Physiological mechanisms through which heat stress compromises reproduction in pigs

Heat/Cold Stress and Methods to Mitigate Its Detrimental Impact on Pork and Poultry Meat: A Review

This paper aims to provide an updated review and current understanding of the impact of extreme temperatures-focusing on heat stress (HS)-on the quality of pork and poultry meat, particularly amidst an unprecedented global rise in environmental temperatures. Acute or chronic HS can lead to the development of pale, soft, and exudative (PSE) meat during short transportation or of dark, firm, and dry (DFD) meat associated with long transportation and seasonal changes in pork and poultry meat. While HS is more likely to result in PSE meat, cold stress (CS) is more commonly linked to the development of DFD meat. Methods aimed at mitigating the effects of HS include showering (water sprinkling/misting) during transport, as well as control and adequate ventilation rates in the truck, which not only improve animal welfare but also reduce mortality and the incidence of PSE meat. To mitigate CS, bedding on trailers and closing the tracks' curtains (insulation) are viable strategies. Ongoing efforts to minimize meat quality deterioration due to HS or CS must prioritize the welfare of the livestock and focus on the scaleup of laboratory testing to commercial applications.

The contribution of biological sex to heat stress-mediated outcomes in growing pigs

Heat stress (HS) negatively impacts a variety of production parameters in growing pigs; however, the impact of biological sex on the HS response is largely unknown. To address this, 48 crossbred barrows and gilts (36.8 ± 3.7 kg BW) were individually housed and assigned to one of three constant environmental conditions: (1) thermoneutral (TN) (20.8 ± 1.6 °C; 62.0 ± 4.7% relative humidity; n = 8/sex), (2) HS (39.4 ± 0.6 °C; 33.7 ± 6.3% relative humidity) for 1 d (HS1; n = 8/sex), or (3) or for 7 d (HS7; n = 8/sex). As expected, HS increased rectal temperature (Tr) following 1 d of HS (1.0 °C; P < 0.0001) and 7 d of HS (0.9 °C; P < 0.0001). By 7 d, heat-stressed gilts were cooler than barrows (0.4 °C; P = 0.016), despite identical heating conditions. There was a main effect of sex such that barrows had higher Tr than gilts (P = 0.031). Heat-stressed pigs on d 1 had marked reductions in feed intake and BW compared to TN (P < 0.0001). One day of HS resulted in negative gain to feed (G:F) in barrows and gilts and was reduced compared to TN (P < 0.0001). Notably, following 1 d of HS, the variability of G:F was greater in gilts than in barrows. Between 1 and 7 d of HS, G:F improved in barrows and gilts and were similar to TN pigs, even though HS barrows had higher Tr than gilts over this period. Heat stress for 1 and 7 d reduced empty gastrointestinal tract weight compared to TN (P < 0.0001). Interestingly, HS7 gilts had decreased gastrointestinal tract weight compared to HS1 gilts (2.43 vs 2.72 kg; P = 0.03), whereas it was similar between HS1 and HS7 barrows. Lastly, a greater proportion of gastrointestinal contents was in the stomach of HS1 pigs compared to TN and HS7 (P < 0.05), which is suggestive of decreased gastric emptying. Overall, HS barrows maintained an elevated Tr compared to HS gilts through the duration of the experiment but also maintained similar growth and production metrics compared to gilts, despite this higher temperature.

Mogroside V alleviates the heat stress-induced disruption of the porcine oocyte in vitro maturation

Heat stress (HS) is a stressor that negatively affect female reproduction. Specially, oocytes are very sensitive to HS. It has been demonstrated that some active compounds can protect oocyte from HS. We previously found that Mogroside V (MV), extracted from Siraitia grosvenorii (Luo Han Guo), can protect oocyte from many kinds of stresses. However, how MV alleviates HS-induced disruption of oocyte maturation remains unknown. In this study, we treated the HS-induced porcine oocytes with MV to examine their maturation and quality. Our findings demonstrate that MV can effectively alleviate HS-induced porcine oocyte abnormal cumulus cell expansion, decrease of first polar body extrusion rate, spindle assembly and chromosome separation abnormalities, indicating MV attenuates oocyte mature defects. We further observed that MV can effectively alleviate HS-induced cortical granule distribution abnormality and decrease of blastocyst formation rate after parthenogenesis activation. In addition, MV treatment reversed mitochondrial dysfunction and lipid droplet content decrease, reduced reactive oxygen species levels, early apoptosis and DNA damage in porcine oocytes after HS. Collectively, this study suggests that MV can effectively protect porcine oocytes from HS.

Effects of evaporative cooling systems on the performance of lactating sows in a tropical climate

This study evaluated litter performance, behavioral and physiological parameters, and milk characteristics of sows submitted to different thermal environments. Fifty sows were distributed in a completely randomized design with two treatments: an evaporative cooling system (ECS) and a conventional system (CS). Sow and its litter were characterized as an experimental unit. The animals were weighed at equalization and weaning. Feed intake, milk production, and bromatological characteristics of milk were measured; the sows respiratory rate, rectal, and surface temperature were monitored. Litter uniformity was determined at equalization and weaning. Behaviors of the sows and litters were monitored for 24 h on the 7th and 15th day of lactation. Temperature and relative humidity inside the maternity was 25.00 to 28.00 °C and 26.00 to 32.55 °C and 30.00 to 70.00% and 70.00 to 88.00%, respectively, considering ECS and CS. Nutritional quality of the milk remained stable during lactation in both systems evaluated. ECS improved the average weight of the piglets, weaning weight, and daily milk production by 0.038, 0.699, and 2.31 kg/day, respectively. Sows housed in the ECS had a reduction in physiological parameters and, increase in inactive alert behavior (1.79 percentage points) and breastfeeding behavior. Piglets showed a decrease of 2.43% in the range of feedings at night and 0.15% during the day. ECS provided better comfort to the sows at the expense of the CS and, consequently, better litter performance.

