Thermoneutral Zone Research Articles

Seasonal variation in roost climate and emergence behaviour in a colony of the highly gregarious wrinkle-lipped free-tailed bat (Mops plicatus)

ABSTRACT As obligate nocturnal mammals, most bats spend the day hiding in dark shelters, sometimes as gregarious colonies. Roosting in such large colonies may have the advantage of reducing thermoregulatory costs, as the heat dissipated by thousands of bodies raises the temperature of the cave interior. However, bats in large aggregations may also suffer from increased predation risk. Here we studied the effect of a highly gregarious Palaeotropical bat, the wrinkle-lipped free-tailed bat (Mops plicatus), on cave temperature and the factors that influence its emergence behaviour. We studied cave temperature, prey abundance, emergence behaviour and attack rates by birds of prey during colony emergence. The study was made at Khao Wongkot Cave, counting more than one million individuals. In all seasons, we observed that the presence of M. plicatus caused relatively higher temperatures of around 30°C inside the cave, while temperatures outside were lower and more variable. This suggests that the body heat of aggregated bats raised the temperature inside the cave, presumably close to the thermo-neutral zone at the roosting sites of bats. Arthropod abundance was highest during late pregnancy/early lactation and lowest during late lactation/post lactation. Bats emerged earliest during the late wet season and latest during the hot season. During periods of high predation risk, bats always emerged as a column, whereas during periods of low predation risk (hot and early wet seasons), individual bats left first, before a column of bats formed, 10 to 20 min after the first individuals exited the cave. Our study highlights that large colonies may provide thermoregulatory benefits that could increase individual fitness. However, aggregations also increase predation costs during emergence. Bats form a column when aerial predator attacks are most frequent. Also, bats seem to adjust their emergence timing in response to seasonal changes in predation risk.

Influence of ambient temperature on resting energy expenditure in metabolically healthy men and women.

It is not yet clear to what extent the physiological regulatory mechanisms that maintain core body temperature are reflected by changes in resting energy expenditure (REE). Particularly in indirect calorimetry with a canopy, the effects of short-term temperature exposures have not yet been investigated. This can be of relevance for the determination of REE in practice. This randomized crossover-study investigated the influence of a 30-minute exposure to 18°C (cool room temperature), 22°C (room temperature), 28°C (thermoneutral zone) and 38°C (heat) on REE determined by assessing the inhaled oxygen volume and the exhaled carbon dioxide volume via indirect calorimetry on four consecutive days. 32 metabolically healthy participants (16 male and 16 female, age: 25 ± 3 years, body mass index: 22.4 ± 1.6 kg/m2) were included in the study after screening examination. Lean body mass, ambient temperature and heart rate were the most important determinants (all P<0.001), and explained 61.3% of the variance in REE. A multivariate linear mixed model analysis revealed that lean mass (15.87 ± 3.66, P<0.001) and ambient temperature (P=0.001) significantly influenced REE. REE significantly differed between 18°C and 28°C (18°C: +96 ± 24 kcal/24 h, P<0.001), 22°C and 28°C (22°C: +73 ± 24 kcal/24 h, P=0.003) and 18°C and 38°C (18°C: +57 ± 23 kcal/24 h, P=0.016). Effects of ambient temperature on REE, especially cold, were detectable after only brief exposure, emphasizing the importance of performing indirect calorimetry with a canopy under controlled environmental conditions. The study was registered with the database "ClinicalTrials.gov" (NCT05505240).Web-Link: Influence of Ambient Temperature on Resting Energy Expenditure of Healthy Adults - Full Text View - ClinicalTrials.gov.

Responses of Poultry to Heat Stress and Mitigation Strategies During Summer in Tropical Countries: A Review&lt;b&gt;&lt;/b&gt;

The poultry industry faces increasing challenges from heat stress caused by global warming, particularly in tropical regions. Heat stress, caused by rising environmental temperatures, undermines the health and productivity of poultry, resulting in significant economic losses. This review comprehensively addresses the physiological and behavioural responses of poultry to heat stress and explores the key mitigation strategies, categorized under genetics, management and feeding. Genetic approaches, like utilizing specific genes in breeding, show promise but require wider adoption. Management practices such as housing design, including orientation, insulation and ventilation, controlled lighting and thermal manipulation are critical to maintaining poultry in their thermoneutral zone. Furthermore, feeding strategies like feed restriction, dual feeding and nutritional manipulation have shown promise in reducing heat stress effects. In addition to feeding strategies, water management is also crucial for mitigating heat stress, especially in tropical areas. Ensuring sufficient water space, maintaining operating waterers, and keeping water cool are essential to encourage adequate drinking. Despite progress, further investigation is required to explore the synergistic effects of combined strategies to improve the resilience of poultry. This review highlights the urgent need for comprehensive approaches to mitigate heat stress in poultry to ensure sustainable productivity under the challenges of global warming

