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Broiler chicks in the immediate posthatch handling period are exposed to thermal stress, with potentially harmful consequences for muscle growth and structure (e.g., less protein and more fat deposition). We addressed the effects of broiler chicks’ exposure to various ambient temperatures during the first 13 D posthatch on their performance, as well as on muscle development and structure, up to day 35. Body weight and pectoralis muscle growth were lower throughout the entire period in the high-heat-exposed chicks (39°C, Hot) and to a lesser extent in the mild-heat-exposed chicks (35°C, Hot Mild) than in the Control chicks that were raised under a commercial protocol. In the cold-exposed chicks (29° C, Cold), BW and pectoralis muscle absolute growth were similar to the Control group throughout the entire period. The lower body and muscle growth in the Hot and Hot Mild groups were reflected in a lower number of myonuclei expressing proliferating cell nuclear cell in pectoralis major muscle cross sections sampled on day 8, in the distribution of myofibers as the experiment progressed, and in mean myofiber diameter on day 35, whereas in the Cold group, these numbers exceeded that of the Control group. However, TUNEL assay revealed similar cell survival in all groups. Hematoxylin–eosin and Oil red O staining revealed the highest fat deposition in the pectoralis muscle derived from the Hot group, whereas lower fat deposition was observed in the Control Cold group. These results were corroborated by immunostaining for CCAAT/enhancer binding protein β in the pectoralis muscle, the levels of which were significantly higher in the Hot and Hot Mild groups on day 35 than in the Control group. Similar results were observed with Sirius red staining for collagen content in the pectoralis muscle. Together, the results imply long-term effects of chronic heat stress vs. cold stress in the early posthatch period on the broiler's body and muscle growth in general and myodegeneration of the pectoralis muscle in particular.

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.

Fowls are endothermic species controlling body temperature (Tb) within a relatively narrow range, despite moderate to extreme changes in environmental conditions. Tb is recognized as the main characteristic that reflects thermal status. Significant developments in the genetic selection of domestic fowl enhanced performance-improved feed efficiency and increased metabolic rate, leading to low capability to balance energy expenditure and maintain body water balance under extreme environmental conditions. This chapter will focus on the effect of combinations of environmental conditions (temperature, ventilation, relative humidity) on thermal status and performance parameters of broilers, turkeys and laying hens. Furthermore, it will offer the use of epigenetic temperature adaptation during embryogenesis as a tool to improve thermotolerance and performance.

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 0.17). 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.

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.

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.

Heat or cold stress, can disrupt well-being and physiological responses in birds. This study aimed to elucidate the effects of continuous heat exposure in the first 2 wk of age on muscle development in broilers, with an emphasis on the pectoralis muscle satellite cell population. Chicks were reared for 13 d under either commercial conditions or a temperature regime that was 5°C higher. Body and muscle weights, as well as absolute muscle growth were lower in heat-exposed chicks from d 6 onward. The number of satellite cells derived from the experimental chicks was higher in the heat-treated group on d 3 but lower on d 8 and 13 compared to controls. This was reflected in a lower number of myonuclei expressing proliferating nuclear cell antigen in cross sections of pectoralis major muscle sampled on d 8. However, a TUNEL assay revealed similar cell survival in both groups. Mean myofiber diameter and distribution were lower in muscle sections sampled on d 8 and 13 in heat-treated versus control group, suggesting that the lower muscle growth is due to changes in muscle hypertrophy. Oil-Red O staining showed a higher number of satellite cells with lipids in the heat-treated compared to the control group on these days. Moreover, lipid deposition was observed in pectoralis muscle cross sections derived from the heat-treated chicks on d 13, whereas the controls barely exhibited any lipid staining. The gene and protein expression levels of CCAAT/enhancer binding protein β in pectoralis muscle from the heat-treated group were significantly higher on d 13 than in controls, while myogenin levels were similar. The results suggest high sensitivity of muscle progenitor cells in the early posthatch period at a time when they are highly active, to chronic heat exposure, leading to impaired myogenicity of the satellite cells and increased fat deposition.

Skeletal muscle satellite cells are a muscle stem cell population that mediate posthatch muscle growth and repair. Satellite cells respond differentially to environmental stimuli based upon their fiber‐type of origin. The objective of this study was to determine how temperatures below and above the in vitro control of 38°C affected the proliferation and differentiation of satellite cells isolated from the chicken anaerobic pectoralis major (p. major) or mixed fiber biceps femoris (b.femoris) muscles. The satellite cells isolated from the p. major muscle were more sensitive to both cold and hot temperatures compared to the b.femoris satellite cells during both proliferation and differentiation. The expressions of myogenic regulatory transcription factors were also different between satellite cells from different fiber types. MyoD expression, which partially regulates proliferation, was generally expressed at higher levels in p. major satellite cells compared to the b.femoris satellite cells from 33 to 43°C during proliferation and differentiation. Similarly, myogenin expression, which is required for differentiation, was also expressed at higher levels in p. major satellite cells in response to both cold and hot temperatures during proliferation and differentiation than b. femoris satellite cells. These data demonstrate that satellite cells from the anaerobic p. major muscle are more sensitive than satellite cells from the aerobic b. femoris muscle to both hot and cold thermal stress during myogenic proliferation and differentiation.

