Quantification of the spatial distribution of surface temperatures of broilers

Separating Chickens' Heads and Legs in Thermal Images via Object Detection and Machine Learning Models to Predict Avian Influenza and Newcastle Disease

Poultry body temperature is closely related to their metabolism and vital activities, which can indicate their physiological status and health. Therefore, monitoring these temperature changes by analyzing thermal images can help in the early and accurate diagnosis of their diseases using a non-destructive method. On the other hand, it is very important to state which part of the bird has the greatest effect on the diagnosis of the disease. This not only speeds up the diagnosis process but also determines an important index for animal pathologists. In this study, an intelligent algorithm was presented with the aim of early diagnosis and classification of two diseases, Avian influenza and Newcastle disease, in the early hours of disease transmission. For this purpose, three different models were developed based on thermal images, including: original images, images with background removal, and images with the head and legs of the chicken separated by the YOLO-v8 model. Then, the features extracted from the thermal images, including texture and color, were evaluated in all three models with a support vector machine (SVM) classifier. Also, the most important and effective features of thermal images for the diagnosis of two diseases, Avian influenza and Newcastle disease, were introduced to other researchers by the Relief feature selection algorithm. The classification results of the original images, images without background and images of the head and legs of chickens for Avian influenza were 75.89, 83.93, and 92.48%, respectively, and for Newcastle disease were 83.04, 91.52, and 94.20% respectively. The model developed for early diagnosis of the disease showed the ability to diagnose the two diseases at 8 h after disease infection with an accuracy of more than 90%. The results show that the contribution of texture-related features is greater than other features extracted from thermal images in the diagnosis of poultry diseases. Also, focusing on the head and feet areas by the YOLO-v8 algorithm will increase the classification accuracy, which allows for more accurate diagnosis in real time and in the early stages of the disease.

Rectal temperature and heat transfer dynamics in the eye, face, and breast of broiler chickens exposed to moderate heat stress

This study aimed to characterize body temperature in finishing broiler chickens and to explore heat transfer dynamics under thermoneutral (TN) and heat stress (HS) conditions. To achieve this, 900 Ross 308 chicks were divided into TN and HS groups, with the HS group subjected to cyclical heat stress (30°C, 45 % RH) from day 28 to day 33 post-hatch. Rectal temperature (Tr) and skin temperature (Ts) at the face (Tsf), eye (Tse), and breast (Tsb) were measured. Tr ranged from 39.1 to 40.6°C under TN and from 40.4 to 43.2°C under HS (Pcondition < 0.001). Core-to-skin temperature gradients were lower under HS (P < 0.0001), indicating reduced heat transfer to the skin. All Ts parameters were higher under HS (P < 0.001), and skin-to-air temperature gradients were also lower (P < 0.0001), reflecting lower heat dissipation. Ts varied significantly across anatomical regions (P < 0.001), and core-to-skin and skin-to-air gradients differed between regions under both conditions (P < 0.001). Strong correlations were observed between Tr and Ts (r = 0.88, 0.89, and 0.92 for Tsb, Tse, and Tsf, respectively), suggesting Ts as a strong predictor of Tr. In conclusion, rectal temperatures in finishing broilers are more variable under HS than under TN. Under HS, some birds continue to exhibit Tr in the physiological range. Under TN, heat is transferred from the core to the eyes at a significantly higher rate than to the face and breast skin. However, the breast skin dissipates heat into the environment at a greater rate than the face and the eyes. These patterns of heat transfer between the core and the skin, and between the skin and the environment are conserved under HS. However, heat transfer rates are significantly reduced leading to increased heat load of the birds. These findings provide further insights into thermoregulation in broiler chickens.

Effect of different crate material types for transit on production, physiological characteristics, and welfare of broilers during the summer season