Heat stress alters the ovarian proteome in prepubertal gilts

Heat stress (HS) occurs when exogenous and metabolic heat accumulation exceeds heat dissipation; a thermal imbalance that compromises female reproduction. This study investigated the hypothesis that HS alters the ovarian proteome and negatively impacts proteins engaged with insulin signaling, inflammation, and ovarian function. Prepubertal gilts (n = 19) were assigned to one of three environmental groups: thermal neutral with ad libitum feed intake (TN; n = 6), thermal neutral pair-fed (PF; n = 6), or HS (n = 7). For 7 d, HS gilts were exposed to 12-h cyclic temperatures of 35.0 ± 0.2 °C and 32.2 ± 0.1 °C, while TN and PF gilts were housed at 21.0 ± 0.1 °C. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed on ovarian protein homogenates. Relative to TN gilts, 178 proteins were altered (P ≤ 0.05, log2foldchange ≥ 1) by HS, with 76 increased and 102 decreased. STRING gene ontology classified and identified 45 biological processes including those associated with chaperone protein refolding, cytoplasmic translational initiation, and immune activation; with a protein-protein interaction web network of 158 nodes and 563 edges connected based on protein function (FDR ≤ 0.05). Relative to PF, HS altered 330 proteins (P ≤ 0.05, log2foldchange ≥ 1), with 151 increased and 179 decreased. Fifty-seven biological pathways associated with protein function and assembly, RNA processing, and metabolic processes were identified, with a protein-protein interaction network of 303 nodes and 1,606 edges. Comparing HS with both the TN and PF treatments, 72 ovarian proteins were consistently altered by HS with 68 nodes and 104 edges, with biological pathways associated with translation and gene expression. This indicates that HS alters the ovarian proteome and multiple biological pathways and systems in prepubertal gilts; changes that potentially contribute to female infertility.

Phenotypic, endocrinological, and metabolic effects of zearalenone exposure and additive effect of heat stress in prepubertal female pigs

Independently, both heat stress (HS) and zearalenone (ZEN) compromise female reproduction, thus the hypothesis that ZEN would affect phenotypic, endocrine, and metabolic parameters in pigs with a synergistic and/or additive impact of HS was investigated. Prepubertal gilts (n = 6-7) were assigned to: thermoneutral (TN) vehicle control (TC; n = 6); TN ZEN (40 μg/kg; TZ; n = 6); pair-fed (PF; n = 6) vehicle control (PC; n = 6); PF ZEN (40 μg/kg; PZ; n = 6); HS vehicle control (HC; n = 7); and HS ZEN (40 μg/kg; HZ; n = 7) and experienced either constant 21.0 ± 0.10 °C (TN and PF) or 35.0 ± 0.2 °C (12 h) and 32.2 ± 0.1 °C (12 h) to induce HS for 7 d. Elevated rectal temperature (P < 0.01) and respiration rate (P < 0.01) confirmed induction of HS. Rectal temperature was decreased (P = 0.03) by ZEN. Heat stress decreased (P < 0.01) feed intake, body weight, and average daily gain, with absence of a ZEN effect (P > 0.22). White blood cells, hematocrit, and lymphocytes decreased (P < 0.04) with HS. Prolactin increased (P < 0.01) in PC and PZ and increased in HZ females (P < 0.01). 17β-estradiol reduced (P < 0.01) in HC and increased in TZ females (P = 0.03). Serum metabolites were altered by both HS and ZEN. Neither HS nor ZEN impacted ovary weight, uterus weight, teat size or vulva area in TN and PF treatments, although ZEN increased vulva area (P = 0.02) in HS females. Thus, ZEN and HS, independently and additively, altered blood composition, impacted the serum endocrine and metabolic profile and increased vulva size in prepubertal females, potentially contributing to infertility.

Chromium Methionine and Ractopamine Supplementation in Summer Diets for Grower-Finisher Pigs Reared under Heat Stress

This study aimed to determine the effects of the dietary supplementation of chromium methionine (CrMet) and ractopamine (RAC) on pigs in the growing-finishing stage under heat stress. The parameters evaluated included productive behavior, blood components, carcass characteristics, organ weight, and meat quality. This study was conducted during the summer season in Sonora, Mexico. The treatments included: (1) control diet (CON), a base diet (BD) formulated to satisfy the nutritional requirements of pigs; (2) RAC, BD plus 10 ppm RAC supplemented during the last 34 days of the study; (3) CrMet-S, BD supplemented with 0.8 ppm of Cr from CrMet during the last 34 days; and (4) CrMet-L, BD supplemented with 0.8 ppm of Cr from CrMet for an 81 d period. RAC supplementation improved the productive behavior and main carcass characteristics of the pigs compared with CON. However, RAC and CrMet supplementation during the last 34 days showed similar results in terms of weight gain, carcass quality, blood components, organ weight, and meat quality. The addition of CrMet-S had a moderate (although not significant) increase in productive performance and carcass weight. These findings are encouraging, as they suggest that CrMet may be a potential alternative for growth promotion. However, more research is needed.

