Heat Stress In Pigs Research Articles

141 Genomic selection for heat stress resilience in pigs: Advancements, applications, and challenges

Abstract Heat stress is a critical challenge to swine productivity and welfare that causes economic losses and endangers food security. As temperatures continue to increase in most pig producing regions, the effects of heat stress on pig production will become more apparent. The detrimental effects of postnatal heat stress on pig performance and welfare are well-defined. Furthermore, data on the effects of in utero heat stress in pigs describes lifelong production and welfare deficits that may be transgenerational. Despite its economic implications and transgenerational effects, heat stress mitigation strategies remain underexplored. Genomic selection offers a promising avenue for addressing swine heat stress, targeting resilient swine phenotypes to minimize adverse outcomes. However, challenges persist in integrating thermotolerance traits with traditional performance metrics, as improved thermotolerance is often unfavorably correlated with production traits. Therefore, effective selection strategies require balancing productive efficiency with climatic resilience and animal welfare breeding goals. As climate change continues to intensify the frequency and severity of heat stress, innovative approaches that prioritize resilience and adaptability are needed to safeguard swine productivity and welfare.

PSIV-10 Thyroid hormone does not protect skeletal muscle mitochondrial function from heat stress in pigs

PSIV-10 Thyroid hormone does not protect skeletal muscle mitochondrial function from heat stress in pigs

Effect of Simultaneous Dietary Supplementation of Betaine, Selenomethionine, and Vitamins E and C under Summer Conditions in Growing-Finishing Pigs.

Heat stress in pigs negatively affects welfare, health, and performance. Osmoprotectants and antioxidants may alleviate oxidative damage during hot periods. We investigated whether an additive-enriched feed can reduce negative effects in pigs during summer conditions. Sixty growing-finishing pigs were allocated into two groups: the control (CF) and summer feed (SF) group. The CF group contained 0.4 mg/kg inorganic selenium and 100 ppm vitamin E, while the SF group contained 0.3 mg/kg inorganic selenium, 0.1 mg/kg selenomethionine, 200 ppm vitamins E and C, and 0.2% betaine. Feed was offered ad libitum. Respiration rate, rectal and skin temperature, behaviour, and weight gain were assessed weekly. Daily measurements of these parameters were performed during a 3-day heat wave (temperature humidity index (THI) ≥ 75) and during an artificial heating period. Individual average daily water intake (ADWI) and feed intake were measured using RFID systems. The ADWI of the SF group did not change during heat load while it increased for the CF group. Independent of dietary treatment, increases in ∆THI or the THI were accompanied by significant increases in both respiration rate and skin temperature. In conclusion, the SF may induce a reduced need to increase ADWI during hot periods. In addition, mainly skin temperatures and especially respiration rates revealed the sensitivity of pigs to heat stress.

Effect of heat stress on the reproductive performance of sows: comparison of different thermal-comfort indices in a temperate climate

Context Heat stress is a major environmental factor negatively affecting animal health and production efficiency of the sow, and causes significant economic losses to the global pig industry. Researchers have developed various thermal indices with different characteristics for assessing the level of heat stress in pigs, including the temperature–humidity index (THI), black globe–humidity index (BGHI), effective temperature (ET), equivalent temperature index of sows (ETIS), and enthalpy (H), among others. Aims The aim of this study was to evaluate the effect of heat stress on reproductive performance by using different thermal indices based on environmental variables in a temperate climate and to compare the goodness-of-fit among them. Methods In total, 2951 sow reproductive records were analysed for a Puebla farm in the northern hemisphere. Key results The overall means for pregnancy, farrowing, and abortion rates over the period from January to December 2020 were 83.1%, 80.67%, and 5.2%, whereas temperature, relative humidity, and air velocity were 24.3°C, 63.0%, and 3.7 m/s respectively. The highest rates of pregnancy and farrowing over the study period were observed in March, while the abortion rate was highest in December. However, the mean daily temperatures exceeded 25°C between March and June, being higher the upper limit of the thermoneutral zone for sows. Many thermal indices have been used to estimate the level of heat stress in pigs, such as the THI, BGHI, ET, and ETIS. We used 11 thermal indices to measure the degree of heat stress affecting fertility traits of animals. Pregnancy and farrowing rates were highest for THI2 and THI6 values, reflecting moderate stress at pregnancy and farrowing periods. Statistically significant differences were found between the THI2, THI4, THI6, and ET values and the pregnancy, farrowing, and abortion rates (P < 0.05). Conclusions Our results showed that the THI2 performs better for evaluating the level of heat stress in sows than do other thermal-comfort indices such as the THI4, THI6, and ET. Implications These results may be useful for accurate assessment of heat stress to mitigate its effects and avoid significant economic losses in sows in temperate climates.

