Black Globe Research Articles (Page 1)

Livestock-forestry (LF) systems enhance the delivery of ecosystem services and sustainability by providing shade, increasing diversity, and improving carbon sequestration. Despite these benefits, more evidence is needed to establish LF systems as a viable alternative for reducing enteric CH4 emissions and improving thermal comfort in beef cattle production. We aimed to evaluate the impact of the forestry component into a forage-based livestock system on animal performance, thermal comfort, and its consequences on enteric CH4 emissions. The experimental design was a randomized complete block with two systems: livestock (L) and LF, each with four replicates. During both seasons, microclimate variables such as relative humidity, photosynthetically active radiation, black globe temperature, and black globe temperature-humidity index were greater in the L system. Plant-part and chemical compositions did not differ between the systems, except for a 10% greater leaf proportion in LF during the rainy season. During the dry season, the LF system showed a 47% greater total gain per ha and 33% greater stocking rate. There was no system effect on CH4 production (g/day). However, in the dry season, LF presented greater CH4 emissions per area. These results indicate that integrating trees into forage-based livestock systems can improve thermal comfort and animal productivity without increasing individual CH4 emission, enhancing long-term productivity and sustainability.

As urbanization accelerates, the urban heat island effect has significantly impacted the ecological environment and public health.Plant communities, particularly different types of forests, play a crucial role in mitigating the heat island effect through transpiration and shading effects. This study explores the thermal environment regulation characteristics of evergreen forests, deciduous forests, and mixed forests across different seasons, with a particular focus on cooling benefits during the summer. The study also analyzes the influence of vegetation density and sky visibility factors on the thermal environment. The results show that the daytime temperature of evergreen forest (EF1) and mixed forest (MF1) ranged from 36°C to 38°C, whereas the temperature of the lawn (LA) rose to nearly 39°C. At night, the temperature of the lawn dropped sharply to 26°C, exhibiting a large diurnal temperature variation. The black globe temperature (from 14:00 to 16:00) showed smaller fluctuations in the evergreen forest and deciduous forest, with temperatures of 45°C and 47°C, respectively, while the black globe temperature of the lawn and control point reached 52°C and 50°C, respectively, demonstrating more dramatic temperature variations. Physiologically equivalent temperature (PET) values revealed that the lawn (LA) and control point (RP) had PET values of 44°C and 42°C during the day, which fell within the "hot" or "very hot" range, whereas the PET value of the evergreen forest (EF1) remained relatively low, in the "comfortable" range (around 35°C). The study suggests that urban green space design should prioritize the planting of evergreen and mixed forests, optimize canopy density, enhance ecological diversity, and avoid excessive exposure from lawns and open areas. Additionally, integrating techniques such as rooftop greening, vertical greening, and water body design can further improve the thermal comfort of urban green spaces and promote the development of livable green cities.

The Mediterranean area is highly vulnerable to climate change. Silvopastoral practices, such as integrating trees into pastureland or grazing in woodland areas, are potential mitigation strategies to improve microclimate conditions and reduce heat stress risks. We conducted a 2-year on-farm experiment to compare growth performance, measuring average daily gain (ADG), hair cortisol accumulation, and blood glucose concentration in Maremmana breed steers and heifers reared in either a silvopastoral (SP) or pastoral (PA) system during spring and summer. Additionally, we monitored microclimate conditions in both systems via the black globe humidity index (BGHI) as a heat stress proxy for outdoor-reared animals. In both years, the highest ADG values were recorded in spring: 1.49kg/day in PA and 1.25kg/day in SP in 2021 and 1.24kg/day in PA and 1.17kg/day in SP in 2022. During spring, PA-reared animals performed best, likely because of favourable microclimate conditions and abundant pasture, making tree shade unnecessary. Conversely, in summer, as heat stress risk increased-indicated by higher BGHI levels-tree presence in the SP system mitigated heat stress impacts on ADG, resulting in superior SP performance over PA. The hair cortisol levels increased in both groups during the summer, with a significantly greater increase in the PA animals. In 2021, cortisol levels reached 35.04pg/mg in PAs and 26.62pg/mg in SPs. In 2022, cortisol levels rose further to 46.56pg/mg in PAs and 42.94pg/mg in SPs. A decrease of glucose levels in PA group was determined but further research is needed to clarify the effects of heat stress on physiological mechanisms that lead to a change in glucose levels. Effective pasture and system management have been shown to increase productivity, with higher spring stocking rates in open pastures improving animal performance in both years.

