Thermal manipulations during broiler embryogenesis improves post-hatch performance under hot conditions

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.

Early posthatch thermal stress affects breast muscle development and satellite cell growth and characteristics in broilers

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.

Evaluation of DNA methylation and mRNA expression of heat shock proteins in thermal manipulated chicken

Thermal manipulation during embryogenesis has been demonstrated to enhance the thermotolerance capacity of broilers through epigenetic modifications. Heat shock proteins (HSPs) are induced in response to stress for guarding cells against damage. The present study investigates the effect of thermal conditioning during embryogenesis and thermal challenge at 42 days of age on HSP gene and protein expression, DNA methylation and in vitro luciferase assay in brain tissue of Naked Neck (NN) and Punjab Broiler-2 (PB-2) chicken. On the 15th day of incubation, fertile eggs from two breeds, NN and PB-2, were randomly divided in to two groups: control (C)-eggs were incubated under standard incubation conditions, and thermal conditioning (TC)-eggs were exposed to higher incubation temperature (40.5°C) for 3 h on the 15th, 16th, and 17th days of incubation. The chicks obtained from each group were further subdivided and reared under different environmental conditions from the 15th to the 42nd day as normal [N; 25 ± 1 °C, 70% relative humidity (RH)] and heat exposed (HE; 35 ± 1 °C, 50% RH) resulting in four treatment groups (CN, CHE, TCN, and TCHE). The results revealed that HSP promoter activity was stronger in CHE, which had lesser methylation and higher gene expression. The activity of promoter region was lesser in TCHE birds that were thermally manipulated at the embryonic stage, thus reflecting their stress-free condition. This was confirmed by the lower level of mRNA expression of all the HSP genes. In conclusion, thermal conditioning during embryogenesis has a positive impact and improves chicken thermotolerance capacity in postnatal life.

l-Leucine acts as a potential agent in reducing body temperature at hatching and affords thermotolerance in broiler chicks

Thermal manipulation (TM) of incubation temperature causes metabolic alterations and contributes to improving thermotolerance in chicks post hatching. However, there has been no report on amino acid metabolism during TM and the part it plays in thermotolerance. In this study, we therefore first analyzed free amino acid concentrations in the embryonic brain and liver during TM (38.6°C, 6h/d during embryonic day (ED) 10 to ED 18). It was found that leucine (Leu), phenylalanine and lysine were significantly decreased in the embryonic brain and liver. We then chose l-Leu and other branched-chain amino acids (l-isoleucine (L-Ile) and l-valine (l-Val)) for in ovo injection on ED 7 to reveal their roles in thermoregulation, growth, food intake and thermotolerance in chicks. It was found that in ovo injection of l-Leu, but not of l-Ileu or l-Val, caused a significant decline in body temperature at hatching and increased food intake and body weight gain in broiler chicks. Interestingly, in ovo injection of l-Leu resulted in the acquisition of thermotolerance under high ambient temperature (35±1°C for 180min) in comparison with the control thermoneutral temperature (28±1°C for 180min). These results indicate that the free amino acid concentrations during embryogenesis were altered by TM. l-Leu administration in eggs caused a reduction in body temperature at hatching, and afforded thermotolerance in heat-exposed young chicks, further suggesting that l-Leu may be one of the key metabolic factors involved in controlling body temperature in embryos, as well as in producing thermotolerance after hatching.

Thermal manipulation during Pre and Post-Hatch on thermotolerance of male broiler chickens exposed to chronic heat stress

The aim of this study was to evaluate the effects of thermal manipulation (TM) during pre and post-hatch periods on thermotolerance of male broiler chickens exposed to chronic heat stress (CHS) during the finisher phase (34 ± 2°C, 6 h/day). Seven hundred fertile eggs of Ross 308 were assigned to the following groups: 1) control group incubated and housed in standard conditions, 2) pre-hatch treatment (PRE), the eggs were exposed to 39.5°C and 65% RH for 12 h, d from embryonic d 7 to 16 and after hatching the chicks where housed in standard conditions; 3 and 4) post-hatch TM at d 3 (PO3) and post-hatch TM at d 5 (PO5), which had the same incubation conditions as control and exposed to 36 to 38°C for 24 h at 3 and 5 days of age, respectively. TM in PRE group resulted in delay in the hatch time (6 h) along with reduction in body weight compared to control (P = 0.02). TM caused a significant reduction of facial surface temperature (FST) until d 28 (P < 0.02), but not significant during CHS. Body weight gain was suppressed in PO3 and PO5 groups at d 14 (P = 0.007) and compensated at d 28. However, TM led to higher BWG (P = 0.000) but lower FCR (P = 0.03) and mortality at the first week of CHS compared to control. European production efficiency index was higher in TM-treated chickens compared to control (P = 0.01). TM reduced the blood concentration of uric acid, total protein, T3, and T4 in which thyroid hormones in PO3 and PO5 treatments showed more reduction rather than other groups. In PRE group, chickens had lower abdominal fat pad than control (P = 0.0001). The relative weight of heart was decreased in TM groups (P = 0.001). It was concluded that TM may induce thermotolerance in growing broilers, possibly through the modification of physiological parameters of broilers especially during the first week of CHS.

