Direct Effects Of Heat Stress Research Articles

The Impact of Climatic Conditions on Oil Content and Quality, in Sunflower

Sunflower (Helianthus annuus L.) crop is grown worldwide, under a range of agro-environments. This crop is primarily grown for its edible oil but also for its achenes (confectionery types), both commonly used in human food. With ongoing climate change, sunflower, as a spring crop, could be more exposed to the direct effect of heat stress and to different drought scenarios, resulting in severe yield losses, oil content decrease and alteration of fatty acids composition. The oil concentration in sunflower (whether linoleic or oleic varieties) is valued above the contribution of genotype, of environment but also of the crop management. In our study, with different sunflower hybrids, experimented in different conditions of the environment, we obtained results on oil content and fatty acids composition. The oil content in kernels is influenced by climate. This depends by air temperature in period of anthesis or during grain filing, also by rainfall. The unsaturated fatty acids of sunflower oil are much more affected by genotype and environment than the saturated ones. Cooler regions offer a more favorable climate for the oil and linoleic acid synthesis. There is an indirect relationship for oleic and linoleic content, in sunflower oil.

Heat stress impacts the multi-domain ruminal microbiota and some of the functional features independent of its effect on feed intake in lactating dairy cows

BackgroundHeat stress (HS) affects the ruminal microbiota and decreases the lactation performance of dairy cows. Because HS decreases feed intake, the results of previous studies were confounded by the effect of HS on feed intake. This study examined the direct effect of HS on the ruminal microbiota using lactating Holstein cows that were pair-fed and housed in environmental chambers in a 2 × 2 crossover design. The cows were pair-fed the same amount of identical total mixed ration to eliminate the effect of feed or feed intake. The composition and structure of the microbiota of prokaryotes, fungi, and protozoa were analyzed using metataxonomics and compared between two thermal conditions: pair-fed thermoneutrality (PFTN, thermal humidity index: 65.5) and HS (87.2 for daytime and 81.8 for nighttime).ResultsThe HS conditions altered the structure of the prokaryotic microbiota and the protozoal microbiota, but not the fungal microbiota. Heat stress significantly increased the relative abundance of Bacteroidetes (primarily Gram-negative bacteria) while decreasing that of Firmicutes (primarily Gram-positive bacteria) and the Firmicutes-to-Bacteroidetes ratio. Some genera were exclusively found in the heat-stressed cows and thermal control cows. Some co-occurrence and mutual exclusion between some genera were also found exclusively for each thermal condition. Heat stress did not significantly affect the overall functional features predicted using the 16S rRNA gene sequences and ITS1 sequences, but some enzyme-coding genes altered their relative abundance in response to HS.ConclusionsOverall, HS affected the prokaryotes, fungi, and protozoa of the ruminal microbiota in lactating Holstein cows to a different extent, but the effect on the structure of ruminal microbiota and functional profiles was limited when not confounded by the effect on feed intake. However, some genera and co-occurrence were exclusively found in the rumen of heat-stressed cows. These effects should be attributed to the direct effect of heat stress on the host metabolism, physiology, and behavior. Some of the “heat-stress resistant” microbes may be useful as potential probiotics for cows under heat stress.

Direct heat stress-induced effects on rumen fermentation characteristics and nutrients degradability in sheep pair-fed alfalfa hay

Aim of the study: To investigate the direct effect of heat stress on rumen fermentation characteristics and nutrients degradability of pair-fed rams to subsequently eliminate the confounding effects of dissimilar feed intake induced by heat stress exposure.Area of study: Saudi Arabia.Material and methods: Five rumen-cannulated desert rams (45 ± 1.63 kg body weight; 2–3 years of age) were placed individually in controlled climatic-chambers to be exposed to two successive periods. The 1st period was a control thermoneutral period (TN; 23.64 ± 0.14 °C; extended for 21 days) followed by a 2nd period of heat stress (HS; 44.26 ± 1.70 °C, for another 21 days). Each period was consisted of a temperature acclimation phase (7 days) and a data collection phase (14 days). Alfalfa hay was offered twice daily during both periods in a pair-fed manner (800 g DM per head and day).Main results: Exposing pair-fed desert rams to elevated ambient temperature had (p<0.05) elevated their respiration rate and skin temperature, without noticeable (p>0.05) changes in their rectal temperature. Most of the rumen fermentation characteristics and nutrients degradability were not affected by HS (p>0.05). However, exposure to HS increased (p<0.05) pre-feeding rumen total volatile fatty acids concentrations, pre-feeding molar proportion of acetate, and post-feeding rumen osmolality.Research highlights: HS had no direct effect on post-feeding rumen fermentation characteristics and nutrients degradability in desert sheep. This implies that strategic approaches to mitigate the adverse effects of HS have to be directed towards promoting feed intake and nutrients utilization under such conditions.

