Sensible heat loss: the broiler's paradox

Birds are better at regulating heat loss through their legs than their bills: implications for body shape evolution in response to climate

Endotherms use their appendages-such as legs, tails, ears and bills-for thermoregulation by controlling blood flow to near-surface blood vessels, conserving heat when it is cold, and dissipating heat in hot conditions. Larger appendages allow greater heat dissipation, and appendage sizes vary latitudinally according to Allen's rule. However, little is known about the relative importance of different appendages for thermoregulation. We investigate physiological control of heat loss via bird bills and legs using infrared thermography of wild birds. Our results demonstrate that birds are less able to regulate heat loss via their bills than their legs. In cold conditions, birds lower their leg surface temperature to below that of their plumage surface, retaining heat at their core. In warm conditions, birds increase their leg surface temperature to above that of their plumage surface, expelling heat. By contrast, bill surface temperature remains approximately 2°C warmer than the plumage surface, indicating consistent heat loss under almost all conditions. Poorer physiological control of heat loss via bird bills likely entails stronger selection for shorter bills in cold climates. This could explain why bird bills show stronger latitudinal size clines than bird legs, with implications for predicting shape-shifting responses to climate change.

Key parameters of physiological responses to acute heat stress in two commercial layers determined by Fisher discriminant analyses

Given the escalating global warming and the intense nature of modern poultry production, layers are becoming increasingly susceptible to heat stress. This stress disrupts the physiological processes of layers, which leads to reduced productivity and welfare. To address this issue, it is crucial to first evaluate the stress response systematically. However, such evaluations are still lacking in this field. The objective of this study was to accurately monitor the impact of thermal stress and identify common and key indicators that would support decision-making to maintain layer welfare and productivity under stress. We constructed two heat stress models to reflect moderate (32 °C) to severe (36 °C) stress effects and obtained a comprehensive profile of blood physiological parameters associated with the layers' responses to heat stress. We found that genetic differences had limited influence on their physiological responses to heat stress after 32 °C heat challenges. Using 8 selected and significantly changed parameters, layers' physiological status under heat stress could be accurately determined (judgmental accuracy of 98%). As ambient temperature increased to 36 °C, birds suffered more severe challenges that parameters changed in larger percentages. Additionally, breed variations of the physiological responses became apparent, a Fisher discriminant function based on 5 selected parameters could distinguish heat stress effects at 32 °C or 36 °C with 80% accuracy. The results obtained from this study provide two discriminant models for assessing heat stress and shed lights on developing effective and widely applicable heat stress mitigation strategies targeting these indicators.

Growth performance and carcass characteristics of Koekoek chickens exposed to temperature variation with supplementary Coriander seed powder

The aim of the present study was to evaluate the effects of ambient temperature and coriander seeds supplementation on growth performance and carcass characteristics of Koekoek chickens. In the experiment, chickens were exposed to two temperature rooms with a heated room of 32 ± 1.2 °C from 11:00 to16:00 h and a normal room temperature with an average maximum and minimum of 23.8 ± 3 °C and 16.6 ± 1.6 °C, respectively, and a relative humidity between 34.5 ± 4 and 44.8 ± 3%. The chickens were supplemented with 0, 5, and 10 g/kg of coriander seed powder. The results showed that the group of Koekoek chickens placed in a heated room had significantly lower (P < 0.05) feed intake and weight gain and significantly higher (P < 0.05) feed conversion ratio than the groups placed at normal room temperature. Water intake was 1.8% higher in the groups placed in a heated room than those placed at normal room temperature. Supplementation with coriander seed powder enhanced growth performance and carcass traits. The carcass weight and breast percentage were higher (P < 0.05) in the groups that received 10 g/kg coriander seed powder. The growth performance of the Koekoek groups supplemented with 10 g/kg coriander seed powder in a heated room also improved significantly compared to groups in a heated room without supplementation. This suggests that the supplementation of coriander seed improves performance, and has a positive potential effect in alleviating the negative effects of heat stress on growth performance of chickens.

Maximum limit of sensible heat dissipation in Japanese quail

Surface temperature can be used as a tool for calculating sensible heat transfer. However, it needs to be associated with air temperature to identify the direction of heat flow (gain or loss). This study quantified sensible heat transfer in Japanese quail as a function of operative temperature. The meteorological variables were air temperature, relative humidity, and black globe temperature. Quail surface temperature was measured on 50 adult Coturnix coturnix japonica individuals 270 days old during 8 days by using a thermographic camera. The data were analyzed by the least-squares method to assess the effects of sex (male and female), period of the day (morning and afternoon), and body region (head, body, and feet). Quail surface temperature was strongly correlated with operative temperature. The total sensible heat flow was 64.02 W m^-2. The morning period had a mean operative temperature of 22.48 °C, providing a higher gradient between air and quail temperature and thereby producing a higher heat flow (82.19 W m^-2). In the afternoon, the heat transfer was lower (45.70 W m^-2) because the operative temperature was higher (30.84 °C). Comparison between sexes showed that heat transfer was higher in females (67.37 W m^-2) than in males (60.53 W m^-2). The head served as an important thermal window, with a heat transfer of 78.24 W m^-2, whereas the body and feet had a transfer of 56.80 W m^-2. Heat transfer by sensible mechanisms was quantified in Japanese quail. Heat transfer depended greatly on ambient temperature. When the operative temperature was below 28 °C, sensible mechanisms were efficient in dissipating heat to the environment. When the ambient temperature exceeded 29 °C, quail could not effectively dissipate heat to the environment through sensible mechanisms. At 30 °C and above, heat loss shifted to heat gain, causing thermal stress in Japanese quail.

