Heat Stress Thresholds Research Articles

Evaluating Heat Stress Effects on Growth in Tunisian Local Kids: Enhancing Breeding Strategies for Arid Environments.

This study evaluates the impact of thermal load on the weights of Tunisian local kids using 24 models with cubic and quadratic Legendre polynomials, based on daily temperatures (Tmin, Tmax, and Tavg) on the day of weight recording and averaged over 7, 14, and 21 days before weighing. The deviance information criterion (DIC) consistently shows that cubic polynomial models offer a better fit than quadratic models, highlighting their superior accuracy in studying the effects of thermal load on kid weights. The models with the best fit utilized average or maximum temperatures over 14 or 21 days. The patterns of response were similar across the temperature variables and periods, showing a stable weight response at lower temperatures (thermoneutral region) followed by a decline as the temperatures increased. The weight loss was -125 g/°C beyond the moderate heat stress threshold (Tavg21 = 17.7 °C) and -450 g/°C beyond the severe heat stress threshold (Tavg21 = 25.3 °C) for Tavg21. The heat stress thresholds for moderate heat stress (HS1) were 8.6 °C for Tmin14, 27.4 °C for Tmax14, and 18.6 °C for Tavg14; moreover, for acute heat stress (HS2), they were 17.2 °C for Tmin14, 32.4 °C for Tmax14, and 25.5 °C for Tavg14. High variability in individual responses was observed, with differences in the slope of response ranging from 2.0 kg/°C for moderate heat stress to around 3.0 kg/°C for severe heat stress for Tavg. The correlations between the weights under different temperatures were low, indicating that rankings based on weight could change with varying heat conditions. The animals with larger weight levels generally demonstrated better heat tolerance, and those with good heat tolerance under moderate conditions were also likely to have good tolerance under severe conditions.

Modelling heat stress effects on milk production traits in Tunisian Holsteins using a random regression approach.

This study investigated the impact of temperature and humidity on milk production traits in Tunisian dairy cows, analysing population-level trends and individual cow responses using various modelling techniques and heat stress (HS) indices. Two distinct datasets were used for this purpose: the first included 551,139; 331,654 and 302,396 test-day records for milk, fat and protein yields, respectively. The second supplemented the production information with daily average (THIavg) and maximum (THImax) temperature-humidity index (THI) data. Three main parts of analyses were conducted simultaneously: classical least squares, identification of HS thresholds and associated production losses and assessment of individual cow responses using random regression models (RRM) fitting various continuous functions that include/exclude individual effects. The best model, determined by goodness-of-fit measurements, was a cubic polynomial function that accounted for individual variation and THIavg as a heat load measure. HS thresholds were established at THIavg/THImax of 70/74 for milk yield, 50/55 for fat percentage, 59/66 for protein percentage, 54/63 for fat yield and 56/66 for protein yield. According to the fitted polynomial models, daily milk production traits showed a curvilinear decline with accelerated loss rates beyond the established thermal thresholds. However, for all models and thermal indices, maximum daily production losses remained below 164 g/day, 4.4 g/day and 6.1 g/day for milk, fat and protein yields, respectively. Despite these losses, the relatively high thermal thresholds and lower associated production losses suggest that Tunisian dairy cows can tolerate high heat loads. Moreover, observed variations in response patterns indicate potential for selecting heat-tolerant individuals within this population.

Examining the impact of dry climates temperature on citrus fruit internal ripening

High temperatures alter the ripening process of citrus fruit, affecting quality, flavor, harvest time and marketing period. For example, citrus fruits ripen faster and are sweeter in tropical hot-humid climates than in Mediterranean warm-dry climates due to higher sugar accumulation and organic acid catabolism. Considering that: 1) over 60 % of the world's citrus exports come from countries with warm Mediterranean climates, and 2) the Mediterranean region is warming 20 % faster than the global average, the citrus industry will face significant challenges in the coming years. The range of high temperatures and the timing at which they determine sugar and acid content in dry climates have not been studied under field conditions. Therefore, a study was undertaken over 6 years to determine the relationship between high temperature and citrus ripening in two dry macroclimates, hot (Arid, in Morocco) and warm (Mediterranean, in Spain), and 5 microclimates of the Mediterranean region.Heat stress in these dry climates correlates with changes in fruit quality (lower juice and sugar content, and higher organic acids), depending on the maximum temperature threshold and the time of onset and duration of heat. In the arid climate, the heat stress threshold was found to be a significant number of days above 35 °C. This was particularly important at the beginning of summer (July in the northern hemisphere). However, in the current Mediterranean climate of Spain, the percentage of summer days above 35 °C is still low indicating that other microclimatic conditions are involved in determining fruit quality. In particular, an increase in the number of days with temperatures between 27 °C and 33 °C in late summer and early autumn was found to correlate with reduced citric acid concentration. Microclimate did not determine sucrose, fructose, and glucose concentrations.

