Heat Stress Responses in Birds: A Review of the Neural Components

Impact of vitamin E and selenium supplementation on growth, reproductive performance, and oxidative stress in dexamethasone-stressed Japanese quail cocks: Vitamin E & selenium in stressed quail cocks

This study investigated the effects of dietary vitamin E (VE) and selenium (Se) supplementation on body weight changes, blood profile, and semen quality in Dexamethasone (DEX)-stressed Japanese quails. One hundred and five 10-week-old quail cocks were acclimated and divided into five treatment groups: negative control - G1, DEX-treated (20 mgL-1 of drinking water) - G2, DEX + VE (180 mg kg diet-1) - G3; DEX + Se (0.3 mg kg diet-1) - G4; and DEX + VE (180 mg kg diet-1) + Se (0.3 mg kg diet-1) - G5. The birds received their respective treatments over 21 days, and various performance, hematological, and semen quality parameters were measured. Results indicated that DEX treatment significantly reduced weight gain (WG) and feed intake (P < 0.05). Supplementation with VE and Se, individually and combined, ameliorated these effects, with groups G3, G4, and G5 showing similar WG to the control. Hematological analysis revealed significant increases (P < 0.05) in packed cell volume, hemoglobin, and white blood cell count in DEX-treated groups compared to G1. Treatment did not affect blood glucose and cholesterol levels (P ≥ 0.05). Plasma antioxidant assays showed elevated superoxide dismutase and catalase functions and reduced malondialdehyde levels in G3, G4, and G5 compared to G2, indicating reduced oxidative stress. No marked differences were seen in the plasma glutathione peroxidase activities across groups. Sperm motility was impaired in the DEX-only group but improved (P < 0.05) with antioxidant supplementation. In conclusion, dietary VE and Se effectively mitigated the negative impacts of DEX-induced stress on growth, antioxidant status, and spermatozoa motility in Japanese quail cocks. VE and Se supplementation could be beneficial in enhancing the welfare and productivity of poultry under stress.

Bridging the divide in organismal physiology: a case for the integration of behaviour as a physiological process

The role of behaviour in animal physiology is much debated, with researchers divided between the traditional view that separates physiology and behaviour, and a progressive perspective that sees behaviour as a physiological effector. We advocate for the latter, and in this Commentary, we argue that behaviour is inherently a physiological process. To do so, we outline the physiological basis for behaviour and draw parallels with recognised physiological processes. We also emphasise the importance of precise language that is shared across biological disciplines, as clear communication is foundational in integrating behaviour into physiology. Our goal with this Commentary is to set the stage for a debate and persuade readers of the merits of including behaviour within the domain of animal physiology. We argue that recognising behaviour as a physiological process is crucial for advancing a unified understanding of physiology, especially in the context of anthropogenic impacts.

Comparative assessment of growth performance, heat resistance and carcass traits in four poultry genotypes reared in hot-humid tropical environment

This study investigated the impact of heat stress on growth and carcass traits in four poultry genotypes-Giriraja, Country chicken, Naked Neck and Kadaknath reared in a hot and humid tropical environment. Birds from all genotypes had ad libitum access to feed and water while being challenged with consistently high environmental temperatures in the experimental shed. Daily diurnal meteorological data were recorded inside and outside the shed. The study specifically examined growth variables and carcass characteristics. Significant differences (p < 0.01) were observed in body weight and average daily gain at various intervals. Notably, feed intake showed significant differences (p < 0.01) across weeks, indicating interactions between genotypes and time intervals. The feed conversion ratio (FCR) varied significantly (p < 0.01), with the highest FCR recorded in the Kadaknath breed. Livability percentages were similar across groups, except for Giriraja, which had significantly lower livability (p < 0.01). Carcass traits, including dressing, wings, feathers and giblet percentages, showed significant differences among genotypes (p < 0.01). Hepatic mRNA expression of growth-related genes revealed numerical variations, with Naked Neck displaying the highest (p < 0.05) fold change in IGF-1 expression compared to other genotypes. The study recognized in the Naked Neck genotype to possess higher resilience in maintaining homoeostasis and uncompromised growth under heat stress, providing valuable insights for sustainable poultry farming in challenging environmental conditions.

