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.

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 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.

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.

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.

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.

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.

Expression of foreign genes in chicks by hydrodynamics-based naked plasmid transfer in vivo

The study of gene function in vivo is considered one of the top achievements of modern biology, inasmuch as it provides tools to study gene function in the context of the whole animal. In chickens, techniques of DNA-mediated gene transfer are less advanced than in other animal or livestock models, and remain a significant challenge. The study presented here is the first to show that a hydrodynamics-based gene-transfer technique, originally developed for naked DNA transfer in mice, can be applied to chickens. Rapid injection of naked plasmids containing expression cassettes into the jugular vein of 6- to 10-day-old chicks resulted in specific expression of the transgenes. A CMV promoter-driven luciferase reporter gene was expressed at significant levels in the liver during the first 3 days post-injection with lower levels also detected in the kidney. Significantly, all injected birds showed detectable levels of luciferase expression. Similarly, injection of a plasmid containing the secreted human coagulation factor IX (hFIX) gene under the control of human alpha-1-anti-trypsin promoter resulted in detectable levels of the hFIX in the plasma during the first 2 days post-injection. The method described herein has the potential for a quick and simple route for gain and loss-of function experiments in chicken liver and kidney, as well as for studying systemic effects of secreted proteins and hormones.

Thermal manipulations during broiler chick embryogenesis: effects of timing and temperature

This study aimed at elucidating the effects of thermal manipulation (TM) during different periods of embryogenesis on hatchability, body weight, and thermoregulation of Ross chicks at hatch, and on the chick's ability to cope with thermal challenge (TC) at 3 d of age. Control embryos were incubated at 37.8 degrees C and 56% RH, whereas the TM embryos were treated for 3 h at 39.5 (1) or 41.0 degrees C (2) and 65% RH, during early embryogenesis (EE), E8 to E10, and late embryogenesis (LE) at E16 to E18. At hatch, after feather drying, BW and body temperature (Tb) were measured, blood was drawn from the jugular vein to measure plasma concentrations of thyroxine (T4), triiodothyronine (T3), and corticosterone. These parameters were also measured in 3-d-old chicks during exposure to TC at 41 degrees C for 6 h. Hatchability was significantly higher in the LE1-treated group than in the other treatments. EE1- and LE1-treated embryos exhibited significantly lower Tb at hatch than the LE2 chicks. Significant hyperthermia was noted in the control chicks during 6 h of TC; it coincided with a higher plasma T3 concentration (P = 0.074). During TC, the LE1-treated chicks exhibited the lowest T3 to T4 ratio and a significantly reduced plasma corticosterone concentration. It can be concluded that TM at 39.5 degrees C for 3 h during E16 to E18 of incubation improved chick's thermotolerance acquisition and reduced the corticosterone level of chicks exposed to TC at the age of 3 d.

The effect of a green and blue monochromatic light combination on broiler growth and development

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.

Ventilation, sensible heat loss, broiler energy, and water balance under harsh environmental conditions

Air velocity (AV) is one of the main environmental factors involved in thermoregulation, especially at high ambient temperatures. To elucidate the effect of AV on performance and thermoregulation of 4- to 7-wk-old broiler chickens, an experiment was conducted using 4 different AV (0.8, 1.5, 2.0, and 3.0 m/s) at constant ambient temperatature (35 +/- 1.0 degrees C) and RH (60 +/- 2.5%). BW, feed intake, and fecal and urinary excretions were monitored in individuals and were used to calculate the amount of energy expended for maintenance. Infrared thermal imaging radiometry was used to measure surface temperatures for the calculation of heat loss by radiation and convection. Brachial vein blood was collected for plasma osmolality and arginine vasotocin analysis. Broilers performed optimally at an AV of 2.0 m/s. Energy expenditure for maintenance was significantly higher under these conditions, suggesting the ability to direct a sufficient amount of energy to control body temperature, while maintaining relatively high growth rates. Convective heat loss increased significantly with increasing AV, whereas radiative heat loss was not affected. Sensible heat loss, expressed as a percentage of energy expenditure for maintenance, was significantly higher at 2.0 m/s compared with 0.8 m/s but significantly lower than that of 3.0 m/s. The high level of heat loss observed at 3.0 m/s probably affected body water balance, as supported by significantly higher plasma osmolality, arginine vasotocin concentration, and the hyperthermic status of these birds. It can be concluded that AV of 2.0 m/s enables broilers to maintain proper performance together with efficient thermoregulation and water balance under harsh environmental conditions.