Effect of heat stress and feeding management on growth performance and physiological responses of finishing pigs.

This study aimed to determine whether pig responses to heat stress (HS) were directly due to heat exposure (regardless of feeding level and pattern) or were indirectly due to the reduction of feed intake (FI) and to determine if increasing feeding frequency (splitting heat increments) can improve pig response to HS. A total of 48 pigs (66.1 ± 1.7 kg) were allocated to four groups in three replicates. After 7 d in thermoneutral (TN) conditions (22 °C; period 1 [P1; day -7 to -1]), pigs were placed in either TN or HS (32 °C) conditions for 20 d (period 2 [P2; day 0 to 19]). The diet was provided either ad libitum (AL; 2 distributions/d) or pair-fed (PF8; 8 distributions/d) using HS-AL pigs as the reference group. Thus, the four experimental groups were TN-AL, HS-AL, TN-PF8, and HS-PF8. The daily ration of PF8 pigs was distributed at every 90-min intervals from 0900 to 1930 hours. Data were analyzed using the PROC MIXED procedure with replicate (n = 3), experimental group (n = 4), and their interactions as fixed effects, and the REPEATED statement was used for repeated measures data. Pigs had a similar average daily feed intake (ADFI) during P1 (P > 0.05). In P2, HS-AL and PF8 pigs had lower ADFI (-19%), average daily gain (-25%), and final body weight (-6.1 kg) than TN-AL pigs (P < 0.01). TN-AL pigs had thicker backfat than TN-PF8 pigs (P < 0.05), while the HS pigs had intermediate results. HS pigs had a higher perirenal fat percentage based on the contrast analysis between PF8 pigs (P < 0.05). Thermoregulatory responses of pigs increased with HS exposure but did not differ between HS or between TN groups (P > 0.05). For TN pigs, variation in muscle temperature (Tmuscle) depended on feeding and physical activity, while for HS pigs, Tmuscle gradually increased throughout the day. The Tmuscle of PF8 pigs increased with each additional meal but plateaued earlier for HS-PF8 than TN-PF8 pigs; an increase in Tmuscle per meal was also lower in HS-PF8 than TN-PF8 (P < 0.05). Exposure to HS decreased plasma T3 and T4 (P < 0.05) and increased plasma creatinine (P < 0.05). Between the PF8 groups, HS pigs also had a transient increase in plasma insulin on day 8 (P < 0.05). The effect of HS on FI decreased the growth rate of pigs but there are heat-induced effects, such as altered physiological responses, which might explain the direct HS effects seen in other literature especially in terms of increased adiposity. The increased feed provision frequency in the present study did not improve the HS response of pigs.

High temperature suppressed SSC self-renewal through S phase cell cycle arrest but not apoptosis

BackgroundHigh temperature has a very adverse effect on mammalian spermatogenesis and eventually leads to sub- or infertility through either apoptosis or DNA damage. However, the direct effects of heat stress on the development of spermatogonial stem cells (SSCs) are still unknown because SSCs are rare in the testes.MethodsIn the present study, we first used in vitro-cultured SSCs to study the effect of heat shock treatment on SSC development. Then, we used RNA-Seq analysis to identify new genes or signalling pathways implicated in the heat stress response.ResultsWe found that 45 min of 43 °C heat shock treatment significantly inhibited the proliferation of SSCs 2 h after treatment but did not lead to apoptosis. In total, 17,822 genes were identified by RNA-Seq after SSC heat shock treatment. Among these genes, we found that 200 of them had significantly changed expression, with 173 upregulated and 27 downregulated genes. The number of differentially expressed genes in environmental information processing pathways was 37, which was the largest number. We screened the candidate JAK-STAT signalling pathway on the basis of inhibition of cell cycle progression and found that the JAK-STAT pathway was inhibited after heat shock treatment. The flow cytometry results further confirmed that heat stress caused S phase cycle arrest of SSCs.ConclusionOur results showed that heat shock treatment at 43 °C for 45 min significantly inhibited SSC self-renewal through S phase cell cycle arrest but not apoptosis.

Season of conception is associated with future survival, fertility, and milk yield of Holstein cows.