Nutritional strategies to mitigate heat stress in pigs; What we have learnt in Australia that can be applied overseas?

Nutritional strategies to mitigate heat stress in pigs; What we have learnt in Australia that can be applied overseas?

Overexpression of heat shock protein 70 induces apoptosis of intestinal epithelial cells in heat-stressed pigs: A proteomics approach

Heat stress (HS)-induced intestinal epithelial cell apoptosis may play a pivotal role in intestinal barrier dysfunction in animals. However, the underlying molecular mechanism by which HS induces apoptosis in intestinal epithelial cells is still poorly understood. Herein, a eukaryotic expression vector for an HSP70 gene was constructed and transfected into intestinal porcine epithelial cells (IPEC-J2). Afterward, functional proteomics approaches followed by liquid-chromatography-tandem mass spectrometry (LC-MS/MS) were used to identify interacting proteins. Analysis of HSP70 transfected IPEC-J2 cells revealed 246 differentially expressed proteins (DEPs), and functional annotation indicated that most DEPs were primarily related to ECM-receptor interaction, focal adhesion, and apoptosis. Furtherly, the apoptosis rate and expression levels of apoptosis-related proteins in HSP70 transfected IPEC-J2 cells were detected, we found that the expression of caspase-3, PARP, and Bax were increased, but Bcl-2 were decreased in transfected cells. Lastly, an in vitro and in vivo heat stress model were established to explore the role of HSP70 in intestinal epithelia cell apoptosis. The results of in vitrol study showed that HS-induced cellular apoptosis and increases of caspase-3, PARP, and Bax, but decreased of Bcl-2 in IPEC-J2 cells. In vivo study, the cell apoptosis were induced significantly in the duodenum, cecum, and colon of heat stressed pigs, and upregulation of HSP70 was also detected in colon tissues. Therefore, it has been shown that HSP70 plays a crucial role in heat stress-induced apoptosis and may provide new insights into the molecular mechanisms of epithelial cell apoptosis induced by heat stress in pigs.

507 Late-Breaking: Heat Stress and Mitoq Supplementation Impact Skeletal Muscle Mitochondrial Capacities in Pigs

Abstract Heat stress can negatively impact pig health and performance but the effects of heat stress on skeletal muscle mitochondrial function are largely unknown. We hypothesized that mitochondrial function and capacity would be impaired in heat stressed (HS) compared to thermoneutral (TN) pigs but mitochondrially-targeted coenzyme Q (MitoQ) supplementation would rescue the impairment. Oxidative portions of the semitendinosus muscle were evaluated from TN and HS gilts receiving no supplementation (CON) or MitoQ for 2 d prior to and during the 24h environmental heat treatment (n = 8 per group). Mitochondrial oxidative phosphorylation (P) and electron transfer (E) capacities were determined via high resolution respirometry and mitochondrial volume density and function were quantified by citrate synthase (CS) and cytochrome c oxidase activities, respectively. Data were analyzed using linear models in SAS v9.4 with fixed effects of heat, MitoQ treatment (trt), and heat×trt interaction. There were trends for the interaction of trt and heat (P≤0.1) on integrative (per mg tissue) and intrinsic (relative to CS) P with complexes I and II (PCI+II), maximum noncoupled E (ECI+II), and E with complex II only (ECII), in which all measures were greater in HS-MitoQ than TN-MitoQ (P≤0.03), but measures did not differ due to HS in CON pigs. The contribution of leak to total E (flux control ratio, FCRLeak) was lesser in HS-MitoQ than HS-CON, TN-CON, and TN-MitoQ (P≤0.02). The FCRPCI was greater (P≤0.05) while the FCRPCI+II was lesser (P=0.01) in TN compared to HS pigs. Finally, the FCRPCI+II was greater (P=0.02) while the FCRECII tended to be lesser (P=0.09) for CON than MitoQ pigs. Neither mitochondrial volume density nor function were affected by HS or MitoQ supplementation. In total, these data indicate improved mitochondrial capacities following heat stress in pigs receiving MitoQ but no difference in mitochondrial capacities in unsupplemented, HS pigs.