Field respirometry in a wild maternity colony of Bechstein's bats (Myotis bechsteinii) indicates higher metabolic costs above rather than below the thermoneutral zone.

In a warming world, it is crucial to understand how rising temperature affects the physiology of organisms. To investigate the effect of a warming environment on the metabolism of heterothermic bats during the costly lactation period, we characterised metabolic rates in relation to roost temperature, the bats' thermoregulatory state (normothermia or torpor), time of day and age of juveniles. In a field experiment, we heated the communal roosts of a wild colony of Bechstein's bats (Myotis bechsteinii) every other day while measuring metabolic rates using flow-through respirometry. As expected, metabolic rates were lowest when the bats were in torpor. However, when bats were normothermic, colder temperatures had little effect on metabolic rates, which we attribute to the thermoregulatory benefits of digestion-induced thermogenesis and social thermoregulation. In contrast, metabolic rates increased significantly at temperatures above the thermoneutral zone. Contrary to our expectations, metabolic rates were not lower in heated roosts, where temperatures remained close to the bats' thermoneutral zone, than in unheated roosts, where temperatures were more variable. Our results show that torpor and digestion-induced thermogenesis are effective mechanisms that allow bats to energetically buffer cold conditions. The finding that metabolic rates increased significantly at temperatures above the thermoneutral zone suggests that the physiological and behavioural abilities of Bechstein's bats to keep energy costs low at high temperatures are limited. Our study highlights that temperate-zone bats are well adapted to tolerate cold temperatures, but may lack protective mechanisms against heat, which could be a threat in times of global warming.

Early detection and progression of insulin resistance revealed by impaired organismal anti-inflammatory heat shock response during ex vivo whole-blood heat-challenge

Chronic inflammatory diseases, e.g., obesity, cardiovascular disease, and type 2 diabetes, progressively suppress the anti-inflammatory heat shock response (HSR) by impairing the synthesis of key components, perpetuating inflammation. Monitoring HSR progression offers predictive value for countering chronic inflammation. This study quantified HSR in high-fat diet (HFD) and normal chow (NC) mice by measuring 70 kDa heat shock protein (HSP70) expression after heat treatment of whole blood samples. To align with human translational relevance, animals were housed within their thermoneutral zone (TNZ). Whole blood was heat-challenged weekly at 42 °C for 1-2 hours over 22 weeks, and ΔHSP70 was calculated as the difference between HSP70 expressions at 42 °C and 37 °C. Results correlated with fasting glycaemia, oral glucose tolerance test (oGTT), intraperitoneal insulin tolerance test (ipITT), and 2-hour post-glucose load glycaemia. ΔHSP70 levels &amp;gt;0.2250 indicated normal fasting glycaemia, while levels 1/2 = 3.14 weeks) compared to NC mice (t1/2 = 8.24 weeks), highlighting compromised anti-inflammatory capacity in both groups of mice maintained at TNZ. Remarkably, even NC mice surpassed insulin resistance thresholds by week 22, relevant as control diets confronted interventions. Observed HSR decline mirrors tissue-level suppression in obese and type 2 diabetic individuals, underscoring HSR failure as a hallmark of obesity-driven inflammation. This study introduces a practical whole-blood assay to evaluate HSR suppression allowing assessment of glycaemic status during obesity onset before any clinical manifestation.

