between the experiments probably related to the length of storage period and the season in which each experiment took place. It was concluded that thermal treatments preincubation or during the sex determination period of incubation had, in general, a positive effect on hatchability, growth performance, and secondary sexual characteristics of broiler males and females, probably caused by the increase of plasma testosterone concentration in both sexes.

Adaptation to hot climate and strategies to alleviate heat stress in livestock production.

Despite many challenges faced by animal producers, including environmental problems, diseases, economic pressure, and feed availability, it is still predicted that animal production in developing countries will continue to sustain the future growth of the world's meat production. In these areas, livestock performance is generally lower than those obtained in Western Europe and North America. Although many factors can be involved, climatic factors are among the first and crucial limiting factors of the development of animal production in warm regions. In addition, global warming will further accentuate heat stress-related problems. The objective of this paper was to review the effective strategies to alleviate heat stress in the context of tropical livestock production systems. These strategies can be classified into three groups: those increasing feed intake or decreasing metabolic heat production, those enhancing heat-loss capacities, and those involving genetic selection for heat tolerance. Under heat stress, improved production should be possible through modifications of diet composition that either promotes a higher intake or compensates the low feed consumption. In addition, altering feeding management such as a change in feeding time and/or frequency, are efficient tools to avoid excessive heat load and improve survival rate, especially in poultry. Methods to enhance heat exchange between the environment and the animal and those changing the environment to prevent or limit heat stress can be used to improve performance under hot climatic conditions. Although differences in thermal tolerance exist between livestock species (ruminants > monogastrics), there are also large differences between breeds of a species and within each breed. Consequently, the opportunity may exist to improve thermal tolerance of the animals using genetic tools. However, further research is required to quantify the genetic antagonism between adaptation and production traits to evaluate the potential selection response. With the development of molecular biotechnologies, new opportunities are available to characterize gene expression and identify key cellular responses to heat stress. These new tools will enable scientists to improve the accuracy and the efficiency of selection for heat tolerance. Epigenetic regulation of gene expression and thermal imprinting of the genome could also be an efficient method to improve thermal tolerance. Such techniques (e.g. perinatal heat acclimation) are currently being experimented in chicken.

Skin surface temperature of broiler chickens is correlated to body core temperature and is indicative of their thermoregulatory status.

Extreme thermal conditions may dramatically affect the performance of broilers and other domestic animals, thereby impairing animal welfare and causing economic losses. Although body core temperature is the parameter that best reflects a bird's thermal status, practical and physiological obstacles make it irrelevant as a source of information on the thermal status of commercial flocks. Advances in the technology of infrared thermal imaging have enabled highly accurate, noncontact, and noninvasive measurements of skin surface temperature. Providing that skin surface temperature correlates with body temperature, this technology could enable acquisition of reliable information on the thermal status of animals, thereby improving diagnoses of environmental stress in a flock. This study of broiler chickens found a strong positive correlation between body core temperature and facial surface temperature, as recorded by infrared thermal imaging. The correlation was equally strong at all ages from 8 to 36 d during exposure to acute heat stress with or without proper ventilation and after acclimation to chronic heat exposure. A similar correlation was found by measurements in commercial flocks of broilers. Measurements of blood plasma concentrations of corticosterone, thyroid hormones, and arginine vasotocin confirmed that metabolic activity was low after acclimation to chronic exposure to heat, whereas ventilation was at least as efficient as acclimation in reducing thermal stress but did not impair metabolism. In light of these novel results, commercial benefits of infrared thermal imaging technology are suggested, especially in climate control for commercial poultry flocks. The application of this technique to other domestic animals should be investigated in future experiments.

Ventilation plays an important role in hens' egg production at high ambient temperature.