The current study investigated the impact of using iron and plastic crates during summer transportation on production, physiological characteristics, and welfare of broiler chickens. A total of 160 Ross 308 male broilers were randomly selected from a battery-caged house at 35 days of age. Their average body weight was 1,866.62 ± 36.048 g (mean ± SEM). Broilers were crated into fixed iron crates with 1.00 m (length) × 0.78 m (width) × 0.26 m (height) and plastic crates with 0.82 m (length) × 0.57 m (width) × 0.29 m (height) dimensions at 173 cm2/kg densities. Afterward, they were transported in the early morning at an average speed of 30-50 km/h for 40 minutes under 30°C and 40% relative humidity, completing a total distance of 20 km. Body weights were recorded before and after completing the journey. Following the weighing of birds, blood samples were collected for blood metabolite (cortisol, glucose, and lactate) analysis. Cervical dislocation was performed to euthanize broilers followed by breast and drumstick collection. Dressing, drumstick, and breast meat were calculated as percentages whereas respiratory frequencies were measured as the number of breaths per minute. Collected breast meat samples were utilized to analyze physiochemical parameters such as pH, color (CIE L*, a*, b*), water holding capacity, and cooking loss. Results from skin temperature assessments showed higher temperatures (p < 0.05) in broilers that were loaded into iron crates, both before (iron, 41.23 ± 0.610°C; plastic, 39.25 ± 0.065°C) and after (iron, 43.53 ± 0.723°C, and plastic, 41.63 ± 0.132°C) completing the journey. However, total skin temperature change was not significantly affected. Importantly, stress-indicating blood metabolite analysis revealed that glucose and lactate levels were lower (p < 0.05) in broilers transported in plastic crates. Nevertheless, cortisol levels remained unaffected by crate materials. Furthermore, transit losses, carcass characteristics, and physiochemical properties were also unaffected despite the dissimilar crate types. In conclusion, the study revealed that plastic is the more advantageous crating material compared to iron. Besides, plastic crates ensure meat quality and animal welfare, as evidenced by blood metabolite levels and skin temperature after transit.

Effect of Density and Lineage on Dorsal Surface Temperature, Performance, and Carcass Condemnation of Broiler Grillers

The aims of this study were (i) to evaluate the effect of density, lineage, age, and time of day on dorsal surface temperature and (ii) to evaluate the effect of density and lineage on performance and carcass condemnations in broiler grillers. The evaluations were carried out in barns with the Dark House system, with two densities, 17 and 19 chickens/m2 and two lineages, Cobb and Ross. The dorsal surface temperature of the chickens was measured by infrared thermography at 7, 14, 21, 23, 25 and 27 days of age, four times a day. The average daily weight gain, feed conversion, mortality, partial carcass condemnations, as well as those due to arthritis and dermatosis were also evaluated. The highest dorsal surface temperatures were observed in Cobbs housed at a density of 17 chickens/m2, and in Ross housed at a density of 19 chickens/m2. Cobbs housed at a 17 chickens/m2 density showed the lowest feed conversion compared to Ross at the same density. Ross showed higher dorsal surface temperatures when compared to Cobbs at 14, 21, and 27 days. Cobbs showed higher percentages of partial carcass condemnation and arthritis compared to Ross. The higher density of broiler grillers in the Dark House system does not influence the dorsal surface temperature, performance, dermatosis, arthritis, and partial carcass condemnations.

Evaluating broiler welfare and behavior as affected by growth rate and stocking density

This study evaluated the welfare and behaviors of Cobb 700 broilers as affected by growth rate (GR) and stocking density (SD). Slower-growth (weight gain < 50 g/d) and medium-growth (weight gain = 50-60 g/d) broilers were produced by providing 57.1% and 78.6% of the feed intake listed in the Cobb 700 production manual for standard (fed ad libitum) broilers (weight gain > 60 g/d). Broilers at all 3 GRs were reared at 2 SDs of 30 and 40 kg/m2. Broiler welfare indicators, including gait score, tibia strength, feather coverage, and footpad condition were evaluated when birds reached 1, 2, and 3 kg of body weight. The activity index was determined by overhead cameras and image processing, and the time spent at feeders was recorded using the radio-frequency identification (RFID) systems. The results show that it took 45 d for standard, 52 d for medium-growth, and 62 d for slower-growth broilers to reach a 3 kg market body weight. Feed conversion ratios (FCR, kg/kg) were 1.57 for standard, 1.67 for medium-growth, and 1.80 for slower-growth broilers. Growth rate and SD had an interaction effect on feather cleanliness (P = 0.03), and belly feather coverage (P = 0.02). Slower-growth broilers were more active and had better feather coverage and gait scores than medium-growth and standard broilers (all P < 0.01) but may feel hungry and depressed, medium-growth broilers spent the most time at the feeder among the 3 growth groups (P = 0.02), and standard broilers showed the best production performance. Broilers at 30 kg/m2 showed better bone strength (P = 0.04), and footpad condition (P < 0.01) compared to those at 40 kg/m2. In conclusion, reducing GR and SD may slightly improve broiler leg health at the high expense of compromised production performance and prolonged production cycles.