Previous studies on broilers conducted in our laboratory showed that intermittent thermal manipulation (TM) of 39.5 °C every 12 h during embryonic days E7–E16 improved thermoregulative parameters in the embryo and post-hatch, as well as the broilers' ability to cope with heat challenge at marketing age. The aim of this study was to investigate the effect of intermittent TM of 39.5 °C (65% RH) for 12 h/d (12 H), during E7–E16, on post-hatch performance and thermoregulation under both optimal and hot conditions. Chicks from the control and TM treatments were raised under “regular” conditions until 21 d of age. Then, each treatment was divided into 2 sub-treatments (growth conditions) – optimal conditions (25 °C) and hot conditions of 32 °C for 12 h/d – until 35 d of age. Under optimal conditions, no difference in growth rates was found between TM and control throughout the growth period, but TM had significantly larger relative breast muscle weight, and on days 13, 25, and 35 breast muscle in the TM treatment contained a higher percentage of large-diameter fibers than controls. Consequently, average fiber diameter was significantly larger in TM than in control. Relative weight of the abdominal fat pad was significantly lower in the TM treatment than in control, under both environmental conditions. Hot conditions negatively affected growth rates of broilers in both treatments. The TM chickens showed no body-weight advantage over controls, nevertheless, feed conversion between days 21 and 35 was lower in the TM chickens of both sexes than in controls. This could be attributed to lower body temperature and lower plasma thyroid hormone levels found in the TM chickens, indicating lower heat production rates. Greater muscle growth and lower relative weight of abdominal fat pad were found in the TM chickens than in controls, under hot conditions. It can be concluded that TM during embryonic development improves performance as well as thermoregulation.

The goals were to elucidate the effects of ventilation rate (VR) coupled with exposure to constant 20 °C or to diurnal temperature cycling on young turkeys' performance and sensible heat loss (SHL). In three experiments male British United Turkeys (BUT), from 3 to 6 weeks of age, were exposed to constant 20 °C, or to 35/25 °C or 30/20 °C diurnal temperature cycling, all at 50% RH and with VR (expressed as air velocity (AV)) ranging from 0.8 to 3.0 m s−1. The 2nd and 3rd of these experiments included a positive control at constant 30 °C and VR of 1.5 m s−1. Weight gain, feed intake, and feed efficiency were measured or calculated, as appropriate; SHL was calculated from measured surface temperature, and plasma concentrations of triiodothyronine (T3) was determined in the 1st experiment. Changes of VR at constant 20 °C did not affect performance, but total SHL increased significantly with increasing VR. Under the 35/25 °C regime a significantly higher BW was recorded, with a similar pattern of feed efficiency, when VR during the hot part of the cycle was 1.5 or 2.0 m s−1 than when it was 0.8 m s−1. In the 3rd experiment, BW in the 35/20 °C treatment was significantly lower than that of the controls. In all experiments, turkeys maintained body temperature (Tb) within the normothermic range, and SHL varied with VR. It can be concluded that although diurnal temperature cycling reflects the natural situation, exposing young turkeys to constant 30 °C combined with optimal ventilation might yield the best performance results.

Les poulets à croissance rapide sont sensibles à la chaleur en période de finition. En effet, leur sélection pour la croissance a favorisé la masse musculaire au détriment d’organes impliqués dans la thermorégulation. Ceci peut se traduire par des baisses de performances en cas de chaleur modérée et chronique, mais également des problèmes de bien-être et des mortalités lors d’un coup de chaleur. Durant la dernière décennie les efforts ont porté sur l’acclimatation à la chaleur pendant la période périnatale, notamment pendant l’embryogenèse. Cette stratégie nécessite de mettre au point les conditions d’incubation (température, phase de l’embryogenèse, durée d’exposition…) qui favorisent la thermotolérance jusqu’en finition. Les conséquences sur les performances des poulets (croissance, qualité de viande…) sont évaluées. L’acclimatation périnatale met en jeu des mécanismes de régulation épigénétiques qui modulent à long terme la température interne des volailles. A terme, si cette technique se révélait applicable à grande échelle, elle pourrait favoriser la robustesse et le bien-être des volailles face aux variations de températures, tout en préservant leurs performances zootechniques. Dans cet article, sont rappelés les principales techniques d’exposition thermique embryonnaire et les fondements physiologiques de leur mise en œuvre. Sont évoquées ensuite les voies de recherche concernant la compréhension des mécanismes mis en jeu et l’intérêt potentiel de cette technique pour la filière avicole., The selection of fast-growing chickens has favored muscle mass without similar improvement of the cardiovascular and respiratory systems involved in thermoregulation. Indeed, broiler chickens have limited capacities to sustain high temperatures, with reduced performances during moderate and chronic heat exposure, and depressed welfare, morbidity and mortality during acute heat exposure. During the last decade, a great effort concerned early thermal acclimation. This strategy requires a fine tuning of incubation conditions (temperature, phasis of embryogenesis, duration of exposure) favoring long term thermotolerance. Consequences on growth performance and meat quality were also evaluated. Perinatal heat acclimation is aimed at inducing epigenetic thermoregulatory mechanisms that modulate body temperature on a long term. If it is further proved to be efficient on a large scale, early thermal acclimation could favor poultry sturdiness towards temperature variations without affecting growth performance. In this paper, we will review the main techniques of early thermal exposure and the physiological bases of their use. We will focus on the research axes concerning the comprehension of underlying mechanisms and the interest of this technique for poultry species.

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.

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.

This study aimed to elucidate the effects of thermal manipulation (TM) during the development and maturation of the thyroid and adrenal axis on broiler chicks hatchability and thermoregulation during hatch, and to evaluate the improvement of thermotolerance acquisition of TM chicks by thermally challenging them post-hatch. Fertile Cobb eggs were divided into three treatments: control, 12 and 24 H. The control eggs were incubated under standard conditions, whereas the 12 and 24 H eggs were incubated from 7 d of incubation (E7) until E16 (inclusive) at 39.5 °C and 65% RH for 12 h/d (12 H) or continuously (24 H). Hatchability, BW and quality of the hatched 24 H chicks were negatively affected, but exhibited significantly improved thermotolerance on heat stress at 3 and 10 d of age for males and females, respectively. It can be concluded that continuous TM during embryogenesis impaired broiler chick performance, but improved their ability to thermoregulate in response to thermal challenge mainly by reducing heat production.

