Heat Stress Alters Ovarian Insulin-Mediated Phosphatidylinositol-3 Kinase and Steroidogenic Signaling in Gilt Ovaries

Heat stress (HS) compromises a variety of reproductive functions in several mammalian species. Inexplicably, HS animals are frequently hyperinsulinemic despite marked hyperthermia-induced hypophagia. Our objectives were to determine the effects of HS on insulin signaling and components essential to steroid biosynthesis in the pig ovary. Female pigs (35 ± 4 kg) were exposed to constant thermoneutral (20°C; 35%-50% humidity; n = 6) or HS conditions (35°C; 20%-35% humidity; n = 6) for either 7 (n = 10) or 35 days (n = 12). After 7 days, HS increased (P < 0.05) ovarian mRNA abundance of the insulin receptor (INSR), insulin receptor substrate 1 (IRS1), protein kinase B subunit 1 (AKT1), low-density lipoprotein receptor (LDLR), luteinizing hormone receptor (LHCGR), and aromatase (CYP19a). After 35 days, HS increased INSR, IRS1, AKT1, LDLR, LHCGR, CYP19a, and steroidogenic acute regulatory protein (STAR) ovarian mRNA abundance. In addition, after 35 days, HS increased ovarian phosphorylated IRS1 (pIRS1), phosphorylated AKT (pAKT), STAR, and CYP19a protein abundance. Immunostaining analysis revealed similar localization of INSR and pAKT1 in the cytoplasmic membrane and oocyte cytoplasm, respectively, of all stage follicles, and in theca and granulosa cells. Collectively, these results demonstrate that HS alters ovarian insulin-mediated PI3K signaling pathway members, which likely impacts follicle activation and viability. In summary, environmentally induced HS is an endocrine-disrupting exposure that modifies ovarian physiology and potentially compromises production of ovarian hormones essential for fertility and pregnancy maintenance.

The control of short-term feed intake by metabolic oxidation in late-pregnant and early lactating dairy cows exposed to high ambient temperatures

The objective of the present study was to integrate the dynamics of feed intake and metabolic oxidation in late pregnant and early lactating Holstein cows under heat stress conditions. On day 21 before parturition and again on day 20 after parturition, seven Holstein cows were kept for 7days at thermoneutral (TN) conditions (15°C; temperature-humidity-index (THI)=60) followed by a 7day heat stress (HS) period at 28°C (THI=76). On the last day of each temperature condition, gas exchange, feed intake and water intake were recorded every 6min in a respiration chamber. Pre- and post-partum cows responded to HS by decreasing feed intake. The reduction in feed intake in pre-partum cows was achieved through decreased meal size, meal duration, eating rate and daily eating time with no change in meal frequency, while post-partum cows kept under HS conditions showed variable responses in feeding behavior. In both pre- and post-partum cows exposed to heat stress, daily and resting metabolic heat production decreased while the periprandial respiratory quotient (RQ) increased. The prolonged time between meal and the postprandial minimum in fat oxidation and the postprandial RQ maximum, respectively, revealed that HS as compared to TN early-lactating cows have slower postprandial fat oxidation, longer feed digestion, and thereby showing a shift from fat to glucose utilization.

Scrotal infrared digital thermography as a predictor of seasonal effects on sperm traits in Braford bulls

The aim of this study was to assess the seasonal effects of the environment on semen quality in bulls, using infrared thermography. Sperm motility (M), mass motion (MM), and vigor (VIG) were evaluated in sperm samples from 17 Bradford bulls aged approximately 24 months at the beginning of the study. Infrared thermography images and data were collected using an infrared FLIR T 300 camera and Quick Report 1.2 SP2 software to determine the temperature of the proximal and distal poles of the testis and to assess the testicular temperature gradient. The seasonal effects on physiological, seminal, and climatic variables were analyzed by the GLM ANOVA and CORR procedures using SAS®. The microclimatic factors were recorded in hourly intervals, and the daily mean temperature and mean relative humidity were calculated to determine the daily temperature-humidity index (THI) every day for 1 year. The temperature gradient (TG) variations of the testes were significantly higher in the autumn (4.5 °C), winter (4.0 °C), and spring (2.9 °C) compared to summer (0.9 °C) (P < 0.05). Ocular globe temperatures were lower in the winter (27.6 °C) and autumn (26.8 °C) compared to summer (33.9 °C) and spring (31.1 °C) (P < 0.05). The average MM (2.58), M (52.64), and VIG (2.70) of the semen decreased in the summer compared to other seasons (P < 0.01). The TG was negatively correlated with THI (-0.44; P < 0.05). For the seminal variables, MaD (-0.45; P < 0.05) and TD (-0.50; P < 0.01) presented a negative correlation with TG. The TG had a positive correlation between M and VIG, which had values of 0.36 and 0.35, respectively (P < 0.05). We have concluded that infrared thermography can be used to assess the testicular temperature gradient and its consequences on physical and quantitative aspects of sperm.