The Effect of Low Temperature on Laying Performance and Physiological Stress Responses in Laying Hens

The present study investigated the effect of low temperature on laying performance, egg quality, body temperature, yolk malondialdehyde, yolk corticosterone, and serum biochemistry in laying hens. A total of 40 laying hens (Hy-Line Brown) aged 36 weeks were housed in one of two environmental chambers kept at 12 ± 4.5 °C (low temperature) or 24 ± 3 °C (normal temperature) for 4 weeks. Low vs. normal temperature significantly increased (p < 0.05) live body weight, feed intake, and feed conversion ratio in laying hens. Skin surface temperature, but not rectal temperature, was decreased in laying hens exposed to low vs. normal temperature. Hens exposed to low temperature laid an intense eggshell color compared with those raised in a normal temperature. Malondialdehyde concentrations in yolk were increased in low-temperature-exposed laying hens compared with those at normal temperature conditions, but this effect was only noted on day 7, post the low-temperature exposure (p = 0.04). Finally, low vs. normal temperature increased the concentrations of total cholesterol and triglyceride in serum. Collectively, this study indicates that exposure to low temperature in laying hens initially disrupted antioxidant system and altered lipid metabolism in laying hens without inducing stress responses.

Effects of drinking water temperature in winter on growth performance, water consumption, surface temperature, and intestinal development of geese from 21 to 49 days of age

This research aimed to investigate the effects of drinking water temperatures on growth performance, water consumption, surface temperature, organ indices, blood parameters, and intestinal development of geese, and determine the optimal drinking water temperature for 21 to 49-d geese. A total of 192 twenty-one-day male Yuzhou white geese were allocated randomly to 4 groups with 8 replicate pens per group according to the drinking water temperature (drinking water temperature [7℃-12℃] at ambient temperature [T_C], 18℃ [T₁], 27℃ [T₂], and 36℃ [T₃], respectively). The results showed that increasing drinking water temperature did not significantly improve the BW, ADG, and ADFI of geese (P > 0.05), whereas drinking warm water of 36℃ for geese had a trend to increase FCR (0.05 < P < 0.1). Geese in group T₂ drank the most water per day on average, whereas geese in group T_C drank the least (P < 0.001). Geese in groups T₁, T₂, and T₃ had higher eyes temperatures than group T_C (P < 0.001). No significant differences were found on the organ indices and blood biochemical parameters (P > 0.05). Geese from group T₁ had higher crypt depth and muscularis thickness of duodenum (P < 0.05), and lower ratio of villus height to crypt depth than other groups (P < 0.001). Geese from group T₁ had higher activities of trypsin in duodenum and jejuna and amylase in jejuna at 49 d than other groups (P < 0.01). Overall, these data indicate drinking water at 18℃ can increase water consumption and eyes temperature, and improve the activity of digestive enzymes and promote intestinal development. Under our experimental conditions, we recommend that the optimal drinking water temperature for geese from 21 to 49 d of age is 18°C.

DISubNet: Depthwise Separable Inception Subnetwork for Pig Treatment Classification Using Thermal Data

Thermal imaging is increasingly used in poultry, swine, and dairy animal husbandry to detect disease and distress. In intensive pig production systems, early detection of health and welfare issues is crucial for timely intervention. Using thermal imaging for pig treatment classification can improve animal welfare and promote sustainable pig production. In this paper, we present a depthwise separable inception subnetwork (DISubNet), a lightweight model for classifying four pig treatments. Based on the modified model architecture, we propose two DISubNet versions: DISubNetV1 and DISubNetV2. Our proposed models are compared to other deep learning models commonly employed for image classification. The thermal dataset captured by a forward-looking infrared (FLIR) camera is used to train these models. The experimental results demonstrate that the proposed models for thermal images of various pig treatments outperform other models. In addition, both proposed models achieve approximately 99.96–99.98% classification accuracy with fewer parameters.

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.

Research Note: Is infrared thermography an appropriate method for early detection and objective quantification of plumage damage in white and brown feathered laying hens?