Erythropoiesis regulation during the development of ascites syndrome in broiler chickens: a possible role of corticosterone

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.

The effect of melatonin administration on circulating plasma luteinizing hormone concentration in castrated White Leghorn roosters

Melatonin (MLT) has a significant role in mammalian reproduction, with little or no effect in birds. In the present study we studied the role of MLT in regulation of luteinizing hormone (LH) secretion in castrated White Leghorn (WL) roosters. In Experiment 1, castrated WL roosters (n = 30) were divided into three groups, and each group (n = 10) was subdivided into two subgroups (n = 5). Birds in one subgroup received an injection of MLT at 5 mg (MLT-5), 20 mg (MLT-20), or 80 mg (MLT-80)/kg BW. Birds in the second subgroup were vehicle-injected and served as controls. Each dose of MLT was administered on a separate day at 1100 h. Blood was sampled 30 min before and 10, 30, 60, and 120 min after MLT or vehicle administration. Ten minutes after MLT administration, a significant reduction in plasma LH was observed in the MLT-20 and -80 groups, i.e., 70.3 +/- 8.3% and 62.2 +/- 4.1% of control values, respectively. In the MLT-80 group, plasma LH further declined to 42.1 +/- 9.7% of control values 60 min after injection. In Experiment 2, 18 castrated WL roosters were divided into three groups of six birds each. Two groups were injected with 80 mg MLT/kg BW at the beginning of the experiment; the second group received an additional dose of 80 mg MLT/ kg BW 140 min after the first injection. The third group was injected twice (as in second group) with vehicle and served as control. Blood was sampled 30 min before and 30, 60, 120, 170, 200, and 240 min after injection. Repeated MLT injection maintained low levels of plasma LH level until the end of the experiment. In Experiment 3, 10 castrated WL roosters were divided into two groups (n = 5). The first group was injected daily, for 10 d, with 80 mg MLT/kg BW, the second group was vehicle-treated and served as a control. At Day 3, there was a significant reduction in plasma LH level in the MLT-treated group, which continued for 7 d. This study demonstrates that, in birds, MLT suppresses LH secretion in a dose- and a time-related manner.

Thermotolerance acquisition in broiler chickens by temperature conditioning early in life--the effect of timing and ambient temperature

Thermal conditioning of chicks results in improvements in performance and thermotolerance at marketing age. Conditioning has been found to be a sensitive process, dependent on age and the temperature used. The objective of this study was to assess the optimal timing and temperature for the conditioning processes. Six separate trials were conducted on male broiler chickens: the first two aimed to find the optimal age for thermal conditioning (1 to 5 d of age); the other four evaluated the optimal thermal conditioning temperature between 36 and 40.5 C. At 42 d of age chickens were thermally challenged to evaluate their ability to cope with acute heat stress. The highest body weight was achieved when thermal conditioning had been applied at the age of 3 d, and it coincided with low feed intake and higher to significantly higher feed efficiency. These treated chickens showed relatively lower mortality rate under thermal challenge and lower to significantly lower Triiodothyronine (T3) concentration in Trial 2. Chicks that had been thermally conditioned at ambient temperatures (Ta) of 36 and 37.5 C at the age of 3 d demonstrated the best performance characteristics and the ability to reduce T3 concentration to the lowest levels during thermal challenge. It can be suggested, therefore, that a Ta between 36.0 and 37.5 C, applied at 3 d of age is optimum for thermal conditioning of broiler chickens.

Association between weight gain, blood parameters, and thyroid hormones and the development of ascites syndrome in broiler chickens

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.