Cardiac performance and heart gene network provide dynamic responses of bay scallop Argopecten irradians irradians exposure to marine heatwaves

The increased frequency of marine heat waves (MHWs) caused by global climate change is predicted to threaten the survival of economic bivalves, therefore having severely adverse effects on local ecological communities and aquaculture production. However, the study of scallops facing MHWs is still scarce, particularly in the scallop Argopecten irradians irradians, which has a significant share of "blue foods" in northern China. In the present study, bay scallop heart was selected to detect its cardiac performance, oxidative impairment and dynamic molecular responses, accompanied by assessing survival variations of individuals in the simulated scenario of MWHs (32 °C) with different time points (0 h, 6 h, 12 h, 24 h, 3 d, 6 d and 10 d). Notably, cardiac indices heart rate (HR), heart amplitude (HA), rate-amplitude product (RAP) and antioxidant enzyme activities superoxide dismutase (SOD) and catalase (CAT) all peaked at 24 h but sharply dropped on 3 d, coinciding with mortality. Transcriptome analysis revealed that the heart actively defended against heat stress at the acute stage (<24 h) via energy supply, misfolded proteins correction and enhanced signal transduction, whereas regulation of the defense response and apoptotic process combined with twice transcription initiation were the dominant responses at the chronic stage (3-10 d). In particular, HSP70 (heat shock protein 70), HSP90 and CALR (calreticulin) in the endoplasmic reticulum were identified as the hub genes (top 5 %) in the HR-associated module via WGCNA (weighted gene co-expression network analysis) trait-module analysis, followed by characterization of their family members and diverse expression patterns under heat exposure. Furthermore, RNAi-mediated knockdown of CALR expression (after 24 h) significantly weakened the thermotolerance of scallops, as evidenced by a drop of 1.31 °C in ABT (Arrhenius break temperature) between the siRNA-injected group and the control group. Our findings elucidated the dynamic molecular responses at the transcriptome level and verified the cardiac functions of CALR in bay scallops confronted with stimulated MHWs.

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

BACKGROUND

Although thermal indices have been proposed for swine, none to our knowledge differentiate by reproductive stage or predict thermal comfort using behavioral and physiological data. The study objective was to develop a behavior and physiology-based decision support tool to predict thermal comfort and stress in multiparous (3.28 ± 0.81) non-pregnant (n = 11), mid-gestation (n = 13), and late-gestation (n = 12) sows.

RESULTS

Regression analyses were performed using PROC MIXED in SAS 9.4 to determine the optimal environmental indicator [dry bulb temperature (T_DB) and dew point] of heat stress (HS) in non-pregnant, mid-gestation, and late-gestation sows with respiration rate (RR) and body temperature (T_B) successively used as the dependent variable in a cubic function. A linear relationship was observed for skin temperature (T_S) indicating that T_DB rather than the sow HS response impacted T_S and so T_S was excluded from further analyses. Reproductive stage was significant for all analyses (P < 0.05). Heat stress thresholds for each reproductive stage were calculated using the inflections points of RR for mild HS and T_B for moderate and severe HS. Mild HS inflection points differed for non-pregnant, mid-gestation, and late gestation sows and occurred at 25.5, 25.1, and 24.0 °C, respectively. Moderate HS inflection points differed for non-pregnant, mid-gestation, and late gestation sows and occurred at 28.1, 27.8, and 25.5 °C, respectively. Severe HS inflection points were similar for non-pregnant and mid-gestation sows (32.9 °C) but differed for late-gestation sows (30.8 °C). These data were integrated with previously collected behavioral thermal preference data to estimate the T_DB that non-pregnant, mid-gestation, and late-gestation sows found to be cool (T_DB < T_DB preference range), comfortable (T_DB = T_DB preference range), and warm (T_DB preference range < T_DB < mild HS).

CONCLUSIONS

The results of this study provide valuable information about thermal comfort and thermal stress thresholds in sows at three reproductive stages. The development of a behavior and physiology-based decision support tool to predict thermal comfort and stress in non-pregnant, mid-gestation, and late-gestation sows is expected to provide swine producers with a more accurate means of managing sow environments.

Hypothalamic-Pituitary-Adrenal Hormones Impair Pig Fertilization and Preimplantation Embryo Development via Inducing Oviductal Epithelial Apoptosis: An In Vitro Study

Previous studies show that stressful events after ovulation in sows significantly impaired the embryo cleavage with a significant elevation of blood cortisol. However, the effects of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and cortisol on fertilization and embryo development remain to be specified, and whether they damage pig embryos directly or indirectly is unclear. This study demonstrated that embryo development was unaffected when pig parthenotes were cultured with different concentrations of CRH/ACTH/cortisol. However, embryo development was significantly impaired when the embryos were cocultured with pig oviductal epithelial cells (OECs) in the presence of CRH/cortisol or cultured in medium that was conditioned with CRH/cortisol-pretreated OECs (CRH/cortisol-CM). Fertilization in CRH/cortisol-CM significantly increased the rates of polyspermy. CRH and cortisol induced apoptosis of OECs through FAS and TNFα signaling. The apoptotic OECs produced less growth factors but more FASL and TNFα, which induced apoptosis in embryos. Pig embryos were not sensitive to CRH because they expressed no CRH receptor but the CRH-binding protein, and they were tolerant to cortisol because they expressed more 11-beta hydroxysteroid dehydrogenase 2 (HSD11B2) than HSD11B1. When used at a stress-induced physiological concentration, while culture with either CRH or cortisol alone showed no effect, culture with both significantly increased apoptosis in OECs. In conclusion, CRH and cortisol impair pig fertilization and preimplantation embryo development indirectly by inducing OEC apoptosis via the activation of the FAS and TNFα systems. ACTH did not show any detrimental effect on pig embryos, nor OECs.