For the standardized assessment of plumage damage in laying hens, imaging techniques can be used in addition to visual plumage scoring (PS). In this study, the diagnostic accuracy of infrared thermography (IRT) was analyzed in white-feathered (WL) and brown-feathered laying hens (BL) with PS as a reference. In 28 flocks, a 3-level PS and IRT were performed 8 times for the dorsal neck, back, and belly plumage. A total of 3,600 records for WL and 7,600 records for BL were available for both PS and IRT in each of the 3 body regions. Receiver operating characteristic (ROC) analyses were used to investigate diagnostic accuracy. High-accuracy detection was found for severe plumage damage on the back (WL—sensitivity: 96.0%, specificity: 98.3%; BL—sensitivity: 96.1%, specificity: 98.9%) and belly plumage (WL—sensitivity: 96.3%, specificity: 95.7%; BL—sensitivity: 95.3%, specificity: 97.2%), but insufficient accuracy for distinguishing between intact plumage and moderate plumage damage in all 3 body regions (sensitivity: 31.7–71.5%; specificity: 70.4–98.1%). The area under the curve (AUC) of the ROC graphs differed significantly between BL and WL for the back and belly plumage (P ≤ 0.05). We concluded that IRT is a suitable tool to objectively detect severe plumage damage but not for early detection of incipient plumage loss.

Central and peripheral effects of L-citrulline on thermal physiology and nitric oxide regeneration in broilers

The mechanism that mediates L-citrulline (L-Cit) hypothermia is poorly understood, and the involvement of nitric oxide signaling has not been fully elucidated. Therefore, this study aimed to determine L-Cit's influence on body temperature and to ascertain the central and peripheral mechanisms associated with this response. Chicks responded to intracerebroventricular (ICV) injection of L-Cit with high and low body temperatures (P < 0.05) depending on the dose tested, for both the surface and rectal temperatures. Peripheral (i.p.) L-Cit injection did not affect body temperature responses. Nitric oxide (NO) concentration and NO synthase (NOS) were influenced with varying doses of L-Cit. Hypothalamic NO was increased at 4 µg L-Cit whereas, plasma iNOS was elevated at 2µg L-Cit treatment. However, i.p. L-Cit did not change the NO content, rather it induced higher (P < 0.05) plasma tNOS and iNOS activity, and further upregulated iNOS and nNOS gene expression in the hypothalamus. In addition, ICV L-Cit potentiated a pro- versus anti-inflammatory milieu with the induction of IL-8, IL-10, and TGFβ (P < 0.05), which may be related to the changes in body temperature. Following ICV L-Cit administration, it was observed that L-Cit caused dose variable changes in the ultrastructure of hypothalamic neurons. The lowest dose was associated with a higher number of dead or degenerating neurons, whereas the highest L-Cit dose had fewer neuronal numbers with larger sizes. Therefore, this study shows that central and peripheral L-Cit administration imposes changes in body temperature, nitric oxide production, and inflammatory responses, in a dose-dependent manner.

Liver Transcriptome Response to Heat Stress in Beijing You Chickens and Guang Ming Broilers

Heat stress is one of the most prevalent issues in poultry production that reduces performance, robustness, and economic gains. Previous studies have demonstrated that native chickens are more tolerant of heat than commercial breeds. However, the underlying mechanisms of the heat tolerance observed in native chicken breeds remain unelucidated. Therefore, we performed a phenotypical, physiological, liver transcriptome comparative analysis and WGCNA in response to heat stress in one native (Beijing You, BY) and one commercial (Guang Ming, GM) chicken breed. The objective of this study was to evaluate the heat tolerance and identify the potential driver and hub genes related to heat stress in these two genetically distinct chicken breeds. In brief, 80 BY and 60 GM, 21 days old chickens were submitted to a heat stress experiment for 5 days (33 °C, 8 h/day). Each breed was divided into experimental groups of control (Ctl) and heat stress (HS). The results showed that BY chickens were less affected by heat stress and displayed reduced DEGs than GM chickens, 365 DEGs and 382 DEGs, respectively. The transcriptome analysis showed that BY chickens exhibited enriched pathways related to metabolism activity, meanwhile GM chickens’ pathways were related to inflammatory reactions. CPT1A and ANGPTL4 for BY chickens, and HSP90B1 and HSPA5 for GM chickens were identified as potential candidate genes associated with HS. The WGCNA revealed TLR7, AR, BAG3 genes as hub genes, which could play an important role in HS. The results generated in this study provide valuable resources for studying liver transcriptome in response to heat stress in native and commercial chicken lines.