Birds dissipate considerable heat through respiratory-evaporative and cutaneous-evaporative mechanisms and sensible heat loss (SHL) via radiation, convection, and conduction. The significance of SHL in laying hens is still to be confirmed. This study aimed to elucidate the effect of ventilation on egg production and quality during exposure to high ambient temperature. Lohman laying hens were raised outdoors up to age 35 wk, and 300 hens with similar egg production were divided among 5 treatments each comprising 4 replicates of 15 hens. Birds in 4 treatments were kept in computerized controlled-environment rooms acclimated to 35°C and 50% RH, with ventilation flow rates of 0.5, 1.5, 2.0, and 3.0 m/s, respectively, and those in the control were kept outdoors. Hens were acclimated to the controlled environment rooms for 1 wk and to the targeted environmental conditions for another week, and then were subjected to measurements for 2 wk. Egg production, mass, and shell density, and feed and water consumption were monitored. Body temperature, SHL, and plasma thyroid hormone concentrations were measured at the end of the experiment. The high environmental temperature impaired egg production and quality: whereas exposure of hens to ventilation flows of 2.0 and 3.0 m/s elicited significant recovery of these parameters with time, exposure to a rate of 0.5 m/s negatively affected these parameters throughout the experimental period. The highest feed intake and water consumption were observed in hens exposed to 2.0 and 3.0 m/s, respectively, and the highest SHL was observed in those exposed to 3.0 m/s. It can be concluded that ventilation rate significantly affected hens exposed to high ambient temperature: high ventilation (3.0 m/s) improved egg production whereas low ventilation (0.5 m/s) negatively affected production and quality.

Improvement of cold resistance and performance of broilers by acute cold exposure during late embryogenesis.

The aim of this study was to fine-tune previous acute cold exposure treatments of broiler embryos during late embryogenesis to improve lifelong cold resistance and performance. Six hundred Cobb hatching eggs were incubated under standard conditions and then exposed to 3 treatments: control; cold treatment in which embryos were exposed to 15°C for 30 min on d 18 and 19 of incubation (30 × 2); and cold treatment similar to 30 × 2 but with 60-min exposures (60 × 2). Egg shell temperature (T(egg)) and heart rate (HR) were monitored pre- and posttreatment. Upon hatching, hatchability, body weight, and body temperature were recorded. From 14 to 35 d of age, three quarters of the chickens in each treatment were raised under ascites-inducing conditions (AIC) and the remaining birds were raised under standard brooding conditions (SBC). The T(egg) and HR decreased significantly in response to increased exposure time on d 18 of incubation. On d 19 of incubation, before the second cold exposure, the 30 × 2 group showed greater T(egg) and HR than the controls, and during the second exposure they maintained these parameters better than the 60 × 2 embryos. No treatment effect on hatchability was observed. At 35 d of age ascites incidence among 30 × 2 chickens under AIC was significantly less than that among the controls (P < 0.01), and body weight of these chickens under either SBC or AIC was significantly higher than that of the controls. Under SBC relative breast muscle weight was significantly higher in 60 × 2 chickens, whereas the relative heart weight was higher in both cold-treated groups than in the controls. It can be concluded that repeated short acute cold exposures during late embryogenesis significantly reduced ascites incidence and improved growth rate under either SBC or AIC. These results may be related to a prenatal epigenetic adaptation of the thermoregulatory and cardiovascular systems to low ambient temperature.

The effects of feed restriction and ambient temperature on growth and ascites mortality of broilers reared at high altitude.

The development of ascites was investigated in broilers at low versus high altitudes, cold versus normal ambient temperatures (AT), and 3 feeding regimens. One-day-old chicks obtained at sea level were reared at high altitude (highA; 1,720 m; n = 576) with 2 AT treatments, low AT from 3 wk onward at highA (highA/cold) and normal AT from 3 wk onward at highA (highA/norm), or at sea level (normal AT from 3 wk onward at low altitude, lowA/norm; n = 540). Under highA/cold, AT ranged between 16 to 17 degrees C in the fourth week, 17 to 19 degrees C in the fifth week, and 19 to 21 degrees C thereafter. Under highA/norm and lowA/norm, AT was 24 degrees C in the fourth week and ranged between 22 to 24 degrees C thereafter. Broilers in each condition were divided into 3 groups: feed restriction (FR) from 7 to 14 d, FR from 7 to 21 d, and ad libitum (AL). Ascites mortality and related parameters were recorded. Low mortality (0.4%) occurred under lowA/norm conditions. Under highA/norm, mortality was lower in females (8.6%) than in males (13.8%) and was not affected by the feeding regimen. The highA/cold treatment resulted in higher mortality but only in males; it was 44.2% among highA/cold AL-fed males and only about 26% under the FR regimens, suggesting that FR helped some males to better acclimatize to the highA/cold environment and avoid ascites. However, mortality was only 13.3% in AL-fed males at highA/norm and FR did not further reduce the incidence of ascites under these conditions. Thus, avoiding low AT in the poultry house by slight heating was more effective than FR in reducing ascites mortality at highA. Compared with FR from 7 to 14 d, FR from 7 to 21 d did not further reduce mortality and reduced growth. At 47 d, the majority of surviving broilers at highA had high levels of hematocrit and right ventricle:total ventricle weight ratio (>0.29), but they were healthy and reached approximately the same BW as their counterparts at low altitude. This finding may suggest that in broilers reared at highA from day of hatch, the elevation in hematocrit and in right ventricle:total ventricle weight ratio happens gradually and therefore is not necessarily indicative of ascites development.