Estimation of the threshold for heat stress and genetic features for milk yield in Mehsana buffaloes in India

Heat stress is one of the primary environmental factors that harm both the productivity and health of buffaloes. The current study was conducted to estimate the threshold of temperature humidity index (THI)1 and genetic features for milk yield of first-lactation Mehsana buffaloes using an univariate repeatability test-day model. The data included 130,475 first lactation test-day milk yield (FLTDMY) records of 13,887 Mehsana buffaloes and the daily temperature and humidity. The statistical model included herd test day as fixed effects, days-in-milk (DIM) classes, age of the animal, as well as random factors such as the additive genetic effect (AGE) of animal in general conditions (intercept), AGE of the buffaloes subjected to heat stress (slope), permanent environmental effect of animal in general conditions (intercept), permanent environmental effect of animal under heat stress conditions (slope) and random residual effect. It was expected that the general effects and the heat-tolerance effects would be correlated, represented by the present investigation's repeatability models. The variance components of FLTDMY in the present study were computed using the REML method. The threshold for THI was 78. At the THI below the threshold, the heritability estimated for the FLTDMY trait was 0.29, and the additive genetic variance (AGV) for heat stress conditions was 0. At THI of 83, AGV for heat stress conditions was highest for FLTDMY. The genetic correlation of general AGE to heat-tolerant AGE was −0.40. The results indicated that a consistent selection for milk production, avoiding the thermal tolerance, may diminish the thermal tolerance capacity of Mehsana buffaloes.

Genetic parameters for novel climatic resilience indicators derived from automatically-recorded vaginal temperature in lactating sows under heat stress conditions

BackgroundLongitudinal records of automatically-recorded vaginal temperature (TV) could be a key source of data for deriving novel indicators of climatic resilience (CR) for breeding more resilient pigs, especially during lactation when sows are at an increased risk of suffering from heat stress (HS). Therefore, we derived 15 CR indicators based on the variability in TV in lactating sows and estimated their genetic parameters. We also investigated their genetic relationship with sows’ key reproductive traits.ResultsThe heritability estimates of the CR traits ranged from 0.000 ± 0.000 for slope for decreased rate of TV (SlopeDe) to 0.291 ± 0.047 for sum of TV values below the HS threshold (HSUB). Moderate to high genetic correlations (from 0.508 ± 0.056 to 0.998 ± 0.137) and Spearman rank correlations (from 0.431 to 1.000) between genomic estimated breeding values (GEBV) were observed for five CR indicators, i.e. HS duration (HSD), the normalized median multiplied by normalized variance (Nor_medvar), the highest TV value of each measurement day for each individual (MaxTv), and the sum of the TV values above (HSUA) and below (HSUB) the HS threshold. These five CR indicators were lowly to moderately genetically correlated with shoulder skin surface temperature (from 0.139 ± 0.008 to 0.478 ± 0.048) and respiration rate (from 0.079 ± 0.011 to 0.502 ± 0.098). The genetic correlations between these five selected CR indicators and sow reproductive performance traits ranged from − 0.733 to − 0.175 for total number of piglets born alive, from − 0.733 to − 0.175 for total number of piglets born, and from − 0.434 to − 0.169 for number of pigs weaned. The individuals with the highest GEBV (most climate-sensitive) had higher mean skin surface temperature, respiration rate (RR), panting score (PS), and hair density, but had lower mean body condition scores compared to those with the lowest GEBV (most climate-resilient).ConclusionsMost of the CR indicators evaluated are heritable with substantial additive genetic variance. Five of them, i.e. HSD, MaxTv, HSUA, HSUB, and Nor_medvar share similar underlying genetic mechanisms. In addition, individuals with higher CR indicators are more likely to exhibit better HS-related physiological responses, higher body condition scores, and improved reproductive performance under hot conditions. These findings highlight the potential benefits of genetically selecting more heat-tolerant individuals based on CR indicators.