Environmental influences during different stages of pregnancy can induce lifelong changes in the structure, physiology, and metabolism of the offspring. Our hypothesis was that season of conception (when the offspring was conceived), associated with heat stress conditions at conception and during the initial stages of embryonic development, affects the lifetime performance and survival of the female offspring after birth. The objective was to analyze the association between month of conception and subsequent survival, fertility, and milk yield in cows maintained on dairy farms in Florida, where the climate during the summer is hot and humid but winters are mild. Initial data consisted of 667,104 Dairy Herd Improvement lactation records from cows calving between 2000 and 2012 in 152 herds. Dates of conception were estimated as birth date minus 280 d. The magnitude of heat stress in each herd was quantified by comparing milk yield during summer and winter. Wood's lactation curves were fitted to adjust milk yields for effects of days in milk, and residuals were obtained for each calendar month. A sine function was fitted on the 12 residuals per farm. The difference between the highest and lowest points on the sine function was termed the seasonality index, a measure of the direct effect of heat stress on milk production. Herds were categorized in 3 levels of seasonality [low (seasonality index values less than the 25th percentile value; <2.84), medium (values within the interquartile range), and high (values greater than the 75th percentile value; >5.22)]. Cows were grouped by their month of conception: summer (July-September) and winter (December-February), and comparisons were performed by parity using logistic regression, ANOVA, and survival analysis. Two models were developed. Model A included the complete population of cows (n = 337,529 lactation records) conceived in winter or summer. Model B included cows (n = 228,257 lactation records) that had parent-average genetic information available to be able to correct for farmer's use of lower genetic merit of sires in summer. Other variables included in the models were month and year of calving, age at first calving, and herd. Models were run per parity group (1, 2, and ≥3). In both models, age at first calving was lower for cows conceived during winter versus summer. The odds (95% confidence interval) of survival to a second calving for cows conceived in winter were 1.21 and 1.15 times the odds of survival for cows conceived in summer for models A and B, respectively. Numbers of days from calving to first breeding and from calving to conception were consistently smaller for winter versus summer months of conception across all parity categories. Milk yields (305 d and by 70 d in milk) were greater for cows conceived in winter versus summer. In conclusion, cows that were conceived in the winter had better subsequent survival and performance than cows that were conceived in the summer. There is evidence that season of conception may have lifelong consequences for the offspring.

The effects of heat stress on protein metabolism in lactating Holstein cows

Heat stress (HS) decreases milk protein synthesis beyond what would be expected based on the concomitant reduction in feed intake. The aim of the present study was to evaluate the direct effects of HS on milk protein production. Four multiparous, lactating Holstein cows (101 ± 10 d in milk, 574 ± 36 kg of body weight, 38 ± 2 kg of milk/d) were individually housed in environmental chambers and randomly allocated to 1 of 2 groups in a crossover design. The study was divided into 2 periods with 2 identical experimental phases (control phase and trial phase) within each period. During phase 1 or control phase (9 d), all cows were housed in thermal neutral conditions (TN; 20°C, 55% humidity) and fed ad libitum. During phase 2 or treatment phase (9 d), group 1 was exposed to cyclical HS conditions (32 to 36°C, 40% humidity) and fed ad libitum, whereas group 2 remained in TN conditions but was pair-fed (PFTN) to their HS counterparts to eliminate the confounding effects of dissimilar feed intake. After a 30-d washout period in TN conditions, the study was repeated (period 2), inverting the environmental treatments of the groups relative to period 1: group 2 was exposed to HS and group 1 to PFTN conditions. Compared with PFTN conditions, HS decreased milk yield (17.0%), milk protein (4.1%), milk protein yield (19%), 4% fat-corrected milk (23%), and fat yield (19%). Apparent digestibility of dry matter, organic matter, neutral detergent fiber, acid detergent fiber, crude protein, and ether extract was increased (11.1-42.9%) in HS cows, as well as rumen liquor ammonia (before feeding 33.2%; after feeding 29.5%) and volatile fatty acid concentration (45.3%) before feeding. In addition, ruminal pH was reduced (9.5 and 6% before and after feeding, respectively) during HS. Heat stress decreased plasma free amino acids (AA; 17.1%) and tended to increase and increased blood, urine, and milk urea nitrogen (17.2, 243, and 24.5%, respectively). Further, HS cows had reduced plasma glucose (8%) and nonesterified fatty acid (39.8%) concentrations compared with PFTN controls. These data suggest that HS increases systemic AA utilization (e.g., decreased plasma AA and increased nitrogen excretion), a scenario that limits the AA supply to the mammary gland for milk protein synthesis. Furthermore, the increase in AA requirements during HS might represent the increased need for gluconeogenic precursors, as HS is thought to prioritize glucose utilization as a fuel at the expense of nonesterified fatty acids.