Feed additives and enrichment materials to reduce chicken stress, maximize productivity, and improve welfare

Environmental stress poses serious threats to animal welfare and production, particularly in poultry, which are susceptible to such stress. It can increase susceptibility to diseases and infections, reduce growth rates and reproductive performance, and increase behavioral issues. Environmental stress caused by conventional housing conditions can negatively affect well-being and productivity. High temperature, overcrowding, poor ventilation, insufficient lighting, and wire cages are some of the most prominent stressors in conventional housing systems. To address environmental stress in chicken farms, some strategies and tools, such as using anti-stress feed additives and enriching cages, can help improve bird behavioral activities and welfare. Breeders can improve overall bird performance by implementing these strategies and creating a more enriched and comfortable environment. Thus, this review discusses the importance of using different feed additives and environmental enrichment materials to reduce stress in chicken farms (broiler and layer) and improve bird productivity and well-being.

Body condition of stranded Razorbills and Atlantic Puffins in the Western Mediterranean

Annual mass migrations of seabirds between their breeding and wintering grounds are critical for ensuring their survival and reproductive success. It is essential to comprehend their physical condition in order to identify the causes of death and to facilitate conservation efforts. This study focuses on evaluating the age, body condition index, and metabolites in liver and muscle (triglycerides, glycerol, glycogen, cholesterol, lactate, and glucose) of stranded Razorbills (n = 84) and Atlantic puffins (n = 11). The study was conducted along the Andalusian coast of Spain during the winter season of 2022-2023. The study examined the body condition of stranded individuals and their metabolic state to determine potential factors that may have caused their deaths. The study found that the majority of stranded individuals were juveniles. Both species exhibited low levels of carbohydrate (glucose and glycogen) in their tissues and high levels of lactate in their muscles. These findings could suggest that the individuals had undergone prolonged, strenuous exercise, demanding energy on anaerobic pathways, which may have been associated with migration. The study highlights the significance of adhering to standardized protocols when assessing the body condition of stranded seabirds. Doing so can help to identify causes of death and facilitate conservation efforts. A proposed index for body condition, which incorporates biometric measurements and individual physical condition, provides a comprehensive means of understanding the health of these unique species. This study underscores the importance of further research into the conservation measures and recommendations for protecting seabird populations. It is critical to comprehend the contributing factors of mass mortality incidents to work towards safeguarding these species and preserving their vital migration patterns.

In-depth transcriptome profiling of Cherry Valley duck lungs exposed to chronic heat stress

Amidst rising global temperatures, chronic heat stress (CHS) is increasingly problematic for the poultry industry. While mammalian CHS responses are well-studied, avian-specific research is lacking. This study uses in-depth transcriptome sequencing to evaluate the pulmonary response of Cherry Valley ducks to CHS at ambient temperatures of 20°C and a heat-stressed 29°C. We detailed the CHS-induced gene expression changes, encompassing mRNAs, lncRNAs, and miRNAs. Through protein-protein interaction network analysis, we identified central genes involved in the heat stress response-TLR7, IGF1, MAP3K1, CIITA, LCP2, PRKCB, and PLCB2. Subsequent functional enrichment analysis of the differentially expressed genes and RNA targets revealed significant engagement in immune responses and regulatory processes. KEGG pathway analysis underscored crucial immune pathways, specifically those related to intestinal IgA production and Toll-like receptor signaling, as well as Salmonella infection and calcium signaling pathways. Importantly, we determined six miRNAs-miR-146, miR-217, miR-29a-3p, miR-10926, miR-146b-5p, and miR-17-1-3p-as potential key regulators within the ceRNA network. These findings enhance our comprehension of the physiological adaptation of ducks to CHS and may provide a foundation for developing strategies to improve duck production under thermal stress.

Embryonic manipulations shape life-long, heritable stress responses through complex epigenetic mechanisms: a review

Enhancing an organism's likelihood of survival hinges on fostering a balanced and adaptable development of robust stress response systems. This critical process is significantly influenced by the embryonic environment, which plays a pivotal role in shaping neural circuits that define the stress response set-point. While certain embryonic conditions offer advantageous outcomes, others can lead to maladaptive responses. The establishment of this response set-point during embryonic development can exert life-long and inheritable effects on an organism's physiology and behavior. This review highlights the significance of multilevel epigenetic regulation and the intricate cross-talk among these layers in response to heat stress during the embryonic period, with a particular focus on insights gained from the avian model.