Spatial Distribution and Trends of Heat Stress in Vietnam

This study investigated the spatial distribution and trend of heat stress in Vietnam using data from 68 meteorological stations between 1979 and 2018. Daily maximum wet-bulb temperature (TWmax), an indicator of heat stress, was computed based on the daily maximum air temperature (Tx) and relative humidity at 13:00 LST (RH13). The results indicate a strong positive correlation (>0.72) between daily TWmax and Tx and a weak relationship between daily TWmax and RH13. Tx and TWmax generally increased across most stations over the study period, while RH13 displayed both negative and positive trends. The heat stress thresholds for each station are defined using the 95th percentile values of TWmax during the baseline period 1979-1998. We found that most parts of Vietnam experienced an increase in heat stress days, with the interquartile range across all stations spanning from 0.8 to 4.2 days per decade. Among seasons, summer contributed the most (typically 52-80%) to the annual number of heat stress days in most sub-regions, except for the Central Highlands and the South, where spring contributed the most (44% and 41%, respectively). Overall, this study provides useful benchmark values for future research on heat stress in Vietnam.

307 Hothog: a Smartphone Application to Support Environmental Management Decisions for Non-Pregnant and Gestating Sows

Abstract Several management practices and technologies have been developed to mitigate thermal stress in swine. However, recommended temperature thresholds for implementing thermal stress mitigation are variable and may not accurately reflect the thermal requirements of non-pregnant and gestating sows with modern genetics. Therefore, a tool to support environmental management decisions for non-pregnant and gestating sows was created. The decision support tool is based on several published works by our group that characterized responses of non-pregnant, mid-gestation, and late-gestation sows across a wide temperature range. Cool, comfortable, and warm ranges were identified based upon behavioral thermal preferendum, and physiological responses were used to determine mild, moderate, and severe heat stress thresholds. The inflection points of respiration rate and body temperature as a function of dry bulb temperature were used to establish heat stress thresholds by gestation stage. Non-pregnant, mid-gestation, and late-gestation sow mild heat stress thresholds differed (P < 0.05) and occurred at 25.5, 25.1, and 24.0 °C, respectively. Body temperature inflection points indicative of moderate heat stress differed by gestation stage (P < 0.05) and occurred at 28.1, 27.8, and 25.5 °C, respectively. Severe heat stress inflection points were lower (P < 0.05) for late-gestation sows (30.8 °C) but were similar for non-pregnant and mid-gestation sows (32.9 °C). Dewpoint influenced heat stress response for mid- and late-gestation sows (P < 0.05) but did not have an effect on non-pregnant sows (P > 0.05). Heat stress threshold data were integrated with behavioral thermal preferendum data. For non-pregnant and mid-gestation sows, similar (P > 0.05) cool (< 13.2°C) and comfortable (13.2 to 16.4°C) temperature ranges were observed. However, late-gestation sows had lower (P < 0.05) cool (< 12.6°C) and comfortable (12.6 to 15.6°C) temperature ranges relative to non-pregnant and mid-gestation sows. The dry bulb temperature (TDB) that non-pregnant, mid-gestation, and late-gestation sows found to be warm was estimated as TDB preference range < TDB < mild heat stress. The decision support tool was integrated into a smartphone application called HotHog. This smartphone application provides hourly and daily predictions of thermal comfort and stress in non-pregnant, mid-gestation, and late-gestation sows. Users can set geographical locations, either manually or by current location, for thermal index predictions. Additionally, hourly and daily precipitation, and temperature predictions are displayed for the selected location. Management observations and mitigation options, as well as expected physiological and behavioral changes, are provided for each thermal index category to help users identify stressed pigs and assist with management decisions. HotHog will support swine producers in making more informed decisions related to in-barn environmental management to reduce the negative effects of thermal stress on sows and their gestating offspring. Furthermore, the tool may be helpful for teaching thermal management to livestock technicians and students.