Heat wave exposure impairs reproductive performance in primiparous sows and gilts in a tropical environment

We studied the effects of heat waves (HW), defined as three consecutive days with an ambient temperature ≥ 25 °C and a temperature and humidity index (THI) > 74, on the reproductive performance of sows. Meteorological data were obtained from the National Institute of Meteorology and reproductive data from a commercial farm with 51,578 inseminations and 49,103 pregnancies from September 5, 2013, to July 12, 2019. Sows were divided into the following groups according to the parity order: group 1 (sows that did not experience HW on the day of insemination) and group 2 (sows exposed to HW on the day of insemination). The percentage of days that pregnant sows were exposed to HW was calculated as 0 to 25% (1), 26 to 50% (2), 51 to 75% (3), and > 75% (4). Out of a total of 2137 days, there were 160 HW and more than 10 HW per month, except in May, June, and July. Gilts in group 2 showed a decrease in the percentage of gestation (98.21% and 98.78%, respectively, P = 0.0267) and the percentage of births compared with those in group 1 (95.53% and 96.61, respectively, P = 0.0065). Primiparous sows in group 2 had a higher percentage of abortions than gilts in group 1 (3.20% and 2.42%, respectively; P = 0.0334). Sows exposed to more than 50% HW during gestation produced more mummified piglets than sows exposed to less than 50% HW. The number of stillborn piglets was higher in sows exposed to temperatures above 25% HW during gestation. The occurrence of heat waves in gilts and primiparous sows impairs reproductive performance.

Heat stress in pigs and broilers: role of gut dysbiosis in the impairment of the gut-liver axis and restoration of these effects by probiotics, prebiotics and synbiotics

Heat stress is one of the most challenging stressors for animal production due to high economic losses resulting from impaired animal’s productivity, health and welfare. Despite the fact that all farm animal species are susceptible to heat stress, birds and pigs are particularly sensitive to heat stress due to either lacking or non-functional sweat glands. Convincing evidence in the literature exists that gut dysbiosis, a term used to describe a perturbation of commensal gut microbiota, develops in broilers and pigs under heat stress. Owing to the protective role of commensal bacteria for the gut barrier, gut dysbiosis causes a disruption of the gut barrier leading to endotoxemia, which contributes to the typical characteristics of heat stressed broilers and growing and growing-finishing pigs, such as reduced feed intake, decreased growth and reduced lean carcass weight. A substantial number of studies have shown that feeding of probiotics, prebiotics and synbiotics is an efficacious strategy to protect broilers from heat stress-induced gut barrier disruption through altering the gut microbiota and promoting all decisive structural, biochemical, and immunological elements of the intestinal barrier. In most of the available studies in heat stressed broilers, the alterations of gut microbiota and improvements of gut barrier function induced by feeding of either probiotics, prebiotics or synbiotics were accompanied by an improved productivity, health and/or welfare when compared to non-supplemented broilers exposed to heat stress. These findings indicate that the restoration of gut homeostasis and function is a key target for dietary interventions aiming to provide at least partial protection of broilers from the detrimental impact of heat stress conditions. Despite the fact that the number of studies dealing with the same feeding strategy in heat stressed pigs is limited, the available few studies suggest that feeding of probiotics might also be a suitable approach to enhance productivity, health and welfare in pigs kept under heat stress conditions. 

‘Can They Take the Heat?’—The Egyptian Climate and Its Effects on Livestock

Egypt already has conditions in summer that cause heat stress for livestock, and predicted climate changes suggest that these will be exacerbated over the course of this century. As well, extreme climatic events make the mitigation of climate change difficult but important to understand. Apart from neonates, farm animals have upper critical temperatures in the region of 25–30 °C, whereas temperatures in summer regularly exceed 40 °C for prolonged periods. The temperature and humidity data were collected half hourly to calculate Temperature Humidity Indices and demonstrate that Egyptian livestock at two centers of livestock production in the country would experience heat stress in summer for extended periods of each day. The impact of rising temperatures on livestock in Egypt was reviewed, where extensive resources to mitigate the impact are not often available. It was found that, although there are some prospects to mitigate some heat stress, by using agroforestry systems of production for example, these are unlikely to have a major impact, and reduced food security may ensue over the course of this century.