Sunflower crop and climate change: vulnerability, adaptation, and mitigation potential from case-studies in Europe

Climate change is characterized by higher temperatures, elevated atmospheric CO2 concentrations, extreme climatic hazards, and less water available for agriculture. Sunflower, a spring-sown crop often cultivated in southern and eastern regions of Europe, could be more vulnerable to the direct effect of heat stress at anthesis and drought during its growing cycle, both factors resulting in severe yield loss, oil content decrease, and fatty acid alterations. Adaptations through breeding (earliness, stress tolerance), crop management (planting dates), and shifting of growing areas could be developed, assessed and combined to partly cope with these negative impacts. New cultivation opportunities could be expected in northern parts of Europe where sunflower is not grown presently and where it could usefully contribute to diversify cereal-based cropping systems. In addition, sunflower crop could participate to the mitigation solution as a low greenhouse gas emitter compared to cereals and oilseed rape. Sunflower crop models should be revised to account for these emerging environmental factors in order to reduce the uncertainties in yield and oil predictions. The future of sunflower in Europe is probably related to its potential adaptation to climate change but also to its competitiveness and attractiveness for food and energy.

Effect of heat stress on age at first calving of Japanese Black cows in Okinawa.

Calving records from birth certificates of cows were analyzed to investigate the effect of heat stress on age at first calving (AFC) of Japanese Black cows. The data set covered 20 years (1990-2009) of calving records. Total number of records was 9279. Daily weather information from weather stations in the vicinity of the farms was used. Temperature-humidity index (THI) fitted to a linear model covered 30 days pre-insemination to 61 days post-insemination. Statistical analysis was conducted with procedures of SAS/STAT. Preliminary analysis showed that THI of the lowest temperature and humidity was most conducive to AFC. Covariance analysis, including main effect of sire, farm and year of insemination and covariates of THI on days showed that regression coefficients of THI on day -7, day -2 and day +31 were statistically significant. The estimated piecewise regression line showed different responses of AFC to THI on days: roof-shasped downward trend on day -7, hockey-stick shaped upward trend on day -2 and day +31. The difference among the estimated regression lines may be caused by direct and indirect factors on reproduction: indirect effect of reduced feed intake, failure of conception at previous insemination, direct effect of heat stress on oocyte and embryo development.

Activation of ubiquitin‐proteasome system components in heat‐stressed pig skeletal muscle

Hyperthermia causes metabolic changes and leads to lower lean tissue accretion and increased adipose tissue deposition in animals. The direct effect of heat stress on muscle breakdown has been reported in poultry, rabbits and lactating cows. Muscle breakdown occurs by activating the ubiquitin‐proteasome system and the autophagy‐lysosome pathways. To study the mechanism by which heat stress induces muscle breakdown, the ubiquitin‐protease system in the pig skeletal muscle was examined. Pigs (35 ± 0.8 kg) were assigned to one of three treatments: thermal neutral fed ad libitum (TN, 21°C, n=8), heat stress fed ad libitum (HS, 35°C, n=8), or thermal neutral, pair‐fed to HS intake (PF, n=8) for 7 days. Longissimus dorsi muscle was biopsied on day 3 and 7 relative to start of treatments for real‐time PCR and immunoblotting assays. Heat stress increased activating transcription factor‐4 (ATF4), a stress‐response transcription factor, mRNA abundance by more than 1.5 fold regardless of days (P &lt; 0.05). Heat stress increased growth arrest and DNA damage‐inducible 45a (Gadd45a) mRNA abundance by about 1.5 fold compared with PF muscle (P &lt; 0.05). Similarly, the protein abundance of skeletal muscle Gadd45a was elevated in HS pigs by 50% as well as in PF pigs compared with TN pigs (P &lt; 0.05). The phosphorylation of GSK3 β was similar between groups on day 3 and not different in HS versus PF and TN muscle. However, PF pigs had significantly higher phosphorylated GSK3β compared with TN pigs (P &lt; 0.05). HS pigs exhibited intermediate atrogin‐1 mRNA abundance, which was not different from either TN or PF pigs. However, HS pigs had a significantly higher muscle ring finger‐1 (MuRF1) mRNA abundance (approximately 2 fold) compared with PF pigs (P &lt; 0.05). In conclusion, heat stress activated components of muscle breakdown by inducing AFT4, which increased Gadd45a expression, and subsequent apparent activation of the ubiquitin‐protease system.Support or Funding InformationResults described herein were supported by Agriculture and Food Research Initiative Competitive Grant nos. 2011‐6700330007 and 2014‐67015‐21627 from the USDA National Institute of Food and Agriculture.