Outdoor thermal perception and heatwave adaptation effects in summer – A case study of a humid subtropical city in China

Heatwaves occur more frequently during the summer owing to global warming, which causes excessive heat stress and thermal discomfort. Heat stress increases overheating risk and impacts people's health and outdoor activities. Assessing outdoor thermal risk and clarifying human thermal responses under outdoor high-temperature conditions are of particular importance. However, the effect of thermal adaptation on people's thermal perception during heatwave conditions requires exploration. This paper aims to provide a comprehensive analysis of human outdoor thermal perception under non-heatwave and heatwave conditions to obtain adaptation-based outdoor thermal benchmarks to estimate the threshold for thermal discomfort and heat stress. Longitudinal and cross-sectional questionnaire surveys are carried out during the summer in public squares in Chongqing. The results showed that thermal perceptions undergo a dynamic change process in summer, which is closely related to an individual's past thermal experience. In comparison with thermal benchmarks under non-heatwave conditions, the neutral, comfortable, and 80% acceptable range of UTCI under heatwave conditions shifted to a higher temperature. For the heatwave period, the neutral UTCI range was from 21.5 °C to 27.9 °C. The modified UTCI ranges for heat stress classifications were obtained, including the 80% acceptable temperature range from 21.4 °C to 30.1 °C. The contributions of this study are in the method of determining outdoor thermal benchmarks in heatwave conditions and clarifying local people's thermal demands. These findings can provide more refined guidance for heat stress assessment and enrich the possibilities for urban design and urban resilience responses to heatwave conditions.

Genomic-enhanced breeding values for heat stress tolerance in Girolando cattle in Brazil

Heat stress is a major challenge for dairy herds and can lead to significant production reduction, mainly in tropical climate. Differences in decreased milk production in animals is associated with genetic variation. The overall goal was to investigate the effect of heat stress in milk yield of Girolando cattle in tropical climate and to identify the most appropriate statistical approach for evaluation and selection for heat tolerance in different breed compositions of Girolando. Therefore, to quantify heat stress effects on milk yield loss in Girolando cattle, random regression models were applied on test-day milk yield records (TDMY) and weather data. In addition, different statistical models were evaluated for estimating variance components and predicting breeding values for heat stress (HS). The data comprised 648,072 TDMY of 69,431 first-lactation Girolando cows of different breed compositions, and 21,147 genotyped animals, with daily temperature and humidity measurements from weather stations closest to the tested herds, between 2000 and 2020. We used daily mean values of temperature-humidity index (THI) for the day of test and the 3 previous days as the measure of HS. Heat stress thresholds estimated for the different breed compositions of Girolando in this study were THI 80 for 1/4H, 1/2H and 5/8H; THI 78 for 3/4H animals and THI 77 for 7/8H animals. Average milk production can decrease by up to 34% due to heat stress. Estimated average heritability for TDMY regressed to the THI was 0.21, while the heritability estimated for TDMY regressed to the DIM was 0.29. A correlation of 0.55 was observed between the GEBVs of HS tolerance and GEBV milk yield. The parameters estimated in this study indicate that genomic selection for heat tolerance in dairy cattle is a step towards ensuring valuable tropical production efficiency and improving animal welfare in the face of predicted increases in heat stress events and increase tropical production efficiency.

Temperature amplification and marine heatwave alteration in shallow coastal bays

Shallow coastal ecosystems are threatened by marine heatwaves, but few long-term records exist to quantify these heatwaves. Here, 40-year records of measured water temperature were constructed for a site in a system of shallow bays with documented heatwave impacts and a nearby ocean site; available gridded sea-surface temperature datasets in the region were also examined. Water temperatures at both sites increased significantly though bay temperatures were consistently 3-4°C hotter in summer and colder in winter and were more variable overall, differences not captured in high-resolution gridded sea-surface temperature datasets. There was considerable overlap in heatwave events at the coastal bay and ocean sites. Annual heatwave exposure was similar and significantly increased at both sites while annual heatwave intensity was significantly higher at the bay site owing to the high variance of the daily temperature anomaly there. Event frequency at both sites increased at a rate of about 1 event/decade. Future simulations indicate all heatwave metrics increase, as do days above 28°C, a heat stress threshold for seagrass. Ocean temperatures on the U.S. mid-Atlantic margin have rarely exceeded this threshold, while summer bay temperatures commonly do, allowing ocean exchange with coastal bays to provide thermal relief to bay ecosystems. This will have changed by 2100, creating a thermal environment that threatens seagrass communities in these systems. Documenting such change requires development of long-term water temperature records in more shallow coastal systems.