Melatonin modulates tonic immobility and vigilance behavioural responses of broiler chickens to lighting regimens during the hot-dry season

Experiments were conducted with the aim of determining the influence of melatonin administration on vigilance and tonic immobility (TI) responses of Marshall broiler chickens. The broiler chickens were reared on different lighting regimens and subjected to heat stress during the hot-dry season. Simple random sampling was used to assign 300 broiler chicks into three groups, comprising 100 broiler chicks each. Group I (12D:12L cycle) was raised under natural photoperiod of 12-h light and 12-h darkness, without melatonin supplementation. Group II (CL) was kept under 24-h continuous lighting, without melatonin administration. Group III (CL+MEL) was raised under 24-h continuous lighting; with melatonin supplementation at 0.5mg/kg per os, via drinking water using a syringe. Beginning from day-old, broiler chickens in group III were individually administered with melatonin once daily for 8weeks at 17:00h. TI was induced by manual restraint, and vigilance elicited at self-righting graded for three days, two weeks apart, in 15 labeled broiler chickens from each of the three groups; at 06:00h, 13:00h and 18:00h, starting from week 4-8. Each broiler chicken was laid on its back in a U-shaped cradle, covered with cloth. Thermal microenvironment parameters of dry bulb temperature (DBT) and relative humidity (RH) were recorded at the experimental site, concurrently during the vigilance and TI tests. Inside the broiler chickens' house, the weekly temperature-humidity index (THI) was lowest at week 4 of the study, with the value of 48.60±0.08°C. At week 4, the relationship between the THI and TI induction attempts was stronger in 12D:12L cycle (r=0.589, P<0.001) than CL (r=0.264, P>0.05) or CL+MEL (r=0.096, P>0.05) broiler chickens. This indicated that the broiler chickens on 12D:12L cycle were more active compared to their melatonin-treated counterparts, apparently due to adverse effects of high DBT and high RH on the broiler chickens during the hot-dry season. The highest numbers of TI induction trial attempts were recorded at 13:00h in 12D:12L cycle and CL groups (2.13±0.34 and 2.15±0.22, respectively), when the broiler chickens were at week 8. The overall mean values of induction trial attempts differed significantly (P<0.0001) between the groups; with the lowest mean values of 1.22±0.4 recorded in CL+MEL broiler chickens. At day 42, the lowest mean TI duration of 101.87±10.24s in the CL group, recorded at 06:00h rose (P<0.001) to 184.07±23.69s at 13:00h. The overall mean duration of TI differed significantly (P<0.0001) again between the groups; with the highest mean duration of 167.82±8.35s, recorded in CL+MEL broiler chickens administered with melatonin. The overall mean vigilance behavioural ranking values of 1.85+0.07 and 1.70+0.08, obtained in 12D:12L cycle and CL broiler chickens, respectively were higher (P<0.0001) than the value of 1.44+0.05 recorded in melatonin-treated broiler chickens. The results indicated that broiler chickens belonging to both 12D:12L cycle and CL groups were more emotional, fearful or anxious, compared to CL+MEL broiler chickens. It was concluded that melatonin administration elicits boldness and confidence by suppressing freezing behaviour in broiler chickens, and it may improve their welfare and productivity.