Early-age heat exposure affects skeletal muscle satellite cell proliferation and differentiation in chicks

Exposure of young chicks to thermal conditioning (TC; i.e., 37 degrees 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 6 together 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.

Air velocity alters broiler performance under harsh environmental conditions

The effect of air velocity (AV) on weight gain, feed intake, and feed efficiency was studied in male broiler chickens exposed to a constant 35 C, 60% RH, and continuous illumination from 4 through 7 wk of age. In two separate trials, AV of 0.5, 1.5, 2.0, and 3.0 m/s (Trial 1) and 1.0, 1.5, 2.0, and 2.5 m/s (Trial 2) were used. The fifth week was used for acclimation to the targeted environmental conditions. Weight gain was significantly higher in broilers exposed to AV of 1.5 and 2.0 m/s in both trials, which coincided with significantly higher feed intake and feed efficiency. Exposure to the low AV (0.5 and 1.0 m/s) resulted in weight gain, feed intake, and feed efficiency that were less than those of broilers exposed to high AV (2.5 and 3.0 m/s). In all treatments, broilers developed hyperthermia, but there were no significant differences in body temperature (Tb) among the birds. It can be concluded that AV has a significant effect on broiler performance; the optimal AV was found to be 1.5 to 2.0 m/s.

Changes in growth and function of chick small intestine epithelium due to early thermal conditioning

The effect of exposure to heat at 3 d of age on small intestine functionality and development was assayed by measuring villus size, proliferating enterocytes, and brush-border membrane (BBM) enzyme expression and activity. Results showed that thermal conditioning caused an immediate effect characterized by lowered triiodothyronine (T3) level, reduced feed intake, and depressed enterocyte proliferation and BBM enzyme activity. A second series of effects, observed 48 h posttreatment, was characterized by elevated T3, increased feed intake, increased enterocyte proliferation, and higher expression and activity of BBM enzymes. The association between ambient temperature, feed intake, growth rate, and plasma T3 levels was reflected in the structure and function of the intestinal tract. The results suggest that thermal conditioning at an early age influences T3 concentrations, which in turn alter the intestinal capacity to proliferate, grow, and digest nutrients. However, these experiments were not able to discriminate between effects due to feed intake and those due to thermal conditioning. The treatments modulated changes in the intestinal tract following thermal treatment.

Early age thermal conditioning and a dual feeding program for male broilers challenged by heat stress

The effects of early age thermal conditioning (TC) and dual feeding on responses of male broilers to a thermal challenge at 34 d of age are reported. Three hundred chicks were randomly divided into two equal groups. One group was exposed to thermal conditioning (38 C, 42% relative humidity for 24 h) at the age of 5 d, and the other group was not exposed. From 11 to 41 d of age, temperature was diurnally cyclic: 26 C (1600 to 0900 h) and 30 C (0900 to 1600 h). From Day 19, a factorial (2 x 2, TC x diet) experiment was conducted using eight pens of six broilers per treatment. Diets were control diet and dual feeding of a high protein fraction (1600 to 0900 h) and an energy-rich fraction (0900 to 1600 h). Growth and feed efficiency were slightly enhanced (+4%) by thermal conditioning and slightly reduced (-4%) by dual feeding. Mortality during thermal challenge was reduced by both factors. [In not conditioned chicks (N), 31 fed a control grower diet (NG) and 12 on a dual feeding program (NDF) died; in thermal conditioned chicks (T), 18 fed a control grower diet (TG) and 11 on a dual feeding program (TDF) died.] Before the thermal challenge period, body temperature (Tb) was consistently reduced in T. During the thermal challenge period, Tb was reduced by thermal conditioning and dual feeding. Measured at the age of 32 d, Tb gave an estimation of the ability of the chickens to cope with heat stress 2 d later. Pectoral mass was increased in TG, whereas the liver and the gizzard were significantly heavier in TDF and NDF. These results suggest that thermal conditioning at 5 d of age induces a consistent metabolic change in broiler males. The dual feeding program might have induced transitory effects on heat production during the heat stress.

Lack of response of laying hens to relative humidity at high ambient temperature

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.