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.

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.

Thermal manipulation (TM) of 39.5°C applied during mid-embryogenesis (embryonic d 7 to 16) has been proven to promote muscle development and enhance muscle growth and meat production in meat-type chickens. This study aimed to elucidate the cellular basis for this effect. Continuous TM or intermittent TM (for 12 h/d) increased myoblast proliferation manifested by higher (25 to 48%) myoblast number in the pectoral muscles during embryonic development but also during the first week posthatch. Proliferation ability of the pectoral-muscle-derived myoblasts in vitro was significantly higher in the TM treatments until embryonic d 15 (intermittent TM) or 13 (continuous TM) compared to that of controls, suggesting increased myogenic progeny reservoir in the muscle. However, the proliferation ability of myoblasts was lower in the TM treatments vs. control during the last days of incubation. This coincided with higher levels of myogenin expression in the muscle, indicating enhanced cell differentiation in the TM muscle. A similar pattern was observed posthatch: Myoblast proliferation was significantly higher in the TM chicks relative to controls during the peak of posthatch cell proliferation until d 6, followed by lower cell number 2 wk posthatch as myoblast number sharply decreases. Higher myogenin expression was observed in the TM chicks on d 6. This resulted in increased muscle growth, manifested by significantly higher relative weight of breast muscle in the embryo and posthatch. It can be concluded that temperature elevation during mid-term embryogenesis promotes myoblast proliferation, thus increasing myogenic progeny reservoir in the muscle, resulting in enhanced muscle growth in the embryo and posthatch.

Enhancing meat production by genetic selection for growth has already produced 5-week-old broilers weighing more than 2 kg. As growth performance characteristics continue to improve and the time it takes to achieve market size decreases, the period of embryonic development becomes a greater proportion of the bird's life. Therefore, in parallel to genetic selection, other approaches, such as environmental manipulations in the embryo or in the early days posthatch, are becoming more relevant for increasing muscle growth and meat production.Recently, we have shown that nutritional treatments, i.e., providing feed immediately posthatch, or environmental treatments, such as heat conditioning or monochromatic green-light illumination during the first days posthatch, increase muscle growth and breast muscle weight at marketing day. In all cases, the increase in muscle growth was due to changes at the cellular and molecular levels leading to increased satellite cell proliferation and differentiation.The significant effects on muscle growth resulting from the treatments in the first days posthatch raised the hypothesis that muscle growth could be affected during the embryonic development. In experiments in which eggs were illuminated under monochromatic green light from embryonic day 5 (E5), there was a positive effect on embryo development and posthatch muscle growth. Further studies revealed that this enhanced muscle weight was due to increased satellite cell number and fiber synchronization during early days posthatch. Thermal manipulation at 38.5°C from E16 to E18 for 3 h/day had a delayed effect on satellite-cell proliferation and differentiation, resulting in enhanced hypertrophy of myofibers at market age.

Recent decades have seen significant progress in the genetic selection of fast-growing meat-type broiler chickens. However, fast growth has coincided with inferior development of the visceral syste...

La selection genetique des poulets de chair a croissance rapide s'est accompagnee d'un developpement insuffisant de leurs organes internes qui limite leur capacite a resister a la chaleur. Les manipulations thermiques (MT) de l'embryon visent a ameliorer l'acquisition de la thermotolerance du poulet. Leur duree pourrait affecter le poids vif (BW) et la temperature corporelle (T b ) des poussins. Cette etude a pour but de rechercher les effets de differentes durees de MT pendant les jours E16 a El 8 de l'embryogenese sur le taux d'eclosion, T b et BW des poussins a la naissance (jO), ainsi qu'a 3 jours (j3) pendant une exposition ou non a un coup de chaleur de 6 h a 41 °C. Les oeufs temoins sont incubes a 37,8 °C pendant 21 jours, tandis que les embryons traites sont en plus soumis a 39,5 °C pendant 3 (Dl), 6 (D2), 12 (D3) ou 24 (D4) h par jour de E16 a E18. Les traitements n'affectent pas BW a j0, mais les taux d'eclosion sont plus eleves chez les embryons D3 et D4 compares aux D1. Tous les traitements diminuent significativement T b par rapport aux temoins a jO, resultat retrouve chez les poussins exposes a un coup de chaleur (C) a j3. Dix-huit heures apres le coup de chaleur, les poussins exposes D1C maintiennent une T b significativement plus faible que celle des poussins D2C, D3C et D4C. Chez les poussins non exposes (N), BW continue a etre similaire entre traitements, alors que chez les poussins exposes (C), BW est plus eleve chez les poussins D2C et D3C que chez les temoins et D1C. Il apparait donc que la meilleure duree de MT dans nos conditions est de 3 h par jour de E16 a El 8 pour l'amelioration de la thermotolerance du poussin, et de 6 a 12 h par jour pour l'initiation de la croissance. Des recherches complementaires sont necessaires pour evaluer ces deux types de reponses a plus long terme.