Effect of L-serine on circadian variation of cloacal and body surface temperatures in broiler chickens subjected to feed restriction during the hot-dry season

The study aimed to evaluate the effects of L-serine on circadian variation of body temperatures in feed-restricted broiler chickens during the hot-dry season. Day-old broiler chicks of both sexes served as subjects; comprising four groups of 30 chicks each: Group A: water ad libitum + 20% feed restriction (FR); Group B: feed and water ad libitum (AL); Group C: water ad libitum + 20% feed restriction + L-serine (200 mg/kg) (FR + L-serine); Group D feed and water ad libitum + L-serine (200 mg/kg) (AL + L-serine). Feed restriction was performed on days 7-14 and L-serine was administered on days 1-14. Cloacal and body surface temperatures, recorded by digital clinical and infra-red thermometers, respectively, and temperature-humidity index were obtained over 26 h on days 21, 28 and 35. Temperature-humidity index (28.07-34.03) indicated broiler chickens were subjected to heat stress. L-serine decreased (P < 0.05) cloacal temperature in FR + L-serine (40.86 ± 0.07 °C), compared to FR (41.26 ± 0.05 °C) and AL (41.42 ± 0.08 °C) broiler chickens. Peak cloacal temperature occurred at 15:00 h in FR (41.74 ± 0.21 °C), FR + L-serine (41.30 ± 0.41 °C) and AL (41.87 ± 0.16 °C) broiler chickens. Fluctuations in thermal environmental parameters influenced circadian rhythmicity of cloacal temperature; especially the body surface temperatures, positively correlated with CT, and wing temperature recorded the closest mesor. In conclusion, L-serine and feed restriction decreased cloacal and body surface temperatures in broiler chickens during the hot-dry season.

A comparative study of acute heat tolerance and meat quality in three chicken breeds

In order to breed a strain that has heat tolerance and meat productivity, the commercial red-feathered Taiwan native chickens were male (F group), and heat stress resistant strain Taiwan native chickens (Taishu-9, bred by the Taiwan Livestock Research Institute) were female (TR9 group) to hybridize to generate offspring (F9 group). Three breeds of birds (male) were conducted to compare acute heat stress and meat quality. At 12 weeks of age, TR9 group showed the significantly lowest activity of plasma creatine kinase upon acute heat stress which indicated heat stress resistant in TR9 group as expected. In addition, only limited thermoregulation was obtained in F9 group, while F group exhibited almost no acute heat stress tolerance ability. After slaughtered at 16 weeks of age, the F group revealed poor meat quality in breast meat as pale, soft, and exudative (PSE)-like muscle samples according to CIE L* and pH value. The F9 group was an offspring of TR9 group with heat tolerance, but it only demonstrated limitation of heat resistance. However, the improve meat quality was obtained in F9 group compared to F group, and that may be contributed from better anti-stress as like as TR9 group during slaughtering process.

Dietary L-citrulline influences body temperature and inflammatory responses during nitric oxide synthase inhibition and endotoxin challenge in chickens

Recent studies have revealed the role of L-citrulline (L-CIT) in thermoregulation, but very little is known about the mechanisms involved. In this study, nitric oxide synthase inhibition and endotoxin-induced fever were used to investigate the effects of L-CIT on body temperature and inflammatory responses. In experiment 1, NW-nitro-L-arginine methyl ester (L-NAME, 150 mg/kg BW), was i. p. injected into chicks fed with basal (CON) or L-CIT diets for 14 days. In experiment 2, Lipopolysaccharide (LPS, 2 mg/kg BW) was i. p. injected following 21d feeding with CON or L-CIT diets. In experiment 3, chickens were injected with either L-NAME, LPS, or L-NAME + LPS following 26 days feeding with CON or L-CIT diets. The rectal (RT), ear (ET), and core body temperature (CBT) of chickens were examined. Results showed that L-NAME effectively decreased the RT, ET, CBT, and plasma NO concentration. In contrast, LPS increased NO levels and initiated hyperthermia by increasing RT, ET, CBT, and PGE2 levels. L-CIT diet reduced the mean CBT in experiment 1 and diminished the NO level, PGE2 level, and mean RT in experiment 3. Co-administration of L-CIT + LPS upregulated IL-6 expression, whereas, LPS injection alone induced IL-10, IL-1β, and TLR4 gene expressions. Therefore, this study reveals that L-CIT-induced hypothermia was related to NO inhibition and a decrease in PGE2 concentration. Conversely, LPS induced hyperthermia was associated with an increase in both NO and PGE2 concentrations.