Behavior and Welfare of Undocked Heavy Pigs Raised in Buildings with Different Ventilation Systems.

Simple SummaryThe relationship between animal welfare and housing conditions is still a matter of debate. The present study aimed to evaluate animal welfare of undocked heavy pigs from the same farm, raised in buildings with different ventilation systems, i.e., mechanical and natural, throughout the fattening period (90–160 kg average weight). Ventilation efficiency was evaluated using computational fluid dynamics. Results showed that overall pigs raised in the mechanical ventilated building were in a more positive affective state. Despite that, with hot temperatures, the higher occurrence of pig soiling indicated heat stress and consequent welfare impairment. The higher frequencies of dog sitting behavior also indicated worsening of welfare conditions in the middle–late phases of fattening, likely imputable to the lack of stimuli and boredom in the pigs.The present study aimed to evaluate animal welfare of pigs from the same farm, raised with two ventilation systems. The study involved 60 pens of fattening pigs, raised in two buildings: one naturally ventilated (NV) and the other mechanically ventilated (MV). Pigs were assessed on three observation days: at 40 kg (T1), 100 kg (T2), and 160 kg (T3) of live weight. Animal-based measures were used such as qualitative behavioral analysis (QBA), behavioral measures (BMs), and lesion and health measures (LHMs). Housing conditions (HCs) measured at each observation day were the number of pigs per pen, space allowance, temperature, light, and CO2. The association study was performed using a general linear model and analysis of variance. Ventilation effect was analyzed by performing computational fluid dynamics. Results showed that overall pigs raised in the MV were in a more positive affective state. Despite that, with hot temperatures, the higher occurrence of pig soiling indicated heat stress in pigs and consequent welfare impairment. The higher frequency of pigs showing dog sitting behavior at T2 and T3 suggest welfare worsening in the last phases of fattening. The study concludes that ventilation system influences animal behavior and overall animal welfare, especially during the warmer season.

Modeling of Heat Stress in Sows-Part 1: Establishment of the Prediction Model for the Equivalent Temperature Index of the Sows.