Impacts of Air Velocity Treatments under Summer Condition: Part I—Heavy Broiler’s Surface Temperature Response

Simple Summary

The surface temperature variation of heavy broilers (42–61 d age) under heat stress is an important indicator of thermal comfort, but it is not well studied and reported yet. This study examined the variation of surface temperatures of broilers through two dynamic air velocity treatments under hot summer conditions. It was discovered that the surface temperatures varied over age, daytime, and environmental factors (air temperature, relative humidity, and temperature humidity index). A simple linear regression model to predict the surface temperature of heavy broilers was developed. The findings from this study will enhance knowledge to understand the broilers’ responses under heat stress, which will be helpful in providing necessary management decisions to create a comfortable thermal environment.

Abstract

Heavy broilers exposed to hot summer conditions experience fluctuations in surface temperatures due to heat stress, which leads to decreased performance. Maintaining a bird’s homeostasis depends on several environmental factors (temperature, relative humidity, and air velocity). It is important to understand the responses of birds to environmental factors and the amount of heat loss to the surrounding environment to create thermal comfort for the heavy broilers for improved performances and welfare. This study investigates the variation in surface temperatures of heavy broilers under high and low air velocity treatments. Daytime, age and bird location’s effect on the surface temperature variation was also examined. The experiment was carried out in the poultry engineering laboratory of North Carolina State University during summers of 2017, 2018, and 2019 as a part of a comprehensive study on the effectiveness of wind chill application to mitigate heat stress on heavy broilers. This live broiler heat stress experiment was conducted under two dynamic air velocity treatments (high and low) with three chambers per treatment and 44 birds per chamber. Surface temperatures of the birds were recorded periodically through the experimental treatment cycles (flocks, 35–61 d) with infrared thermography in the morning, noon, evening, and nighttime. The overall mean surface temperature of the broilers under two treatments was found to be 35.89 ± 2.37 °C. The variation in surface temperature happened due to air temperature, thermal index, air velocity, bird’s age, daytime, and position of birds inside the experimental chambers. The surface temperatures were found lower under high air velocity treatment and higher under low air velocity treatment. During the afternoon time, the broilers’ surface temperatures were higher than other times of the day. It was also found that the birds’ surface temperature increased with age and temperature humidity indices. Based upon the experimental data of five flocks, a simple linear regression model was developed to predict surface temperature from the birds’ age, thermal indices, and air velocity. It will help assess heavy broilers’ thermal comfort under heat stress, which is essential to provide a comfortable environment for them.

Which factor is more important: Intensity or duration of episodic heat stress on broiler chickens?

With the current global warming, there is a predicted increase in frequency, intensity and duration of heat waves in future. Little is known of how this could affect the welfare of broiler chickens. Sixty-four broiler chickens were subjected to either high heat stress (HHS; 32 °C, 70% RH for 3 h), moderate heat stress (MHS; 30 °C, 70% RH for 6 h), or normal conditions (NC: 20 °C, 50% RH for 6 h) for two consecutive days. On both days, the temperature-ID chips on all chipped birds were scanned during pre-heat stress (PrHS), end of 3 h (3HS) and 6 h (6HS) of heat stress using a pocket reader. Half of the chip birds' CBT was measured at the end of each hour of heat stress (HS: 1^st -3^rd hour). Surface body temperatures (SBTs) from under the wing (WT), feet (FT), cloaca (CLT) and comb (CT) were measured. Blood samples, feed intake, daily weight gain and mortality was also monitored. Data was analysed using General Linear Model and simple linear regression. At 3HS, CBT/ΔCBT and all SBTs showed this trend: HHS>MHS>NC (P<0.001). The regression equations to predict ΔCBT in HHS and MHS are ΔCBT = 0.917 + 0.663 h, P<0.05 and ΔCBT = 0.371 + 0.338 h, P<0.05 respectively. Blood pH, pCO₂, iCa, HCO₃^- and TCO₂ showed same trend: HHS, MHS > NC (P<0.05). Comparing HHS for 3 h with MHS and NC for 6 h shows that CBT/ΔCBT, WT and CLT in HHS, MHS>control (P<0.001) while FT and CT showed a different trend (HHS > MHS > NC, P<0.001). pCO_2, feed intake and daily weight gain showed same trend (HHS, MHS > control). Temperature-ID chip (a less invasive technique) gave CBT/ΔCBT values that corresponded with the degree of heat stress experienced by the birds. Broilers were more tolerant to MHS than HHS after 3 h but MHS for 6 h and HHS for 3 h had similar impact.