The effects of various atmospheric ammonia concentrations (X ± S.E.; 16 ± 2; 28 ± 3; 39 ± 4; and 54 ± 5 ppm) at high ambient temperature (Ta = 32 °C) and relative humidity (rh = 60- 65%) on the performance and thermoregulation of male broiler chickens were studied. Body weight declined significantly and proportionally with increasing ammonia concentration in the air. The decline in body weight coincided with a similar pattern in feed intake. Feed efficiency did not differ significantly among treatments, but the broilers exposed to the lowest concentration of ammonia showed the highest feed efficiency. Chickens exposed to the lowest ammonia concentrations regu- lated Tb at significantly lower levels (41.5 °C at 16 ppm and 41.9 °C at 28 ppm) than those at the highest concentrations (42.3 °C at 39 and 54 ppm). Arterial pH increased with increasing ammonia concentration and was similar in the upper 2 concentrations of ammonia. A similar but opposite trend was found in the partial pressure of arterial CO 2 . Plasma triiodothyronine (T 3 ) concentration did not differ significantly among treatments. It can be concluded that exposure to increased ammonia con- centrations impairs broiler performance. It may also be suggested that ammonia can affect the ability of the chickens to control Tb effectively. ammonia / broiler / performance / body temperature / triiodothyronine

Previous reports have suggested that green light enhances broiler growth at an early age, whereas blue light enhances growth at older ages. The aim of this study was to examine the effect of a switch in monochromatic light at 2 ages on growth and development of broilers. Male chicks (Anak, n = 640) were used. After hatch, chicks were weighed, wing-banded, and blocked into treatment groups. Chicks were grown in 1-m2 pens in 8 isolated light-proof rooms (20 birds/pen). The light treatments were (1) Control white (mini-incandescent lamps), 2) blue light-emitting diode (LED) lamps, 3) green LED lamps, 4) blue LED switching to green at 10 d of age, 5) blue LED switching to green at 20 d of age, 6) green LED switching to blue at 10 d of age, and 7) green LED switching to blue at 20 d of age. There were 8 pens for treatment 1, and 4 pens for each of the other treatments. The light schedule was 23L:1D, and intensity was 0.1 watts/m2. BW and feed consumption were recorded. Green light birds were significantly heavier at 4 d of age. Switching light at 10 d of age from green to blue caused a further increase in BW. This improved growth was maintained until the end of the experiment. Light switching from blue to green at 20 d of age also improved growth as compared with white light. Average feed efficiency and mortality rate did not differ between groups. No association was observed among light treatment, performance, and plasma triiodothyronine concentration. We suggest that green light stimulated growth of birds at early age, and shifting birds to a different light environment at 10 or 20 d of age might further stimulate growth.

Caloric restriction (CR) can extend the life-span of multiple species and is the only intervention known to attenuate aging in mammals. Mechanisms mediating the CR influence are as yet unclear. To get insight into these mechanisms we took advantage of alphaMUPA transgenic mice that have previously been reported to spontaneously eat less and live longer compared with their wild-type (WT) control. Here we report that mitochondria isolated from young adult alphaMUPA livers showed increased susceptibility to calcium-induced high-amplitude swelling, increased cytochrome c release and enhanced glutathione levels. Furthermore, young adult alphaMUPA mice showed significantly enhanced caspase-3 activity in liver homogenates, increased fraction of apoptotic hepatocytes, and a lower level of serum IGF-1. In addition, alphaMUPA mice showed a decreased rate of spontaneously occurring lung tumors at an old age. Short-term (8 weeks) calorically restricted WT mice also showed an increase of mitochondrial swelling and caspase-3 activity compared with ad libitum (AL) fed WT mice. These results provide the first indication that CR can enhance mitochondrion-mediated apoptotic capacity. Collectively, the results are consistent with the possibility that long lasting, moderately increased apoptotic capacity, possibly linked in part to IGF-1 and GSH modulation, could play a role in the CR-induced anti-aging influence in mice.

The ascites syndrome in broiler chickens is attributed to metabolic burdening, which results from intensive genetic selection for rapid growth coupled with exposure to extreme environmental conditions, such as low ambient temperature. These conditions impose on the broilers difficulties in fulfilling tissue demands for oxygen, and the birds exhibit a decrease in blood oxygen saturation and high hematocrit values. It is unknown whether the increase in hematocrit results from alteration in erythropoiesis or from fluid exudation out of the blood system to the abdominal cavity. The present study was conducted to examine the association between abnormal stress response and erythropoiesis process in ascitic broilers. Ascitic chickens revealed a uniquely continuous stress response: expressing an increase (P < or = 0.05) in plasma corticosterone concentration 2 to 3 wk before death. At 5 wk of age, ascitic broilers exhibited an increase (P < 0.05) in hematocrit, blood cell count, and packed cells and blood volumes, with no significant change in plasma volume. These results confirm an accelerated erythropoiesis process in ascitic birds. Increased blood cell production in ascitic birds was matched by an increase (P < 0.05) in the proportion of immature red blood cells (23%) in comparison with broilers that remained healthy (7%), and by decreased (P < 0.05) hemoglobin content relative to red blood cells. We conclude that continually increased corticosterone concentrations, as an inducer of erythropoiesis proliferation and differentiation arrest, in ascitic chickens, resulted in increased production of red blood cells (partially immature) with decreased hemoglobin content; this decrease in hemoglobin might have contributed to enhanced development of hypoxemia and to aggravation of the syndrome.

Body temperature ( T b ) regulation, which is an exclusive characteristic of endothermic birds and mammals, allows for the adaptation of processes and survival under varied environmental conditions. This chapter focuses on the evolution of endothermy, which enables the maintenance of T b within a relatively small range; the mechanisms of heat production and heat loss; various strategies to maintain T b ; the development of endothermy during embryogenesis; and the cost of endothermy in various ecological niches.

The influence of short repetitive cold exposure at an early age (cold conditioning—exposure to 15°C for 3 h at 3 and 4 days of age) on chickens’ thermotolerance during cold challenge (15°C) at 21 days of age was examined. The first cold exposure elicited a dramatic decline in body temperature (Tb) and a significant elevation in stress response (plasma corticosterone concentration); the second cold exposure resulted in moderate Tb and stress responses. Thereafter, the corticosterone concentration remained at a significantly lower level. Acute cold challenge of conditioned broilers at 21 days of age revealed better Tb and stress recovery during the first 24 h, and a significantly lower mortality rate thereafter. Conditioned chickens exposed to optimal conditions (22°C) achieved significantly higher body weights than others. It may be concluded that early cold conditioning improves thermotolerance in broiler chickens in later life.