In order to compare the surface temperature of body extremities of Tharparkar and Karan Fries cattle under extreme climatic conditions during summer and winter season, the present study was carried out under standard managemental conditions. Environmental parameters, including temperature and humidity, were recorded daily, and Temperature Humidity Index (THI) and Black Globe Humidity Index (BGHI) were calculated to assess the level of thermal comfort on cattle. Thermal imaging (Infradred thermography, IRT) of body extremities (muzzle, nose bridge, ear tip and base, fetlock, and knee) were recorded twice weekly during winter (Dec. 2022–Jan. 2023), spring (Feb.–March 2023), and summer (June–July 2023) season. Skin extremities temperature was highest during summer followed by spring and winter season in both the breeds of cattle. Significant (p

Abstract Better understanding of the physical drivers of sufficiently realistic representation of human heat stress is crucial for improving prediction and enhancing preparedness. Wet‐bulb globe temperature (WBGT) is a standard metric for workplace heat stress; however, its calculation involves complex parameterizations of radiative and convective energy exchange, making it difficult to understand the driving mechanisms behind WBGT changes. To address this issue, we introduce a sensitivity framework to analytically evaluate WBGT's response to meteorological input changes. By examining the form of sensitivity coefficients, we gain insights into the interactive effects of multiple environmental parameters in controlling WBGT. Given constant wind and solar radiation, the natural wet‐bulb and black globe temperatures change at the same rate and direction as the wet‐ and dry‐bulb temperatures, despite considerable differences in their absolute values. The framework, while having state‐dependent sensitivity coefficients, can be linearized, transforming WBGT into a linear combination of temperature, specific humidity, surface pressure, and terms representing wind and solar radiation effects. These explicit and mathematically tractable relations between WBGT and more intuitively understandable variables enable leveraging established theories and methods to understand the driving mechanisms of WBGT changes. We apply the framework to understand the physical drivers of regional WBGT scaling with global warming and extreme WBGT synoptic events. The sensitivity framework also provides a customizable approach to develop locally tuned linear approximations of WBGT, with clear expectations regarding the direction and magnitude of the induced biases. It can also be used to diagnose sources of biases in existing simplified WBGT approximations.

This study aimed to investigate the effect of different shade structures on the physiological and behavioral responses of sows in free-range systems in a tropical climate. Six non-pregnant DanBred sows were studied from November to December 2019 at the University of Brasília, Federal District, Brazil. The sows were distributed in a double 3 × 3 Latin square design in six paddocks, each containing one of the three artificial shade treatments, so that each artificial shade treatment was present in two paddocks. In each evaluated paddock there was a Caryocar Brasiliense, a native tree from Brazilian Cerrado with 6.0m mean height, as well as a mud pool, to allow the sows to perform natural behaviors. Treatments included shade provided by a black net (blocking 80% of radiation), shade provided by a heat-reflective net (blocking 80% of radiation), and both nets combined. Black globe, dry bulb, and wet bulb temperatures, relative humidity, and wind speed were measured at 1min intervals between 8:00 and 16:00h during 18 non-consecutive days. For behavioral observation, an ethogram was developed describing sows' site preferences, body posture and activities of interest. Vaginal and body surface temperatures were measured every 1min and respiratory rate every 20min. Micrometeorological and physiological data were analyzed using SAS software. The means were compared using Tukey's test with a significance level of 5%. Behavioral data were subjected to frequency analysis and chi-square tests at the 5% significance level. Shade treatments affected (p < 0.05) all meteorological, behavioral, and physiological variables. The combined use of heat-reflective and black nets provided the best meteorological results, being more frequently used by sows than tree shade. However, shade type did not physiologically influence internal body temperature, surface temperature, or respiratory rate, demonstrating the importance of behavioral expression for thermoregulation.