Understanding the role of temperature in seasonal timing: Effects on behavioural, physiological and molecular phenotypes

Organisms adapt to daily and seasonal environmental changes to maximise their metabolic and reproductive fitness. For seasonally breeding animals, photoperiod is considered the most robust cue to drive these changes. It, however, does not explain the interannual variations in different seasonal phenotypes. Several studies have repeatedly shown the influence of ambient temperature on the timing of different seasonal physiologies including the timing of migration, reproduction and its associated behaviours, etc. In the present review, we have discussed the effects of changes in ambient temperature on different seasonal events in endotherms with a focus on migratory birds as they have evolved to draw benefits from distinct but largely predictable seasonal patterns of natural resources. We have further discussed the physiological and molecular mechanisms by which temperature affects seasonal timings. The primary brain area involved in detecting temperature changes is the hypothalamic preoptic area. This area receives thermal inputs via sensory neurons in the peripheral ganglia that measure changes in thermoregulatory tissues such as the skin and spinal cord. For the input signals, several thermal sensory TRP (transient receptor potential ion channels) channels have been identified across different classes of vertebrates. These channels are activated at specific thermal ranges. Once perceived, this information should activate an effector function. However, the link between temperature sensation and the effector pathways is not properly understood yet. Here, we have summarised the available information that may help us understand how temperature information is translated into seasonal timing.

Performance, HSP70 expression, antioxidant enzymes, oxidative DNA damage biomarkers, metabolic hormones, and intestinal microbiota of broiler chickens fed mistletoe leaf powder supplemented diets under tropical high ambient temperatures

The study investigated the impact of Mistletoe Leaf Powder (MLP) supplementation on some parameters in heat-stressed broiler chickens. The standard baseline diets, comprising four different formulations, were provided during the starter and finisher stages. Chickens were randomly assigned to the 4 dietary groups: a negative control (CON) with no supplementation, a positive control (VTC) with 200 mg/kg vitamin C, and 2 experimental treatment groups with 2500 mg/kg (MLP2) and 5000 mg/kg (MLP5) MLP supplementation. The Body Weight Gain (BWG) in MLP2 and MLP5 treatment groups was comparable (P > 0.05) to those in VTC, while the CON group exhibited significantly (P < 0.05) lower BWG. Feed consumption was significantly (P < 0.05) lower broiler chickens in the CON group compared to those VTC, MLP2, and MLP5. Heat shock protein 70 (HSP70) levels were lower in broiler chickens belonging to VTC, MLP2, and MLP5 groups compared to those in CON, and MLP2 showed no difference (P > 0.05) from MLP5 and VTC. Serum glutathione peroxidase and catalase concentrations were higher (P < 0.05) in birds belonging to MLP5, MLP2, and VTC groups compared to CON. The 8-hydroxy-2'-deoxyguanosine concentration was lower (P < 0.05) in birds of VTC, MLP2, and MLP5 compared to the CON, with VTC showing the least concentration. Serum insulin levels were higher (P < 0.05) in MLP5 compared to those in CON, while serum triiodothyronine and leptin concentrations were lower (P < 0.05) in CON compared to birds in VTC, MLP2, and MLP5. Microbiota analysis revealed that the Coliform bacteria population was higher (P < 0.05) in birds belonging to CON compared to those in VTC, MLP2, and MLP5 groups, whereas lactic acid-producing bacteria were significantly (P < 0.05) lower in birds of CON and highest in MLP2 and MLP5 groups. In conclusion, dietary supplementation of MLP at 5000 mg/kg enhanced performance, oxidative status, influenced metabolic hormones, and gut microbiota in broiler chickens raised under high ambient temperature.

Environmental drivers behind the genetic differentiation in mountain chickadees (Poecile gambeli)

Anthropogenic climate change has a large impact on wildlife populations and the scale of the impacts has been increasing. In this study, we utilised 3dRAD sequence data to investigate genetic divergence and identify the environmental drivers of genetic differentiation between 12 populations of mountain chickadees, family Paridae, sampled across North America. To examine patterns of genetic variation across the range, we conducted a discriminant analysis of principal components (DAPC), admixture analysis, and calculated pairwise Fst values. The DAPC revealed four clusters: southern California, eastern Rocky Mountains, northwestern Rocky Mountains, and Oregon/northern California. We then used BayeScEnv to highlight significant outlier SNPs associated with the five environmental variables. We identified over 150 genes linked to outlier SNPs associated with more than 15 pathways, including stress response and circadian rhythm. We also found a strong signal of isolation by distance and local temperature was highly correlated with genetic distance. Maxent simulations showed a northward range shift over the next 50 years and a decrease in suitable habitat, highlighting the need for immediate conservation action.