The effects of intermittent feeding and cold water on welfare status and meat quality in broiler chickens reared under daily heat stress

This study was aimed to determine the effects of feeding type (ad libitum: AF and intermittent: IF) and water temperature (normal: NW and cold: CW) treatments on welfare status and meat quality in fast-growing broiler chickens reared under daily heat stress between 22 and 42 days of age. The chickens' panting rate and rectal temperature were determined at 4, 5, and 6 weeks of age and twice a week in 3 female and 3 male chickens in each pen. Welfare traits such as foot pad dermatitis (FPD), hock burn (HB), breast burn (BB), and leg problems (LP) were examined individually at 42 days of age. At day 43, 3 male and 3 female chickens per pen were randomly selected and slaughtered after an 8-h fasting period; pH and color (lightness (L*), redness (a*), and yellowness (b*)) of breast and thigh meat were determined. AF × C W chickens had significantly higher panting rates at all ages than the other groups (P < 0.05). While FPD and LP were not affected by feeding type and water temperature treatments, interaction effects on HB and BB were found significant (P < 0.05). The HB and BB levels were the lowest in AF × NW chickens (P < 0.05). While treatments did not change to any color traits in breast meat (P > 0.05), interactions significantly affected the yellowness (b*) value in the thigh (P < 0.05). In conclusion, management practices such as IF and CW in fast-growing broilers could not completely reduce the undesirable effects of heat stress on some welfare and meat quality traits, and in some cases, even caused more negativity.

A Heuristic and Data Mining Model for Predicting Broiler House Environment Suitability

The proper combination of environment and flock-based variables plays a critical role in broiler production. However, the housing environment control is mainly focused on temperature monitoring during the broiler growth process. The present study developed a novel predictive model to predict the broiler (Gallus gallus domesticus) rearing conditions' suitability using a data-mining process centered on flock-based and environmental variables. Data were recorded inside four commercial controlled environment broiler houses. The data analysis was conducted in three steps. First, we performed an exploratory and descriptive analysis of the environmental data. In the second step, we labeled the target variable that led to a specific broiler-rearing scenario depending on the age of the birds, the environmental dry-bulb temperature and relative humidity, the ammonia concentration, and the ventilation rate. The output (final rearing condition) was discretized into four categories ('Excellent', 'Good', 'Moderate', and 'Inappropriate'). In the third step, we used the dataset to develop tree models using the data-mining process. The random-tree model only presented accuracy for predicting the 'Excellent' and 'Moderate' rearing conditions. The decision-tree model had high accuracy and indicated that broiler age, relative humidity, and ammonia concentration play a critical role in proper rearing conditions. Using a large amount of data allows the data-mining approach to building up 'if-then' rules that indicate suitable environmental control decision-making by broiler farmers.

L-Citrulline Influences the Body Temperature, Heat Shock Response and Nitric Oxide Regeneration of Broilers Under Thermoneutral and Heat Stress Condition

Heat stress (HS) adversely affects several physiological responses in organisms, but the underlying molecular mechanisms involved are yet to be fully understood. L-Citrulline (L-Cit) is a nutraceutical amino acid that is gaining research interest for its role in body temperature regulation and nitric oxide synthesis. This study investigated whether dietary supplementation with L-Cit (1% of basal diet) could ameliorate the effects of acute HS on thermotolerance, redox balance, and inflammatory responses of broilers. Ross 308 broilers (288 chicks) were subjected to two environments; thermoneutral at 24°C (TNZ) or HS at 35°C for 5 h, and fed two diets; control or L-Cit. The results showed that HS increased the ear, rectal (RT), and core body (CBT) temperatures of broilers, along with higher respiratory rate. The RT and CBT readings were intermittently affected with time effect, whereas, L-Cit supplementation lowered the mean CBT than the control diet. Antioxidant assays showed that superoxide dismutase was increased during HS, while, catalase was promoted by L-Cit supplementation. In addition, L-Cit induced glutathione peroxidase activity compared to the control diet during HS. Hypothalamic heat shock protein (HSP)-90 was upregulated by HS, but L-Cit downregulated heat shock factor (HSF)-1, and HSP 60 mRNA expressions. HSF 3 mRNA expression was downregulated by L-Cit under TNZ condition. More so, HS increased the plasma nitric oxide (NO) concentration but lowered the total NO synthase (tNOS) activity. In contrast, L-Cit supplementation limited NO production but increased the tNOS activity. Arginase activity was increased in the control fed group during HS but L-Cit supplementation lowered this effect. The NOS-COX pathway was significantly affected under TNZ condition, since L-Cit supplementation downregulated the mRNA expression of iNOS-COX2 in the hypothalamus, and further reduced the serum PGE2 concentration. Together, these data indicates that L-Cit influenced the antioxidant defense, heat shock response and nitric oxide regeneration both under thermoneutral and HS conditions; and that L-Cit may be directly and/or indirectly involved in the central regulation of body temperature.