Spatial Distribution and Trends of Heat Stress in Vietnam

This study investigates the spatial distribution and trend of heat stress in Vietnam using data from 68 meteorological stations across the country’s seven climatic sub-regions between 1979 and 2018. Daily maximum wet-bulb temperature (TWmax), an indicator of heat stress, was computed based on the daily maximum air temperature (Tx) and relative humidity at 13:00 LST (RH13). Results indicate a strong positive correlation (>0.97) between daily TWmax and Tx and a weaker relationship between daily TWmax and RH13. Tx and TWmax experienced a general increasing trend across most stations over the study period, while RH13 displayed both negative and positive trends. Vietnam’s heat stress thresholds were found to be higher than those in many other parts of the world due to the country’s location and its temperature-humidity conditions. The study identifies most parts of Vietnam have experienced an increase in heat stress days, typically ranging from 5 to 12 days per decade. Among the four seasons, summer contributed the most (50-80%) to the annual number of heat stress days in most sub-regions, except for the Central Highlands and the South where spring had the highest contribution (65-80%). Overall, this study provides useful benchmark values for future research on heat stress in Vietnam.

Estimating stocking weights for Atlantic salmon to grow to market size at novel aquaculture sites with extreme temperatures

Land-based hatcheries are now capable of growing large Atlantic salmon (Salmo salar) post-smolts (approximately 150 – 1000 g), which means that marine net-pens can be stocked with substantially larger fish compared to traditional stocking sizes (< 150 g). This stocking strategy typically aims to reduce the time required for fish to grow to market size in the marine environment and limit risks (e.g., exposure to pathogens and diseases, opportunities for escapes). This study investigates another potential application of this strategy: the use of novel sites in areas previously considered unsuitable for aquaculture due to seasonally cold temperatures. The thermal-unit growth coefficient (TGC) model was applied to estimate the stocking weight needed to reach a harvest size of 5.5 kg, based on observed degree days for three sites. High resolution, depth-partitioned temperature time series from coastal locations in Atlantic Canada were used to represent a short, medium, and long growing season, as constrained by seasonal temperature extremes. Growing days for model inputs were defined as temperatures > 4 °C and trending up for stocking, < 18 °C to account for heat stress, and > -0.7 °C to avoid superchill conditions. Different TGC values were applied to simulate remedial, average, and elite growth performance. There was a range of model stocking weight estimates for each site (1.5 – 2.5 kg, 0.94 – 2.8 kg, and < 0.1 – 0.52 kg, for the short, medium, and long season sites, respectively). Results were sensitive to the number of degree days, heat stress threshold, and TGC value. At the two sites where season length was constrained by superchill, fish with a stocking weight of approximately 1.5 kg could grow to market size in shallow water depths (< 15 m), assuming elite growth performance. This investigation suggests that with appropriate growth performance assumptions and high-resolution temperature data, large post-smolt stocking strategies could enable the use of novel sites in coastal areas previously considered unsuitable for aquaculture.

Auxin‐dependent regulation of cell division rates governs root thermomorphogenesis

Roots are highly plastic organs enabling plants to adapt to a changing below‐ground environment. In addition to abiotic factors like nutrients or mechanical resistance, plant roots also respond to temperature variation. Below the heat stress threshold, Arabidopsis thaliana seedlings react to elevated temperature by promoting primary root growth, possibly to reach deeper soil regions with potentially better water saturation. While above‐ground thermomorphogenesis is enabled by thermo‐sensitive cell elongation, it was unknown how temperature modulates root growth. We here show that roots are able to sense and respond to elevated temperature independently of shoot‐derived signals. This response is mediated by a yet unknown root thermosensor that employs auxin as a messenger to relay temperature signals to the cell cycle. Growth promotion is achieved primarily by increasing cell division rates in the root apical meristem, depending on de novo local auxin biosynthesis and temperature‐sensitive organization of the polar auxin transport system. Hence, the primary cellular target of elevated ambient temperature differs fundamentally between root and shoot tissues, while the messenger auxin remains the same.

Evaluating phenotypes associated with heat tolerance and identifying moderate and severe heat stress thresholds in lactating sows housed in mechanically or naturally ventilated barns during the summer under commercial conditions.