Effects of heat stress on metabolism, digestibility, and rumen epithelial characteristics in growing Holstein calves.

To distinguish between the direct effects of heat stress (HS) and reduced DMI on metabolic and physiological variables, morphometry, and gene expression of transporters involving in ruminal VFA absorption, 16 Holstein bull calves (178.1 ± 7.55 kg of BW) were used in a randomized complete design using 2 experimental periods. In period 1 (P1), all animals were housed in thermoneutral (TN) conditions (20.7 ± 3.0°C and a temperature-humidity index [THI] of 65.2 ± 3.1) and fed ad libitum for 8 d. In period 2 (P2; 9 d), half of the calves ( = 8) were subjected to HS condition (29.9 to 41.0°C and a THI ≥ 85 for 8 h/d) and the other half ( = 8) were maintained in TN conditions but were pair fed (pair-fed thermoneutral [PFTN]) to the HS calves. Heat stress decreased DMI (20%; < 0.01) and, by design, PFTN calves had similar reduced intakes. During P1, ADG was similar between groups (1.7 kg/d), but ADG was reduced similarly for both groups (0.14 kg/d) during P2 ( < 0.01). Compared with P1, HS calves had decreased plasma glucose levels (12.5%; < 0.01) in P2. Basal insulin levels increased in P2 for HS calves (71%; < 0.03), but there was no difference between periods for PFTN calves. Circulating NEFA concentrations did not differ between periods in the HS calves, but PFTN animals had increased basal NEFA levels (100%; < 0.01). Compared with P1, HS calves had increased blood urea nitrogen concentration in P2 ( < 0.01) but blood urea nitrogen did not differ between periods in the PFTN calves. Heat stress had no measurable effect on nutrient digestibility. Rumen papillae height increased (51%; < 0.04) in HS calves whereas papillae top width decreased (40%; < 0.03), but there was no difference between treatments for other morphometric parameters. Gene expression of VFA transporters in rumen epithelium was not affected by thermal treatments. These results confirmed that short-term HS in the current study had no effect on diet digestibility, rumen morphology, or VFA transporters genes. Therefore, HS-induced decrease in DMI is in large part responsible for gross changes in BW in growing calves (albeit tissue composition of growth is not unknown).

The impact of in utero heat stress and nutrient restriction on progeny body composition

We recently demonstrated that in utero heat stress (IUHS) alters future tissue accretion in pigs, but whether this is a conserved response among species, is due to the direct effects of heat stress (HS) or mediated by reduced maternal feed intake (FI) is not clear. Study objectives were to compare the quantity and rate of tissue accretion in rats exposed to differing in utero thermal environments while eliminating the confounding effect of dissimilar maternal FI. On d3 of gestation, pregnant Sprague–Dawley rats (189.0±5.9g BW) were exposed to thermoneutral (TN; 22.2±0.1°C; n=8), or HS conditions (cyclical 30 to 34°C; n=8) until d18 of gestation. A third group was pair-fed to HS dams in TN conditions (PFTN; 22.2±0.1°C; n=8) from d4 to d19 of gestation. HS increased dam rectal temperature (p=0.01; 1.3°C) compared to TN and PFTN mothers, and reduced FI (p=0.01; 33%) compared to TN ad libitum fed controls. Although litter size was similar (p=0.97; 10.9 pups/litter), pup birth weight was reduced (p=0.03; 15.4%) in HS compared to PFTN and TN dams. Two male pups per dam [n=8 in utero TN (IUTN); n=8 IUHS; n=8 in utero PFTN (IUPFTN)] were selected from four dams per treatment based on similar gestation length, and body composition was determined using dual-energy x-ray absorptiometry (DXA) on d26, d46, and d66 of postnatal life. Whole-body fat content increased (p=0.01; 11.2%), and whole-body lean tissue decreased (p=0.01; 2.6%) in IUPFTN versus IUTN and IUHS offspring. Whole-body composition was similar between IUHS and IUTN offspring. Epididymal fat pad weight increased (p=0.03; 21.6%) in IUPFTN versus IUHS offspring. In summary and in contrast to pigs, IUHS did not impact rodent body composition during this stage of growth; however, IUPFTN altered the future hierarchy of tissue accretion.