Effects of repeated thermal manipulation of broiler embryos on hatchability, chick quality, and post-hatch performance

The current study aimed to evaluate the effects of embryonic thermal manipulation (TM) on hatching criteria, chick quality, and subsequent growth performance of broiler chickens under heat stress (HS) condition. Two thousand fertile eggs were randomly divided between 2 groups and incubated under standard (37.8 °C and 56% relative humidity (RH)) and TM (39.5 °C and 65% RH) conditions. Temperature and humidity were identical in both groups within the first 10 days. The eggs in the TM group were exposed to 39.5 °C and 65% RH for 3 h/day from 11 to 16 days of incubation. Egg weight (EW) was measured in 1, 11, and 18 days of incubation, and eggshell temperature (EST) was recorded daily. Chick quality was, also, evaluated according to the Tona method on hatch day. Samples of the chicks (n = 20) were euthanized and dissected at 0-day post-hatch, and different carcass parts were weighed, and blood samples were collected for hormones analysis. The post-hatch growth performance of both groups was also recorded under HS (37 °C for 5 h beginning at 22 days) condition. The results showed that TM did not significantly affect hatchability and embryonic mortality (P > 0.05). The female chick percentage was higher in the TM group (P < 0.05). Eggshell temperature and serum concentrations of corticosterone and T₄ were significantly higher in the TM compared with the control chicks (P < 0.05). The chick length was considerably shorter in TM chicks (P < 0.05). Chick quality was not influenced by TM. There was no significant difference between the two groups in the post-hatch growth performance (P > 0.05). In conclusion, exposing broiler embryos to the controlled TM did not have adverse effects on chick quality and post-hatch growth performance.

Response of turkey pectoralis major muscle satellite cells to hot and cold thermal stress: Effect of growth selection on satellite cell proliferation and differentiation

Satellite cell (SCs), the main progenitors for post-hatch poultry muscle growth, has maximal mitotic activity and sensitivity to temperature during the first week after hatch. The objective of the present study was to determine the effect of hot and cold temperatures on the proliferation and differentiation of SCs from pectoralis major (P. major) muscle of fast-growing 1-week-old Nicholas commercial (NC) turkeys compared to Randombred Control Line 2 (RBC2) turkeys representing commercial turkeys from 1966. Three temperature regimens were used: SCs proliferation at 38 °C (control) with differentiation at 43° or 33 °C; proliferation at 43° or 33 °C with differentiation at 38 °C; or both proliferation and differentiation at 43°, 38°, or 33°C. Satellite cell proliferation and differentiation increased at 43 °C and decreased at 33 °C in both lines. When a thermal challenge was administered during proliferation, greater stimulatory or suppressive effects on differentiation were observed compared to if the thermal challenge was applied only during differentiation in both lines. Expression of myoblast determination protein 1 during proliferation showed a higher increase in the NC line compared to the RBC2 line at 43 °C. Increased myogenin expression was observed in all hot treatment groups in the NC line but was only observed in the RBC2 line if the hot treatment was administered throughout proliferation and differentiation. Cold treatment suppressed myogenin expression independent of line. These results suggest turkey P. major muscle SCs are more sensitive to environmental temperatures during proliferation, and SCs from growth-selected NC turkeys are more sensitive to thermal stress compared to the RBC2 turkeys.

Impacts of heat stress on meat quality and strategies for amelioration: a review

During the summer, high ambient temperature and humidity cause economic loss to the global livestock industry via reduced livestock productivity and increased mortality. The problem of heat stress (HS) is likely to be exacerbated by global warming and climate change. Recent research has shown that HS not only leads to physiological and metabolic perturbations in live animals but can also affect carcass and meat quality characteristics plausibly by altering the rate and extent of postmortem muscle glycolysis and resultant pH. However, these impacts of HS are not consistent across species. Higher incidence of pale soft and exudative (PSE) meat has been reported in poultry. On the contrary, higher incidence of high ultimate pH and dark firm and dry (DFD) meat or no impacts of HS have been reported in sheep and cattle. With the limited data on HS impacts on meat quality of ruminants, it is difficult to explain the exact mechanisms driving these variable impacts. However, it is hypothesized that the severity and duration of HS may lead to variable impacts due to lack of opportunity to adapdate to acute heat exposure. Longer HS exposure may allow ruminants to adapdate to heat and may not record any negative impacts on meat quality. This paper reviews the recent research on impacts of HS on meat quality characteristics and identify the key areas of further research required to better understand these negative impacts to develop strategies for amelioration. In addition, some mitigation strategies of HS have also been discussed which include both managemental and nutritional interventions.