An accurate understanding of heat stress (HS) temperatures and phenotypes that indicate HS tolerance is necessary to improve swine HS resilience. Therefore, the study objectives were 1) to identify phenotypes indicative of HS tolerance, and 2) to determine moderate and severe HS threshold temperatures in lactating sows. Multiparous (4.10 ± 1.48) lactating sows and their litters (11.10 ± 2.33 piglets/litter) were housed in naturally ventilated (n = 1,015) or mechanically ventilated (n = 630) barns at a commercial sow farm in Maple Hill, NC USA between June 9 and July 24, 2021. In-barn dry bulb temperatures (TDB) and relative humidity were continuously recorded for naturally ventilated (26.38 ± 1.21°C and 83.38 ± 5.40%, respectively) and mechanically ventilated (26.91 ± 1.80°C and 77.13 ± 7.06%, respectively) barns using data recorders. Sows were phenotyped between lactation d 11.28 ± 3.08 and 14.25 ± 3.26. Thermoregulatory measures were obtained daily at 0800, 1200, 1600, and 2000h and included respiration rate, and ear, shoulder, rump, and tail skin temperatures. Vaginal temperatures (TV) were recorded in 10min intervals using data recorders. Anatomical characteristics were recorded, including ear area and length, visual and caliper-assessed body condition scores, and a visually assessed and subjective hair density score. Data were analyzed using PROC MIXED to evaluate the temporal pattern of thermoregulatory responses, phenotype correlations were based on mixed model analyses, and moderate and severe HS inflection points were established by fitting TV as the dependent variable in a cubic function against TDB. Statistical analyses were conducted separately for sows housed in mechanically or naturally ventilated barns because the sow groups were not housed in each facility type simultaneously. The temporal pattern of thermoregulatory responses was similar for naturally and mechanically ventilated barns and several thermoregulatory and anatomical measures were significantly correlated with one another (P < 0.05), including all anatomical measures as well as skin temperatures, respiration rates, and TV. For sows housed in naturally and mechanically ventilated facilities, moderate HS threshold TDB were 27.36 and 26.69°C, respectively, and severe HS threshold TDB were 29.45 and 30.60°C, respectively. In summary, this study provides new information on the variability of HS tolerance phenotypes and environmental conditions that constitute HS in commercially housed lactating sows.

Methods for detecting heat stress in hutch-housed dairy calves in a continental climate

Dairy calves exposed to solar radiation, elevated ambient temperature, and humidity are at risk of impaired welfare and productivity. Initial detection of thermal discomfort requires determination of optimal heat stress indicators and thresholds. Such values have recently been established in calves in chronic, subtropical, and acute continental environments but not in continuous, temperate conditions. Herein, the objectives were to determine associations between animal-based and environmental heat stress indicators and establish environmental breakpoints for hutch-raised dairy calves during a continental summer. From June to August, dairy calves (n = 63; 14 to 42 d of age) were individually hutch-housed and managed according to the dairy standard operating procedures in Arlington, Wisconsin. Calf respiration rates (RR), rectal temperatures (RT), shaved or unshaved skin temperatures (ST), and hutch internal and external air speed were measured thrice weekly at 0700 and 1400 h after a 15 min hutch restriction. Environmental indices including dry bulb temperature (Tdb), black globe temperature, and relative humidity were measured every 15 min, averaged hourly, and used to calculate temperature-humidity index (THI) using 8 different equations (THI1-8). Correlation and linear regression models were used to determine relationships within and between animal-based and environmental indicators. Environmental breakpoints were established using segmented regression models to estimate THI and Tdb thresholds for abrupt changes in animal responses. There were strong, positive correlations between animal-based indicators and Tdb or THI1-8, with the strongest association observed between unshaved ST and Tdb (r = 0.80). The linear regression of animal-based indicators with the best fit included Tdb or Tdb plus relative humidity and air speed. The threshold at which RR and RT began to rise was at a THI of 69 for both or at a Tdb of 21.0 or 21.5°C, respectively. No threshold was established for ST. Together, these outcomes indicate that Tdb is an appropriate measurement to detect thermal discomfort for calves in a temperate summer climate and individual hutch housing. Monitoring of calves is warranted before ambient temperature reaches 21.0°C, corresponding to RR of 40 breaths per minute and RT of 38.5°C, to promote calf comfort and reduce the risk of hyperthermia-related welfare and productivity consequences.

A behavior and physiology-based decision support tool to predict thermal comfort and stress in non-pregnant, mid-gestation, and late-gestation sows.