Simple SummarySows are susceptible to heat stress. Various indicators can be found in the literature assessing the level of heat stress in pigs, but none of them is specific to assess the sows’ thermal condition. Moreover, previous thermal indices have been developed by considering only partial environment parameters, and the interaction between the index and the animal’s physiological response are not always included. Therefore, this study aims to develop and assess a new thermal index specified for sows, called equivalent temperature index for sows (ETIS), with a comprehensive consideration of the influencing factors. An experiment was conducted, and the experimental data was applied for model development and validation. The equivalent temperatures have been transformed on the basis of equal effects of air velocity, relative humidity, floor heat conduction and indoor radiation on the thermal index, and used for the ETIS combination. The correlations between ETIS and sow’s physiological parameters were performed. In the comparison with other thermal indices, the ETIS had the best performance (R = 0.82) using experimental data obtained from the sow house. In addition, the comfort threshold of ETIS has been classified for evaluating heat stress levels in the sow. This study concludes that the newly developed ETIS can be used to assess the degree of thermal comfort for sows.Heat stress affects the estrus time and conception rate of sows. Compared with other life stages of pigs, sows are more susceptible to heat stress because of their increased heat production. Various indicators can be found in the literature assessing the level of heat stress in pigs. However, none of them is specific to assess the sows’ thermal condition. Moreover, thermal indices are mainly developed by considering partial environment parameters, and there is no interaction between the index and the animal’s physiological response. Therefore, this study aims to develop a thermal index specified for sows, called equivalent temperature index for sows (ETIS), which includes parameters of air temperature, relative humidity and air velocity. Based on the heat transfer characteristics of sows, multiple regression analysis is used to combine air temperature, relative humidity and air velocity. Environmental data are used as independent variables, and physiological parameters are used as dependent variables. In 1029 sets of data, 70% of the data is used as the training set, and 30% of the data is used as the test set to create and develop a new thermal index. According to the correlation equation between ETIS and temperature-humidity index (THI), combined with the threshold of THI, ETIS was divided into thresholds. The results show that the ETIS heat stress threshold is classified as follows: suitable temperature ETIS < 33.1 °C, mild temperature 33.1 °C ≤ ETIS < 34.5 °C, moderate stress temperature 34.5 °C ≤ ETIS < 35.9 °C, and severe temperature ETIS ≥ 35.9 °C. The ETIS model can predict the sows’ physiological response in a good manner. The correlation coefficients R of skin temperature was 0.82. Compared to early developed thermal indices, ETIS has the best predictive effect on skin temperature. This index could be a useful tool for assessing the thermal environment to ensure thermal comfort for sows.

Identification of trailer heat zones and associated heat stress in weaner pigs transported by road in tropical climates.

Heat stress is major welfare concern during transport of pigs in tropical climates, which can also lead to direct production costs. This study evaluated the dynamics of heat zones through the load and their relationship with heat stress of weaner pigs during road transport in a tropical climate. Both environmental (e.g. temperature and relative humidity) and physiological (e.g. respiratory frequency and lactate) measures were recorded from four vehicle journeys (70km distance, 216 weaner pigs within each trailer load) within Ceará, northeastern Brazil. Geostatistics and fluid dynamics simulation techniques were applied to understand the dynamics of heat zones and ventilation patterns the truckload. Statistics based on canonical discriminant analysis and ANOVA were performed to verify the relationship between heat zones and heat stress in pigs. The results showed that, during transport, the generation of heat zones occurred with different magnitudes along the load (P< 0.05), which was harmonized by the ventilation dynamics. There was a heat core with high energy content, in the front region of the lower deck (LD) of the trailer. In this zone, weaners pigs had higher rectal temperature (+1.8°C temperature difference), respiratory frequency (LD=94±1.3 breaths/min; UD=86±1.3 breaths/min), and blood cortisol concentration (LD=32.9±0.8ng/mL; UD=30.18±0.6ng/mL) (all P< 0.05). Weaners pigs transported in the upper deck (UD) compartments had the highest skin temperature (LD=38.13±0.3°C; UD=38.9±0.22°C) and the highest mean values of blood lactate (LD=65.5±1.11m/M; UD=71.60±1.19m/M) and Creatine kinase (LD=3891.23±69U/L; UD=4107.43±62U/L) (P< 0.05). Weaners transported in compartments of the LD of trailer were more susceptible to heat stress, while weaners in the UD compartments were more susceptible to physical stress and muscle exhaustion. These results provide additional evidence of heat zones within trailer compartments and highlight the requirement for the planning of pig transport operations in tropical climates to mitigate risks of heat stress.

Betaine and Isoquinoline Alkaloids Protect against Heat Stress and Colonic Permeability in Growing Pigs.