Effect of acute heat stress on cognitive performance of chickens in a feed-related discriminant task

Little is known about immediate and long-lasting effect of acute heat stress on chicken cognition. Thirty-five, 9-week-old birds were trained to differentiate two cone colours; white (rewarded, R; with feed underneath) and black (unrewarded, UR; empty). The sixteen birds that learnt the task were randomly assigned to three temperature regimens (TR: 22-24 °C (control), 30-32 and 36-38 °C for 3h/day) for three consecutive days during which rectal (RT), wing (WT) and eye (ET) temperatures were monitored. After the 3 h of exposure, birds were allowed to rest for 1 h before the commencement of the discriminant task. The latencies to open the cones (R and UR) and proportion of cones opened were recorded. A long-lasting effect was tested a week after exposure to TR. TR had a significant effect on RT, WT and ET. The motivation to turn over R cones was weaker in birds exposed to 36-38 °C than birds exposed to 22-24 °C. Also, the proportion of R cones opened were fewer in birds that experienced TR of 36-38 °C compared to birds exposed to 22-24 °C and 30-32 °C specifically on two out of the three cognitive test days (Days 1 and 3). Latency and proportion of UR cones opened was not affected by TR. RT, WT and ET were all negatively and significantly correlated with latency to open the UR cones. Previous exposure of birds to three TR had no effect on the latency to open both cones but the proportion of R cones opened was greater in birds exposed to 30-32 °C compared to the 22-24 °C birds. In conclusion, an immediate (36-38 °C) and long-lasting effect (30-32 °C) of acute heat stress was associated with a weak motivation to perform feed related discrimination task.

Changes in facial surface temperature of laying hens under different thermal conditions

OBJECTIVE

The purpose of this study was to identify through infrared thermal imaging technology the facial surface temperature (FST) of laying hens in response to the variations in their thermal environment, and to identify the regional differences in FST to determine the most stable and reliable facial regions for monitoring of thermoregulatory status in chickens.

METHODS

Thirty Hy-Line Brown hens (25-week-old) were sequentially exposed to three different thermal conditions; optimal (OT, 22°C±2°C), low (LT, 10°C±4°C), and high temperature (HT, 30°C±2°C). The mean values of FST in five facial regions including around the eyes, earlobes, wattles, beak and nose, and comb were recorded through infrared thermography. The maximum FST (MFST) was also identified among the five face-selective regions, and its relationship with temperature-humidity index (THI) was established to identify the range of MFST in response to the variations in their thermal environment.

RESULTS

Hens exposed to OT condition at 15:00 displayed a higher temperature at wattles and around the eyes compared to other regions (p<0.001). However, under LT condition at 05:00 to 08:00, around the eyes surface temperature showed the highest value (p<0.01). In HT, wattles temperature tended to show the highest temperature over almost time intervals. Main distribution regions of MFST were wattles (63.3%) and around the eyes (16.7%) in OT, around the eyes (50%) in LT, and wattles (62.2%) and comb (18.3%) in HT. The regression equation between MFST and THI was estimated as MFST = 35.37+ 0.2383×THI (R2 = 0.44; p<0.001).

CONCLUSION

The FST and the frequency of MFST in each facial region of laying hens responded sensitively to the variations in the thermal environment. The findings of this experiment provide useful information about the effect of the thermal conditions on the specific facial regions, thus offering an opportunity to stress and welfare assessment in poultry research and industry.

Effects of heat stress on the gut health of poultry

Stress is a biological adaptive response to restore homeostasis, and occurs in every animal production system, due to the multitude of stressors present in every farm. Heat stress is one of the most common environmental challenges to poultry worldwide. It has been extensively demonstrated that heat stress negatively impacts the health, welfare, and productivity of broilers and laying hens. However, basic mechanisms associated with the reported effects of heat stress are still not fully understood. The adaptive response of poultry to a heat stress situation is complex and intricate in nature, and it includes effects on the intestinal tract. This review offers an objective overview of the scientific evidence available on the effects of the heat stress response on different facets of the intestinal tract of poultry, including its physiology, integrity, immunology, and microbiota. Although a lot of knowledge has been generated, many gaps persist. The development of standardized models is crucial to be able to better compare and extrapolate results. By better understanding how the intestinal tract is affected in birds subjected to heat stress conditions, more targeted interventions can be developed and applied.