Body size influences the capacity to cope with extreme cold or hot temperatures in the striped hamster

Body size of organisms is a key trait influencing nearly all aspects of their life history. Despite growing evidence of Bergmann's rule, there is considerably less known about the links between body size and the maximum capacity to thermoregulate of an animal in response to extreme cold or hot environment. Thermal characteristics such as resting metabolic rate (RMR) and non-shivering thermogenesis (NST), and the upper- and lower- critical temperatures of the thermal neutral zone (TNZ) were investigated in small and large body sized striped hamsters (Cricetulus barabensis). The maximum capacity to thermoregulate in response to extreme cold (-15°C) or hot temperature (38°C) was also examined, where both, different sized hamsters had similar RMR and NST regardless of temperature exposure. The large hamsters had 29.9% more body mass compared to small hamsters. The large hamsters showed a wider TNZ, with lower, lower-critical temperature, and showed considerable hyperthermia at the end of a 17-hours hot exposure. In contrast, the small hamsters showed hypothermia following a 17-hours cold exposure relative to large hamsters. In addition, the large hamsters showed 17.2% lower basal thermal conductance, and 14.9% lower maximum thermal conductance than the small hamsters after cold exposure, and 22.6% lower thermal conductance following heat exposure. Several molecular markers indicative of thermogenesis and oxidative stress did not differ significantly between the large and small hamsters. These findings suggest that individuals with larger body sizes have greater capacity to thermoregulate to cope with extreme cold, and a reduced capacity in response to extreme hot. In contrast, smaller individuals demonstrated the opposite trend. Body size may decide the capacity to thermoregulate to cope with extreme cold and heat, within which body heat dissipation is likely more important than heat production.

Floor position in multitier broiler closed houses and its impact on microclimatic, air quality and litter conditions

This study aimed to evaluate the effects of floor position in a multitier closed house on microcli-matic air quality and litter conditions. Fourteen thousand and five hundred unsexed Ross broiler chick-ens with a DOC body weight of 45.84 ± 2.40 g were placed on each floor of a three-tier closed house and allocated to a randomized block design consisted of 3 treatments and 18 replications. Each floor measured 12x78x2 m3. The maintenance procedure was applied according to the integrated partnership company guidelines PT Tumbuh Optimal Prima, with an observation period of 28 days. The treatments applied were as follows: T1= placement of broiler chickens on the 1st floor, T2= placement of broiler chickens on the 2nd floor, and T3= placement of broiler chickens on the 3rd floor. Microclimate condi-tions (temperature, RH, wind speed, temperature humidity index, wind chill effect, and calculated real feel temperature) and air quality parameters (NH3, CO2, O2, TVOC, and HCHO) were measured daily on each floor. Litter conditions, included water content, litter temperature, NH3 content, pH, and caking were measured weekly. The results revealed that during the starter phase (weeks 1–2), the microclimat-ic conditions and air quality of the 3rd floor were significantly better (P&lt;0.05) than those of the 1st floor and 2nd floor, a trend was continued during weeks 3–4. Notably, the results obtained on the 1st and 2nd floors were still within the normal range for the broiler thermoneutral zone. Conversely, the 3rd floor litter was generally poorer, with significantly higher (P&lt;0.05) moisture content, temperature, and cak-ing than the lower floors, particularly in weeks 3–4. However, broiler placement on different floors did not significantly affect the litter pH (P&gt;0.05). In conclusion, the microclimatic conditions and air quali-ty of the 3rd floor were generally superior to those of the lower floors over the 4-week rearing period, whereas the litter quality was inferior.

Plunge-diving into dynamic body acceleration and energy expenditure in the Peruvian booby.

Daily energy expenditure (DEE) is the result of decisions on how to allocate time among activities (resting, commuting and foraging) and the energy costs of those activities. Dynamic body acceleration (DBA), which measures acceleration associated with movement, can be used to estimate DEE. Previous studies of DBA-DEE correlations in birds were carried out on species foraging below their thermoneutral zone, potentially decoupling the DBA-DEE relationship. We used doubly labelled water (DLW) to validate the use of DBA on plunge-diving seabirds, Peruvian boobies (Sula variegata), foraging in waters above their thermoneutral zone (>19°C). Mass-specific DEEDLW in boobies was 1.12 kJ day-1g-1, and higher in males than in females. DBA alone provided the best fitting model to estimate mass-specific DEEDLW compared with models partitioned per activity and time budget models. Nonetheless, the model parametrizing activity at and away from their onshore breeding colony was the most parsimonious (r=0.6). This r value, although high, is lower than that of all other avian studies, implying that temperature is not the main cause of DBA-DEE decoupling in birds. Time at the colony (∼80% of the day) was the largest contributor to DEE as it was the most time-consuming activity and involved nest defence. However, foraging was the most power-consuming activity (4.6 times higher activity-specific metabolic rate than resting at the colony), and commuting flight was higher than in other gliding seabirds. In short, DBA alone can act as a proxy for DEE, opening avenues to measure the conservation energetics of this seabird in the rapidly changing Peruvian Humboldt Current system.