Heat stress (HS) compromises productivity of pork production, in part as a result of increased oxidative stress and inflammatory responses, particularly within the gastrointestinal tract. This study aimed to investigate whether plant-derived betaine and isoquinoline alkaloids could ameliorate HS in pigs. Fifty female Large White × Landrace grower pigs, which were acclimated to control (CON), control plus betaine (BET), or control plus isoquinoline alkaloids (IQA) diets for 14 days were then exposed to heat stress or thermoneutral condition. Both BET and IQA partially ameliorated increases in respiration rate (p = 0.013) and rectal temperature (p = 0.001) associated with HS conditions. Heat stress increased salivary cortisol concentrations and reduced plasma creatinine, lactate, and thyroid hormone concentrations. Heat stress increased colon FD4 permeability, which was reduced by IQA (p = 0.030). Heat stress increased inflammation in the jejunum and ileum, as indicated by elevated interleukin-1β (p = 0.022) in the jejunum and interleukin-1β (p = 0.004) and interleukin-8 (p = 0.001) in the ileum. No differences in plasma total antioxidant capacity (TAC) were observed with HS, but betaine increased plasma TAC compared to IQA. Dietary BET increased betaine concentrations in the jejunum, ileum (p < 0.001 for both), plasma, liver, kidney (p < 0.010 for all), urine (p = 0.002) and tended to be higher in muscle (p = 0.084). Betaine concentration was not influenced by HS, but it tended to be higher in plasma and accumulated in the liver. These data suggest that betaine and isoquinoline alkaloids supplementation ameliorated consequences of heat stress in grower pigs and protected against HS induced increases in colonic permeability.

Genome-Wide Transcriptome and Metabolome Analyses Provide Novel Insights and Suggest a Sex-Specific Response to Heat Stress in Pigs.

Heat stress (HS) negatively impacts pig production and swine health. Therefore, to understand the genetic and metabolic responses of pigs to HS, we used RNA-Seq and high resolution magic angle spinning (HR-MAS) NMR analyses to compare the transcriptomes and metabolomes of Duroc pigs (n = 6, 3 barrows and 3 gilts) exposed to heat stress (33 °C and 60% RH) with a control group (25 °C and 60% RH). HS resulted in the differential expression of 552 (236 up, 316 down) and 879 (540 up, 339 down) genes and significant enrichment of 30 and 31 plasma metabolites in female and male pigs, respectively. Apoptosis, response to heat, Toll-like receptor signaling and oxidative stress were enriched among the up-regulated genes, while negative regulation of the immune response, ATP synthesis and the ribosomal pathway were enriched among down-regulated genes. Twelve and ten metabolic pathways were found to be enriched (among them, four metabolic pathways, including arginine and proline metabolism, and three metabolic pathways, including pantothenate and CoA biosynthesis), overlapping between the transcriptome and metabolome analyses in the female and male group respectively. The limited overlap between pathways enriched with differentially expressed genes and enriched plasma metabolites between the sexes suggests a sex-specific response to HS in pigs.

PSVII-6 Precision feeding and reduced crude protein on nitrogen efficiency of pigs raised under tropical conditions

Abstract Feeding pigs with low protein diets is suggested to attenuate the negative effects of heat stress in pigs reared in hot climate areas, without changes on pigs performance. This study aimed to evaluate the nitrogen balance of pigs raised under tropical conditions and fed in conventional group-phase feeding systems (CON) or fed individually with daily tailored diets (IPF) receiving diets formulated with low (LCP) or high (HCP) crude protein. Sixty male castrated pigs (39kg±0.98) were assigned to 4 treatments in a 2×2 factorial arrangement. The experiment lasted 56 days (phase 1: d 0–28, and 2: d 29–56). CON fed pigs received within each phase a constant blend of diets A (high nutrient) and B (low nutrient density) supplying the estimated nutrient requirements of the group, whereas IPF pigs received daily a personalized blend providing the estimated amount of nutrients. Body lean was assessed by a dual-energy X-ray absorptiometry at the beginning and at the end of each phase and converted to body protein. Data were analyzed using the MIXED procedure of SAS including the fixed effects of feeding system, feed formulation, and their interactions. Pigs receiving LCP diets reduced the CP intake in 27% (P &amp;lt; 0.001). However, IPF pigs consumed on average 15% less CP than CON pigs (P &amp;lt; 0.001). Regardless of the reduced CP intake, LCP fed pigs showed a greater N retention than pigs receiving HCP diets during the first phase (P &amp;lt; 0.01). Moreover, pigs fed LCP diets excreted 30% less N to the environment than pigs fed HCP diets (P &amp;lt; 0.001). When LCP diets are complemented with the use of IPF technique, the N excreted can be reduced 18% more than in CON system (P &amp;lt; 0.001). Our results indicate that LCP diets and IPF are feasible to improve the nitrogen utilization of pigs raised under tropical conditions.