Influence of thermal stimulation during the late phase of incubation on hatching results and post-hatch broiler performance under commercial conditions

Two experiments, which differed in breeder age, strain and season, were conducted to study the influence of low-intensity, short-duration thermal stimuli during the late phase of incubation on hatchability and performance. The first experiment conducted in April-June used eggs from Cobb × Ross broiler breeders at 35-41 weeks of age and the second experiment performed in February-April used eggs from Hubbard × Cobb broiler breeders at 49-53 weeks of age. Eggs in the test group had the same physical environment as eggs in the control group except that incubation temperature was increased by 1˚C for 2 h/d above the control group from 18 to 20 d of incubation (DI). The results demonstrated that thermal stimulation of 1˚C for 2 h/d above control incubation temperature during 18-21DI did not have any adverse effects on hatch and post-hatch performance of broilers. In both experiments, treatment did not significantly alter the secondary sex ratio in hatched chickens, but hatch residue showed that the proportion of unhatched male embryos was significantly lower in the test groups than in the control groups. In the first experiment, thermal stimulation improved feed conversion by 1.82% compared with the control.

Incubation Temperature during Fetal Development Influences Morphophysiological Characteristics and Preferred Ambient Temperature of Chicken Hatchlings

Skin and feather characteristics, which play a critical role in body temperature maintenance, can be affected by incubation circumstances, such as incubation temperature. However, no study to date has assessed the influence of incubation temperature during the fetal stage on morphometric characteristics and vascular development of the skin, feather characteristics, and their relationship to hormone levels and preferred temperature in later life in chickens. Broiler breeder eggs were exposed to low (36°C), control (37.5°C), or high (39°C) temperatures (treatments LT, CK, and HT, respectively) from day 13 of incubation onward, because it is known that the endocrine axes are already established at this time. During this period, eggshell temperature of HT eggs (38.8±0.33°C) was higher than of LT (37.4±0.08°C) and CK eggs (37.8 ±0.15°C). The difference between eggshell and incubator air temperature diminished with the increasing incubation temperature, and was approximately zero for HT. HT hatchlings had higher surface temperature on the head, neck, and back, and thinner and more vascularized skin than did CK and LT hatchlings. No differences were found among treatments for body weight, total feather weight, number and length of barbs, barbule length, and plasma T4 concentration. LT hatchlings showed lower plasma T3 and GH, as well as lower T3/T4 ratio and decreased vascularity in the neck, back, and thigh skin compared to CK hatchlings. On the other hand, HT hatchlings had decreased skin thickness and increased vascularity, and preferred a higher ambient temperature compared to CK and HT hatchlings. In addition, for all treatments, surface temperature on the head was higher than of the other body regions. We conclude that changes in skin thickness and vascularity, as well as changes in thyroid and growth hormone levels, are the result of embryonic strategies to cope with higher or lower than normal incubation temperatures. Additionally exposure to increased temperature during incubation is an environmental factor that can exert early-life influence on ambient temperature preference of broiler hatchlings in later life.

Effect of Embryonic Thermal Exposure on Heat Shock Proteins (HSPs) Gene Expression and Serum T3 Concentration in Two Broiler Populations

The present experiment was conducted to evaluate the Hsp-70, 27 and Ubiquitin mRNA expressions and serum T3 concentration in synthetic colored broiler female lines, Punjab Broiler-2 (PB-2), and Naked neck (NN) broiler chicken whose eggs were exposed to 2°C increased incubation temperature for 3 hours each on the 16th, 17 th, and 18th day of incubation. Another set of eggs were incubated at normal conditions that were utilized as the control. A total of 432 chicks, 216 from each breed (PB-2; NN) and treatment (Heat exposed: HE; normal: N), were randomly distributed and reared at high ambient temperatures (32°C-45°C) during the summer season in battery brooders. Birds were sacrificed at 0 and the 28th day post hatch and different tissues (heart, liver, muscle, spleen, and bursa) were collected to study Hsps and ubiquitin mRNA expression. There was no difference between the breeds and age of slaughter in Hsp-70 mRNA expression. The Hsp(70, 27, and ubiquitin) mRNA expression was significantly (P≤0.001) lower in HE birds than that of N birds in PB-2 chickens. Nonsignificant variation was observed in NN chicken. The Hsp-70 mRNA expression was highest in bursa and lowest in muscle and liver. Serum T3 concentration was similar in both HE and N birds. The study concludes that exposure to increased temperature during incubation results in reduced expressions of Hsp mRNA in almost all tissues indicating better thermotolerance of the HE birds.