Young turkeys exposed to low ambient temperature ( T a ) showed significantly reduced body weight, which coincided with a reduction in energy intake and with changes in the circulatory system to accommodate higher oxygen demand. These changes included a significant increase in hematocrit, hemoglobin concentration, plasma triiodothyronine (T 3 ) concentration, blood volume, and blood oxygen capacity. At the relatively high T a , changes to accommodate heat dissipation included significant increases in plasma volume and panting rate. These compensations were sufficient to control body temperature ( T b ). However, the higher energy expenditure for maintenance followed by significantly higher plasma triiodothyronine (T 3 ) concentration, but with lower energy intake at low T a , suggest a physical limitation in the ability to further increase energy intake as T a declines.

International audience; 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.

Exposure of young chicks to thermal conditioning (TC; i.e., 37°C for 24 h) resulted in significantly improved body and muscle growth at a later age. We hypothesized that TC causes an increase in satellite cell proliferation, necessary for further muscle hypertrophy. An immediate increase was observed in satellite cell DNA synthesis in culture and in vivo in response to TC of 3-day-old chicks to levels that were significantly higher than those of control chicks. This was accompanied by a marked induction of insulin-like growth factor-I (IFG-I), but not hepatocyte growth factor in the breast muscle. No significant difference between treatments in plasma IGF-I levels was observed. A marked elevation in muscle regulatory factors on day 5, followed by a decline in cell proliferation on day 6together with continuous high levels of IGF-I in the TC chick muscle may indicate accelerated cell differentiation. These data suggest a central role for IGF-I in the immediate stimulation of satellite cell myogenic processes in response to heat exposure.

The present study examined the association between thyroid hormones and the development of ascites on one hand and the ability to predict ascites from growth rate and hematocrit on the other hand. Ascites syndrome was induced in broiler chickens in two trials by exposing the chicks to low ambient temperature (Ta) and by supplying a pellet form of diet. Weight gain, hematocrit, hemoglobin, and plasma thyroxin (T4) and triiodothyronine (T3) concentrations were measured weekly for each bird, and comparisons were made between birds that eventually died from ascites and those that did not. Mortality from ascites amounted to 24.3 and 24.2% in Trials 1 and 2, respectively. Weight gain did not differ between ascitic and healthy chickens up to approximately 2 wk before death but was significantly lower in the ascitic broilers 1 to 2 wk before death. Hematocrit was significantly higher in broilers with ascites with the exception of ascitic broilers that died at the age of 7 wk (Trial 1). In ascitic broilers, T4 and T3 concentrations declined significantly during the week of death. The present findings raise the question of whether the association between low levels of thyroid hormones and the development of ascites is one of the physiological responses in the syndrome cascade, or whether the failure to maintain thyroid hormones concentration is one of the triggers of the syndrome initiation. This question requires further investigation. It can be concluded that a high rate of weight gain is not always a good predictor of ascites development. Hematocrit and thyroid hormones can provide a good indication but only during the last week of life, and not in all cases. None of these parameters, however, can predict the development of ascites at an early age.

1. The effects of relative humidity (rh=40% to 70%) at high ambient temperature (Ta) on the performance of laying hens at different ages (8 to 10 months, Trial 1; and 16 to 18 months, Trial 2) was evaluated. Laying hens were exposed to 25 degrees C (control) for 3 weeks and thereafter acclimated for 1 week to 35 degrees C and 4 different rh. 2. Body weight declined significantly in young and older hens exposed to 60% or 70% and 70% rh, respectively: Food intake declined with increasing Ta, except in the case of older hens exposed to 60% rh, for which it remained relatively constant. Water consumption, however, increased with increasing Ta but the increase was significant in young hens exposed to 70% rh only. 3. Egg production was not affected by the changes in Ta. However, a decrease in egg production was observed in older hens exposed to 60% rh. 4. Egg weight (EW), shell weight (SW) and shell thickness (ST) were significantly reduced by exposure to elevated Ta, whereas % breakage significantly increased. In young hens, a response to rh was exhibited in ST which was significantly higher in hens exposed to the low rh (40% to 45%) than in those exposed to the highest rh (70% to 75%). 5. It can be concluded that Ta is the main environmental factor affecting young and older laying hens while the effect of rh is minor.

AlphaMUPA is a line of transgenic mice that, compared with their wild type (WT) counterparts, spontaneously eat less (approximately 20%) and live longer (average approximately 20%), thus resembling dietary-restricted (DR) mice. Here, we show that body temperature was significantly reduced in alphaMUPA compared with WT throughout a wide range of ages. Plasma corticosterone was significantly higher in young alphaMUPA compared to young WT; however, it significantly declined in aged alphaMUPA, but not in aged WT. In addition, age-associated thymus involution occurred in alphaMUPA as it did in WT. Thus alphaMUPA mice appear to largely resemble, but also to somewhat differ from diet-restricted animals. We also report on four new transgenic lines that, like alphaMUPA, produced in the brain the mRNA that encodes the extracellular protease urokinase (uPA); however, transgenic uPA expression was most extensive and widespread in the alphaMUPA brain, where it also occurred in the hypothalamus. AlphaMUPA was also the only line that ate less, but also showed another characteristic, high frequency leg muscle tremor seen only at unstable body states. We hypothesize that transgenic uPA in the brain could have caused the alphaMUPA phenotypic alterations. Thus alphaMUPA offers a unique transgenic model of inherently reduced eating to investigate the homeostatic state of delayed aging at the systemic and single-cell levels.