PSIV-8 Effect of selenium and superoxide dismutase supplementation on heat stressed pigs

Abstract Heat stress (HS) compromises efficient production of pigs, in part by increasing oxidative stress and inflammation. Therefore the aim of this experiment was to investigate if supplementation of the anti-oxidants selenium or superoxide dismutase (SOD) could ameliorate HS in the pig. Sixty-four female Large White x Landrace pigs (av. 27.75) were acclimated one of the following diets: control (standard grower diet), selenium (Se, + 0.3 ppm organic Se), recombinant SOD (rSOD, 50 IU/d) and Se plus rSOD (SS) for 14 days under thermoneutral conditions (TN, 200C). All rSOD was administered top dressed in liquid form. Pigs were then moved to climate rooms and housed under TN or heat-stress (8 h 350C, 16h 280C/d) for 3 days and blood, urine and tissue collected for analysis terminally on d3. All data was analysed using an ANOVA with Tukeys post-hoc tests. Heat stress increased respiration rate (RR), reduced blood pCO2 and HCO3-, which coupled with a lower base excess indicated that the pigs were experiencing respiratory alkalosis. Furthermore HS increased rectal and skin temperatures, and reduced thyroid hormone (T4) concentrations, however HSP 27 and 70 concentrations were not influenced. Heat stress increased plasma adiponectin and IL-1b, reduced SOD and TNF-a, while no changes in IL-6 and leptin were observed. The effects of the anti-oxidant diets were that Se and SS increased RR, however parameters of respiratory alkalosis were not negatively influenced. The Se diet reduced T4 independently of HS. No improvement in plasma SOD was observed with the rSOD diets, but rSOD reduced adiponectin in HS pigs and both rSOD and SS reduced IL-6 overall. In conclusion a reduction in inflammatory responses were observed with the antioxidants Se and rSOD, including during HS and therefore may be a useful addition to existing amelioration strategies to ameliorate seasonal heat stress in pigs.

Infrared thermography as a non-invasive method for the evaluation of heat stress in pigs kept in pens free of cages in the maternity

Infrared thermography is a non-invasive method of body surface temperature analysis in pigs. This study aimed to evaluate the body surface temperature of sows and piglets kept in individual pens free of cages with or without cooling system with the use of infrared thermography. The study was conducted during the summer and autumn in Pirassununga, Brazil. Twenty-six sows during lactating phase and 281 piglets until 21 days-old were evaluated in two treatments: cooled pens with fans and water sprinklers on the roof and non-cooled pens. Both areas had ceramic roof tiles. Thermographic images were collected at intervals of seven days in the morning and afternoon in sows and randomly in five piglets per litter, and salivary cortisol were collected only on sows. The thermographic images were analyzed using the software IRSoft Version 3.6 Testo. Every three days respiratory rate and rectal temperatures were collected from sows and five piglets per litter. It was included fixed effect of treatment, period of the day, seasons and their interactions, besides the correlations of Pearson. In summer and autumn, the hottest surface area of sows was the mammary gland and the coldest the vaginal. For the piglets, the hottest area in the summer was the head and the coldest the snout. Summer presented the highest surface temperatures of the sugarcane bagasse bed, concrete floor and roof. No correlations were found between air temperature of and facilities. The respiratory rate presented moderate correlation with the back and with the snout of the sows. Rectal temperatures were higher in summer and in the afternoon, but it was similar between treatments. Although the cooling system had reduced the air temperature of the pens free of cage, it was not enough to reduce body superficial temperatures of the sows and piglets during lactating phase. Nevertheless, the use of infrared thermography allows to identify the hottest and coldest surface body areas of pigs and can be a tool to assess pig facilities and animal welfare.