The effect of light intensity on growth and development of turkey toms

1. The effect of light intensities from 10 to 700 lux on the performance of 5 to 18 week-old turkey males was studied in 2 trials. 2. Body weight of 18 week-old turkeys, in both experiments, was highest under the lowest light intensity This coincided with higher weight gain and lower food intake, which resulted in significantly better food conversion efficiency 3. Light intensity affected heart muscle weight but not weight of breast muscle, abdominal fat or testis as proportions of body weight. 4. The decline in plasma T3 concentration with age differed from other treatments at the low light intensity, which resulted in a significantly higher T3 concentration in turkeys exposed to 10 lux at the age of 10 to 15 weeks. 5. It is concluded that light intensity significantly affects food conversion efficiency in turkey males. This is likely to be related to differential investment of energy expenditure for maintenance.

Relative humidity at moderate ambient temperatures: its effect on male broiler chickens and turkeys

1. The effect of relative humidity (RH, 40% to 75%) at moderate ambient temperatures (Ta, 28 degrees and 30 degrees C) on the performance and thermoregulation of male broiler chickens and turkeys was studied at the age of 4 to 8 weeks. 2. Weight gain and food intake of male broiler chickens were significantly higher at 60% to 65% RH but food conversion efficiency was not affected by RH. In male turkeys, no effect of RH on performance was recorded. 3. Both chickens and turkeys controlled body temperature at normothermic levels during exposure to the experimental environmental conditions. 4. The rate of panting estimated from blood pH and pCO2 was lower in chickens exposed to 28 degrees C than to 30 degrees C. In turkeys, the rate was lower than that recorded in chickens at both Ta(s). 5. Plasma T3 was positively and significantly correlated with food intake. 6. It may be concluded that RH plays a role in the performance of chickens exposed to 30 degrees and 28 degrees C. whereas male turkeys must respond to RH at Ta >30 degrees C.

AlphaMUPA mice: a transgenic model for increased life span

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.

Effect of early-stage thermal conditioning and food restriction on performance and thermotolerance of male broiler chickens

1. The effects of early-age thermal conditioning and food restriction on performance and thermotolerance were studied in male broiler chickens, in 2 trials. 2. Chickens were exposed to 36 degrees +/- 1 degree C and 70% to 80% relative humidity (RH) for 24 h at the age of 5 d (thermal conditioning, TC), or to food restriction (FR) at the age of 7 to 14 d, or to both treatments (TC+FR), while a control group was reared under standard conditions. At the age of 42 d, chickens were thermally challenged by a heat stress of 350 degrees +/- 1 degree C and 20% to 30% RH for 6 h. 3. In both experiments, weight gain of the TC chickens between the ages of 7 and 42 d was significantly higher than those of other treatments and was associated with higher food intake. 4. Early-age TC significantly increased body temperature (Tb). Thermal challenge at the age of 42 d markedly increased Tb in all groups but that of the TC groups was the lowest. 5. Mortality during thermal challenge was significantly lower in the treated chickens, except for the FR group in trial 2. 6. Plasma triiodothyronine (T3) concentration was greatly depressed in all treatment groups during the thermal challenge. However, the lowest concentration was observed in the TC group, suggesting that these chickens exhibit the lowest rate of heat production under such conditions. 7. Thermal conditioning reduced the increase of haematocrit with age, whereas food restriction resulted in an increase in haematocrit immediately after FR. Thermal challenge resulted in a haematocrit decline in all groups, with the lowest values in the TC and TC+FR chickens. 8. It can be concluded that, because the TC treatment improved thermotolerance (possibly by reducing heat production) and performance, it has advantages over the FR and TC+FR treatments.