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.

Physiological parameters in broiler lines divergently selected for the incidence of ascites.

Ascites syndrome (AS) is manifested in flocks of contemporary broilers that are allowed to fully manifest their genetic potential for rapid growth. After successful selection, a pair of divergent lines was established, AS-susceptible (AS-S) and AS-resistant (AS-R). These lines facilitate comparisons between genetically resistant and susceptible healthy young broilers when reared under standard brooding conditions (SBC). The aim of the present study was to look for predictive indicators for AS susceptibility by comparing relevant physiological parameters in the AS-S and AS-R lines under SBC and after exposure to extreme ascites-inducing conditions (AIC). In this design, a trait differing significantly between the 2 lines under SBC is expected to be a reliable indicator for selection against AS susceptibility in breeding stocks when reared under noninducing conditions. Males from the AS-S and AS-R lines were reared together under SBC to 19 d of age, then under the AIC protocol. Cumulative incidence of AS mortality was 93.2% in the AS-S line and only 9% in the AS-R line, confirming the genetic divergence between the lines. Exposure to AIC enhanced the imbalance between oxygen demands and supply in the AS-S birds and induced differences in blood parameter level between the 2 lines. The AS-S birds exhibited elevated hematocrit and red blood cell counts and a decline in oxygen saturation in the arterial blood. No difference in hemoglobin concentration was found, but calculation of hemoglobin content per 1,000 red blood cells revealed a significant reduction in hemoglobin content in the AS-S birds. Under SBC, there were no significant differences between the lines for hematocrit, red blood cell count, hemoglobin concentration, hemoglobin count per 1,000 red cells, and blood oxygen saturation. However, heart rate during the first week of life was significantly higher in the AS-S birds than in the AS-R birds on d 1 and 7, suggesting that high heart rate may potentially serve as an early criterion for selection against AS susceptibility.

Broiler incubation. 2. Interaction of incubation and brooding temperatures on broiler chick feed consumption and growth.

The effect of either hot or cool brooding litter temperature on feed consumption, BW, and mortality of broiler chicks that had been exposed to either normal or high temperature during latter stages of incubation was studied in 2 experiments. The duration of experiments 1 and 2 was 14 and 21 d, respectively, with BW and feed consumption determined at 2, 5, 7, and 14 d of age in experiment 1 and at 7, 14, and 21 d of age in experiment 2. High incubator temperature after embryonic d 16 decreased chick feed consumption and BW at all ages in both experiments. Hot brooding litter temperature increased feed consumption at 2 and 5 d in experiment 1 and at 7 d in experiment 2 but decreased feed consumption at 14 and 21 d in experiment 2. Feed consumption was also influenced by the incubation temperature x brooding litter temperature interaction. From 0 to 2 d or 0 to 7 d in experiments 1 and 2, respectively, the highest to lowest feed consumption was exhibited by the normal-hot, high-hot, normal-cool, and high-cool interaction groups but the order changed to normal-cool, normal-hot approximately high-cool, and high-hot from 7 to 14 and 14 to 21 d in experiment 2. Significant effects on mortality were observed in experiment 2 only where males exhibited greater mortality that was most evident in the combination of high temperature incubation followed by cool brooding. Excessive (high) eggshell temperature during the latter stages of incubation reduced feed consumption and BW through 21 d of age. However, the results showed that the hot brooding litter temperature supported increased feed consumption during the first few days of brooding even for the chicks that had been subjected to high incubation temperature. Hot brooding also reduced male mortality in experiment 2. Nonetheless, hot brooding litter temperatures should be limited as extending beyond a few days eventually decreased feed consumption.