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.

Evaluation of the effects of chromium supplementation on growth and nitrogen balance of camel calves under summer conditions

One of the most important problems in the production of camels in arid and semi-arid zones is the reduced feed intake and consequent low growth rate during summer. Under these stressful environmental conditions, chromium (Cr) supplementation to the diet of growing camel calves may be beneficial. Therefore, the objective of this study was to evaluate the effects of feeding a diet supplemented with different levels of Cr on growth performance of camel calves reared in a hot arid environment. A total of 15 male camel calves (4-5-month-old, 123 ± 7 kg body weight) were used in this study. The animals were divided into three equal groups (A, B, C), 5 animals each, and housed individually under shelter. Camel calves were fed ad libitum on either total mixed ration (TMR) without Cr supplementation (group A), TMR supplemented with 0.5 mg Cr/kg DM (group B), or TMR supplemented with 1.0 mg Cr/kg DM (group C). Supplementation of 0.5 mg Cr/kg DM to the diet of camel calves did not alter feed intake, however, increased not significantly (P = 0.086) average daily gain (ADG) and N retention. Plasma cortisol level was reduced by 10%, and feed utilization efficiency was improved by 12% in 0.5 mg Cr/kg DM-supplemented group compared to the control. Thus, 0.5 mg Cr/kg DM dietary supplementation to camel calves reared under hot summer condition increased weight gain by 17% and reduced feeding cost of producing a unit of weight by 11%.

Physiological consequences of heat stress in pigs

Heat stress negatively influences the global pork industry and undermines genetic, nutritional, management and pharmaceutical advances in management, feed and reproductive efficiency. Specifically, heat stress-induced economic losses result from poor sow performance, reduced and inconsistent growth, decreased carcass quality, mortality, morbidity, and processing issues caused by less rigid adipose tissue (also known as flimsy fat). When environmental conditions exceed the pig’s thermal neutral zone, nutrients are diverted from product synthesis (meat, fetus, milk) to body temperature maintenance thereby compromising efficiency. Unfortunately, genetic selection for both increased litter size and leaner phenotypes decreases pigs’ tolerance to heat, as enhanced fetal development and protein accretion results in increased basal heat production. Additionally, research has demonstrated that in utero heat stress negatively and permanently alters post-natal body temperature and body composition and both variables represent an underappreciated consequence of heat stress. Advances in management (i.e. cooling systems) have partially alleviated the negative impacts of heat stress, but productivity continues to decline during the warm summer months. The detrimental effects of heat stress on animal welfare and production will likely become more of an issue in regions most affected by continued predictions for climate change, with some models forecasting extreme summer conditions in key animal-producing areas of the globe. Therefore, heat stress is likely one of the primary factors limiting profitable animal protein production and will certainly continue to compromise food security (especially in emerging countries) and regionalise pork production in developed countries. Thus, there is an urgent need to have a better understanding of how heat stress reduces animal productivity. Defining the biology of how heat stress jeopardises animal performance is critical in developing approaches (genetic, managerial, nutritional and pharmaceutical) to ameliorate current production issues and improve animal wellbeing and performance.

Nutritional strategies to alleviate heat stress in pigs

Pigs are comparatively less heat tolerant than other species of production animals, which poses challenges for stock productivity and management during seasonal heat waves that occur in summer. The issues surrounding heat and pig production are predicted to increase, based on the actions of climate change increasing the intensity, frequency and duration of heat waves. Furthermore, future growth areas of pig production are going to be in tropical regions such as South-east Asia and Latin America. Efforts by the pig to dissipate excess body heat come at a cost to health and divert energy away from growth, compromising efficient pig production. Management of heat stress requires multiple strategies, and recent research is improving the understanding of the application of nutritional strategies to ameliorate the effects of heat stress. In particular the use of feed additives is an important, flexible and economical method to alleviate heat stress and the intensive nature of pig production lends itself to the use of additives. Some specific examples include antioxidants, betaine and chromium, which have been proved effective or being tested in mitigating some certain impacts of heat stress in pigs. The aim of this review is to summarise recent advances in the nutritional management of heat stress in pigs.