The management of thermal environments in animal production facilities presents significant challenges, requiring continuous adjustments to meet animals’ physiological needs. This study evaluated the effects of green roofs on the thermal environment and comfort indices in small-scale poultry house prototypes, comparing facilities with and without green roof installations. The research tested various roof types (ceramic, fiber cement, and metal) combined with emerald grass (Zoysia japonica) green roof systems. Parameters measured included air temperature, relative humidity, internal roof surface temperature, Temperature and Humidity Index (THI), Black Globe Humidity Index (BGHI), Human Comfort Index (HCI), and Thermal Radiation Load (TRL) under both open and closed conditions. Results showed that green roofs reduced indoor air temperature by up to 2.4 °C in open prototypes and 10.6 °C in closed prototypes during peak heat periods. In combinations using green roofs with fiber cement tiles, internal roof surface temperature decreased by 24.0 °C in open prototypes and 27.0 °C in closed configurations. The implementation of green roofs resulted in THI reductions of 2.3 and 8.1 units in open and closed prototypes, respectively, BGHI decreases of 2.8 and 11.3 units, and TRL reductions of 21.0 W/m2 and 74.0 W/m2. HCI measurements confirmed improved thermal comfort conditions with green roof installations in both settings. This study concludes that green roofs effectively enhance the thermal environment by reducing bioclimatic indices during hot periods while maintaining stable conditions during cooler weather, thereby improving overall thermal comfort in animal facilities.

The aim of this research was to create an embedded device based on Internet of Things (IoT) technology that could measure air temperature, humidity, pressure and altitude using a single sensor. Using this data, the device is able to calculate indices such as Black Globe Temperature (BGT), Temperature and Humidity Index (THI) and Temperature, Globe and Humidity Index (TGUI). This equipment is compact, measuring just 6 centimeters, and has Wi-Fi connectivity, which makes it an IoT device. This allows the data to be sent to a web server, where the farmer or any user with access can view the animals' thermal comfort conditions in real time. This visualization can be done conveniently on desktops, notebooks or smartphones, from anywhere in the world. In this way, the IoT equipment helps the producer make decisions, avoiding productivity losses, health problems and guaranteeing product quality by preventing possible thermal stress caused to the animals.

The present study aimed to evaluate the effects of different nutritional plans on meat quails subjected to heat stress. A total of 324 quails male European quails (Coturnix coturnix coturnix) were used, with an average initial weight of 121.48 g ± 3.1 g, distributed in a completely randomized design with nine treatments and six repetitions of six birds each. The diets were evaluated from 22 to 42 days of age, according to the following treatments: T1 - Control diet; T2 - Moderate crude protein (CP) reduction, without amino acid supplementation (AA); T3 - Moderate CP reduction with supplementation of methionine (Met) and cystine (Cys); T4 - Moderate CP reduction with Met, Cys, and lysine (Lys) supplementation; T5 - Moderate CP reduction with Met, Cys, Lys, and threonine (Thr) supplementation; T6 - Severe CP reduction, without AA supplementation; T7 - Severe CP reduction with Met and Cys supplementation; T8 - Severe CP reduction with Met, Cys, and Lys supplementation; T9 - Severe CP reduction with Met, Cys, Lys, and Thr supplementation. The room temperature was maintained at 30°C, with relative humidity at 76.42%, and a black globe humidity index (BGHI) of 82.19. No significant (p > 0.05) effect of protein reduction or amino acid supplementation was observed on live weight, feed intake, carcass weight, yield, breast, legs, heart, and gizzard. However, significant effects were observed on weight gain (p < 0.04), feed conversion (p < 0.05), liver weight (p < 0.001), and liver yield (p < 0.001). In hot environments, crude protein in the diet of meat quails can be reduced from 22 to 17.6%, with adequate methionine supplementation to achieve 0.800% digestible Met + Cys during the growth phase (22-42 days). These nutritional strategies may optimize performance, reduce costs, and provide environmental benefits by decreasing nitrogen excretion. Future research should investigate the interactions between diet, heat stress, and quail performance, focusing on different amino acid combinations and their impacts on bird health and productivity under varied thermal conditions.