Although thermal indices have been proposed for swine, none to our knowledge differentiate by reproductive stage or predict thermal comfort using behavioral and physiological data. The study objective was to develop a behavior and physiology-based decision support tool to predict thermal comfort and stress in multiparous (3.28 ± 0.81) non-pregnant (n = 11), mid-gestation (n = 13), and late-gestation (n = 12) sows. Regression analyses were performed using PROC MIXED in SAS 9.4 to determine the optimal environmental indicator [dry bulb temperature (TDB) and dew point] of heat stress (HS) in non-pregnant, mid-gestation, and late-gestation sows with respiration rate (RR) and body temperature (TB) successively used as the dependent variable in a cubic function. A linear relationship was observed for skin temperature (TS) indicating that TDB rather than the sow HS response impacted TS and so TS was excluded from further analyses. Reproductive stage was significant for all analyses (P < 0.05). Heat stress thresholds for each reproductive stage were calculated using the inflections points of RR for mild HS and TB for moderate and severe HS. Mild HS inflection points differed for non-pregnant, mid-gestation, and late gestation sows and occurred at 25.5, 25.1, and 24.0°C, respectively. Moderate HS inflection points differed for non-pregnant, mid-gestation, and late gestation sows and occurred at 28.1, 27.8, and 25.5°C, respectively. Severe HS inflection points were similar for non-pregnant and mid-gestation sows (32.9°C) but differed for late-gestation sows (30.8°C). These data were integrated with previously collected behavioral thermal preference data to estimate the TDB that non-pregnant, mid-gestation, and late-gestation sows found to be cool (TDB < TDB preference range), comfortable (TDB = TDB preference range), and warm (TDB preference range < TDB < mild HS). The results of thisstudy provide valuable information about thermal comfort and thermal stress thresholds in sows at three reproductive stages. The development of a behavior and physiology-based decision support tool to predict thermal comfort and stress in non-pregnant, mid-gestation, and late-gestation sows is expected to provide swine producers with a more accurate means of managing sow environments.

400 Improving Heat Stress Resilience to Reduce the Negative Effects of pre- and Postnatal Heat Stress in Swine

Abstract Heat stress will become a more substantial issue for swine production as global temperatures continue to rise. Efforts have been made to mitigate the negative impacts of heat stress through advances in genetic selection, nutrition, precision technology, and management practices. However, heat stress is still a limiting factor to swine production that must be addressed. A key aspect to mitigating heat stress-related production losses in swine may be developing better management approaches and genetic selection techniques to improve heat stress resilience. This is especially true for heat stress sensitive populations such as gestating and lactating sows. Gestating and lactating sows are considered heat stress sensitive due to greater metabolic heat production resulting from fetal growth and milk production, respectively. Additionally, swine offspring are adversely affected by in utero heat stress, which imprints long-term negative phenotypes that reduce health and productivity regardless of environmental conditions. To address these concerns, swine producers have implemented a variety of cooling and management strategies to mitigate heat stress. However, the recommended or perceived heat stress temperature thresholds for implementation may not accurately reflect the thermal requirements of modern swine with current genetics or at variable gestation stages leading to ineffective use. As such, a re-evaluation of heat stress thresholds for modern swine is warranted. Additionally, genetic selection for productivity traits (e.g., litter sizes and lean growth) has increased metabolic heat production resulting in increased heat stress sensitivity. Therefore, the ability to perform large-scale measures of and implement heat stress tolerance traits within breeding populations may be advantageous for producers to improve heat stress resilience within their herds. Taken together, as heat stress becomes a greater issue for the swine industry, it will become increasingly important to develop sustainable approaches that improve swine heat stress resilience while maintaining or improving producer profitability.

Cooling temperature humidity index-days as a heat load indicator for milk production traits

Well-defined and accurate climatic indicators are important for evaluating heat stress in dairy cattle. This is imperative for sound management decisions for mitigating production losses. The most popular indicator for heat stress is the temperature humidity index (THI). Other heat stress indicators have been developed but remain largely unexploited. There is, therefore, possibly room to improve the THI and explore new indicators suitable for predicting production losses due to heat stress in dairy cattle. In this study, we apply the degree-day concept to develop temperature humidity index-day (THI-day). We defined the cooling THI-day as the hourly cumulative THI units above the heat stress threshold for milk production traits over the entire day. We then modeled reaction norms for cooling THI-day to analyze the effect of cumulative heat load expressed by THI-day on milk production traits. Milk performance records were from 16,216,145 monthly test-day records for the Fleckvieh breed for the period 2010 to 2019 in southern Bavaria, Germany. Individual cow records were averaged by herd and test-day resulting in 797,455 herd test-day records from 9,726 herds. Weather data for the same period were provided by the German Meteorological Service. Results indicated that cooling THI-day provided significant (p &amp;lt; 0.001) additional information to the conventional THI models. We found out that reaction norm models of average herd milk yield that do not account for the cumulative heat load tend to underestimate the effects of heat stress on milk production traits. Reaction norms modeled with cooling THI-day were more plausible for milk production traits that have a defined heat stress threshold including milk yield, protein yield, and milk urea.