Large-Scale Phenotyping of Livestock Welfare in Commercial Production Systems: A New Frontier in Animal Breeding

Genomic breeding programs have been paramount in improving the rates of genetic progress of productive efficiency traits in livestock. Such improvement has been accompanied by the intensification of production systems, use of a wider range of precision technologies in routine management practices, and high-throughput phenotyping. Simultaneously, a greater public awareness of animal welfare has influenced livestock producers to place more emphasis on welfare relative to production traits. Therefore, management practices and breeding technologies in livestock have been developed in recent years to enhance animal welfare. In particular, genomic selection can be used to improve livestock social behavior, resilience to disease and other stress factors, and ease habituation to production system changes. The main requirements for including novel behavioral and welfare traits in genomic breeding schemes are: (1) to identify traits that represent the biological mechanisms of the industry breeding goals; (2) the availability of individual phenotypic records measured on a large number of animals (ideally with genomic information); (3) the derived traits are heritable, biologically meaningful, repeatable, and (ideally) not highly correlated with other traits already included in the selection indexes; and (4) genomic information is available for a large number of individuals (or genetically close individuals) with phenotypic records. In this review, we (1) describe a potential route for development of novel welfare indicator traits (using ideal phenotypes) for both genetic and genomic selection schemes; (2) summarize key indicator variables of livestock behavior and welfare, including a detailed assessment of thermal stress in livestock; (3) describe the primary statistical and bioinformatic methods available for large-scale data analyses of animal welfare; and (4) identify major advancements, challenges, and opportunities to generate high-throughput and large-scale datasets to enable genetic and genomic selection for improved welfare in livestock. A wide variety of novel welfare indicator traits can be derived from information captured by modern technology such as sensors, automatic feeding systems, milking robots, activity monitors, video cameras, and indirect biomarkers at the cellular and physiological levels. The development of novel traits coupled with genomic selection schemes for improved welfare in livestock can be feasible and optimized based on recently developed (or developing) technologies. Efficient implementation of genetic and genomic selection for improved animal welfare also requires the integration of a multitude of scientific fields such as cell and molecular biology, neuroscience, immunology, stress physiology, computer science, engineering, quantitative genomics, and bioinformatics.

Timing Is Everything-The High Sensitivity of Avian Satellite Cells to Thermal Conditions During Embryonic and Posthatch Periods

Myofiber formation is essentially complete at hatch, but myofiber hypertrophy increases posthatch through the assimilation of satellite cell nuclei into myofibers. Satellite cell proliferation and differentiation occur during the early growth phase, which in meat-type poultry terminates at around 8 days posthatch. Thus, any factor that affects the accumulation of satellite cells during late-term embryogenesis or early posthatch will dictate long-term muscle growth. This review will focus on the intimate relationship between thermal conditions during chick embryogenesis and the early posthatch period, and satellite cell myogenesis and pectoralis growth and development. Satellite cells are highly sensitive to temperature changes, particularly when those changes occur during crucial periods of their myogenic activity. Therefore, timing, temperature, and duration of thermal treatments have a great impact on satellite cell activity and fate, affecting muscle development and growth in the long run. Short and mild thermal manipulations during embryogenesis or thermal conditioning in the early posthatch period promote myogenic cell proliferation and differentiation, and have long-term promotive effects on muscle growth. However, chronic heat stress during the first 2 weeks of life has adverse effects on these parameters and may lead to muscle myopathies.

Comparison of mathematical and comparative slaughter methodologies for determination of heat production and energy retention in broilers

Understanding factors affecting ME availability for productive processes is an important step in optimal feed formulation. This study compared a modelling methodology with the comparative slaughter technique (CST) to estimate energy partitioning to heat production and energy retention (RE) and to investigate differences in heat dissipation. At hatch, 50 broilers were randomly allocated in one of 4 pens equipped with a precision feeding station. From day 14 to day 45, they were either fed with a low-ME (3,111 kcal/kg ME) or a high-ME (3,383 kcal/kg ME) diet. At day 19, birds were assigned to pair-feeding in groups of 6 with lead birds eating ad libitum (100%) and follow birds eating at either 50, 60, 70, 80, or 90% of the paired lead's cumulative feed intake. Heat production and RE were estimated by CST and with a nonlinear mixed model explaining daily ME intake (MEI) as a function of metabolic BW and average daily gain (ADG). The energy partitioning model predicted MEI = (145.10 + u) BW^0.83 + 1.09 × BW^−0.18 × ADG^1.19 + ε. The model underestimated heat production by 13.4% and overestimated RE by 22.8% compared with the CST. The model was not able to distinguish between net energy for gain values of the diets (1,448 ± 18.5 kcal/kg vs. 1,493 ± 18.0 kcal/kg for the low-ME and high-ME diet, respectively), whereas the CST found a 148 kcal/kg difference between the low-ME and high-ME diets (1,101 ± 22.5 kcal/kg vs. 1,249 ± 22.0 kcal/kg, respectively). The estimates of the net energy for gain values of the 2 diets decreased with increasing feed restriction. The heat increment of feeding did not differ between birds fed with the low- or high-ME diet (26% of MEI). Additional measurements on heat dissipation, physical activity, and immune status indicated that the energetic content of the diet and feed restriction affect some parameters (shank temperature, feeding station visits) but not others (leukocyte counts, heterophil to lymphocyte ratio, and immune cell function).