Screening of heat stress-related biomarkers in chicken serum through label-free quantitative proteomics

Heat stress (HS) can result in sudden death and is one of the most stressful and costly events in chicken. Currently, biomarkers used clinically to detect heat stress state in chickens are not optimal, especially for living ones. Analysis of changes in serum proteins of heat-stressed chickens can help to identify some novel convenient biomarkers for this. Twenty-four chickens were exposed to HS at 42°C ± 1°C with a relative humidity of 65% for continuous 5 h in a single day, and 10 birds were used as controls (Con). During HS, 15 dead chickens were categorized as heat stress death group (HSD), and 9 surviving ones served as heat stress survivor group (HSS). Label-free quantitative proteomics (LFQP) was used to analyze differentially expressed proteins (DEPs) in serum of tested animals. Candidate proteins associated with HS were validated by enzyme-linked immunosorbent assay (ELISA). Diagnostic value of candidate biomarkers was assessed using receiver operating characteristic (ROC) curve analysis. Source of the selected proteins was analyzed in liver tissues with immunohistochemistry and in cell culture supernatant of primary chicken hepatocytes (PCH) using ELISA. In this study, compared to Con, LFQP identified 123 and 53 significantly different serum proteins in HSD and HSS, respectively. Bioinformatics analysis showed that XDH, POSTN, and HSP90 were potential HS biomarkers in tested chickens, which was similar with results from serum ELISAs and immunohistochemistry in liver tissues. The ROC values of 0.793, 0.752, and 0.779 for XDH, POSTN, and HSP90, respectively, permitted the distinction of heat-stressed chickens from the control. Levels of 3 proteins above in the cell culture supernatant of PCH showed an increasing trend as HS time increased. Therefore, considering that mean concentration of POSTN in serum was higher than that of HSP90, XDH, and POSTN may be optimal biomarkers in serum for detecting HS level in chickens, and mainly secreted from hepatocytes. The former indicates that heat-stressed chickens are in a damaged state, and the latter implies that chickens can repair heat stress damage.

Rye-grass-derived probiotics alleviate heat stress effects on broiler growth, health, and gut microbiota

The primary aim of this study was to assess the impact of liquid (S-LAB) and lyophilized (L-LAB) probiotics sourced from Rye-Grass Lactic Acid Bacteria on broilers experiencing heat stress. The study involved 240 broiler chicks divided into six groups. These groups included a negative control (Control) with broilers raised at a normal temperature (24 °C) on a basal diet, and positive control groups (S-LAB and L-LAB) with broilers under normal temperature receiving a lactic acid bacteria supplement (0.5 mL/L) from rye-grass in their drinking water. The heat stress group (HS) comprised broilers exposed to cyclic heat stress (5-7 h per day at 34-36 °C) on a basal diet, while the heat stress and probiotic groups (S-LAB/HS and L-LAB/HS) consisted of broilers under heat stress supplemented with the rye-grass-derived lactic acid bacteria. Results indicated that heat stress without supplementation (HS) led to reduced body weight gain, T3 levels, citrulline, and growth hormone levels, along with an increased feed conversion ratio, serum corticosterone, HSP70, ALT, AST, and leptin levels. Heat stress also negatively impacted cecal microbiota, decreasing lactic acid bacteria (LABC) while increasing E. coli and coliform bacteria (CBC) counts. Probiotic supplements (S-LAB/HS and L-LAB/HS) mitigated these effects by enhancing broilers' resilience to heat stress. In conclusion, rye grass-derived S-LAB and L-LAB probiotics can effectively support broiler chickens under heat stress, promoting growth, liver function, hormonal balance, gut health, and cecal microbiome ecology. These benefits are likely mediated through improved gut health.

Wild white-capped noddies keep a cool head in a heated situation

Sunning, or sunbathing, is a behavior observed in diverse birds from at least 50 taxonomic families. While sunning, birds exhibit signs of heat stress, notably panting, indicating a risk of overheating. Given that even modest increases in brain temperature can impair brain function, sunning birds may have mechanisms that selectively cool the brain. Sunning birds could cool the brain using active physiological mechanisms (e.g., an ophthalmic rete or sleeping) or passive adaptations, such as light-colored plumage over the cranium. White-capped noddies are tropical seabirds that sunbathe in direct sunlight on cloudless days. Using infrared thermography on wild birds, we found that the white cap is 20 °C cooler than that of the black back while sunning. A deceased bird showed the same thermal profile, indicating that this difference arises from dichromatic coloration and not underlying physiology. Thus, the white cap may extend the duration of time noddies can sunbathe and keep the brain cool, near core body temperature, while allowing the rest of the body to heat up, perhaps to displace or kill parasites.