Response of turkeys to relative humidity at high ambient temperature

1. The effects of relative humidity on growth rate and thermoregulation at high ambient temperature were evaluated in turkeys. Male turkeys were exposed to ambient temperature (Ta) of 35 degrees C and relative humidity (RH) of 40% to 75% and 50% to 85%, at ages of 13 to 19 weeks (trial 1) and 10 to 15 weeks (trial 2), respectively. 2. Body weight and food intake in both trials increased as RH increased up to 70% to 75%. When RH increased further to 80% to 85% (Trial 2) both body weight and food intake declined significantly. 3. Blood CO2 partial pressure (pCO2) did not change significantly at different RHs (trial 1). However, in trial 2 it dropped significantly at 80% to 85% RH. This response coincided with an increase in blood pH. 4. The effect of RH on body temperature (Tb) was not significant in either trial. 5. Triiodothyronine (T3) concentrations increased with the increase in RH up to 70% to 75% RH (trials 1 and 2). A significant decrease was observed when RH was further increased to 80% to 85% RH (Trial 2). Positive linear correlations between T3 and food intake or weight gain were observed in both trials. 6. The results indicate that turkeys can thermoregulate efficiently in the face of extreme changes in RH and that only at high RH (above 75%) did the performance of turkeys deteriorate.

Research notes: Effect of environmental temperature on broiler chickens subjected to growth restriction at an early age

An experiment was carried out to evaluate the effect of early growth restriction (EGR) induced by feed restriction on the ability of male broiler chickens to withstand exposure to high environmental temperatures. A 2 x 4 factorial arrangement of treatments was employed to determine whether such an exposure affects the beneficial effect of EGR on performance and carcass quality. Chicks consumed feed ad libitum or were feed-restricted from 6 to 12 d of age (to achieve 60% growth of the ad libitum birds). From 4 to 8 wk of age, the chickens were kept in temperature-controlled chambers at 25, 30, 35 C and a diurnal cyclic temperature of 25:35 C. Weight gain, feed intake, and feed efficiency from 6 to 8 wk of age (after acclimatization to the various temperatures) and BW at 8 wk of age were significantly (P < or = 0.05) depressed by the high temperatures (35 and 25:35 C) compared with values observed at 25 and 30 C. Early growth restriction did not affect these variables. Relative heart, liver, and breast meat weights at 8 wk of age were decreased significantly with increasing temperature. Relative liver weight was also decreased significantly in the EGR chicks, whereas breast yield was increased significantly in these birds. Relative abdominal fat pad size was not affected by increasing the temperature from 25 to 35 C, but it was significantly lower in chickens kept at 25:35 C than in those kept at 25 and 35 C. Early growth restriction significantly reduced the size of abdominal fat. Because no significant interactions between EGR and ambient temperature on the above mentioned variables were observed during 4 to 8 wk of age, it is concluded that EGR can not alleviate the adverse effect of high ambient temperature on performance, nor can high ambient temperature obliterate the beneficial effect of EGR in improving feed efficiency and reducing fattening.

Thermoregulation in naked neck chickens subjected to different ambient temperatures

1. Heterozygous (Na/na) naked neck chickens and their normally feathered (na/na) sibs, were exposed to constant ambient temperatures (Ta) ranging between 15 and 35 degrees C and 12h: 12h diurnal high:low temperatures of 15 degrees C:35 degrees C. 2. No significant effect of genotype was obtained in weight gain and food intake. However, the naked neck birds tended to gain somewhat more weight at high Ta and consume more food at low Ta. 3. At 35 degrees C Na birds showed better regulation of body temperature (Tb) and demonstrated considerably higher radiation from the neck. 4. The greater food intake of the naked neck chickens at 15 degrees C was associated with significantly higher packed cell volume, haemoglobin concentration, heart and liver size. These appear to involve both higher heat production and haemodynamic changes to accommodate the higher oxygen demands of the naked neck chickens at low Ta. 5. The results indicate the ability of the naked neck chickens, on the one hand to thermoregulate at low Tas and, on the other their slightly better capacity to maintain Tb at high Tas. However, no genotype advantage was obtained under diurnal cyclic temperature conditions.