Genetic architecture related to contour feathers density in an F2 resource population via a genome-wide association study

The density of contour feathers is an important trait as it is closely related to heat dissipation in birds. Thus, identification of the major genes that control this trait will be useful to improve heat tolerance in chicken. So far, no GWAS study for the density of contour feathers in birds has been previously published; therefore, this study was aimed to identify genomic regions controlling the density of contour feathers. A total of 1252 hens were genotyped, using the 600 K Affymetrix Axiom Chicken Genotyping Array. The association analyses were performed using the GenABEL package in the R program. In brief, 146 significant SNP markers were mainly located on chromosome 1 and were identified to associate with the density of contour feathers in the current GWAS analysis. Moreover, we identified several within/nearby candidate genes (SUCLA2, DNAJC15, DHRS12, MLNR, and RB1) that are either directly or indirectly involved in the genetic control of the density of contour feathers in chicken. This study laid the foundation for studying the mechanism that underlies the density of chicken feathers. Furthermore, it is feasible to shear the back feathers of live chickens and measure the density of the feathers to improve heat tolerance in breeding practice.

Heat stress management in poultry farms: A comprehensive overview

Heat stress causes significant economic losses in poultry production, especially in tropical and arid regions of the world. Several studies have investigated the effects of heat stress on the welfare and productivity of poultry. The harmful impacts of heat stress on different poultry types include decreased growth rates, appetites, feed utilization and laying and impaired meat and egg qualities. Recent studies have focused on the deleterious influences of heat stress on bird behaviour, welfare and reproduction. The primary strategies for mitigating heat stress in poultry farms have included feed supplements and management, but the results have not been consistent. This review article discusses the physiological effects of heat stress on poultry health and production and various management and nutritional approaches to cope with it.

Animal thermoregulation: a review of insulation, physiology and behaviour relevant to temperature control in buildings

Birds and mammals have evolved many thermal adaptations that are relevant to the bioinspired design of temperature control systems and energy management in buildings. Similar to many buildings, endothermic animals generate internal metabolic heat, are well insulated, regulate their temperature within set limits, modify microclimate and adjust thermal exchange with their environment. We review the major components of animal thermoregulation in endothermic birds and mammals that are pertinent to building engineering, in a world where climate is changing and reduction in energy use is needed. In animals, adjustment of insulation together with physiological and behavioural responses to changing environmental conditions fine-tune spatial and temporal regulation of body temperature, while also minimizing energy expenditure. These biological adaptations are characteristically flexible, allowing animals to alter their body temperatures to hourly, daily, or annual demands for energy. They exemplify how buildings could become more thermally reactive to meteorological fluctuations, capitalising on dynamic thermal materials and system properties. Based on this synthesis, we suggest that heat transfer modelling could be used to simulate these flexible biomimetic features and assess their success in reducing energy costs while maintaining thermal comfort for given building types.

Update of model to predict sensible heat loss in broilers

The present study was conducted to adjust and adapt some parameters of the model of production and heat loss by convection and conduction, so as to predict the actual feed intake (aFI) of broilers reared in sheds. The re-parameterised models were the sensible heat loss by convection from surface (HS) and by conduction (HC) in birds. The HS model was re-parameterised to calculate the heat loss of poultry reared in sheds and the parameters of thermal resistance of feathers (RF) and skin (RS) of poultry were inserted. The HC model was re-parameterised for birds in sheds and the RF, RS and the thermal resistance of the litter (R) were inserted. The re-parameterised HS model was HS = [A × QV × (TB – TA)]/[(TB – 17) × (RF + RS)], where TA is the air temperature, QV is the volume factor, TB is the surface temperature of the bird (°C) and A was estimated to be 11.94 watts (W). The values found in the model ranged from 0.75 W for birds with 100 g BW subjected to 33°C TA, 50% HU, 0.1 m/s wind speed (V) and 12.53 W for birds with 4100 g subjected to 33°C TA, 80% HU and 0.1 m/s V. The values found in the re-parameterised HC model (HC = [(TB – TC) × k × AR × QA]/[L × (RF + RS + R)], where K is the thermal conductivity of the litter, AR is the contact area of bird with the litter and QA is the area factor, and L is the litter height) ranging from 0.017 W to chickens with 100 g BW in comfortable conditions and 0.17 W for birds with 4100 g in thermal discomfort condition. The present study showed that the re-parameterisation of heat-loss equations is more accurate to predict the heat flux in broilers under different environmental conditions.