Effects of dairy products on intestinal integrity in heat-stressed pigs

Heat stress compromises intestinal integrity which may partially explain its negative effects on animal health and productivity. Research suggests that challenged intestinal barrier function improves with dietary dairy products in various models. Thus, the study objective was to evaluate the effects of bovine milk whey protein (WP) and colostral whey protein (CWP) on intestinal integrity in heat-stressed pigs. Crossbred gilts (39 ± 3 kg body weight) were fed 1 of 4 diets (n = 8 pigs/diet): control (Ct), control diet containing an 80% WP and 20% CWP product (WP80), control diet containing a 98% WP and 2% CWP product (WP98), and control diet containing a 100% WP product (WP100). After 7d on experimental diets, pigs were exposed to constant heat stress conditions (32 °C) for 24h. There were no treatment differences in growth or body temperature indices prior to heat stress. During heat exposure, both rectal temperature and respiration rate increased (+0.85 °C and 3-fold, respectively; P < 0.01), and feed intake and body weight decreased (44% and -0.5kg, respectively; P < 0.01), but neither variable was affected by dietary treatments. Plasma L-lactate and D-lactate concentrations increased (36%; P < 0.01) and tended to increase (19%; P = 0.09) with heat stress. After 24h of heat exposure, WP100-fed pigs had lower plasma D-lactate relative to Ct-fed pigs. Ileal transepithelial electrical resistance was decreased (37%; P = 0.02) in WP80 pigs, compared with controls. No differences were detected in other intestinal integrity ex vivo measurements. These data demonstrate that dietary WP and CWP did not mitigate intestinal integrity dysfunction during severe heat stress.

Grape seed extract supplementation attenuates the heat stress-induced responses of jejunum epithelial cells in Simmental × Qinchuan steers

Grape seed extract (GSE), a rich source of polyphenols, is reported to possess antioxidant, anti-inflammatory and immunomodulatory properties. The objective of the present study was to determine whether GSE could attenuate the heat stress-induced responses of jejunum epithelial cells (JEC) in cattle. The JEC of a steer (Simmental × Qinchuan) were exposed to heat stress for 2 h in the absence (0 μg/ml) or presence (10, 20, 40 and 80 μg/ml) of GSE in the culture medium. When cultured at 40°C, JEC supplemented with GSE exhibited increased glutathione peroxidase activity (P= 0·04), viability (P= 0·004), and mRNA expression of epidermal growth factor (EGF; P= 0·03) and EGF receptor (EGFR; P = 0·01). Under the same conditions, the cells exhibited decreased mRNA expression of IL-8 (P= 0·01) and TNF-α (P= 0·03) and decreased protein concentrations of IL-1β (P= 0·02), Toll-like receptor 4 (TLR4; P= 0·04) and heat shock protein 70 (HSP70; P< 0·001). When cultured at 43°C, JEC supplemented with GSE exhibited increased catalase activity (P= 0·04), viability (P< 0·001), and mRNA expression of EGF (P< 0·001) and EGFR (P< 0·001) and decreased protein concentrations of IL-1β (P< 0·001), TLR4 (P= 0·03) and HSP70 (P< 0·001), as well as mRNA expression of IL-8 (P< 0·001), TLR4 (P= 0·002) and TNF-α (P< 0·001). Temperature × GSE concentration interactions were also observed for the concentrations of IL-1β (P< 0·001), IL-8 (P< 0·001), TNF-α (P= 0·01) and HSP70 (P= 0·04) and viability (P< 0·001) of JEC. The results of the present study indicate that GSE can attenuate the responses of JEC induced by heat stress within a certain range of temperatures.