Short communication: Hepatic progesterone-metabolizing enzymes cytochrome P450 2C and 3A in lactating cows during thermoneutral and heat stress conditions

Two experiments were performed to determine the effects of heat stress (HS) and insulin on hepatic mRNA abundance of enzymes responsible for metabolizing progesterone [cytochrome P450 2C and 3A (CYP2C and CYP3A)]. To distinguish the direct effects of HS from decreased dry matter intake, cohorts were pair fed (PF) in thermoneutral conditions to match the intake of the HS cows during both experiments. In the first experiment, multiparous late-lactation Holstein cows (n=12, 305±33 d in milk) housed in climate-controlled chambers were subjected to 2 experimental periods: (1) thermoneutral (TN) conditions (18°C, 20% humidity) with ad libitum intake (TN and well fed) for 9 d; and (2) either HS conditions (cyclical temperature 31–40°C, 20% humidity) fed for ad libitum intake (n=6), or TN conditions and PF to match the HS animal (n=6) for 9 d. To evaluate hepatic gene expression during experiment 1, biopsies were obtained at the end of each period. In the second experiment, multiparous mid-lactation Holstein cows (n=12, 136±8 DIM) were housed and fed in conditions similar to those described for the first experiment. Liver biopsies were obtained immediately before and after an insulin tolerance test administered on d 6 of each period. No effects of exogenous insulin were observed on any of the tested variables, nor were there interactions between environment (TN/HS or well fed/PF) and insulin administration. Heat stress decreased hepatic CYP2C expression during both experiments. The relative abundance of CYP3A was not affected by environmental conditions in the late-lactation cows (first experiment), but was reduced by HS in the mid-lactation cows (second experiment). Interestingly, during experiment 2, hepatic CYP3A expression also decreased during PF. These results suggest that HS reduces the capacity of the liver to metabolize progesterone through distinct effects on CYP2C and CYP3A, and that the effects appear to vary based upon stage of lactation. Ultimately, HS may affect reproductive outcomes by reducing the abundance of the enzymes responsible for the breakdown of progesterone. This reduction could serve as a beneficial adaptation for rescuing early embryos or may be detrimental, as it affects feedback mechanisms necessary for proper cyclicity.

Effects of heat stress on carbohydrate and lipid metabolism in growing pigs.

Heat stress (HS) jeopardizes human and animal health and reduces animal agriculture productivity; however, its pathophysiology is not well understood. Study objectives were to evaluate the direct effects of HS on carbohydrate and lipid metabolism. Female pigs (57 ± 5 kg body weight) were subjected to two experimental periods. During period 1, all pigs remained in thermoneutral conditions (TN; 20°C) and were ad libitum fed. During period 2, pigs were exposed to: (1) constant HS conditions (32°C) and fed ad libitum (n = 7), or (2) TN conditions and pair-fed (PFTN; n = 10) to minimize the confounding effects of dissimilar feed intake. All pigs received an intravenous glucose tolerance test (GTT) and an epinephrine challenge (EC) in period 1, and during the early and late phases of period 2. After 8 days of environmental exposure, all pigs were killed and tissue samples were collected. Despite a similar reduction in feed intake (39%), HS pigs tended to have decreased circulating nonesterified fatty acids (NEFA; 20%) and a blunted NEFA response (71%) to the EC compared to PFTN pigs. During early exposure, HS increased basal circulating C-peptide (55%) and decreased the insulinogenic index (45%) in response to the GTT. Heat-stressed pigs had a reduced T3 to T4 ratio (56%) and hepatic 5′-deiodinase activity (58%). After 8 days, HS decreased or tended to decrease the expression of genes involved in oxidative phosphorylation in liver and skeletal muscle, and ATGL in adipose tissue. In summary, HS markedly alters both lipid and carbohydrate metabolism independently of nutrient intake.

The global effect of heat on gene expression in cultured bovine mammary epithelial cells.

Heat stress (HS) in hot climates is a major cause that strongly negatively affects milk yield in dairy cattle, leading to immeasurable economic loss. The heat stress response of bovine mammary epithelial cells (BMECs) is one component of the acute systemic response to HS. Gene networks of BMECs respond to environmental heat loads with both intra- and extracellular signals that coordinate cellular and whole-animal metabolism. Our experimental objective was to characterize the direct effects of heat stress on the cultured bovine mammary epithelial cells by microarray analyses. The data identified 2716 differentially expressed genes in 43,000 transcripts which were changed significantly between heat-stressed and normal bovine mammary epithelial cells (fold change ≥2, P ≤ 0.001). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that these differentially expressed genes are involved in different pathways that regulate cytoskeleton, cell cycle, and stress response processes. Our study provides an overview of gene expression profile and the interaction between gene expression and heat stress, which will lead to further understanding of the potential effects of heat stress on bovine mammary glands.