The implementation of poultry houses with enhanced control over environmental variables represents a solution to the growing demands for production and animal welfare. This study assessed the internal environment of dark-house poultry houses for broilers on a weekly basis throughout a production cycle. Data were collected over six weeks, from March to April 2016 involving 40,000 Cobb500TM broilers. A Hobo® datalogger continuously monitored the temperature (°C), relative humidity (%), dew point temperature (°C), and black globe temperature (°C) at 15 min intervals. The indices analyzed included the temperature and humidity index (THI), the black globe and humidity index (BGHI), and enthalpy (H). In the first week, both the THI and BGHI indicated favorable conditions for the birds, with the THI ranging from 72.4 to 80 and the BGHI from 77 to 81.6. Between the second and fifth weeks, the THI conditions varied between thermal comfort and discomfort, from 56.6 to 72. In the sixth week, all indices indicated discomfort, reflecting increased metabolism and population density. The dark-house system demonstrated a feed efficiency of 51%, an accumulated mortality rate of 1.97%, and a total production of 99,873 kg of meat. The study highlights the importance of continuously monitoring and adjusting environmental conditions to optimize production and enhance bird welfare.

Abstract Humid heat and associated heat stress have increased in frequency, intensity, and duration across the globe, particularly at lower latitudes. One of the more robust metrics for heat stress impacts on the human body is wet-bulb globe temperature (WBGT), because it incorporates temperature, humidity, wind speed, and solar radiation. WBGT can typically only be measured using nonstandard instrumentation (e.g., black globe thermometers). However, estimation formulas have been developed to calculate WBGT using standard surface meteorological variables. This study evaluates several WBGT estimation formulas for the southeastern United States using North Carolina Environment and Climate Observing Network (ECONet) and U.S. Military measurement campaign data as verification. The estimation algorithm with the smallest mean absolute error was subsequently chosen to evaluate summer WBGT trends and extremes at 39 ASOS stations with long continuous (1950–2023) data records. Trend results showed that summer WBGT has increased throughout much of the southeastern United States, with larger increases at night than during the day. Although there were some surprisingly large WBGT trends at higher elevation locations far from coastlines, the greatest increases were predominantly located in the Florida Peninsula and Louisiana. Increases in the intensity and frequency of extreme (90th percentile) WBGTs were particularly stark in large coastal urban centers (e.g., New Orleans, Tampa, and Miami). Some locations like New Orleans and Tampa have experienced more than two additional extreme heat stress days and nights per decade since 1950, with an exponential escalation in the number of extreme summer nights during the most recent decade. Significance Statement Humid heat and associated heat stress pose threats to health in the moist subtropical climate of the southeastern United States. Wet-bulb globe temperature (WBGT) is a robust metric for heat stress but must be estimated using complex algorithms. We first evaluated the accuracy of three WBGT algorithms in the southeastern United States, using measured verification data. Subsequently, we used the most accurate algorithm to investigate WBGT trends and extremes since 1950 in 39 cities. Results showed that summer heat stress has increased throughout the region, especially at night. Increases in the intensity and frequency of extreme heat stress were most prevalent at urban coastal locations in Florida and Louisiana, emphasizing the impacts of increased urbanization and evaporation on heat stress.

Abstract Extreme heat such as that seen in the United States and Europe in summer 2022 can have significant impacts on human health and infrastructure. The Occupational Safety and Health Administration (OSHA) and the U.S. Army use wet-bulb globe temperature (WBGT) to quantify the impact of heat on workers and inform decisions on workload. WBGT is a weighted average of air temperature, natural wet-bulb temperature, and black globe temperature. A local hourly, daily, and monthly WBGT climatology will allow those planning outdoor work to minimize the likelihood of heat-related disruptions. In this study, WBGT is calculated from the ERA5 reanalysis and is validated by the Oklahoma Mesonet and found to be adequate. Two common methods of calculating WBGT from meteorological observations are compared. The Liljegren method has a larger diurnal cycle than the Dimiceli method, with a peak WBGT about 1°F higher. The high- and extreme-risk categories in the southern U.S. Great Plains (USGP) have increased from 5 days per year to 15 days from 1960 to 2020. Additionally, the largest increases in WBGT are occurring during DJF, potentially lengthening the warm season in the future. Heat wave definitions based on maximum, minimum, and mean WBGT are used to calculate heat wave characteristics and trends with the largest number of heat waves occurring in the southern USGP. Further, the number of heat waves is generally increasing across the domain. This study shows that heat wave days based on minimum WBGT have increased significantly which could have important impacts on human heat stress recovery.