Evaluating the efficacy of probiotics and ascorbic acid as anti-stress agents against heat stress in broiler chickens.

Heat stress poses a substantial challenge to poultry production worldwide, highlighting the urgent need for effective management strategies. This study investigated the efficacy of probiotics (Saccharomyces cerevisiae) and ascorbic acid as antistress agents using cloacal and body surface temperatures (CT and BST) as heat stress biomarkers in broiler chickens. A total of 56 broiler chicks were used for the experiment and were divided into four distinct groups: control, probiotics (1 g/kg of feed), ascorbic acid (200 mg/kg of feed) and the combination of probiotics and ascorbic acid (1 g/kg and 200 mg/kg of feed, respectively). The study lasted 35 days; measurements were taken for ambient temperature (AT), CT, and BST. The ambient temperature in the pens consistently exceeded the thermoneutral zone (TNZ) established for broiler chickens. The CT values for broiler chickens in the probiotic group were significantly lower (p < 0.05) compared to the control group. Additionally, the BST values in the probiotic and probiotic + ascorbic acid groups were significantly lower (p < 0.05) than those in the control group. The findings suggest that incorporating probiotics, with or without ascorbic acid, can effectively reduce CT and BST values in broiler chickens thereby, enhancing thermoregulation when compared to the control group. This implies that using probiotics in poultry diets may enhance health and growth performance, potentially leading to better feed efficiency and reduced reliance on antibiotics. Implementing these dietary strategies could improve the productivity and welfare of broiler chickens in commercial settings.

Evolutionary shifts in the thermal biology of a subterranean mammal: the effect of habitat aridity.

Subterranean mammals representing a single subspecies occurring along an aridity gradient provide an appropriate model for investigating adaptive variation in thermal physiology with varying levels of precipitation and air temperature. This study examined the thermal physiological adaptations of common mole-rats (Cryptomys hottentotus hottentotus) across five populations along an aridity gradient, challenging the expectation that increased aridity would lead to reduced metabolic rate, lower body temperatures and broader thermoneutral zones. No significant, consistent differences in metabolic rate, body temperature or thermal conductance were observed between populations, suggesting uniform thermoregulatory mechanisms across habitats. Instead, behavioural strategies such as huddling and torpor may play a more prominent role than physiological adaptations in managing temperature regulation and water balance. The study also observed osmoregulatory differences, with populations employing distinct behavioural cooling strategies in response to water availability. These results underscore the need for further research into the responses of subterranean species to climate change, particularly in understanding how increasing global temperatures and aridification might influence species distribution if they lack the physiological capacity to adapt to future climatic conditions.

Minor Modification in Asbestos Roof of Cow Shed for Reduction of Heat Stress in Dairy Cows during Summer Season

Thermo neutral zone (TNZ) is the range of ambient temperature &amp; humidity in which animals feel comfortable and their production level is optimum. When temperature humidity index (THI) goes above 72, the dairy cows begin to show symptoms of mild heat stress, which affects the milk production in dairy animals during summer season in India. Asbestos and GI sheet are commonly used as roofing material in many cattle farms throughout the world. This experiment was carried out on apparently healthy cross bred jersey cows receiving balanced ration during the month of May in the livestock farm of OUAT, Bhubaneswar for one week. The existing cattle shed was partitioned into three compartments by raising brick walls, each having the dimension of 30 x 25 ft size. The asbestos roof of first one was covered with 90 % grade green shed-net. Over the asbestos roof of second compartment, heat reflective white colour was painted and asbestos roof of third one was left as such. From 8.00 AM to 5.00PM, the THI of the normal asbestos roof shed varied from mild to moderate heat stress range. But THI of both shed-net covered shed and heat reflective colour painted shed was found to be within the mild heat stress range i.e. 72-79 during noon indicating a comfortable ambient condition for the animals in summer season when the outside ambient temperature went up to 40 0C during noon. No significant (P&gt;0.05) change in the milk production was observed among the groups during the week. However, a decrease (P&lt;0.05) of 0.43, 0.25 and 0.38 L in milk yield of the cows was observed when they were kept under normal asbestos shed, heat reflective colour painted shed and shed-net covered shed, respectively. From the study, this can be concluded that the impact of heat stress on milk production can be reduced by painting the rood of the shed with heat reflective colour paint.