Thermal manipulation during broiler chicken embryogenesis: Effect on mRNA expressions of Hsp108, Hsp70, Hsp47 and Hsf-3 during subsequent post-hatch thermal challenge

Effects of thermal manipulation during broiler chicken embryonic days 12-18 on body temperature (T(b)) and mRNA expressions of Hsp108, Hsp70, Hsp47 and Hsf-3 in muscle, heart and brain tissues during subsequent thermal challenge (TC) were investigated. Fertile chicken eggs were divided randomly into four groups (n=375): eggs in the control group were maintained at 37.8°C and 56% (RH). Eggs in TM1 group were subjected to TM at 39°C for 9h during ED 12-18. Eggs in the TM2 and TM3 groups were subjected to the same protocol of TM1 except for increasing the period of exposure to 12h and 18h, respectively. During TC (43°C for 6h) at days 10 and 28, T(b) of TM chicks was significantly lower compared to controls. Furthermore, significant changes in mRNA expressions of Hsp108, Hsp70 and Hsp47 in muscle, heart and brain tissues were observed.

The genetic basis of pectoralis major myopathies in modern broiler chicken lines

This is the first report providing estimates of the genetic basis of breast muscle myopathies (BMM) and their relationship with growth and yield in broiler chickens. In addition, this paper addresses the hypothesis that genetic selection for increase breast yield has contributed to the onset of BMM. Data were analyzed from ongoing recording of BMM within the Aviagen breeding program. This study focused on three BMM: deep pectoral myopathy (DPM; binary trait), white striping (WS; 4 categories) and wooden breast (WB; 3 categories). Data from two purebred commercial broiler lines (A and B) were utilized providing greater than 40,000 meat quality records per line. The difference in selection history between these two lines has resulted in contrasting breast yield (BY): 29% for Line A and 21% for Line B. Data were analyzed to estimate genetic parameters using a multivariate animal model including six traits: body weight (BW), processing body weight (PW), BY, DPM, WB, and WS, in addition to the appropriate fixed effects and permanent environmental effect of the dam. Results indicate similar patterns of heritability and genetic correlations for the two lines. Heritabilities (h²) of BW, PW and BY ranged from 0.271–0.418; for DPM and WB h² <0.1; and for WS h² ≤0.338. Genetic correlations between the BMM and BW, PW, or BY were ≤0.132 in Line A and ≤0.248 in Line B. This paper demonstrates the polygenic nature of these traits and the low genetic relationships with BW, PW, and BY, which facilitates genetic improvement across all traits in a balanced breeding program. It also highlights the importance of understanding the environmental and/or management factors that contribute greater than 65% of the variance in the incidence of white striping of breast muscle and more than 90% of the variance of the incidence of wooden breast and deep pectoral myopathy in broiler chickens.

The effect of temperature on apoptosis and adipogenesis on skeletal muscle satellite cells derived from different muscle types

Satellite cells are multipotential stem cells that mediate postnatal muscle growth and respond differently to temperature based upon aerobic versus anaerobic fiber-type origin. The objective of this study was to determine how temperatures below and above the control, 38°C, affect the fate of satellite cells isolated from the anaerobic pectoralis major (p. major) or mixed fiber biceps femoris (b. femoris). At all sampling times, p. major and b. femoris cells accumulated less lipid when incubated at low temperatures and more lipid at elevated temperatures compared to the control. Satellite cells isolated from the p. major were more sensitive to temperature as they accumulated more lipid at elevated temperatures compared to b. femoris cells. Expression of adipogenic genes, CCAAT/enhancer-binding protein β (C/EBPβ) and proliferator-activated receptor gamma (PPARγ) were different within satellite cells isolated from the p. major or b. femoris. At 72 h of proliferation, C/EBPβ expression increased with increasing temperature in both cell types, while PPARγ expression decreased with increasing temperature in p. major satellite cells. At 48 h of differentiation, both C/EBPβ and PPARγ expression increased in the p. major and decreased in the b. femoris, with increasing temperature. Flow cytometry measured apoptotic markers for early apoptosis (Annexin-V-PE) or late apoptosis (7-AAD), showing less than 1% of apoptotic satellite cells throughout all experimental conditions, therefore, apoptosis was considered biologically not significant. The results support that anaerobic p. major satellite cells are more predisposed to adipogenic conversion than aerobic b. femoris cells when thermally challenged.