To Flee or Not to Flee: How Age, Reproductive Phase, and Mate Presence Affect White Stork Flight Decisions

Recognizing, assessing, and responding to threats is critical for survival in the wild. Birds, especially in their role as parents, must decide whether to flee or delay flight when threatened. This study examines how age, reproductive stage, and the presence of a mate influence flight initiation distance (FID) and nest recess duration in white storks. Analyzing the data with a generalized additive mixed model (GAMM), we found significant correlations between FID and age, reproductive stage, and presence of a mate. These results suggest that the trade-off between current and future reproduction shifts during critical breeding periods, such as incubation and nestling care. To increase breeding success, White Storks appear willing to take risks and extend their stay in the nest when offspring are most valuable and vulnerable. In the presence of a mate, individuals leave the nest earlier, suggesting possible sexual conflict over parental care. The duration of nest abandonment is consistent with FID, except for age. These results illustrate how parental age, brood value, vulnerability, and sexual dynamics influence white stork flight decisions in complex ways. Understanding these dynamics enriches our knowledge of bird behavior and adaptations to environmental challenges and highlights the complexity of parental decision making.

Incubation Temperature and Lighting: Effect on Embryonic Development, Post-Hatch Growth, and Adaptive Response

During incubation, the content of the egg is converted into a chick. This process is controlled by incubation conditions, which must meet the requirements of the chick embryo to obtain the best chick quality and maximum hatchability. Incubation temperature and light are the two main factors influencing embryo development and post-hatch performance. Because chicken embryos are poikilothermic, embryo metabolic development relies on the incubation temperature, which influences the use of egg nutrients and embryo development. Incubation temperature ranging between 37 and 38°C (typically 37.5–37.8°C) optimizes hatchability. However, the temperature inside the egg called “embryo temperature” is not equal to the incubator air temperature. Moreover, embryo temperature is not constant, depending on the balance between embryonic heat production and heat transfer between the eggshell and its environment. Recently, many studies have been conducted on eggshell and/or incubation temperature to meet the needs of the embryo and to understand the embryonic requirements. Numerous studies have also demonstrated that cyclic increases in incubation temperature during the critical period of incubation could induce adaptive responses and increase the thermotolerance of chickens without affecting hatchability. Although the commercial incubation procedure does not have a constant lighting component, light during incubation can modify embryo development, physiology, and post-hatch behavior indicated by lowering stress responses and fearful behavior and improving spatial abilities and cognitive functions of chicken. Light-induced changes may be attributed to hemispheric lateralization and the entrainment of circadian rhythms in the embryo before the hatching. There is also evidence that light affects embryonic melatonin rhythms associated with body temperature regulation. The authors’ preliminary findings suggest that combining light and cyclic higher eggshell temperatures during incubation increases pineal aralkylamine N-acetyltransferase, which is a rate-limiting enzyme for melatonin hormone production. Therefore, combining light and thermal manipulation during the incubation could be a new approach to improve the resistance of broilers to heat stress. This review aims to provide an overview of studies investigating temperature and light manipulations to improve embryonic development, post-hatch growth, and adaptive stress response in chickens.

Effect of Stressors on the mRNA Expressions of Neurosecretory Protein GL and Neurosecretory Protein GM in Chicks

We recently discovered novel cDNAs encoding the precursors of two small secretory proteins, neurosecretory protein GL (NPGL) and neurosecretory protein GM (NPGM), in the mediobasal hypothalamus (MBH) of chickens. In addition, we found colocalization of NPGL, NPGM, and histidine decarboxylase (HDC; histamine-producing enzyme) in same neurons of the medial mammillary nucleus of the hypothalamus. In this study, we elucidated the effect of several stresses, including food deprivation, environmental heat, inflammation, and social isolation, on the mRNA expression of NPGL, NPGM, and HDC in chicks using real-time PCR. Food deprivation for 24 h increased NPGM mRNA expression in the MBH. On the other hand, an environmental temperature of 37°C for 24 h did not affect their mRNA expression. Six hours after intraperitoneal injection of lipopolysaccharide, an inducer of inflammation, the mRNA expression of NPGM, but not that of NPGL and HDC increased. Social isolation for 3 h induced an increase in the mRNA expression of NPGL, NPGM, and HDC. These results indicate that NPGM, but not NPGL or HDC, may participate in several physiological responses to stress in chicks.