Assessing the winter indoor environment with different comfort metrics in self-built houses of hot-humid areas: Does undercooling matter for the elderly?

ABSTRACT Objectives Agricultural workers are at risk of heat-related illness, which is preventable. Few field studies have compared farmworker-relevant heat exposure in different conditions. We examined heat exposure over time in different potential shade and work locations to inform future occupational heat prevention approaches. Methods We assessed heat exposure in Eastern Washington State (WA) cherry and grape fields in August 2022. QUESTemp° monitors recorded Wet Bulb Globe Temperature (WBGT) and Black Globe Temperature (BGT) every 10 min from approximately 07:00–14:00 for three days in the center of crop rows (mid-row), under portable shade structures (shade), and in open field (open) locations. Linear mixed effects regression (LMER) models compared WBGT and BGT among field locations. Hourly time-weighted average WBGT and comparisons with occupational exposure limits (OELs) were computed for different hypothetical work-rest cycles during the hottest sampling hours, assuming different worker effort levels, rest locations (mid-row versus shade), and acclimatization statuses. Results Across all crops and locations during the study period, the mean/SD air temperature was 31°C (88°F)/3.9°C (6.9°F), with a maximum temperature of 39°C (102°F) and a mean/SD relative humidity of 30%/9.6%. LMER models suggested no significant difference in mid-row versus open WBGT but significantly lower WBGT in shade versus open locations for both cherries (main effect −5.14: 95% confidence interval [CI] −6.97,−3.32) and grapes (−6.20: 95%CI −7.73,−4.67), though this difference diminished over the course of the day. BGT was significantly higher in the mid-row than the shade (cherries main effect 14.33: 95%CI 9.52,19.13 and grapes 17.10: 95%CI 13.44,20.75). During the hottest sampling hour, the exceedances of OELs were reduced with assumptions of increased shaded break lengths, reduced effort level, and acclimatization. Conclusions Shade canopies, but not the crops studied, provided significant reductions in heat exposure. We observed increased protection from heat assuming longer shaded breaks and reduced effort levels. Results highlight the need for additional field research on the effectiveness, feasibility, and acceptability of different shade types and work-rest cycles to guide employer optimization of best practices for worker protections, including acclimatization before high heat, sufficient shaded rest time, reduced effort levels as the day warms, and avoiding work in peak heat.

Simple SummaryThe objective of this study was to evaluate the thermal comfort of Nelore cattle (Bos indicus) managed in silvopastoral and traditional systems associated with rumination behavior in a humid tropical environment in the Eastern Amazon, Brazil. The thermoregulatory responses of 20 uncastrated male Nelore cattle in silvopastoral and traditional systems from June to July 2023 were evaluated. Physiological variables were measured, including respiratory rate (RR), rectal temperature (RT) and body surface temperature (BST). The RR was higher in the traditional system and RT showed significant variations over the collection periods. The black globe temperature and humidity index (BGHI) indicated mild to moderate stress. The silvopastoral system showed advantages in RR, RT and in rumination behavior. The results suggest that air temperature (AT) significantly influenced RR and thermal comfort in both systems, and that the SP system offers more thermal comfort advantages compared to the TS system.The objective of this study was to evaluate the thermal comfort of Nelore cattle (Bos indicus) managed in silvopastoral and traditional systems associated with rumination behavior in a humid tropical environment in the Eastern Amazon, Brazil. The study was carried out on a rural property in Mojuí dos Campos, Pará, Brazil, during the transition period of the year, from June to July 2023. Over these two months, six consecutive data collection days were held. We selected 20 clinically healthy non-castrated male Nelore cattle, aged between 18 and 20 months, with an average weight of 250 kg and body condition score of 3.5 (1–5). These animals were randomly divided into two groups: traditional system (TS) and silvopastoral system (SS). The physiological variables evaluated included RR, RT and BST. The variables were analyzed using the linear mixed model. For agrometeorological variables, higher values were observed between 10:00 a.m. (33 °C) and 6:00 p.m. (30 °C), with the highest temperature observed at 4:00 p.m. (40 °C). The RR showed interactions (p = 0.0214) between systems and times; in general, higher RR were obtained in the Traditional. The animals’ RT showed no significant difference (p < 0.05) between the production systems, but there was a statistically significant difference in relation to the time of collection (p < 0.0001). In the BGHI, it was possible to observe that there was mild stress in the period from 22:00 at night to 6:00 in the morning and moderate stress in the period of greatest increase in temperature, from 10:00 in the morning to 18:00 at night. BST showed no statistical difference between the regions studied or between the SP (35.6 °C) and TS (36.25 °C) systems. RT in the TS showed a positive correlation with AT (r = 0.31507; p = 0.0477). RT in the SP showed a positive correlation with THI (r = 35583; p = 0.0242). On the other hand, RT in the SP (r = 0.42873; p = 0.0058) and ST (r = 0.51015; p = 0.0008) showed a positive correlation with BGHI. RR in the TS showed a positive correlation with BGHI (r = 0.44908; p = 0.0037). The greatest amounts of rumination were carried out by animals in the SP system, generally ruminating lying down (p < 0.05). With regard to rumination behavior in the morning and afternoon, there were higher numbers of WS and LD in the TS (p > 0.05). Most of the time, the cattle were LD during the morning and afternoon shifts, and at night and dawn they were WS in the TS. Therefore, the SP offers more thermal comfort advantages compared to the TS system.