At high ambient temperature ( T a =35°C) weight gain and feed intake declined significantly. At 15°C weight gain was similar to that at 25°C, at the cost of increased feed intake. Under diurnal cyclic temperature, weight gain and feed intake were significantly lower than in the average corresponding temperature. In all treatments the turkeys’ body temperature ( T b ) was at the lower level of normothemia known for broiler chickens at a similar age. The blood system compensated for changes in T a by increasing hematocrit, hemoglobin concentration and heart muscle weight at low T a , and by plasma expansion and increased panting at high T a . Plasma (T 3 ) concentration was positively correlated with feed intake and weight gain.

Broiler chicks were conditioned by exposure to heat stress early in life to elucidate physiological mechanisms and possible involvement of the known heat shock proteins (HSPs) in the induction of thermotolerance. Chicks were exposed to 36 +/- 1 degree C; 70-80% relative humidity (rh) for 24 hours at the age of 5 days. During conditioning, weight gain was depressed. Due to accelerated growth during the postconditioning period, a complete compensation for lost weight gain was achieved by the conditioned group. At the age of 42 days, challenge with acute heat stress of 35 +/- 1 degree C; 25-30% rh resulted in a large increase in cloacal temperature of the control chickens and by a more moderate increase in the conditioned chickens. Mortality during the thermal challenge was significantly higher in the control chickens than in the conditioned ones. Conditioning at an early age resulted in reduced plasma triiodothyronine (T3) concentration and hemodynamic changes (significant decrease in heart weight and hematocrit). The synthesis rate of 70 and 90 kDa HSPs during the first hour of heat challenge, accelerated gradually in control chickens, whereas in the conditioned chickens it accelerated only after 3 hours and in a more moderate response. These results suggest that HSP's response does not play a major role in the conditioning-induced mechanism leading to acquisition of thermotolerance in chickens.

The necessity to improve broiler thermotolerance and live performance led to the following hypothesis: Appropriate comprehensive incubation treatments that include significant temperature management changes will promote angiogenesis and will improve acquisition of thermotolerance and carcass quality of heavy broilers through epigenetic adaptation. It was based on the following questions: 1. Can TM during embryogenesis of broilers induce a longer-lasting thermoregulatory memory (up to marketing age of 10 wk) that will improve acquisition of thermotolerance as well as increased breast meat yield in heavy broilers? 2. The improved sensible heat loss (SHL) suggests an improved peripheral vasodilation process. Does elevated temperature during incubation affect vasculogenesis and angiogenesis processes in the chick embryo? Will such create subsequent advantages for heavy broilers coping with adverse hot conditions? 3. What are the changes that occur in the PO/AH that induce the changes in the threshold response for heat production/heat loss based on the concept of epigenetic temperature adaptation? The original objectives of this study were as follow: a. to assess the improvement of thermotolerance efficiency and carcass quality of heavy broilers (~4 kg); b. toimproveperipheral vascularization and angiogenesis that improve sensible heat loss (SHL); c. to study the changes in the PO/AH thermoregulatory response for heat production/losscaused by modulating incubation temperature. To reach the goals: a. the effect of TM on performance and thermotolerance of broilers reared to 10 wk of age was studied. b. the effect of preincubation heating with an elevated temperature during the 1ˢᵗ 3 to 5 d of incubation in the presence of modified fresh air flow coupled with changes in turning frequency was elucidated; c.the effect of elevated temperature on vasculogenesis and angiogenesis was determined using in ovo and whole embryo chick culture as well as HIF-1α VEGF-α2 VEGF-R, FGF-2, and Gelatinase A (MMP2) gene expression. The effects on peripheral blood system of post-hatch chicks was determined with an infrared thermal imaging technique; c. the expression of BDNF was determined during the development of the thermal control set-point in the preoptic anterior hypothalamus (PO/AH). Background to the topic: Rapid growth rate has presented broiler chickens with seriousdifficulties when called upon to efficiently thermoregulate in hot environmental conditions. Being homeotherms, birds are able to maintain their body temperature (Tb) within a narrow range. An increase in Tb above the regulated range, as a result of exposure to environmental conditions and/or excessive metabolic heat production that often characterize broiler chickens, may lead to a potentially lethal cascade of irreversible thermoregulatory events. Exposure to temperature fluctuations during the perinatal period has been shown to lead to epigenetic temperature adaptation. The mechanism for this adaptation was based on the assumption that environmental factors, especially ambient temperature, have a strong influence on the determination of the “set-point” for physiological control systems during “critical developmental phases.” Recently, Piestunet al. (2008) demonstrated for the first time that TM (an elevated incubation temperature of 39.5°C for 12 h/d from E7 to E16) during the development/maturation of the hypothalamic-hypophyseal-thyroid axis (thermoregulation) and the hypothalamic-hypophyseal-adrenal axis (stress) significantly improved the thermotolerance and performance of broilers at 35 d of age. These phenomena raised two questions that were addressed in this project: 1. was it possible to detect changes leading to the determination of the “set point”; 2. Did TM have a similar long lasting effect (up to 70 d of age)? 3. Did other TM combinations (pre-heating and heating during the 1ˢᵗ 3 to 5 d of incubation) coupled with changes in turning frequency have any performance effect? The improved thermotolerance resulted mainly from an efficient capacity to reduce heat production and the level of stress that coincided with an increase in SHL (Piestunet al., 2008; 2009). The increase in SHL (Piestunet al., 2009) suggested an additional positive effect of TM on vasculogenesis and angiogensis. 4. In order to sustain or even improve broiler performance, TM during the period of the chorioallantoic membrane development was thought to increase vasculogenesis and angiogenesis providing better vasodilatation and by that SHL post-hatch.