Incubation temperature alters thermal preference and response to heat stress of broiler chickens along the rearing phase

The current study aimed to investigate whether embryonic temperature manipulation may alter thermal preference throughout the rearing phase of broiler chickens and how this manipulation may affect response to thermal challenge, metabolism, growth rate and feed intake rate. Eggs were exposed to a constant incubation temperature [machine temperatures: 36°C (Low), 37.5°C (Control), and 39°C (High); eggshell temperature of 37.4 ± 0.08°C, 37.8 ± 0.15°C, and 38.8 ± 0.33°C, respectively] from d 13 till hatching. Low treatment chickens showed lower plasma T3 and GH levels at d 1 of age and lower T3 level at d 42 of age compared to the Control treatment. Preferred ambient, rectal temperature, T4 level, growth rate, food intake rate, and response to thermal challenge were not altered in these chickens. On the other hand, High-treatment chickens exhibited high preferred ambient temperature and rectal temperature during the first 2 wk post-hatch, lower plasma T3 level at d 21 and 42 and a delayed increase in respiratory movement in response to thermal challenge compared to the Control treatment. However, chickens subjected to the Control and High treatments did not differ in T4 and GH level and performance. We conclude that exposure to high temperature during late embryonic development has long-lasting effects on the thermoregulatory system of broiler chickens by affecting the heat tolerance of these chickens. Moreover, the preferred ambient temperature of the chickens from heat-treated eggs correspond to those recommended for the strain under study, whereas for the cold-treated and control-chickens it was 1°C below, indicating that incubation temperature might have consequences on the ambient temperature chickens require during the rearing phase.

Temperature effect on proliferation and differentiation of satellite cells from turkeys with different growth rates

Poultry selected for growth have an inefficient thermoregulatory system and are more sensitive to temperature extremes. Satellite cells are precursors to skeletal muscle and mediate all posthatch muscle growth. Their physiological functions are affected by temperature. The objective of the current study was to determine how temperature affects satellite cells isolated from the pectoralis major (p. major) muscle (breast muscle) of turkeys selected for increased 16 wk body weight (F line) in comparison to a randombred control line (RBC2) from which the F line originated. Pectoralis major muscle satellite cells were thermally challenged by culturing between 33°C and 43°C to analyze the effects of cold and heat on proliferation and differentiation as compared to control temperature of 38°C. Expression levels of myogenic regulatory factors: myogenic differentiation factor 1 (MYOD1) and myogenin (MYOG) were quantified by quantitative polymerase chain reaction (qPCR). At all sampling times, proliferation increased at a linear rate across temperature in both the RBC2 and F lines. Differentiation also increased at a linear rate across temperature from 33 to 41°C at all sampling times in both the F and RBC2 lines. Satellite cells isolated from F line turkeys were more sensitive to both hot and cold temperatures as proliferation and differentiation increased to a greater extent across temperature (33 to 43°C) when compared with the RBC2 line. Expression of MYOD1 and MYOG increased as temperatures increased from 33 to 41°C at all sampling times in both the F and RBC2 lines. These results demonstrate that satellite cell function is sensitive to both cold and hot temperatures and p. major muscle satellite cells from F line turkeys are more sensitive to temperature extremes than RBC2 satellite cells.

Dietary but not in ovo feeding of Silybum marianum extract resulted in an improvement in performance, immunity and carcass characteristics and decreased the adverse effects of high temperatures in broilers

A total of 360 fertile eggs from a broiler breeder strain (Ross 308) were used for in ovo feeding (IOF) of 0, 100 and 200 mg/kg Silybum marianum water extract at 17.5 d of incubation. After hatching, 240 chicks were transferred to the experimental cages. The diets consisted of two types; one of them without extract and the other one containing 100 mg/kg of Silybum marianum extract. Then chicks were exposed to elevated temperatures 4°C above optimum from 7 to 28 d of age for 4 h per d and after 28 d they were kept at optimum temperature. The chicks were divided into 6 treatments with 4 replicates as a completely randomised 2 × 3 factorial design. There was no effect of IOF of Silybum marianum extract on hatchability, body weight (BW) of hatched chicks or hatched chick BW/initial egg weight ratio. Chickens fed on the diet containing the extract had the highest feed intake, daily weight gains (DWGs), final BW and lowest feed conversion ratio. At 28 d, the weights of heart, spleen and bursa of birds in the treatment groups given extract were higher, but abdominal fat weights were lower. At 42 d in those fed extract in the diet, the weights of spleen and bursa were higher and abdominal fat weights were lower than the other groups. No differences were observed between groups in body temperature before application of the higher temperature but at 21 d and 28 d the body temperature of chicks given the Silybum marianum extract was lower than the other treatments during the elevated temperatures. In birds fed on the extract in the diet, HDL and cholesterol concentrations were lowest at 28 d, whereas blood glucose levels were higher in the other treatments. At 42 d the cholesterol concentration was significantly lower in birds given extract in their diet. These results indicated that dietary feeding of Silybum marianum extract resulted in an improvement in performance, immunity and carcass characteristics and decreased the adverse effects of the higher temperatures, specifically in reducing blood fat reduction, but IOF of the extract did not have an effect.