Thermal manipulation during embryogenesis improves certain semen parameters in layer breeder chicken during hot climatic conditions

Thermal manipulation during incubation has been shown to improve post hatch performance in poultry. The aim of the present experiment was to evaluate thermal manipulation on semen quality of roosters during hot climatic conditions. Eggs obtained after artificial insemination from Dahlem Red layer breeders were randomly divided into two groups control (C) and heat exposed (HE). C group eggs were incubated at 37.5°C throughout the incubation period while the HE group eggs were exposed to higher temperature 40.5°C from 15th to 17th day of incubation for 3h each day. The relative humidity was maintained at 65% in both the groups throughout incubation. The chicks hatched were reared separately under standard husbandry conditions. During high ambient temperature semen from roosters (45 weeks of age) was collected and evaluated for different gross parameters, sperm chromatin integrity and sperm HSP27 and HSP70 gene expression by real-time PCR. The seminal plasma was evaluated for lipid peroxidation, ferric ion reducing antioxidant power (FRAP), triiodothyronine (T3) and matrix metalloproteinase-2 (MMP-2) activity. The shed average Temperature Humidity Index (THI) during the experiment period was 78.55. The percent live sperm and FRAP level were significantly (P<0.05) higher and sperm gene expressions were significantly (P<0.05) lower in the HE group. No differences in other parameters were observed between the groups. Thus from the results it could be concluded that thermal manipulation during incubation improves certain semen parameters of roosters at high ambient temperature.

Thermal manipulation during embryogenesis affects myoblast proliferation and skeletal muscle growth in meat-type chickens

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.

Vitamin C prevents the effects of high rearing temperatures on the quality of broiler thigh meat1

We investigated the effects of incubation temperatures and vitamin C injections into eggs (treatments: 37.5ºC, 39ºC, 39ºC+vitamin C) on resultant chick pectoralis major and sartorius muscle fiber hypertrophy, as well as their effects on the quality of breast and over-thigh meat of broilers reared under cold, control, or hot temperatures. Incubation at 39ºC increased the shear force and reduced meat redness in breast meat (P < 0.05). Vitamin C prevented these high temperature incubation effects [shear force (kgf cm(-2)): 37.5ºC = 2.34, 39ºC = 2.79, 39ºC+vitamin C = 2.44; redness: 37.5ºC = 2.64, 39ºC = 1.90, 39ºC+vitamin C = 2.30], but reduced water content (37.5ºC = 74.81%, 39ºC = 74.53%, 39ºC+vitamin C = 69.39%) (P < 0.05). Cold rearing temperatures increased breast meat redness (a*: cold = 2.78, control = 2.12, hot = 1.98), while hot rearing temperatures reduced the muscle fiber area (cold = 5.413 μm(2), control = 5.612 μm(2), hot = 4.448 μm(2)) (P < 0.05) without altering meat quality (P > 0.05). Hot rearing temperatures increased the cooking loss (cold = 30.10%, control = 33.66%, hot = 37.01%), shear force (cold = 3.05 kgf cm(-2), control = 3.43 kgf cm(-2), hot = 4.29 kgf cm(-2)) and redness (a*: cold = 4.63, control = 3.55, hot = 3.20) in the over-thigh meat of broilers from eggs incubated at 37.5ºC, increasing the area of muscle fibers, while cold rearing temperatures diminished cooking loss and shear force, reducing the muscle fiber area (P < 0.05). Incubation at 39ºC and 39ºC+vitamin C prevented the effects of hot and cold rearing temperatures, by diminishing and increasing the muscle fiber area, respectively.

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

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

The timing of embryonic exposure to elevated temperature alters stress endocrinology in domestic chickens (Gallus domesticus)

Patterns of glucocorticoid (GC) release in response to stimuli vary both among individuals and within individuals across their lifetime. While much work has focused on how the prenatal steroid environment can affect GC release, relatively little is known about how environmental parameters, such as incubation temperature affect GCs. We tested the hypothesis that variation and timing of elevated incubation temperature within the thermoneutral zone can alter the pattern of GC release. We incubated domestic chicken eggs (Gallus domesticus) at the optimal incubation temperature (37.5 °C) or at a slightly higher temperature (+1.1 °C) either early, late, or throughout incubation. At three weeks post-hatch, all birds were (i) exposed to a capture-restraint stress to measure stress-induced GC release (naïve). Three days following the naïve stressor, birds were (ii) exposed to a heat challenge, which was followed the next day by a second capture-restraint stress (post-heat challenge). Regardless of treatment, birds had similar patterns of GC release following the naïve stress series. However, during the post-heat challenge stress series, birds incubated at optimal temperatures increased their peak GC release. In contrast, birds exposed to slightly elevated temperatures for any period of development failed to increase peak GC release, and their specific response varied with timing of exposure to the elevated incubation temperature. Our results demonstrate that subtle variation in the embryonic environment, such as elevated incubation temperature within the thermoneutral zone, can impact the pattern of GC release of offspring. Further work is needed to understand the mechanisms underlying these changes and the relationship between fitness and environmentally-altered phenotypes.