Chicks were conditioned by exposure to heat stress (36 ± 1 C; 70 to 80% RH) for 24 h at the age of 5, or 5 and 7 d. During conditioning, weight gain was depressed. Due to accelerated growth during the postconditioning period, a complete compensation for lost weight gain was achieved by the group conditioned at 5 d, but only a partial compensation was obtained in the group conditioned at both 5 and 7 d. At the age of 42 d, challenge with acute heat stress (35 ± 1 C; 20 to 30% RH) resulted in a large increase in cloacal temperature of the controls and a more moderate increase in the conditioned chickens. Mortality during the thermal challenge was significantly higher in the controls than that of the previously exposed (conditioned) groups. Conditioning at an early age resulted in hemodynamic changes (significant decrease in heart weight and hematocrit) and reduced plasma triiodothyronine (T3) concentration. The results suggest that reduced T3 and hemodynamic changes may be part of the mechanism associated with improved thermotolerance by early age temperature conditioning.

1. Male broiler chickens were exposed in separate experiments to: (a) constant ambient temperatures (Ta) ranging between 10 and 35 degrees C; (b) 12 h:l2 h diurnal high-low temperature of 10:30 degrees C, 15:35 degrees C and 15:30 degrees C in different trials; and (c) 12 h of 30 or 35 degrees C and 12 h of variable lower temperature. 2. A progressive decline in weight gain and food intake was obtained as Ta increased from 18 to 35 degrees C. Under diurnally cycling temperature, weight gain and food intake were lower than in the average corresponding constant temperature, with the exception of chickens exposed to 15 : 30 degrees C, where weight gain and food intake were not significantly different from those of the constant average temperature. 3. As the diurnal cold period was made colder, chickens exposed during half of the diurnal cycle to high temperature (30, 35 degrees C) demonstrated a significant (P= 0.05) increase in weight gain and food intake. 4. There was a good correlation between plasma triiodothyronine (T3) and Ta. The correlation between T3 and food intake was highly significant, but that between T3 and weight gain was poor. 5. The results indicate the difficulties in predicting the performance of broilers exposed to diurnally cycling temperatures from knowledge of the average temperature.

In broilers, the immediate post-hatch handling period exposes chicks to cold or hot thermal stress, with potentially harmful consequences to product quantity and quality that could threaten poultry meat marketability as a healthy, low-fat food. This lower performance includes adverse effects on muscle growth and damage to muscle structure (e.g., less protein and more fat deposition). A leading candidate for mediating the effects of thermal stress on muscle growth and development is a unique group of skeletal muscle cells known as adult myoblasts (satellite cells). Satellite cells are multipotential stem cells that can be stimulated to follow other developmental pathways, especially adipogenesis in lieu of muscle formation. They are most active during the first week of age in broilers and have been shown to be sensitive to environmental conditions and nutritional status. The hypothesis of the present study was that immediate post-hatch thermal stress would harm broiler growth and performance. In particular, growth characteristics and gene expression of muscle progenitor cells (i.e., satellite cells) will be affected, leading to increased fat deposition, resulting in long-term changes in muscle structure and a reduction in meat yield. The in vitro studies on cultured satellite cells derived from different muscle, have demonstrated that, anaerobic pectoralis major satellite cells are more predisposed to adipogenic conversion and more sensitive during myogenic proliferation and differentiation than aerobic biceps femoris cells when challenged to both hot and cold thermal stress. These results corroborated the in vivo studies, establishing that chronic heat exposure of broiler chicks at their first two week of life leads to impaired myogenicity of the satellite cells, and increased fat deposition in the muscle. Moreover, chronic exposure of chicks to inaccurate temperature, in particular to heat vs. cold, during their early posthatch periods has long-term effects of BW, absolute muscle growth and muscle morphology and meat quality. The latter is manifested by higher lipid and collagen deposition and may lead to the white striping occurrence. The results of this study emphasize the high sensitivity of muscle progenitor cells in the early posthatch period at a time when they are highly active and therefore the importance of rearing broiler chicks under accurate ambient temperatures. From an agricultural point of view, this research clearly demonstrates the immediate and long-term adverse effects on broiler muscling and fat formation due to chronic exposure to hot stress vs. cold temperatures at early age posthatch. These findings will aid in developing management strategies to improve broiler performance in Israel and the USA. BARD Report - Project4592 Page 2 of 29

1. 1. At 35°C, the response functions of body weight gain and feed intake of 5–8 week old chickens to relative humidity (RH) were bell shaped with maxima at 60–65%, corresponding to minima in core and skin temperature, blood pH, and to maxima in blood pCO2. 2. 2. In 5–8 week old turkeys, weight gain and feed intake declined only with the increase from 40–45% to 50–55% in RH. Core and skin temperature, and blood acid-base were not affected by RH. 3. 3. Plasma (T3) concentration was positively correlated with feed intake.

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.

1. 1. Changes in food consumption and fermentation capacity were examined in mole-rats housed at 23 and 30°C. 2. 2. At both temperatures animals maintained body mass. Food consumption was lower at the higher temperature and led to a similar decline in caecal mass. 3. 3. Caecal dry matter content and fermentation efficiency were unaffected by food intake. However, gas production per animal decreased markedly with the reduced food intake. 4. 4. The drop in fermentation in response to decreased food intake led to a concomitant decrease in heat production. This would be highly advantageous for chthonic rodents residing during summer in warm humid plugged burrows.

Naked mole rats (Heterocephalus glaber) lead a strictly subterranean existence and appear to be naturally deficient in cholecalciferol (D3). Oral supplementation with D3(Ds) led to a 1.8-fold increase in food intake and the associated enlargement (1.4-fold) of the caecum. The effect of Ds, and the concomitant increase in food intake, on caecal fermentation efficiency when animals were fed on a carrotbased diet was determined by measuring the rate of both gas production and short-chain fatty acid (SCFA) production. Microbial-controlled fermentation processes in the caecum were enhanced with Dswhen compared with animals not receiving a D3supplement (Dn). Both the rates of gas production (Dn10.76 (SE 0.77), Ds15.20 (SE 1.77) ml/g dry matter (DM) per h) and SCFA production (Dn463.0 (SE 33.7), Ds684.3 (SE 74.8)μmol/g DM per h) increased more than 1.4-fold per g DM caecal substrate. These factors contributed to the higher digestibility of the food in Dsanimals. The larger quantity of energy available to D3-replete naked mole rats was not used in anabolic processes, for these animals maintained mass. These findings suggest that metabolic rate in D3-replete animals was elevated. Thus, despite improved gut function, D3-replete animals may be disadvantaged by their higher energy and food requirements in their natural milieu.