Vocalisation sound pattern identification in young broiler chickens

In this study, we describe the monitoring of young broiler chicken vocalisation, with sound recorded and assessed at regular intervals throughout the life of the birds from day 1 to day 38, with a focus on the first week of life. We assess whether there are recognisable, and even predictable, vocalisation patterns based on frequency and sound spectrum analysis, which can be observed in birds at different ages and stages of growth within the relatively short life of the birds in commercial broiler production cycles. The experimental trials were carried out in a farm where the broiler where reared indoor, and audio recording procedures carried out over 38 days. The recordings were made using two microphones connected to a digital recorder, and the sonic data was collected in situations without disturbance of the animals beyond that created by the routine activities of the farmer. Digital files of 1 h duration were cut into short files of 10 min duration, and these sound recordings were analysed and labelled using audio analysis software. Analysis of these short sound files showed that the key vocalisation frequency and patterns changed in relation to increasing age and the weight of the broilers. Statistical analysis showed a significant correlation (P<0.001) between the frequency of vocalisation and the age of the birds. Based on the identification of specific frequencies of the sounds emitted, in relation to age and weight, it is proposed that there is potential for audio monitoring and comparison with 'anticipated' sound patterns to be used to evaluate the status of farmed broiler chicken.

Mean surface temperature prediction models for broiler chickens-a study of sensible heat flow

Body surface temperature can be used to evaluate thermal equilibrium in animals. The bodies of broiler chickens, like those of all birds, are partially covered by feathers. Thus, the heat flow at the boundary layer between broilers' bodies and the environment differs between feathered and featherless areas. The aim of this investigation was to use linear regression models incorporating environmental parameters and age to predict the surface temperatures of the feathered and featherless areas of broiler chickens. The trial was conducted in a climate chamber, and 576 broilers were distributed in two groups. In the first trial, 288 broilers were monitored after exposure to comfortable or stressful conditions during a 6-week rearing period. Another 288 broilers were measured under the same conditions to test the predictive power of the models. Sensible heat flow was calculated, and for the regions covered by feathers, sensible heat flow was predicted based on the estimated surface temperatures. The surface temperatures of the feathered and featherless areas can be predicted based on air, black globe or operative temperatures. According to the sensible heat flow model, the broilers' ability to maintain thermal equilibrium by convection and radiation decreased during the rearing period. Sensible heat flow estimated based on estimated surface temperatures can be used to predict animal responses to comfortable and stressful conditions.

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.

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

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

Dietary self-selection by broilers at normal and high temperature changes feed intake behavior, nutrient intake, and performance

Self-selection assumes that at high ambient temperature, birds are able to select a diet from different sources to minimize the heat load associated with the ingested nutrient metabolism. The objective was to test the hypothesis that young chickens are able to compose an adequate ration by adjusting dietary nutrient intake from 3 different diets that vary in energy and in protein contents from a cafeteria system at high temperature (HT; 31-32°C) and at normal temperature (NT; 31-21°C). Night temperature was set at 25°C at HT and at 18°C at NT and 12 h dark:12 h light. Control birds were fed a standard control diet (CP: 215 g/kg; ME: 2,895 kcal/kg) for broiler chickens. The choice-fed birds could choose between the control diet, a high-protein diet (CP: 299 g/kg; ME: 2,780 kcal/kg), and a high-energy diet (CP: 150.7 g/kg; ME: 3,241 kcal/kg). The diets had similar pellet size and color. Birds had access to each diet in a separate feeding trough from 1 to 42 d of age. Results showed that broilers spent 3.3% more time eating at NT than at HT and showed 42% more panting behavior at HT than at NT. High temperature decreased feed intake, protein intake, energy intake, and BW gain. Choice-fed birds had similar feed intake and BW gain, 14% lower protein intake, and 6.4% higher energy intake than control-fed birds. Body temperature and heterophil/lymphocyte ratio were higher at HT than at NT. Water intake was 8% higher in control-fed birds than in choice-fed birds but similar at both temperature regimens. It can be concluded that broilers can compose a diet by selecting less protein but higher energy density from different diets compared with the control. Choice-fed birds had similar feed efficiency as control-fed birds at HT, indicating similar body composition for both groups. Extra energy intake of choice-fed birds at HT was used for panting activity.