Porcine endometrial heat shock proteins are differentially influenced by pregnancy status, heat stress, and altrenogest supplementation during the peri-implantation period

Heat stress (HS) deleteriously affects multiple components of porcine reproduction and is causal to seasonal infertility. Environment-induced hyperthermia causes a HS response (HSR) typically characterized by increased abundance of intracellular heat shock proteins (HSP). Gilts exposed to HS during the peri-implantation period have compromised embryo survival, however if (or how) HS disrupts the porcine endometrium is not understood. Study objectives were to evaluate the endometrial HSP abundance in response to HS during this period and assess the effect of oral progestin (altrenogest; ALT) supplementation. Postpubertal gilts (n = 42) were artificially inseminated during behavioral estrus (n = 28) or were kept cyclic (n = 14), and randomly assigned to thermal neutral (TN; 21 ± 1 °C) or diurnal HS (35 ± 1 °C for 12 h/31.6 ± 1 °C for 12 h) conditions from day 3 to 12 postestrus (dpe). Seven of the inseminated gilts from each thermal treatment group received ALT (15 mg/d) during this period. Using quantitative PCR, transcript abundance of HSP family A (Hsp70) member 1A (HSPA1A, P = 0.001) and member 6 (HSPA6, P < 0.001), and HSP family B (small) member 8 (HSB8, P = 0.001) were increased while HSP family D (Hsp60) member 1 (HSPD1, P = 0.01) was decreased in the endometrium of pregnant gilts compared to the cyclic gilts. Protein abundance of HSPA1A decreased (P = 0.03) in pregnant gilt endometrium due to HS, while HSP family B (small) member 1 (HSPB1) increased (P = 0.01) due to HS. Oral ALT supplementation during HS reduced the transcript abundance of HSP90α family class B member 1 (HSP90AB1, P = 0.04); but HS increased HSP90AB1 (P = 0.001), HSPA1A (P = 0.02), and HSPA6 (P = 0.04) transcript abundance irrespective of ALT. ALT supplementation decreased HSP90α family class A member 1 (HSP90AA1, P = 0.001) protein abundance, irrespective of thermal environment, whereas ALT only decreased HSPA6 (P = 0.02) protein abundance in TN gilts. These results indicate a notable shift of HSP in the porcine endometrium during the peri-implantation period in response to pregnancy status and heat stress.

Impact of heat stress on prolactin-mediated ovarian JAK-STAT signaling in postpubertal gilts

Heat stress (HS) compromises almost every aspect of animal agriculture including reproduction. In pigs, this infecundity is referred to as seasonal infertility (SI), a phenotype including ovarian dysfunction. In multiple species, HS-induced hyperprolactinemia has been described; hence, our study objectives were to characterize and compare HS effects on circulating prolactin (PRL) and ovarian Janus kinase/signal transducer and activator of transcription (JAK-STAT) signaling during the follicular (FOL) or luteal (LUT) phases of the estrous cycle in postpubertal gilts. Gilts were estrus synchronized using altrenogest and environmental treatments began immediately after altrenogest withdrawal. For the FOL study: postpubertal gilts were allocated to constant thermoneutral (TN; n = 6; 20 ± 1.2 °C) or cyclical HS (n = 6; 25 to 32 ± 1.2 °C) conditions for 5 d. In the LUT study: postpubertal gilts were assigned to either TN (n = 7; 20 ± 2.6 °C) or cyclical HS (n = 7; 32 to 35 ± 2.6 °C) conditions from 2 to 12 days postestrus (dpe). Blood was collected by jugular venipuncture for PRL quantification on day 5 in the FOL and on day 0 and day 12 in the LUT gilts. Ovaries and corpora lutea (CL) were obtained from euthanized FOL and LUT gilts on day 5 and day 12, respectively. Western blotting was performed to quantify prolactin receptor (PRLR) and JAK/STAT pathway protein abundance. In the FOL phase, no difference (P = 0.20) in circulating PRL between thermal groups was observed. There was no effect (P ≥ 0.34) of HS on PRLR, signal transducer and activator of transcription 3 (STAT3), signal transducer and activator of transcription 5α (STAT5α), and phosphorylated signal transducer and activator of transcription α/β tyrosine 694/699 (pSTAT5α/β^Tyr694/699) abundance and Janus kinase 2 (JAK2), phosphorylated janus kinase 2 tyrosine 1007/1008 (pJAK2^Tyr1007/1008), STAT1, phosphorylated signal transducer and activator of transcription 1 tyrosine 701 (pSTAT1^Tyr701), phosphorylated signal transducer and activator of transcription 1 serine 727 (pSTAT1^Ser727), and phosphorylated signal transducer and activator of transcription 3 tyrosine 705 (pSTAT3^Tyr705) were undetectable in FOL gilt ovaries. Ovarian pSTAT5α/β^Tyr694/699 abundance tended to moderately increase (4%; P = 0.07) in FOL gilts by HS. In the LUT phase, circulating PRL increased progressively from 2 to 12 dpe, but no thermal treatment-induced difference (P = 0.37) was noted. There was no effect (P ≥ 0.16) of HS on CL abundance of PRLR, pJAK2^Tyr1007/1008, JAK2, STAT1, pSTAT1^Tyr701, pSTAT1^Ser727, pSTAT3^Tyr705, STAT5α, or pSTAT5α/β^Tyr694/699. In LUT phase, CL STAT3 abundance was increased (11%; P < 0.03) by HS. There was no impact of HS (P ≥ 0.76) on levels of pJAK2^Tyr1007/1008 and pSTAT5α/β^Tyr694/699 in LUT gilts; however, the CL pSTAT3^Tyr705:STAT3 ratio tended to be decreased (P = 0.10) due to HS. These results indicate an HS-induced estrous cycle-stage-dependent effect on the ovarian JAK/STAT pathway, establishing a potential role for this signaling pathway as a potential contributor to SI.