Effect of acquisition of improved thermotolerance on the induction of heat shock proteins in broiler chickens

The role of heat shock proteins (HSP) in the protection of cells from heat stress is well established. However, very little is known about their contribution to thermotolerance in the complexity of a whole homeotherm animal. Here we report on the analysis of protein synthesis in lung and heart muscle tissues of broiler chickens following exposure to high ambient temperature. Half of the flock was treated by an early age exposure to heat (conditioning), to improve thermotolerance. In contrast to what has been expected, lower levels of HSP induction was observed in the treated chickens. We suggest that 1) the induction of HSP in the heart and lung tissues of the whole animal correlates with the body temperature and 2) HSP response does not represent a part of the long-term mechanism that is evoked by the early age conditioning.

Blood system response of chickens to changes in environmental temperature

Hemodynamic changes were studied in broiler chickens during exposure to constant temperatures (10 to 35 C) or diurnal temperature cycles (10:30 C and 15:35 C), and during acute heat or cold. Packed cell volume (PCV) was significantly high at low constant temperatures (10 and 15 C), whereas at high temperatures (30 and 35 C) plasma volume (PV) was significantly high. A linear relationship between hematocrit and heart weight was observed and indicates an adaptation of heart mass to changes in cardiac output and hematocrit to meet the demands of increased basal metabolic rate. Only during the diurnal temperature cycle of 15:35 C did a significant increase in PV occur when ambient temperature (Ta) was raised form 15 to 35 C. Acute exposure of chickens to high temperature did not affect PV or PCV, but resulted in hyperthermia (44.7 +/- 0.4 C). Changes in PCV are probably related to modulation of the supply of oxygen to accommodate changes in heat production. The significant hypervolemia observed at high temperatures could occur to provide the fluid needed for heat dissipation by panting. The lack of response of the blood system to acute temperature changes may be at least partially responsible for the chickens' failure to control body temperature.

Induction of thermotolerance in chickens by temperature conditioning: heat shock protein expression

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.

A novel 29-kDa chicken heat shock protein

The family of small heat shock proteins is the more variable among the highly conserved superfamily of heat shock proteins (HSP). Using a metabolic labeling procedure with tissue explants, we have detected in chickens a new member of the small HSP family with an apparent molecular weight of 29-kDa. This protein was induced in broiler chickens' heart muscle and lungs following an in vivo heat stress. The 29-kDa band appears after 3 h of heat stress, much later than the induction of HSP 90, HSP 70, and HSP 27. The late onset of induction suggests that HSP 29 plays a more specific role of a "second stage defense protein".

Effects of diurnally cycling versus constant temperatures on chicken growth and food intake

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.

Induction of thermotolerance in male broiler chickens by temperature conditioning at an early age

Chicks were conditioned by exposure to heat stress (36 +/- 1 C; 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 control 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.

Fibre utilization by Kalahari dwelling subterranean Damara mole-rats (Cryptomys damarensis) when fed their natural diet of gemsbok cucumber tubers (Acanthosicyos naudinianus)

Kalahari dwelling Damara mole-rats (Cryptomys damarensis) naturally feed on a high fibre diet of underground gemsbok cucumber tubers, Acanthosicyos naudinianus. We investigated the degree of fibre utilization and fermentation on this diet by measuring caecal characteristics (namely temperature, pH and weight) and in vitro rates of gas and short chain fatty acid (SCFA) production in these underground dwelling hind-gut fermentors. Rectal temperatures (33.8 +/- 0.6 degrees C) were consistently higher than caecal temperatures (33.3 +/- 0.6 degrees C). Furthermore, a 0.8 degrees C gradient of temperatures existed within the caecum, with the lowest temperature occurring in the corpus caeci. Both rates of gas production (4.74 +/- 0.6 ml/g dry matter/hr) and SCFA production (266.80 +/- 9.251 mumol/caecum per hr) were high, with proportionately more acetic acid produced than any other SCFA. Nevertheless, the initial concentrations of SCFAs present in the caecum were low (52 +/- 17 mM) implying a rapid rate of absorption of these SCFAs. The high rates of fermentation provide a considerable amount of energy that would otherwise be trapped in fibre and thus unavailable to the animal. This highly efficient caecal fermentation enables the Damara mole-rat to maximally exploit the underground food resources in the arid-zone ecotope.