HEAT STRESS IN BROILERS AND THE NEED OF CLIMATIZATION SYSTEMS

Broilers have better production rates when housed in thermal comfort conditions, outside of this zone the poultry need to maintain homeothermy. The heat production and thermal exchanges are related to body weight and available surface for heat exchange. The genetic evolution of broilers ensured high production with improvement in the feed conversion and reducing the slaughter time. The faster weight gain difficult sensible heat exchange, increasing the needs for climatization systems, in days with high temperatures. Changes in heat waves frequency and days with extreme temperatures are challenging situations for ventilation and evaporative cooling systems in broiler facilities. This review discusses heat exchanges of broilers and the challenges in maintaining the thermal comfort zone in poultry facilities, in a reality of increase of heat stress conditions.

Hot chicks, cold feet

Infrared thermography (IRT) is increasingly applied as a noninvasive technique for measuring surface body temperature alterations related to e.g. stress, emotions and leg pathologies in avian species. As a basis for the validation of IRT as a future tool for veterinary diagnostics such as detection and/or prediction of subclinical footpad pathologies in broiler chickens, this study explored effects of manual restraint at two different ages on footpad temperatures. Head region temperatures were applied as additional measures of emotional arousal and stress. The study demonstrated that footpad temperatures dropped during 10min of restraint (p<0.001, -0.45°C 95% CI (-0.49, -0.41) per min), whilst head region temperatures (e.g. nostril, wattle, eye, and average head temperature) rose (p=0.004, 0.76°C 95% CI (0.39, 1.15) per 10min), which is consistent with body temperature alterations during emotional arousal and stress, termed stress-induces hyperthermia. Temperature differed between 30 and 36 d (p<0.001, 1.71°C 95% CI (1.04, 2.38) per week), but it is impossible to draw conclusions whether this effect was caused by age or by conditioning. Furthermore, sequential sampling order affected temperature (p=0.04, 0.13°C 95% CI (0.01, 0.25)). In conclusion, one needs to take into account the duration of handling and restraint during the assessment of footpad temperatures, as well as the chickens age, previous experience and sequential sampling order, when using IRT technology as a future noninvasive tool to study temperature alterations associated with subclinical footpad pathologies in broiler chickens.

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.

Cloacal and surface temperatures of tom turkeys exposed to different rearing temperature regimes during the first 12 weeks of growth

Years of genetic selection have caused an increase in growth rate and market body mass in agricultural poultry species compared to earlier genetic strains, potentially altering their physiological requirements. The objective of this study was to expose Hybrid Converter tom turkeys on a weekly basis to the recommended rearing temperature regime (TCON: control) or 4°C below the recommended standard (TTRT: treatment) to determine their thermal responses. Once per week for 12 weeks, 12 turkeys were individually exposed to either TCON or TTRT for a 2-h period. Surface temperatures of the breast (TBREAST), wing (TWING), drumstick (TDRUM), head (THEAD), and shank (TSHANK) were measured at 20-min intervals using an infrared camera, while a thermal data logger measured the skin surface temperature under the wing (TLOGGER) at 30-s intervals. The cloacal temperature (TCORE) was measured using a medical thermometer at the start and end of the exposure period. Regardless of exposure temperature, the TBREAST (TCON: P<0.001 and TTRT: P<0.001), TWING (TCON: P<0.001 and TTRT: P<0.001), and TDRUM (TCON: P<0.001 and TTRT: P<0.001) decreased from weeks 4 to 6 and remained constant from weeks 1 to 3 and 8 to 12. THEAD was elevated in week 2 (TCON: P<0.001) or week 3 (TTRT: P<0.001), TSHANK increased slightly during week 3 for both TCON (P<0.001) and TTRT (P<0.001), and TLOGGER (TCON: P<0.001 and TTRT: P=0.001) and TCORE (TCON: P<0.001 and TTRT: P<0.001) were lower during the first week. Thereafter, THEAD, TSHANK, TLOGGER, and TCORE remained constant. Exposure to TTRT resulted in lower TBREAST, TWING, and TDRUM compared to TCON. Generally, THEAD, TSHANK, TLOGGER, and TCORE were not affected by the different exposure temperatures. The data demonstrated that the degree of thermal response expressed is dependent on the location of measurement, age, and exposure temperature.