WOS: 000276893800017, PubMed ID: 20371850, 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 treatmentresulted 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., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); Research and Application Center of Science and Technology of Ege UniversityEge University; Volcani Center, This study was funded by the Scientific and Technological Research Council of Turkey (TUBITAK), Research and Application Center of Science and Technology of Ege University, and The Volcani Center.

Calcium flux and mode of uptake were investigated in an underground dwelling mole-rat, Cryptomys damarensis, fed diets of varying Ca content. The amount of dietary Ca positively influenced the amounts ingested, absorbed and retained. The linear relationship between ingested and absorbed Ca was significantly (P less than 0.001) correlated, implying that this process is nonsaturable. When mole-rats were fed a diet low in Ca, apparent fractional absorption of Ca was high (85.88%). This increased still further when the diet was changed to a food of greater Ca content (96.13%, carrots; 96.97%, gemsbok cucumber). Mineral homeostasis is regulated at the intestinal level in most mammals. Regardless of dietary Ca content, uptake of 45Ca (examined via the everted gut sac technique) was passive, confirming that absorption is via a nonsaturable process. Plasma Ca concentrations were not tightly regulated, yet when fed the diet with the highest Ca content, mole-rats were not hypercalcemic. Regardless of diets, Ca apparent fractional retention was positive, and approached physiological maxima (greater than 97%). Cryptomys damarensis, in using highly efficient modes of mineral uptake and retention, is therefore capable of fully exploiting the limited food resources of their arid ecotope.

The necessity to improve broiler thermotolerance and performance led to the following hypothesis: (a) thethermoregulatory-response threshold for heat production can be altered by thermal manipulation (TM) during incubation so as to improve the acquisition of thermotolerance in the post-hatch broiler;and (b) TM during embryogenesis will improve myoblast proliferation during the embryonic and post-hatch periods with subsequent enhanced muscle growth and meat production. The original objectives of this study were as follow: 1. to assess the timing, temperature, duration, and turning frequency required for optimal TM during embryogenesis; 2. to evaluate the effect of TM during embryogenesis on thermoregulation (heat production and heat dissipation) during four phases: (1) embryogenesis, (2) at hatch, (3) during growth, and (4) during heat challenge near marketing age; 3. to investigate the stimulatory effect of thermotolerance on hormones that regulate thermogenesis and stress (T₄, T₃, corticosterone, glucagon); 4. to determine the effect of TM on performance (BW gain, feed intake, feed efficiency, carcass yield, breast muscle yield) of broiler chickens; and 5. to study the effect of TM during embryogenesis on skeletal muscle growth, including myoblast proliferation and fiber development, in the embryo and post-hatch chicks.This study has achieved all the original objectives. Only the plasma glucagon concentration (objective 3) was not measured as a result of technical obstacles. Background to the topic: Rapid growth rate has presented broiler chickens with seriousdifficulties when called upon to efficiently thermoregulate in hot environmental conditions. Being homeotherms, birds are able to maintain their body temperature (Tb) within a narrow range. An increase in Tb above the regulated range, as a result of exposure to environmental conditions and/or excessive metabolic heat production that often characterize broiler chickens, may lead to a potentially lethal cascade of irreversible thermoregulatory events. Exposure to temperature fluctuations during the perinatal period has been shown to lead to epigenetic temperature adaptation. The mechanism for this adaptation was based on the assumption that environmental factors, especially ambient temperature, have a strong influence on the determination of the “set-point” for physiological control systems during “critical developmental phases.” In order to sustain or even improve broiler performance, TM during the period of embryogenesis when satellite cell population normally expand should increase absolute pectoralis muscle weight in broilers post-hatch. Major conclusions: Intermittent TM (39.5°C for 12 h/day) during embryogenesis when the thyroid and adrenal axis was developing and maturing (E7 to E16 inclusive) had a long lasting thermoregulatory effect that improved thermotolerance of broiler chickens exposed to acute thermal stress at market age by lowering their functional Tb set point, thus lowering metabolic rate at hatch, improving sensible heat loss, and significantly decreasing the level of stress. Increased machine ventilation rate was required during TM so as to supply the oxygen required for the periods of increased embryonic development. Enhancing embryonic development was found to be accomplished by a combination of pre-incubation heating of embryos for 12 h at 30°C, followed by increasing incubation temperature to 38°C during the first 3 days of incubation. It was further facilitated by increasing turning frequency of the eggs to 48 or 96 times daily. TM during critical phases of muscle development in the late-term chick embryo (E16 to E18) for 3 or 6 hours (39.5°C) had an immediate stimulatory effect on myoblast proliferation that lasted for up to two weeks post-hatch; this was followed by increased hypertrophy at later ages. The various incubation temperatures and TM durations focused on the fine-tuning of muscle development and growth processes during late-term embryogenesis as well as in post-hatch chickens.

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.

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.

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.

In recent decades, the rate of weight gain of meat-type broiler chickens has increased significantly [25, 26]. In the 1960s, a commercial broiler chicken reached the market weight of 2.2 kg by 12 weeks of age; today, broilers attain this same market weight at less than 6 weeks. This impressive improvement is due to the knowledge accumulated by industry poultry managers and researchers from different disciplines – geneticists, nutritionists, physiologists and veterinarians – who have contributed to the optimisation of broiler performance.