Impact of climate change on the dairy industry in temperate zones: Predications on the overall negative impact and on the positive role of dairy goats in adaptation to earth warming

The environment within which domesticated livestock production, agricultural crops and related management practices developed over the past 10,000 years is rapidly changing due to human-induced climate change (CC). Nowadays, even countries located within the temperate zone are affected by changes in global warming. These changes are associated with unprecedented events of extreme high ambient temperature (above 40°C) and seasonal changes. The number of days with temperature humidity index (THI) above a specific comfort threshold (>68) has noticeably increased in recent years in European countries located within the temperate zone. The rate of global warming, including in the temperate zone, is expected to continue to vulnerable in coming years. Agricultural production from crops and livestock, and thus global food security, is already affected by CC and will continue to be influenced by global warming. Thus, these changes will continue to affect the dairy industry directly and indirectly. The most significant indirect effect is expected to result from cruel reduction in worldwide grains (concentrate feedstuffs) production. This change will impose need to tradeoff between the diminished food sources: using higher proportions of grains production for human nutrition, instead of feeding it to livestock. Similar conflict is expected to be relevant in using high-quality forages that can be used as edible food for humans. Heat stress imposed by high ambient temperature in temperate zones, such as in Germany, northern Italy and the US was identified in recent years as a major factor that affect negatively milk production, reproduction, and the health of dairy cows. Heat stress also has shown to increase appreciably cow's mortality in those areas. On the other hand, there is no evidence that dairy goat production in temperate zones is affected so far; though, evidence for such an effect was notice in desert and Mediterranean (e.g., Turkey) countries. The major aim of this critical review is to analyze the literature in order to predict how the current trend in harshening of the impact of climatic changes affect dairy industry and to forecast how CC will affect the dairy cows and goat industry in countries located within the temperate zone? Particularly, the direct effects of heat stress on milk production are emphasized. Among domestic ruminants, goats are the most adapted species to imposed heat stress in terms of production, reproduction and resistance to diseases. The main conclusion that can be made is that uttermost scenarios of climatic change will negatively affect the dairy industry and that the importance of goats to the dairy industry will increase in proportion to the severances of changes in environmental temperature.

Future consequences and challenges for dairy cow production systems arising from climate change in Central Europe – a review

It is well documented that global warming is unequivocal. Dairy production systems are considered as important sources of greenhouse gas emissions; however, little is known about the sensitivity and vulnerability of these production systems themselves to climate warming. This review brings different aspects of dairy cow production in Central Europe into focus, with a holistic approach to emphasize potential future consequences and challenges arising from climate change. With the current understanding of the effects of climate change, it is expected that yield of forage per hectare will be influenced positively, whereas quality will mainly depend on water availability and soil characteristics. Thus, the botanical composition of future grassland should include species that are able to withstand the changing conditions (e.g. lucerne and bird's foot trefoil). Changes in nutrient concentration of forage plants, elevated heat loads and altered feeding patterns of animals may influence rumen physiology. Several promising nutritional strategies are available to lower potential negative impacts of climate change on dairy cow nutrition and performance. Adjustment of feeding and drinking regimes, diet composition and additive supplementation can contribute to the maintenance of adequate dairy cow nutrition and performance. Provision of adequate shade and cooling will reduce the direct effects of heat stress. As estimated genetic parameters are promising, heat stress tolerance as a functional trait may be included into breeding programmes. Indirect effects of global warming on the health and welfare of animals seem to be more complicated and thus are less predictable. As the epidemiology of certain gastrointestinal nematodes and liver fluke is favourably influenced by increased temperature and humidity, relations between climate change and disease dynamics should be followed closely. Under current conditions, climate change associated economic impacts are estimated to be neutral if some form of adaptation is integrated. Therefore, it is essential to establish and adopt mitigation strategies covering available tools from management, nutrition, health and plant and animal breeding to cope with the future consequences of climate change on dairy farming.