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.

Detection of long-term influence of prenatal temperature stimulation on hypothalamic type-II iodothyronine deiodinase in juvenile female broiler chickens using a novel immunohistochemical amplification protocol

It has been clearly shown that early environmental stimulation may have long-lasting influence on body functions. Because of the strong relationship between thermoregulation and other homeostatic linked physiological parameters, perinatal thermal manipulation will also have an impact on other body functions like reproduction. As a maturation stimulant for later reproductive performance, hypothalamic type-2 iodothyronine deiodinase (Dio2) expression was investigated in 35day old immature female broilers with and without embryonic temperature stimulation. For the first time, human-specific Dio2 primary antibodies combined with additional amplification enabled the immunohistochemical detection of hypothalamic Dio2 protein in birds. The novel protocol includes an additional amplification step involving swine-anti-rabbit/mouse/goat antibodies against both goat anti-Dio2 primary and rabbit anti-goat biotinylated secondary commercial antibodies in the standard diaminobenzidine protocol. However, significant Dio2 expression was exclusively found in perinatally short-term temperature stimulated hens. Caudal but not rostral hypothalamic slices revealed that elevating incubation temperature by 1°C for 2h daily, from day 18 of embryonic development until hatching, induced a statistical significant expression of Dio2 within the subcommisural organ and the median eminence. This ample expression of Dio2 protein within caudal but not rostral hypothalamic slices of embryonic temperature stimulated chickens, leads to the assumption of a novel physiological prospective for embryonic thermal manipulation involving the suppression of thyroid hormone and the boosting of hypothalamic Dio2-induced FSH secretion to considerably advance the age of photoinduced egg production. It could be also of practicable relevance for broiler breeder females, and needs further investigations.

Thermal manipulation during embryogenesis has long-term effects on muscle and liver metabolism in fast-growing chickens

Fast-growing chickens have a limited ability to tolerate high temperatures. Thermal manipulation during embryogenesis (TM) has previously been shown to lower chicken body temperature (T_b) at hatching and to improve thermotolerance until market age, possibly resulting from changes in metabolic regulation. The aim of this study was to evaluate the long-term effects of TM (12 h/d, 39.5°C, 65% RH from d 7 to 16 of embryogenesis vs. 37.8°C, 56% RH continuously) and of a subsequent heat challenge (32°C for 5 h at 34 d) on the mRNA expression of metabolic genes and cell signaling in the Pectoralis major muscle and the liver. Gene expression was analyzed by RT-qPCR in 8 chickens per treatment, characterized by low T_b in the TM groups and high T_b in the control groups. Data were analyzed using the general linear model of SAS considering TM and heat challenge within TM as main effects. TM had significant long-term effects on thyroid hormone metabolism by decreasing the muscle mRNA expression of deiodinase DIO3. Under standard rearing conditions, the expression of several genes involved in the regulation of energy metabolism, such as transcription factor PGC-1α, was affected by TM in the muscle, whereas for other genes regulating mitochondrial function and muscle growth, TM seemed to mitigate the decrease induced by the heat challenge. TM increased DIO2 mRNA expression in the liver (only at 21°C) and reduced the citrate synthase activity involved in the Krebs cycle. The phosphorylation level of p38 Mitogen-activated-protein kinase regulating the cell stress response was higher in the muscle of TM groups compared to controls. In conclusion, markers of energy utilization and growth were either changed by TM in the Pectoralis major muscle and the liver by thermal manipulation during incubation as a possible long-term adaptation limiting energy metabolism, or mitigated during heat challenge.

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

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

Are thyroid hormones mediators of incubation temperature-induced phenotypes in birds?

Incubation temperature influences a suite of traits in avian offspring. However, the mechanisms underlying expression of these phenotypes are unknown. Given the importance of thyroid hormones in orchestrating developmental processes, we hypothesized that they may act as an upstream mechanism mediating the effects of temperature on hatchling phenotypic traits such as growth and thermoregulation. We found that plasma T₃, but not T₄ concentrations, differed among newly hatched wood ducks (Aix sponsa) from different embryonic incubation temperatures. T₄ at hatching correlated with time spent hatching, and T₃ correlated with hatchling body condition, tarsus length, time spent hatching and incubation period. In addition, the T₃ : T₄ ratio differed among incubation temperatures at hatch. Our findings are consistent with the hypothesis that incubation temperature modulates plasma thyroid hormones which in turn influences multiple aspects of duckling phenotype.

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.