313 Selection to mitigate heat stress in pigs.

313 Selection to mitigate heat stress in pigs.

ESTIMATION OF RESPIRATORY FREQUENCY AND RECTAL TEMPERATURE ON PIGS IN HEAT STRESS BY FUZZY LOGIC

ABSTRACT Physiological parameters such as respiratory frequency and rectal temperature stand out as indicators for heat stress in pigs, however, requiring time and labor for measurements. The possibility of using infrared thermography associated with prediction systems of these physiological variables can help in decision making, allowing greater welfare and productivity of the animals. With this objective, an experiment was carried out with growing pigs submitted to acute and chronic heat stress, working with a thermoneutrality temperature (22° C) and heat stress (34° C). The results were used for the development of a fuzzy model using as input variables: air dry bulb temperature (°C), average surface temperature (°C) and, as output variables: respiratory frequency (movements/minute) and rectal temperature (°C). The method of inference used was the one of Mamdani having been elaborated six rules and the defuzzification technique used was the one of the Center of Gravity. In the obtained results on simulation model when compared with experimental data was evidenced satisfactory efficiency in respiratory frequency determination and the rectal temperature, in which the R2 values calculated were respectively 0.997 and 0.951 for acute stress and 0.993 and 0.964 for chronic heat stress.

Adipose tissue-specific responses reveal an important role of lipogenesis during heat stress adaptation in pigs.

Elevated ambient temperature causes heat stress in pigs, resulting in reduced animal performance. To better understand tissue responses to heat stress in pigs, we conducted a study in which pigs were subjected to four treatments: acute (24 h) heat stress (AHS) at 35 °C ± 1 ambient temperature, chronic (7 d) heat stress at 35 °C ± 1 (HS) or normal ambient temperature (20 °C± 1) for 7 d with ad-libitum feeding (Con) or with pair-feeding to the feed intake (FI) of the HS pigs (PF). Heat stress decreased FI by approximately 36% and 64% in HS and AHS treatments respectively, compared with Con (P < 0.01). Concentration of free fatty acids (FFA) was elevated in AHS compared to HS (P = 0.031). Serum insulin concentration was lower in PF than Con (P = 0.045). Blood urea nitrogen (BUN) concentration was elevated in HS compared with Con and PF (P = 0.008), but lower (P < 0.021) in AHS compared to HS. In the subcutaneous adipose tissue, the mRNA and protein abundance of PCK1 were higher (P < 0.05) in the HS treatment than Con and PF, and also higher (P < 0.05) in HS than AHS. However, there was no difference in GK mRNA between Con, PF, and HS, although its expression was lower (P = 0.003) in AHS vs. HS. Protein abundance of the ER stress marker, CCAT/enhancer-binding homologous protein (CHOP), was higher in PF than Con (P < 0.05), and higher (P = 0.033) in HS than AHS in subcutaneous fat. In mesenteric fat, PCK1 mRNA was higher (P < 0.001) in the HS than Con and PF treatments. Additionally, expression of PCK1 was lower (P = 0.039) in AHS vs. HS. Expression of PCK1 was downregulated (P < 0.05) in the liver of PF pigs compared to other treatments, but most other genes measured were not affected by treatment in the liver and muscle tissues. These results confirm that heat stress induces a robust adipose tissue response in favor of increased lipid storage. This indicates that adipose tissue might play an important role in heat stress adaptation.

Characterizing the acute heat stress response in gilts: I. Thermoregulatory and production variables.