Seasonal and depth-dependent thermoregulatory benefits of burrows for wombats – The largest burrowing marsupials

Mammals use burrows to behaviourally thermoregulate, save water, and avoid predation. The advantages of burrows vary not only seasonally but also with burrow depth. To quantify these effects, we used biophysical ecological models, which predict an animal's energetic and hydric costs within a characterised microclimate. For Australia's three extant wombat species, we quantified variation in the energetic advantage of burrows spatially, temporally, and with burrow depth. We simulated resting wombats with different traits (e.g., body size, fur) in different microclimates (above ground and burrows of varying depth) at six sites across Australia, two for each wombat species, over five years (1980, 1990, 2000, 2010, 2020). We assessed time spent within their thermoneutral zone—heat production equals heat loss thus minimising energy and water expenditure —and frequency of extreme heat stress (i.e., no viable hydric solution for the conditions stipulated). Our findings show that burrows are essential for reducing energetic and hydric costs and for survival during the hottest season in areas with no shade, e.g., the semi-arid zone. We found no evidence that extreme heat stress has increased temporally i.e., due to climate change, but it was frequently predicted in shallow burrows in 2020, having rarely been previously forecast. For energy requirements, we found lower thermoregulatory costs for deeper burrows in the cold season and for shallow burrows in the hot season. This work underscores the critical balance between wombat survival, burrow utility, and environmental dynamics, offering new insights into mechanisms that dictate mammal behaviour from a thermoregulatory perspective.

Optimally warm roost temperatures during lactation do not improve body condition in a long-lived bat.

Lactation is the most energetically demanding time in the life of female mammals. To maximize lifetime reproductive success, females of long-lived species, such as bats, face a trade-off between investing in current and future reproduction. However, it is unclear whether global warming could influence this trade-off through shifts in the energy budget: warmer temperatures may reduce thermoregulatory costs, leaving mothers with more energy available for maternal care or for improving their own body condition (BC), which may increase survival and ensure future reproduction. Here, we investigated whether lactating Bechstein's bats (Myotis bechsteinii) allocate the energy saved in optimally warm roosts into their own BC. We analysed a 14-year dataset on the individual BC of 237 females marked with radio-frequency identification tags from four wild maternity colonies. In two of the colonies, the temperature in the roosts, in which the females raised their offspring, was artificially kept in the bats' thermoneutral zone to reduce their thermoregulation costs. We found that BC shortly after the lactation period did not differ between mothers from heated and non-heated colonies. Our results suggest that mothers do not invest the energy saved in warmer roosts in their own BC, consistent with an increased investment in maternal care.

Impact of heat stress on female reproduction in farm animals: challenges and possible remedies

Global warming poses significant challenges to agriculture, particularly within the livestock industry. Heat stress in animals refers to the physiological and metabolic distress experienced when environmental heat causes an animal’s body temperature to exceed its thermoneutral zone. Heat stress has a significant detrimental impact on reproductive outcomes, posing a direct threat to the profitability of livestock operations. Heat stress disrupts the normal hormonal balance essential for reproduction in female livestock, adversely affecting events of folliculogenesis and embryogenesis. As a result, the developmental competence of oocytes is compromised, which is crucial for successful fertilization and reproduction. Consequently, heat stress can lead to issues such as immature oocytes, atypical or sluggish embryonic development, silent estrus, and increased pregnancy loss causing a decline in reproductive rates and livestock owners face substantial financial losses. Despite using various cooling strategies, such as water sprinkler systems, cooling shades, and cooling devices, these measures are often insufficient to restore normal reproductive rates. Therefore, it is crucial to implement and explore novel strategies to enhance reproductive efficiency during periods of heat stress. Potential mitigation techniques include estrus synchronization, artificial insemination, hormonal alterations, embryo transfer, genetic engineering, sophisticated breeding strategies, the use of nutraceuticals, and changes in management practices. This review aims to consolidate recent findings on the adverse effects of heat stress on female reproduction, especially in tropical environments, and to evaluate potential strategies for improving summer fertility of livestock. Bangladesh Journal of Animal Science 53(3): 77-100, 2024