Heat stress in a temperate climate leads to adapted sensor-based behavioral patterns of dairy cows

Most research on heat stress has focused on (sub)tropical climates. The effects of higher ambient temperatures on the daily behavior of dairy cows in a maritime and temperate climate are less studied. With this retrospective observational study, we address that gap by associating the daily time budgets of dairy cows in the Netherlands with daily temperature and temperature-humidity index (THI) variables. During a period of 4 years, cows on 8 commercial dairy farms in the Netherlands were equipped with neck and leg sensors to collect data from 4,345 cow lactations regarding their daily time budget. The time spent eating, ruminating, lying, standing, and walking was recorded. Individual cow data were divided into 3 data sets: (1) lactating cows from 5 farms with a conventional milking system (CMS) and pasture access, (2) lactating cows from 3 farms with an automatic milking system (AMS) without pasture access, and (3) dry cows from all 8 farms. Hourly environment temperature and relative humidity data from the nearest weather station of the Dutch National Weather Service was used for THI calculation for each farm. Based on heat stress thresholds from previous studies, daily mean temperatures were grouped into 7 categories: 0 = (<0°C), 1 = (0-12°C, reference category), 2 = (12-16°C), 3 = (16-20°C), 4 = (20-24°C), 5 = (24-28°C), and 6 = (≥28°C). Temperature-humidity index values were grouped as follows: 0 = (THI <30), 1 = (THI 30-56, reference category), 2 = (THI 56-60), 3 = (THI 60-64), 4 = (THI 64-68), 5 = (THI 68-72) and 6 = (THI ≥72). To associate daily mean temperature and THI with sensor-based behavioral parameters of dry cows and of lactating cows from AMS and CMS farms, we used generalized linear mixed models. In addition, associations between sensor data and other climate variables, such as daily maximum and minimum temperature, and THI were analyzed. On the warmest days, eating time decreased in the CMS group by 92 min/d, in the AMS group by 87 min/d, and in the dry group by 75 min/d compared with the reference category. Lying time decreased in the CMS group by 36 min/d, in the AMS group by 56 min/d, and in the dry group by 33 min/d. Adaptation to daily temperature and THI was already noticeable from a mean temperature of 12°C or a mean THI of 56 or above, when dairy cows started spending less time lying and eating and spent more time standing. Further, rumination time decreased, although only in dry cows and cows on AMS farms. With higher values for daily mean THI and temperature, walking time decreased as well. These patterns were very similar for temperature and THI variables. These results show that dairy cows in temperate climates begin to adapt their behavior at a relatively low mean environmental temperature or THI. In the temperate maritime climate of the Netherlands, our results indicate that daily mean temperature suffices to study the effects of behavioral adaptation to heat stress in dairy cows.

Epigenetic effects of climate on dairy parameters of Prim’Holstein breed in west coast Algeria

This research aimed to evaluate the effect of the epigenetic climatic factor of heat stress expressed by the THI on some parameters of milk production of Prim'Holsteins cows kept in the climate of the Algerian West coast. The THI was used as an indicator of the heat stress threshold. A sample of 75 lactating cows was divided into three groups according to THI level. The cows of group 1, with severe stress (THI&gt;78), those of group 2, with light stress (THI 72-78), and those of group 3 in thermal comfort (THI&lt;72). The daily milk production (DMY), the Physico-chemical quality (TB, TP, and EST), and the hygienic quality (total flora FMAT) of raw milk showed a decrease with the increase of the THI threshold. A significant effect (p&lt;0.05) of heat stress is recorded on the Physico-chemical and microbiological parameters of milk. The FMAT count values of raw milk samples were highest for groups 1 and 2, while a low bacterial load was recorded for group 3 (THI&lt;72). Heat stress had a negative impact on the performance of Prim'Holsteins cows. These preliminary results show the severity of the negative impact of heat stress in the littoral region on the production and the physicochemical and hygienic quality of milk and will serve as a useful guide for farmers to adopt actions to mitigate the impact within the barns for the sustainability of livestock.