Identifying traits associated with susceptibility or tolerance to heat stress (HS) is a prerequisite for developing strategies to improve efficient pork production during the summer months. Study objectives were to determine the relationship between the thermoregulatory and production responses to acute HS in pigs. Prepubertal gilts (n = 235; 77.9 ± 1.2 kg BW) were exposed to a thermoneutral (TN) period (P1, 24 h; 21.9 ± 0.5 °C, 62 ± 13% RH; fed ad libitum) followed immediately by a subsequent acute HS period (P2, 24 h; 29.7 ± 1.3 °C, 49 ± 8% RH; fed ad libitum). Rectal temperature (TR), skin temperature (TS), and respiration rate (RR) were monitored and BW and feed intake (FI) were determined. All pigs had increased TR, TS, and RR (0.80 °C, 5.65 °C, and 61.2 bpm, respectively; P < 0.01) and decreased FI and BW (29% and 1.10 kg, respectively; P < 0.01) during P2 compared to P1. Interestingly, body temperature indices did not explain variation in FI during P2 (R2 ≤ 0.02). Further, the percent change in BW during P2 was only marginally explained by each body temperature index (R2 ≤ 0.06) or percent change in FI (R2 = 0.14). During HS, TR was strongly correlated with P1 TR (r = 0.72, P < 0.01), indicating a pig's body temperature during TN conditions predicts the severity of hyperthermia during HS. Additionally, the change in TR (ΔTR, HS TR - TN TR) was larger in pigs retrospectively classified as susceptible (SUS) as compared to tolerant (TOL) pigs (1.05 vs. 0.51 °C, respectively; P < 0.01). In summary, thermoregulatory responses and production variables during acute HS are only marginally related. Further, changes in BW and FI were unexpectedly poorly correlated during acute HS (r = 0.34; P < 0.01). Collectively, suboptimal growth is largely independent on the thermoregulatory response and hypophagia during acute HS. Consequently, incorporating solely body temperature indices into a genetic index is likely insufficient for substantial progress in selecting HS tolerant pigs.

Fermentation products as feed additives mitigate some ill-effects of heat stress in pigs.

Heat stress (HS) may result in economic losses to pig producers across the USA and worldwide. Despite significant advancements in management practices, HS continues to be a challenge. In this study, an in-feed antibiotic (carbadox, CBX) and antibiotic alternatives ( [XPC], and [SGX] fermentation products) were evaluated in a standard pig starter diet as mitigations against the negative effects of HS in pigs. A total of 100 gilts were obtained at weaning (6.87 ± 0.82 kg BW, 19.36 ± 0.72 d of age) and randomly assigned to dietary treatments (2 rooms/treatment, 2 pens/room, 6 to 7 pigs/pen). After 4 wk of dietary acclimation, half of the pigs in each dietary group (1 room/dietary treatment) were exposed to repeated heat stress conditions (RHS; daily cycles of 19 h at 25°C and 5 h at 40°C, repeated for 9 d), and the remaining pigs were housed at constant thermal neutral temperature (25°C, [NHS]). Pigs subjected to RHS had elevated skin surface temperature ( < 0.05; average 41.7°C) and respiration rate ( < 0.05; 199 breaths per minute (bpm) during HS, and overall reduced ( < 0.05) BW, ADG, ADFI, and G:F regardless of dietary treatment. Independent of diet, RHS pigs had significantly shorter ( < 0.05) jejunum villi on d 3 and d 9 compared to NHS pigs. Heat stress resulted in decreased villus height to crypt depth ratio (V:C) in pigs fed with control diet with no added feed additive (NON) and CBX diets at d 3, whereas the pigs fed diets containing XPC or SGX showed no decrease. Transcriptional expression of genes involved in cellular stress (, , , ), tight junction integrity (, , ), and immune response (, , and ) were measured in the ileum mucosa. Pigs in all dietary treatments subjected to RHS had significantly higher ( < 0.05) transcript levels of and , and an upward trend ( < 0.07) of mRNA expression. RHS pigs had higher ( < 0.05) transcript levels of and in NON diet, in XPC and CBX diets, and in SGX diet compared to the respective diet-matched pigs in the NHS conditions. Neither RHS nor diet affected peripheral natural killer () cell numbers or NK cell lytic activity. In conclusion, pigs subjected to RHS had decreased performance, and supplementation with fermentation products in the feed (XPC and SGX) protected pigs from injury to the jejunum mucosa.