Effects of mammalian in utero heat stress on adolescent body temperature

In utero hyperthermia can cause a variety of developmental issues, but how it alters mammalian body temperature during adolescence is not well-understood. Study objectives were to determine the extent to which in utero hyperthermia affects future phenotypic responses to a heat load. Pregnant first parity pigs were exposed to thermal neutral (TN) or heat stress (HS) conditions during the entire gestation. Of the resultant offspring, 12 were housed in TN conditions, and 12 were maintained in HS conditions for 15 days. Adolescent pigs in HS conditions had increased rectal temperature and respiration rate (RR) compared to TN pigs, regardless of gestational treatment. Within the HS environment, no gestational difference in RR was detected; however, GHS pigs had increased rectal temperature compared to GTN pigs. As rectal temperature increased, GTN pigs had a more rapid increase in RR compared to the GHS pigs. Adolescent HS decreased nutrient intake, and body weight gain, but neither variable was statistically influenced by gestational treatments. In summary, in utero HS compromises the future thermoregulatory response to a thermal insult.

Heat stress causes oxidative stress but not inflammatory signaling in porcine skeletal muscle

Heat stress is associated with death and other maladaptions including muscle dysfunction and impaired growth across species. Despite this common observation, the molecular effects leading to these pathologic changes remain unclear. The purpose of this study was to determine the extent to which heat stress disrupted redox balance and initiated an inflammatory response in oxidative and glycolytic skeletal muscle. Female pigs (5-6/group) were subjected to thermoneutral (20 °C) or heat stress (35 °C) conditions for 1 or 3 days and the semitendinosus removed and dissected into red (STR) and white (STW) portions. After 1 day of heat stress, relative abundance of proteins modified by malondialdehyde, a measure of oxidative damage, was increased 2.5-fold (P < 0.05) compared with thermoneutral in the STR but not the STW, before returning to thermoneutral conditions following 3 days of heat stress. This corresponded with increased catalase and superoxide dismutase-1 gene expression (P < 0.05) and superoxide dismutase-1 protein abundance (P < 0.05) in the STR but not the STW. In the STR catalase and total superoxide dismutase activity were increased by ~30% and ~130%, respectively (P < 0.05), after 1 day of heat stress and returned to thermoneutral levels by day 3. One or 3 days of heat stress did not increase inflammatory signaling through the NF-κB pathway in the STR or STW. These data suggest that oxidative muscle is more susceptible to heat stress-mediated changes in redox balance than glycolytic muscle during chronic heat stress.

The Nexus of Environmental Quality and Livestock Welfare

In recent years, the livestock production industry has been receiving pressure to assess and improve production practices in two seemingly unrelated areas: environmental quality and animal welfare. In this article, we argue that the nexus of these two areas of study should be a priority for future research and that the integration of these disciplines in research, extension, and education efforts has the potential to improve the sustainability of production livestock agriculture.

Effects of supplemental zinc amino acid complex on gut integrity in heat-stressed growing pigs

Heat stress (HS) jeopardizes livestock health and productivity and both may in part be mediated by reduced intestinal integrity. Dietary zinc improves a variety of bowel diseases, which are characterized by increased intestinal permeability. Study objectives were to evaluate the effects of supplemental zinc amino acid complex (ZnAA) on intestinal integrity in heat-stressed growing pigs. Crossbred gilts (43±6 kg BW) were ad libitum fed one of three diets: (1) control (ZnC; 120 ppm Zn as ZnSO4; n=13), (2) control+100 ppm Zn as ZnAA (Zn220; containing a total of 220 ppm Zn; n=14), and (3) control+200 ppm Zn as ZnAA (Zn320; containing a total of 320 ppm Zn; n=16). After 25 days on their respective diets, all pigs were exposed to constant HS conditions (36°C, ∼50% humidity) for either 1 or 7 days. At the end of the environmental exposure, pigs were euthanized and blood and intestinal tissues were harvested immediately after sacrifice. As expected, HS increased rectal temperature (P⩽0.01; 40.23°C v. 38.93°C) and respiratory rate (P⩽0.01; 113 v. 36 bpm). Pigs receiving ZnAA tended to have increased rectal temperature (P=0.07; +0.27°C) compared with ZnC-fed pigs. HS markedly reduced feed intake (FI; P⩽0.01; 59%) and caused BW loss (2.10 kg), but neither variable was affected by dietary treatment. Fresh intestinal segments were assessed ex vivo for intestinal integrity. As HS progressed from days 1 to 7, both ileal and colonic transepithelial electrical resistance (TER) decreased (P⩽0.05; 34% and 22%, respectively). This was mirrored by an increase in ileal and colonic permeability to the macromolecule dextran (P⩽0.01; 13- and 56-fold, respectively), and increased colonic lipopolysaccharide permeability (P⩽0.05; threefold) with time. There was a quadratic response (P⩽0.05) to increasing ZnAA on ileal TER, as it was improved (P⩽0.05; 56%) in Zn220-fed pigs compared with ZnC. This study demonstrates that HS progressively compromises the intestinal barrier and supplementing ZnAA at the appropriate dose can improve aspects of small intestinal integrity during severe HS.