Effect of repetitive acute cold exposures during the last phase of broiler embryogenesis on cold resistance through the life span.

The time just before hatch is critical, because the embryo shifts toward internal and external pipping. This study aimed to determine the beneficial effect of repeated acute reductions of the incubation temperature during the last phase of broiler embryogenesis on posthatch cold tolerance and on the development of ascites syndrome. Fertile eggs were incubated at 37.8 degrees C and 56% RH. At 18 and 19 d of incubation, 3 treatments were conducted, comprising 2 or 3 exposures to 15 degrees C for 30 or 60 min each. During these cold exposures, egg temperature was measured by infrared thermography to determine sensible heat loss from the eggs. At hatch, BW and body temperature were measured. At 3 and 14 d of age, chicks were challenged by cold exposure to 10 degrees C for 3 h. From 14 d of age onward, three-quarters of the chicks were raised under ascites-inducing conditions (AIC) and the others were raised under regular conditions. The sensible heat loss from the eggs was 512 +/- 66 cal and 718 +/- 126 cal for 30 and 60 min of cold exposure, respectively. No effect of treatment on hatchability was observed, but body temperature and BW were greater to significantly greater in the treated chicks. Cold challenges at 3 and 14 d of age revealed a relative thermoregulatory advantage of embryos exposed to cold for 60 min. Under AIC, fewer treated chickens than controls developed ascites. At 38 d of age, BW and relative breast muscle weight were numerically to significantly greater in the treated chicks than in the control chicks when both were raised under regular conditions, whereas no differences were observed among the chicks raised under AIC. Repeated brief acute cold exposures during the last phase of embryogenesis appeared to improve the ability of growing broilers to withstand low ambient temperatures during their life span. Moreover, chickens treated during embryogenesis improved their performance under regular growth conditions.

Thermal manipulations during broiler embryogenesis: effect on the acquisition of thermotolerance.

Rapid growth rate has presented broiler chickens with serious difficulties when called on to thermoregulate efficiently in hot environmental conditions. Altering the incubation temperature may induce an improvement in the acquisition of thermotolerance (AT). This study aimed to elucidate the effect of thermal manipulations (TM) during the development of the thyroid and adrenal axis of broiler embryos on the potential of broilers to withstand acute thermal stress at marketing age. Cobb broiler embryos were subjected to TM at 39.5 degrees C and 65% RH from embryonic day 7 to 16 (inclusive), either continuously (24 h) or intermittently (12 h). After hatching chicks were raised under standard conditions to 35 d of age and then subjected to thermal challenge (35 degrees C for 5 h). Continuous TM caused a significant decline in hatchability, coupled with significantly lower BW and body temperature at hatching. The intermittent (12-h) chicks showed results similar to the controls but had significantly lower body temperature. Thermal challenge at marketing age demonstrated a significant improvement in AT in both the 12- and 24-h TM-treated broilers, which was characterized by a significantly lower level of stress (as evidenced by the level of plasma corticosterone) and rate of mortality. It was concluded that TM during the portion of embryogenesis when the thyroid and adrenal axis develop and mature had a long-lasting effect and improved the AT of broiler chickens. Whereas intermittent TM had no significant effect on hatchability and performance parameters, continuous TM negatively affected these parameters.

The effect of ventilation on performance body and surface temperature of young turkeys.

Efficient ventilation affects thermoregulation and, thereby, the performance of domestic fowl. This became crucial as genetic selection for growth development significantly coupled with increased metabolic rate. The specific aims of this study were to elucidate a) the effects of different rates of ventilation on young turkey performance during exposure to constant 35, 30, and 25 degrees C and b) their effects on body temperature and surface temperature. In 3 separate experiments, turkeys were raised under regular conditions up to 3 wk of age. Thereafter, they were acclimated for 1 wk to the targeted ambient temperatures (T(a)) and to air velocities of 0.8, 1.5, 2.0, or 2.5 m/s and raised under those conditions up to 6 wk of age. Turkeys exposed to 35 degrees C performed optimally at an air velocity (AV) of 2 m/s; they exhibited significantly higher feed intake and significantly lower body temperature. At 30 degrees C, performance was optimal at AV of 1.5 to 2.5 m/s and significantly lower at 0.8 m/s. Performance of turkeys exposed to 25 degrees C did not vary with AV. Comparison of BW and feed intakes of turkeys exposed to the 3T(a) levels revealed significantly higher feed intake at 25 degrees C but similar BW compared with those exposed to 30 degrees C, meaning that those exposed to 25 degrees C used more energy for maintenance than for growth. In general, surface temperature of the body declined significantly with T(a), whereas that of the face and legs was significantly lower at 25 degrees C. It can be concluded that AV affects the performance of young turkeys. The range of AV within which BW was optimal expanded as T(a) declined. It can be further concluded that the combination of 30 degrees C with AV from 1.5 to 2.5 m/s was optimal for young turkeys.