Insights into molecular pathways and fatty acid membrane composition during the temperature stress response in the murine C2C12 cell model

Daily and seasonal temperature fluctuations are inevitable due to climate change, which highlights the importance of studying the detrimental effects of temperature fluctuations on the health, productivity, and product quality of farm animals. Muscle membrane composition and the molecular signals are vital for muscle cell differentiation and muscle growth, but their response to temperature stress is not well characterized. Temperature changes can lead to modification of membrane components of the cell, which may affect its surroundings and intracellular signaling pathways. Using C2C12 myoblast cells as a model of skeletal muscle development, this study was designed to investigate the effects of high temperature (39 °C and 41 °C) and low temperature (35 °C) on molecular pathways in the cells as well as the cell membrane fatty acid composition. Our results show that several genes were differentially expressed in C2C12 cells cultured under heat or cold stress, and these genes were enriched important KEGG pathways including PI3K-Akt signaling pathway, lysosome and HIF- signaling pathway, Wnt signaling pathway and AMPK signaling pathway. Our analysis further reveals that several membrane transporters and genes involved in lipid metabolism and fatty acid elongation were also differentially expressed in C2C12 cells cultured under high or low temperature. Additionally, temperature stress shifts the fatty acid composition in the cell membranes, including the proportion of saturated, monounsaturated and polyunsaturated fatty acids. This study revealed an interference between fatty acid composition in the membranes and changing molecular pathways including lipid metabolism and fatty acids elongation mediated under thermal stress. These findings will reinforce a better understanding of the adaptive mechanisms in skeletal muscle under temperature stress.

Climate Change and Livestock Production: A Literature Review

Globally, the climate is changing, and this has implications for livestock. Climate affects livestock growth rates, milk and egg production, reproductive performance, morbidity, and mortality, along with feed supply. Simultaneously, livestock is a climate change driver, generating 14.5% of total anthropogenic Greenhouse Gas (GHG) emissions. Herein, we review the literature addressing climate change and livestock, covering impacts, emissions, adaptation possibilities, and mitigation strategies. While the existing literature principally focuses on ruminants, we extended the scope to include non-ruminants. We found that livestock are affected by climate change and do enhance climate change through emissions but that there are adaptation and mitigation actions that can limit the effects of climate change. We also suggest some research directions and especially find the need for work in developing country settings. In the context of climate change, adaptation measures are pivotal to sustaining the growing demand for livestock products, but often their relevance depends on local conditions. Furthermore, mitigation is key to limiting the future extent of climate change and there are a number of possible strategies.

Characterizing the effect of incrementally increasing dry bulb temperature on linear and nonlinear measures of heart rate variability in nonpregnant, mid-gestation, and late-gestation sows

Characterizing the sow physiological response to an increased heat load is essential for effective heat stress mitigation. The study objective was to characterize the effects of a 400-min heating episode on sow heart rate variability (HRV) at different reproductive stages. HRV is a commonly used noninvasive proxy measure of autonomic function. Twenty-seven sows were enrolled in the study according to their gestation stage at time of selection: 1) nonpregnant (NP; n = 7), 2) mid-gestation (MID; 57.3 ± 11.8 d gestation; n = 11), and 3) late-gestation (LATE; 98.8 ± 4.9 d gestation; n = 8). The HRV data utilized in the study were collected from each pig as the dry bulb temperature in the room increased incrementally from 19.84 ± 2.15 °C to 35.54 ± 0.43 °C (range: 17.1-37.5 °C) over a 400-min period. After data collection, one 5-min set of continuous heart rate data were identified per pig for each of nine temperature intervals (19-20.99, 21-22.99, 23-24.99, 25-26.99, 27-28.99, 29-30.99, 31-32.99, 33-34.99, and 35-36.99 °C). Mean inter-beat interval length (RR), standard deviation of r-r intervals (SDNN), root mean square of successive differences (RMSSD), high frequency spectral power (HF), sample entropy (SampEn), short-term detrended fluctuation analysis (DFAα1), and three measures (%REC, DET, LMEAN) derived from recurrence quantification analysis were calculated for each data set. All data were analyzed using the PROC GLIMMIX procedure in SAS 9.4. Overall, LATE sows exhibited lower RR than NP sows (P < 0.01). The standard deviation of r-r intervals and RMSSD differed between each group (P < 0.01), with LATE sows exhibiting the lowest SDNN and RMSSD and NP sows exhibiting the greatest SDNN and RMSSD. Late-gestation sows exhibited lower HF than both MID and NP sows (P < 0.0001), greater DFA values than NP sows (P = 0.05), and greater DET compared to MID sows (P = 0.001). Late-gestation also sows exhibited greater %REC and LMEAN compared to MID (P < 0.01) and NP sows (all P < 0.01). In conclusion, LATE sows exhibited indicators of greater autonomic stress throughout the heating period compared to MID and NP sows. However, temperature by treatment interactions were not detected as dry bulb increased. Future studies are needed to fully elucidate the effect of gestational stage and increasing dry bulb temperature on sow HRV.