Climate change impact assessment: the role of climate extremes in crop yield simulation

This work was aimed at assessing the role of climate extremes in climate change impact assessment of typical winter and summer Mediterranean crops by using Regional Circulation Model (RCM) outputs as drivers of a modified version of the CropSyst model. More specifically, climate change effects were investigated on sunflower (Helianthus annuus L.) and winter wheat (Triticum aestivum L.) development and yield under the A2 and B2 scenarios of the IPCC Special Report on Emissions Scenarios (SRES). The direct impact of extreme climate events (i.e. heat stress at anthesis stage) was also included. The increase in both mean temperatures and temperature extremes under A2 and B2 scenarios (2071–2100) resulted in: a general advancement of the main phenological stages, shortening of the growing season and an increase in the frequency of heat stress during anthesis with respect to the baseline (1961–1990). The potential impact of these changes on crop yields was evaluated. It was found that winter and summer crops may possess a different fitting capacity to climate change. Sunflower, cultivated in the southern regions of the Mediterranean countries, was more prone to the direct effect of heat stress at anthesis and drought during its growing cycle. These factors resulted in severe yield reduction. In contrast, the lower frequency of heat stress and drought allowed the winter wheat crop to attain increased yields with respect to the baseline period. It can be concluded that the impact of extreme events should be included in crop-modelling approaches, otherwise there is the risk of underestimating crop yield losses, which in turn would result in the application of incorrect policies for coping with climate change.

Effects of heat stress and nutrition on lactating Holstein cows: II. Aspects of hepatic growth hormone responsiveness

Heat stress (HS) is a multibillion-dollar problem for the global dairy industry, and reduced milk yield is the primary contributor to this annual economic loss. Feed intake declines precipitously during HS but accounts for only about 35% of the decreased milk synthesis, indicating that the physiological mechanisms responsible for decreased milk production during HS are only partly understood. Thus, our experimental objectives were to characterize the direct effects of HS on the somatotropic axis, a primary regulator of metabolism and milk yield. We recently reported no differences in mean growth hormone (GH) concentrations, GH pulsatility characteristics, or GH response to growth hormone releasing factor in HS versus pair-fed (PF) thermoneutral controls. Despite similarities in circulating GH characteristics, plasma insulin-like growth factor (IGF)-I concentrations were reduced during heat stress conditions but not in PF animals, suggesting that uncoupling of the hepatic GH-IGF axis may occur during HS. We investigated this possibility by measuring proximal indicators of hepatic GH signaling following a GH bolus. Heat stress but not PF decreased abundance of the GH receptor and GH-dependent signal transducer and activator of transcription (STAT)-5 phosphorylation. Consistent with reduced GH signaling through STAT-5, basal hepatic IGF-I mRNA abundance was lower in HS cows. Thus, the reduced hepatic GH responsiveness (in terms of IGF-I gene expression) observed during HS appears to involve mechanisms at least partially independent of reduced nutrient intake. The physiological significance of reduced hepatic GH receptor abundance during HS is unclear at this time. Aside from reducing IGF-I production, it may reduce other GH-sensitive bioenergetic processes such as gluconeogenesis.

The Effect of Heat Stress on Ovarian Function of Laying Hens

Reproductive failure associated with heat stress is a well-known phenomenon. The mechanism involved in this failure is not clearly understood. In order to test a possible direct effect of heat stress on ovarian function, 36 White Leghorn laying hens were housed in individual cages in 2 temperature- and light-controlled rooms (n = 18). At 31 wk of age, one group was exposed daily for 12 h to high temperature (42 +/- 3 degrees C), and the second group was maintained under thermoneutral conditions (24 to 26 degrees C) and served as control. Body temperature, feed intake, egg production, and egg weight were recorded daily; heparinized blood samples were drawn every 3 d for plasma hormonal level of luteinizing hormone, follicular stimulating hormone, progesterone, 17beta-estradiol, and testosterone. Six days after exposure half of the birds in each group were killed, and the ovary and oviduct were weighed and preovulatory follicles removed and extracted for mRNA of Cytochrome P 450 aromatase, 17-alpha hydroxylase. The same procedure was repeated 9 d later with the rest of the birds. Short and long heat exposure caused significant hyperthermia and reduction of egg production, egg weight, ovarian weight, and the number of large follicles. In addition, a significant reduction in plasma progesterone and testosterone was detected 2 d after exposing the birds to heat stress, and plasma 17beta-estradiol was significantly reduced 14 d after initiation of heat stress. Short exposure to heat stress caused significant reduction in mRNA expression of cytochrome P450 17-alpha hydroxylase, exposing the birds to long-term heat stress caused significant reduction in expression of mRNA of both steroidogenic enzymes. No significant change was found in plasma luteinizing hormone and follicular stimulating hormone levels during the entire experimental period. We suggest a possible direct effect of heat stress on ovarian function.