Thermoregulatory responses of chicks (Gallus domesticus) to low ambient temperatures at an early age.

The potential to induce improved thermotolerance in broiler chickens is of great importance. Thermal conditioning is one of the management tools used to improve thermotolerance, enabling broilers to cope with extreme environmental conditions. This study investigated the effects of exposing chicks to low ambient temperature (T(a)) on-chick body (T(b)), surface (T(s)) temperatures and total sensible heat loss (SHL) by convection and radiation from the body and from 2 main radiative organs, the face and the legs. At 3, 4, or at both 3 and 4 d of age, chicks were exposed to 5 degrees C for 1.5 h a day (to avoid mortality) or to 10 or 15 degrees C for 3 h a day. In general, in all treatments, the results during exposure to cold differed significantly from the control. A second cold exposure (on d 4 after a first exposure on d 3) clearly enhanced the chicks' ability to maintain on-chick body surface temperatures during exposure to 15 degrees C and to recover much faster from cold exposure. A dramatic decline in average surface temperature was observed during the first 15 min of chicks' exposure to the various low ambient temperatures in all ages, reaching the lowest values in the 5 degrees C treated chicks. The face responded immediately to cold exposure by significantly increasing its SHL to a level that then remained relatively steady (15 degrees C) or declined moderately with time (10 and 5 degrees C). In the legs, however, a significant and continuous decline in SHL was exhibited in all ages. The dynamics of SHL from the legs differed from that from the face, suggesting that the legs are a major organ for vasomotor responses, whereas the face is a more conservative vasoregulatory organ. It is concluded that repetitive exposure to cold may enhance thermotolerance, and that this is partially related to the vasomotor responses. This is the first report quantifying the differentiation between the legs as a responsive vasomotor organ and the face as a conservative vasomotor one.

Effects of thermal manipulation during early and late embryogenesis on thermotolerance and breast muscle characteristics in broiler chickens.

Genetic selection has significantly improved the muscle development of fast-growing broiler chickens in the last 50 yr. However, improvement in muscle growth has coincided with relatively poor development of visceral systems, resulting in impaired ability to cope with high environmental temperatures. The aim of this study was to elucidate the effects of thermal manipulation (TM) during different periods of embryogenesis on chick hatchability, BW and thermoregulation upon hatching, on their ability to cope with thermal challenge at 42 d of age, and on carcass and breast meat traits. Control embryos were incubated at 37.8 degrees C. The TM embryos were incubated at 37.8 degrees C and treated for 3 h at 39.5 degrees C on the following days of embryogenesis: E8 to E10 [early (EA)], E16 to E18 [late (LA)], and both E8 to E10 and E16 to E18 (EA-LA). Body weight and body temperature (T(b)) were measured at hatching and throughout the growth period as well as during exposure of 42-d-old chickens to a thermal challenge at 35 degrees C for 6 h. The LA and EA chicks exhibited significantly lower T(b) than control chicks (37.9 vs. 38.2 degrees C) at hatching, but during the growth period, differences in T(b) between treated and control chicks decreased with age. Significant hyperthermia (over 44 degrees C) was monitored in all groups during the thermal challenge, but mortality was higher in treated than in control chickens. No effect of treatments on BW was found during the entire growth period. However, breast yield was higher in LA chickens than in controls at slaughter. The EA and EA-LA treatments slightly decreased the ultimate pH of breast meat, whereas the LA treatment had no effect. In conclusion, none of the TM conditions tested in the present study were able to improve long-term thermotolerance in chickens. Late treatment favored breast muscle growth without affecting ultimate pH and drip loss of breast meat.