Heat Stress-Mediated Activation of Immune-Inflammatory Pathways

Physiological changes in animals exposed to elevated ambient temperature are characterized by the redistribution of blood toward the periphery to dissipate heat, with a consequent decline in blood flow and oxygen and nutrient supply to splanchnic tissues. Metabolic adaptations and gut dysfunction lead to oxidative stress, translocation of lumen contents, and release of proinflammatory mediators, activating a systemic inflammatory response. This review discusses the activation and development of the inflammatory response in heat-stressed models.

Effects of cooling systems on physiological responses and intestinal microflora in early gestating sows exposed to high-temperature stress

This study was conducted to investigate the effect of cooling systems on reproductive performance, body temperature, blood metabolites, and the intestinal microbiome in early gestating sows exposed to high ambient temperature. In total, 39 pregnant sows (Landrace × Yorkshire; 2 parities) were randomly assigned to and maintained in the following three treatment groups (13 sows per group) over days 0 to 35 of pregnancy: (i) air cooling (AC; 26.87 ± 1.23°C), (ii) water-drip cooling (WC; 28.81 ± 0.91°C), and (iii) a lack of cooling with heat stress (HS; 30.72 ± 0.70°C). Backfat thickness was measured before and after HS. Feces were collected on day 0 and 35 d of the trial for microbiome analysis, whereas blood was taken at day 35 of pregnancy and analyzed. Reproductive performance and physiological responses were identified at day 35. Respiration rate along with rectal and skin temperatures were lower (p < 0.05) in the AC group than in the HS and WC groups. Serum blood urea nitrogen values were increased (p < 0.05) in the WC group compared with those measured in the AC and HS groups. Triiodothyronine was found at greater levels (p < 0.05) in the AC than in the HS group. Reproductive performance was not affected by the cooling systems. At the phylum level, fecal pathogenic Spirochaete and Euryarchaeota were found in higher numbers (p < 0.05) in all groups after HS. Similarly, at the genus level, the amount of Treponema was greater (p < 0.05) in all groups after HS. In conclusion, our results suggest that AC or WC can ameliorate or mitigate the adverse effects of HS on the physiological parameters of pregnant sows reared under high temperatures.

Effect of heat stress on growth and production performance of livestock and poultry: Mechanism to prevention

Heat stress is a widespread phenomenon in domestic animal feeding in tropical and sub-tropical areas that are subjected to a growing negative effect in livestock and poultry due to global warming. It leads to reduced food intake, retarded growth, intestinal disequilibrium, lower reproductive performance, immunity and endocrine disorders in livestock and poultry. Many studies show that the pathogenesis of heat stress is mainly related to oxidative stress, hormone secretion disorder, cytokine imbalance, cell apoptosis, cell autophagy, and abnormal cell function. Its mechanism refers to activation of mitogen-activated protein kinase (MAPK) signaling pathway and nuclear factor kappa B (NF-κB) signaling pathway, the fluctuation of tight junction protein and heat shock protein expression, and protein epigenetic modification. This manuscript reviews the mechanism of heat stress through an insight into the digestive, reproductive, immune, and endocrine system. Lastly, the progress in prevention and control techniques of heat stress has been summarized.

Rapamycin administration during an acute heat stress challenge in growing pigs

Study objectives were to determine the effects of rapamycin (Rapa) on biomarkers of metabolism and inflammation during acute heat stress (HS) in growing pigs. Crossbred barrows (n = 32; 63.5 ± 7.2 kg body weight [BW]) were blocked by initial BW and randomly assigned to 1 of 4 environmental-therapeutic treatments: 1) thermoneutral (TN) control (n = 8; TNCon), 2) TN and Rapa (n = 8; TNRapa), 3) HS control (n = 8; HSCon), or 4) HS and Rapa (n = 8; HSRapa). Following 6 d of acclimation to individual pens, pigs were enrolled in two experimental periods (P). During P1 (10 d), pigs were fed ad libitum and housed in TN conditions (21.3 ± 0.2°C). During P2 (24 h), HSCon and HSRapa pigs were exposed to constant HS (35.5 ± 0.4°C), while TNCon and TNRapa pigs remained in TN conditions. Rapamycin (0.15 mg/kg BW) was orally administered twice daily (0700 and 1800 hours) during both P1 and P2. HS increased rectal temperature and respiration rate compared to TN treatments (1.3°C and 87 breaths/min, respectively; P < 0.01). Feed intake (FI) markedly decreased in HS relative to TN treatments (64%; P < 0.01). Additionally, pigs exposed to HS lost BW (4 kg; P < 0.01), while TN pigs gained BW (0.7 kg; P < 0.01). Despite marked changes in phenotypic parameters caused by HS, circulating glucose and blood urea nitrogen did not differ among treatments (P > 0.10). However, the insulin:FI increased in HS relative to TN treatments (P = 0.04). Plasma nonesterified fatty acids (NEFA) increased in HS relative to TN treatments; although this difference was driven by increased NEFA in HSCon compared to TN and HSRapa pigs (P < 0.01). Overall, circulating white blood cells, lymphocytes, and monocytes decreased in HS compared to TN pigs (19%, 23%, and 33%, respectively; P ≤ 0.05). However, circulating neutrophils were similar across treatments (P > 0.31). The neutrophil-to-lymphocyte ratio (NLR) was increased in HS relative to TN pigs (P = 0.02); however, a tendency for reduced NLR was observed in HSRapa compared to HSCon pigs (21%; P = 0.06). Plasma C-reactive protein tended to differ across treatments (P = 0.06) and was increased in HSRapa relative to HSCon pigs (46%; P = 0.03). Circulating haptoglobin was similar between groups. In summary, pigs exposed to HS had altered phenotypic, metabolic, and leukocyte responses; however, Rapa administration had limited impact on outcomes measured herein.