Our aim was to develop and validate separate whole body sweat rate prediction equations for moderate to high-intensity outdoor cycling and running, using simple measured or estimated activity and environmental inputs. Across two collection sites in Australia, 182 outdoor running trials and 158 outdoor cycling trials were completed at a wet-bulb globe temperature ranging from ∼15°C to ∼29°C, with ∼60-min whole body sweat rates measured in each trial. Data were randomly separated into model development (running: 120; cycling: 100 trials) and validation groups (running: 62; cycling: 58 trials), enabling proprietary prediction models to be developed and then validated. Running and cycling models were also developed and tested when locally measured environmental conditions were substituted with participants' subjective ratings for black globe temperature, wind speed, and humidity. The mean absolute error for predicted sweating rate was 0.03 and 0.02 L·h-1 for running and cycling models, respectively. The 95% confidence intervals for running (+0.44 and -0.38 L·h-1) and cycling (+0.45 and -0.42 L·h-1) were within acceptable limits for an equivalent change in total body mass over 3 h of ±2%. The individual variance in observed sweating described by the predictive models was 77% and 60% for running and cycling, respectively. Substituting measured environmental variables with subjective assessments of climatic characteristics reduced the variation in observed sweating described by the running model by up to ∼25%, but only by ∼2% for the cycling model. These prediction models are publicly accessible (https://sweatratecalculator.com) and can guide individualized hydration management in advance of outdoor running and cycling.NEW & NOTEWORTHY We report the development and validation of new proprietary whole body sweat rate prediction models for outdoor running and outdoor cycling using simple activity and environmental inputs. Separate sweat rate models were also developed and tested for situations where all four environmental parameters are not available, and some must be subsequently estimated by the user via a simple rating scale. All models are freely accessible through an online calculator: https://sweatratecalculator.com. These models, via the online calculator, will enable individualized hydration management for training or recreational cycling or running in an outdoor environment.

Little has been studied about microclimate and the thermal comfort during the implementation of silvopastoral systems. This study aimed to evaluate the microclimate and thermal comfort during the implementation of High Biodiversity Silvopastoral System with Nuclei (SPSnu). Three treatments were investigated, SPSnu with 5 and 10% of the pasture area with nuclei, (SPSnu5 and SPSnu10, respectively), and treeless pasture (TLP). Each treatment was subdivided into 4 areas: within the nuclei, around the nuclei, around the nuclei with shade and internuclei. The analyzed variables were soil surface temperature, air temperature, wind speed, relative humidity, black globe temperature and the Heat Load Index (HLI) at 20 and 120cm height. We hypothesized that the wind speed reduction associated with insufficient shade projection typical of the first years of SPSs may interfere in microclimate and thermal comfort during the hot seasons. SPSnu5 and SPSnu10 had a reduction in wind speed of 51.58% and 68.47% respectively when compared to TLP at 20cm. Soil surface temperature and air temperature at 120cm were higher for SPSnu than TLP. The same effect was observed for the HLI. At 20cm, HLI indicated better thermal comfort in TLP than in the SPSnu treatments. The lack of shade projection from young nuclei in conjunction with the decrease of wind speed between the nuclei caused a higher air temperature and HLI in the SPSnu treatments, we called this conditions, windbreak countereffect. Farmers must knowledge this effect when implementing SPSs, and when necessary, mitigate with the proper management decisions.