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.

Regional differences in the surface temperature of Naked Neck laying hens in a semi-arid environment

The aim of this study was to evaluate the regional differences in the surface temperature of Naked Neck hens that were subjected to different temperatures in a semi-arid environment. The surface temperature was measured in four body regions (face, neck, legs and feathered area) of 60 Naked Neck hens. The following environmental variables were measured at the center of the shed: the black globe temperature (T G ), air temperature (T A ), wind speed (U) and relative humidity (R H ). The T A was divided into three classes: 1 (24.0-26.0 °C), 2 (26.1-28.9 °C) and 3 (29.0-31.0 °C). An analysis of variance was performed by the least squares method and a comparison of the means by the Tukey-Kramer test. The results showed a significant effect of T A class, the body region and the interaction between these two effects on the surface temperature. There was no significant difference between the T A classes for the face and neck. The legs and feathered area showed significant differences between the T A classes. Regarding the effect of body regions within each T A class, there was a significant difference among all regions in the three T A classes. In all T A classes the neck had the highest average followed by the face and legs. The feathered area showed the lowest average of the different T A classes. In conclusion, this study showed that there are regional differences in the surface temperature of Naked Neck hens, with the legs acting as thermal windows.

On the exploitation of mid-infrared iridescence of plumage for remote classification of nocturnal migrating birds

A challenging task in ornithology lies in identifying high-altitude nocturnal migrating bird species and genders. While the current approaches including radar, lunar obscuration, and single-band thermal imaging provide means of detection, a more detailed spectral or polarimetric analysis of light has the potential for retrieval of additional information whereby the species and sex could be determined. In this paper, we explore remote classification opportunities provided by iridescent features within feathers in the mid-infrared region. Our approach first involves characterizing the microstructural features of the feather by using rotation and straining, and a scheme for their remote detection is proposed by correlating these microstructural changes to spectral and polarimetric effects. Furthermore, we simulate the spectral signature of the entire bird by using a model that demonstrates how classification would be achieved. Finally, we apply infrared hyperspectral polarization imaging, showing that the net iridescent effect persists for the bird as a whole.

The viability and performance under hot conditions of featherless broilers versus fully feathered broilers

Hot conditions decrease the difference between ambient temperature (AT) and the average temperature of the body surface. A smaller difference reduces the rate of sensible heat loss of excessive internal heat, elevates the body temperature (BT), and may lead to mortality during heat waves. Under conditions of chronic heat, broilers avoid lethal BT elevation by reducing their feed intake; consequently, growth rate and meat yield are lower. Practices to avoid hot conditions are costly, whereas breeding for heat tolerance offers a sustainable approach. Being featherless was shown to provide heat tolerance; this was reevaluated in experimental broilers with a growth rate similar to that of contemporary commercial broilers. In experiment 1, 26 featherless birds and 49 feathered siblings (sibs) were reared at warm AT and exposed to moderate and acute heat waves. The featherless birds maintained normal BT under a moderate heat wave, with a slight elevation under an acute heat wave, and only 1 bird died. In contrast, the heat waves led to a significant elevation in BT of the feathered sibs, and 34% of them died. In experiment 2, featherless broilers were compared with feathered sibs and commercial broilers at 2 AT treatments: a constant temperature of 25°C (control AT) or a constant temperature of 35°C (hot AT). The birds were reared to 46 or 53 d at the control and hot AT, respectively, and the measured traits included BT, growth, and weight of the whole body and carcass parts (breast meat, legs, wings, and skin). At the hot AT, only the featherless broilers maintained a normal BT; their mean d 46 BW (2,031g) was significantly higher than that of birds maintained at the control AT, and it increased to 2,400 g on d 53, much higher than the corresponding means of all feathered broilers (approximately 1,700 g only). Featherless broilers had significantly higher breast meat yield (approximately 20% in both AT), lower skin weight, and supposedly better wing quality. These results confirmed that being featherless improved the livability and performance of fast-growing broilers in hot conditions and suggests that introduction of the featherless phenotype into commercial broiler stocks would facilitate highly efficient yet low-cost production of broiler meat under hot conditions.