Chronic whole-body heat treatment in obese insulin-resistant C57BL/6J mice

Aim This study examined the effects of hyperthermic therapy (HT) on mice fed normal chow or a high-fat diet (HFD) for 18 or 22 weeks, undergoing four or eight weekly HT sessions. Methods Mice were housed within their thermoneutral zone (TNZ) to simulate a physiological response. HFD-induced obesity-related changes, including weight gain, visceral fat accumulation, muscle loss (indicative of obesity sarcopenia), glucose intolerance, and hepatic triglyceride buildup. Main Results HT upregulated HSP70 expression in muscles, mitigated weight gain, normalised QUICK index, and reduced plasma HSP70 concentrations. It also lowered the H-index of HSP70 balance, indicating improved immunoinflammatory status, and decreased activated caspase-1 and proliferative senescence in adipose tissue, both linked to insulin resistance. Conclusion The findings suggest that even animals on a “control” diet but with insufficient physical activity and within their TNZ may experience impaired glycaemic homeostasis.

Seasonal and between-population variation in heat tolerance and cooling efficiency in a Mediterranean songbird

Discrete populations of widely distributed species may inhabit areas with marked differences in climatic conditions across geographic and seasonal scales, which could result in intraspecific variation in thermal physiology reflecting genetic adaptation, phenotypic plasticity, or both. However, few studies have evaluated inter-population variation in physiological responses to heat. We evaluated within- and inter-population seasonal variation in heat tolerance, cooling efficiency and other key thermoregulatory traits in two Mediterranean populations of Great tit Parus major experiencing contrasting thermal environments: a lowland population subject to hotter summers and a higher annual thermal amplitude than a montane population. Specifically, we measured heat tolerance limits (HTL), body temperature, resting metabolic rate, evaporative water loss, and evaporative cooling efficiency (the ratio between evaporative heat loss to metabolic heat production) within and above the thermoneutral zone during winter and summer. Heat tolerance during summer was greater in lowland than in montane birds; indeed, lowland birds seasonally increased this trait to a significant level, while montane ones did to a lesser extent. Besides, lowland birds showed greater evaporative cooling efficiency during summer (possibly due in part to reductions in total endogenous heat load), while surprisingly montane ones showed the opposite trend. Thus, lowland birds displayed greater seasonal flexibility in HTL, body temperature and resting metabolic rate above thermoneutrality, thus giving some support to the climatic variability hypothesis — that flexibility in thermoregulatory traits should increase with climatic variability. Our results partially support the idea that songbirds’ adaptive thermoregulation in the heat is flexible, highlighting the importance of considering intraspecific variation in thermoregulatory traits when modelling the future distribution and persistence of species under different climate change scenarios.

Thermal constraints and gender-related differences in the activity patterns of the monomorphic rodent Clyomys laticeps

Abstract The daily activity pattern of animals can be classified as diurnal, nocturnal, crepuscular, and cathemeral reflecting strategic decisions to maximize mating and foraging while reducing predation risks and thermal constraints. Among monomorphic mammals, competition for resources and gender-related differences in physiology and reproductive strategies may translate into different activity patterns of males and females. Therefore, to understand the daily activity pattern both aboveground and belowground of the semifossorial rodent Clyomys laticeps, we tested the following hypotheses: (1) males and females differ in their diel activity patterns; (2) males are active for longer periods than females due to a promiscuous mating system and female site fidelity; and (3) higher maximum temperatures restrain C. laticeps activity. The study was carried out in the Serra de Caldas Novas State Park (Goiás, Brazil) in the Cerrado biome. The activity of C. laticeps was recorded using the telemetry technique over 5 days and nights (twice in each season, rainy and dry, between 2019 and 2021). Clyomys laticeps activity was bimodal, with 2 peaks around dawn and dusk, resembling a crepuscular pattern. Temporal segregation in male and female activity patterns was restricted to the dry season, when female activity was more diurnal than males who were mainly nocturnal. Intersexual competition for resources or male-avoidance behavior by females during the dry food scarcity season could contribute to this pattern, although it may also be explained by gender-related differences in thermal tolerances. Overall, males were active for longer periods than females, probably as a strategy to increase mating opportunities among the former and site fidelity in the latter. Finally, temperature imposed major constraints on C. laticeps activities who preferred milder temperatures and avoided being active in temperatures above their thermoneutral zone.