Physiological responses and lactational performances of late-lactation dairy goats under heat stress conditions

Eight Murciano-Granadina dairy goats in late lactation were exposed to different ambient conditions, using metabolic cages in a climatic chamber. The experimental design was a crossover (2 periods of 35 d and 4 goats each) and conditions were (1) thermal neutral (TN; 15 to 20 °C day-night) and (2) heat stress (HS; 12-h day at 37 °C and 12-h night at 30.5 °C). Humidity was maintained at 40% and light-dark was constant (12-12h). The forage:concentrate ratio was adjusted daily for maintaining similar value in TN and HS goats (70:30). Water was freely available at ambient temperature. Rectal temperature and respiratory rate (0800, 1200 and 1700 h) and milk yield were recorded daily, whereas milk composition, nonesterified fatty acids and haptoglobin in blood were analyzed weekly. At d 25, additional blood samples were taken for analysis of metabolites and indicators of the acid-base balance. Digestibility coefficients and N balance were determined (d 31 to 35) and body weight was recorded (d 35). Compared with TN goats, HS goats experienced greater rectal temperature (+0.58 °C), respiratory rate (+48 breaths/min), water intake (+77%) and water evaporation (+207%). Intake of HS goats rapidly declined until d 7 (-40%), partially recovered from d 7 to 19, and steadied thereafter (-14%). No changes in digestibility or N balance were detected. Blood nonesterified fatty acids and haptoglobin peaked at d 7 in HS goats but did not vary thereafter. Although milk yield did not vary by treatment, milk of HS goats contained -12.5% protein and -11.5% casein than TN goats. Panting reduced concentration and pressure of CO₂ in the blood of HS goats, but they were able to maintain their blood pH similar to the TN group by lowering HCO₃(-) and increasing Cl(-) concentrations in their blood. In conclusion, HS dairy goats showed dramatic physiological changes during the first week of treatment and partially recovered thereafter. They were able to maintain milk yield by losing body mass, but milk protein content and protein yield were depressed. Further research is needed to assess the response of dairy goats to HS at earlier stages of lactation.

2011 and 2012 Early Careers Achievement Awards: metabolic priorities during heat stress with an emphasis on skeletal muscle

Environmental heat stress undermines efficient animal production resulting in a significant financial burden to agricultural producers. The reduction in performance during heat stress is traditionally thought to result from reduced nutrient intake. Recently, this notion has been challenged with observations indicating that heat-stressed animals may exploit novel homeorhetic strategies to direct metabolic and fuel selection priorities independent of nutrient intake or energy balance. Alterations in systemic physiology support a shift in metabolism, stemming from coordinated interactions at whole-body and tissue-specific levels. Such changes are characterized by increased basal and stimulated circulating insulin concentration in addition to the ostensible lack of basal adipose tissue lipid mobilization coupled with reduced adipocyte responsiveness to lipolytic stimuli. Hepatic and skeletal muscle cellular bioenergetics also exhibit clear differences in carbohydrate production and use, respectively, due to heat stress. The apparent dichotomy in intermediary metabolism between the 2 tissue types may stem from factors such as tricarboxylic acid cycle substrate flux and mitochondrial respiration. Thus, the heat stress response markedly alters postabsorptive carbohydrate, lipid, and protein metabolism through coordinated changes in fuel supply and use across tissues in a manner that is distinct from commonly recognizable changes that occur in animals on a reduced plane of nutrition. Perhaps most intriguing is that the coordinated systemic, cellular, and molecular changes appear conserved across physiological states and among different ruminant and monogastric species. Ultimately, these changes result in the reprioritization of skeletal muscle fuel selection during heat stress, which may be important for whole-body metabolism and overall physiological adaptation to hyperthermia.