Quantifying the impact of thermal stress on milk yields is essential to effectively manage present and future risks in dairy systems. Despite the existence of numerous heat indices designed to communicate stress thresholds, little information is available regarding the accuracy of different indices in estimating milk yield losses from both cold and heat stress at large spatio-temporal scales. To address this gap, we comparatively analyzed the performance of existing thermal indices in capturing US milk yield response to both cold and heat stress at the national scale. We selected four commonly used thermal indices: the Temperature and Humidity Index (THI), Black Globe Humidity Index (BGHI), Adjusted Temperature and Humidity Index (THIadj), and Comprehensive Climate Index (CCI). Using a statistical panel regression model with observational and reanalysis weather data from 1981-2020, we systematically compared the patterns of yield sensitivities and statistical performance of the four indices. We found that the US state-level milk yield variability was better explained by the THIadj and CCI, which combine the effects of temperature, humidity, wind, and solar radiation. Our analysis also reveals a continuous and nonlinear responses of milk yields to a range of cold to heat stress across all four indices. This implies that solely relying on fixed thresholds of these indices to model milk yield changes may be insufficient to capture cumulative thermal stress. Cold extremes reduced milk yields comparably to those impacted by heat extremes on the national scale. Additionally, we found large spatial variability in milk yield sensitivities, implying further limitations to the use of fixed thresholds across locations. Moreover, we found decreased yield sensitivity to thermal stress in the most recent two decades, suggesting adaptive changes in management to reduce weather-related risks.

Mammals in arid zones have to trade off thermal stress, predation pressure, and time spent foraging in a complex thermal landscape. We quantified the relationship between the environmental heat load and activity of a mammal community in the hot, arid Kalahari Desert. We deployed miniature black globe thermometers within the existing Snapshot Safari camera trap grid on Tswalu Kalahari Reserve, South Africa. Using the camera traps to record species' activity throughout the 24-h cycle, we quantified changes in the activity patterns of mammal species in relation to heat loads in their local environment. We compared the heat load during which species were active between two sites with differing predator guilds, one where lion (Panthera leo) biomass dominated the carnivore guild and the other where lions were absent. In the presence of lion, prey species were generally active under significantly higher heat loads, especially during the hot and dry spring. We suggest that increased foraging under high heat loads highlights the need to meet nutritional requirements while avoiding nocturnal activity when predatory pressures are high. Such a trade-off may become increasingly costly under the hotter and drier conditions predicted to become more prevalent as a result of climate change within the arid and semi-arid regions of southern Africa.

Climate change imposes detrimental heat stress, which disrupts the thermo-regulatory balance of cattle and buffaloes. Quantifying heat stress through bioclimatic indices is a vital step for identifying suitable mitigation/adaptation strategies. So, the trend of different comfort indices for cattle was computed (2000-2019) and used for estimating milk production as these indices provide a holistic view of the bovine’s thermoneutral status. The trend analysis of seasonal comfort index (CI) through box plot analysis indicated that Black Globe Humidity Index (BGHI) had shifted from ‘Low Impact’ to ‘High Impact’, Temperature Humidity Index (THI) had shifted from ‘Normal’ to ‘Danger’ and Comprehensive Climate Index (CCI) had shifted from ‘No stress’ to ‘Mild stress’ from winter to summer season indicating the impact of heat stress during the latter period. The milk production in April had a significant correlation with BGHI, Heat Load Index (HLI), Respiration Rate (RR), THI, CCI, and Equivalent Temperature Index (ETI). Milk production in May and June had a significant relationship with ETI and THI. Lactation-wise milk production analysis indicated that sixth lactation is related to ETI and HLI. Fourth and second lactation had a significant relation with all indices estimated and the first stage of lactation with BGHI, ETI, and RR. The CI with the highest correlation coefficients were used to develop a regression model for a respective month and lactation stage.