PSII-14 Climate and conception: Investigating the resilience of equine embryo survival to ambient temperatures in southeast Texas

Abstract Amidst the unique challenges posed by the humid and hot climate of southeast Texas, this study aimed to assess the establishment of pregnancy from transferred equine embryos, hypothesizing that an increase in ambient temperature would lead to a decrease in pregnancy establishment. To achieve this, we utilized 17 embryo donors and 46 recipient mares (3 to 9 yr of age), all anatomically and clinically normal with no history of reproductive problems. Breeding records for 49 transferred d 8, grade-1 embryos from a single private horse farm in southeast Texas, along with the reported high and low ambient temperatures on the day of transfer, were analyzed using logistic regression via PROC GLIMMIX in SAS v9.4 with fixed effects for the reported high and low ambient temperatures on the day of transfer, with a random statement for donor and sire. The pregnancy rate for all embryo transfers was 79%. Surprisingly, our results revealed that neither the reported high ambient temperatures (P = 0.16) nor reported low ambient temperatures (P = 0.19) significantly influenced the likelihood of pregnancy establishment observed at d 14 post-ovulation of transferred equine embryos. Furthermore, no statistically significant influence (P &amp;gt; 0.05) on pregnancy establishment was observed when embryo transfers were conducted outside of the thermal neutral zone (5°C to 20°C). Within the context of our study, these results suggest that environmental temperatures in southeast Texas do not significantly impact equine pregnancy outcomes.

Comparative Study of Thermoregulatory and Thermogenic Characteristics of Three Sympatric Rodent Species: The Impact of High-temperature Acclimation

Background: Ambient temperature is one of the important factors affecting the survival of small mammals in the wild and different animals have different ways of regulating when face the same environmental temperature and different temperatures will also make the same species adjust the energy budget. Therefore, it is helpful to further understand the survival and adaptation patterns of different animals to study the different adjustment modes of animals in the same region in the face of high temperature environment. Methods: In the present study, three rodents, Apodemus chevrieri, Eothenomys miletus and E. olitor, were exposed to a high temperature (Ta) of 30°C for 28 days. And then body mass, body temperature (Tb), resting metabolic rate (RMR) and thermal conductance (C) were measured at Ta from 5°C to 35°C. Result: The results showed that Tb of all three mammals increased significantly with the increase of Ta. And thermal neutral zones (TNZ) among three animals were all 25°C-30°C. Moreover, RMR increased with the increase of Ta above the upper critical temperature Within the range of 30°C to 35°C. C values in three mammals maintained stable within the Ta of 5°C-25°C, which increased with the increase of Ta above 25°C. All of the results suggested that three sympatric rodent species raised their Tb, narrowed their TNZ and changed C values to adapt to the high temperature. Moreover, change amplitudes of thermoregulation characteristics in E. olitor were small, indicating that E. olitor may have the strong adaptability under high temperature acclimation.

TRPV1 Activation Antagonizes High-Fat Diet-Induced Obesity at Thermoneutrality and Enhances UCP-1 Transcription via PRDM-16.

Body weight is a balance between energy intake and energy expenditure. Energy expenditure is mainly governed by physical activity and adaptive thermogenesis. Adaptive dietary thermogenesis in brown and beige adipose tissue occurs through mitochondrial uncoupling protein (UCP-1). Laboratory mice, when housed at an ambient temperature of 22-24 °C, maintain their body temperature by dietary thermogenesis, eating more food compared to thermoneutrality. Humans remain in the thermoneutral zone (TNZ) without expending extra energy to maintain normal body temperature. TRPV1 activation by capsaicin (CAP) inhibited weight gain in mice housed at ambient temperature by activating UCP-1-dependent adaptive thermogenesis. Hence, we evaluated the effect of CAP feeding on WT and UCP-1-/- mice maintained under thermoneutral conditions. Our research presents novel findings that TRPV1 activation by CAP at thermoneutrality counters obesity in WT mice and promotes PRDM-16-dependent UCP-1 transcription. CAP fails to inhibit weight gain in UCP-1-/- mice housed at thermoneutrality and in adipose tissue-specific PRDM-16-/- mice. In vitro, capsaicin treatment increases UCP-1 transcription in PRDM-16 overexpressing cells. Our data indicate for the first time that TRPV1 activation counters obesity at thermoneutrality permissive for UCP-1 and the enhancement of PRDM-16 is not beneficial in the absence of UCP-1.