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

Impact of manganese amino acid complex on tissue-specific trace mineral distribution and corpus luteum function in gilts

Functional corpora lutea (CL) are required for pregnancy establishment and gestational maintenance in swine, and CL function is susceptible to environmental influences. Manganese (Mn) could be critical in regulating CL function since it is a component of the antioxidant enzyme Mn superoxide dismutase (MnSOD) as well as enzymes involved in cholesterol and steroid hormone synthesis. We hypothesized that a more bioavailable dietary Mn source would increase Mn content in the CL thereby influencing luteal function during the mid-luteal phase of the estrous cycle. Postpubertal gilts (n = 32) were assigned to one of four gestation diets. The control diet (CON) met or exceeded National Research Council (2012) requirements and was formulated to contain 20 parts per million (ppm) of added Mn in the form of Mn sulfate. Three additional diets included 20 (treatment [TRT]1), 40 (TRT2), or 60 (TRT3) ppm of added Mn from a Mn-amino acid complex (Availa-Mn; Zinpro Corporation) instead of Mn sulfate. Dietary treatment began at estrus synchronization onset and continued through 12 days post estrus (dpe) of the ensuing estrous cycle. Blood samples were collected at estrus onset, which was assigned as 0 dpe, as well as 4, 8, and 12 dpe. Gilts were euthanized and tissues were collected at 12 dpe. Serum progesterone (P4) increased (P < 0.01) from 0 to 12 dpe but was unaffected by dietary treatment (P = 0.15) and there was no effect of the interaction between day and treatment (P = 0.85). Luteal Mn content increased (P ≤ 0.05) by 19%, 21%, and 24% in gilts fed TRT1, TRT2, and TRT3, respectively, compared to CON. Luteal P4 concentrations decreased (P = 0.03) 25%, 26%, and 32% in gilts fed TRT1, TRT2, and TRT3, respectively, compared to CON. Relative to CON gilts, CL calcium content decreased (P = 0.02) by 36%, 24%, and 34% for TRT1, TRT2, and TRT3 gilts, respectively. Collectively, these data support the hypothesis that feeding a more bioavailable Mn source increases Mn accumulation in CL tissue. If and how this influences CL function may be related to altered luteal P4 concentrations.

Boron Attenuates Heat Stress-Induced Apoptosis by Inhibiting Endoplasmic Reticulum Stress in Mouse Granulosa Cells

Heat stress-induced apoptosis in granulosa cells is mediated by multiple apoptotic signaling pathways, including endoplasmic reticulum (ER) stress. Boron is a naturally occurring trace element with several cytoprotective properties. Nonetheless, the molecular mechanisms involved in the protective functions of boron in granulosa cells undergoing apoptosis caused by heat stress (HS) remain unclear. In this study, we investigated the role of boric acid, a predominant chemical form of boron, in HS-induced apoptotic damage in mouse granulosa cells (mGCs) and explored the underlying mechanisms. We found that HS treatment suppressed cell viability; increased the apoptotic rate of cells; potentiated the activity of caspase-3, a key player in the caspase-mediated apoptotic signaling pathway; and activated ER stress markers, including glucose-regulated protein 78 (GRP78) and CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) in mGCs. However, boric acid treatment effectively alleviated the effects of both HS-induced and thapsigargin (an ER stress agonist)-induced apoptosis, such as the enhanced activity of caspase-3 and increase in GRP78 and CHOP expression. Moreover, treatment with 4-phenylbutyrate (4-PBA), an ER stress antagonist, significantly attenuated these HS-induced adverse effects in mGCs. In addition, boric acid supplementation in the culture medium significantly restored the decreased estradiol levels in heat-treated mGCs. The administration of boric acid to female mice previously exposed to hyperthermal conditions effectively restored the levels of serum estradiol in vivo. Collectively, these findings suggest that HS induces apoptosis in mGCs via ER stress pathways and that boron has a protective effect against these adverse effects. This study provides novel insights into the benefits of using boron against heat-induced apoptosis.

Is Magnesium Supplementation an Effective Nutritional Method to Reduce Stress in Domestic Pigs? A Systematic Review

In commercial pig production, stressful events are common and can have detrimental impacts on the pig's health and welfare, as well as on the performance of the farm. Supplementary magnesium may reduce stress, and subsequent harmful and aggressive behaviors, that occur during stressful events, such as regrouping. However, reports on the efficacy of this treatment are mixed. We aimed to systematically review the studies in which magnesium was given to pigs to examine the effects on measures of stress. Of the 16 studies included in the final corpus, 10 reported at least one statistically significant beneficial effect of supplementary magnesium on reducing stress. However, two studies found that magnesium significantly increased stress suggesting supplementary dietary magnesium may be harmful in some cases. Overall, there are a limited number of studies investigating the possible effect of magnesium on reducing stress in pigs, and although results were varied, the majority found beneficial effects of supplementary magnesium.

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.

Controlled elevated temperatures during early-mid gestation cause placental insufficiency and implications for fetal growth in pregnant pigs

It is known that pig offspring born from pregnant pigs exposed to elevated ambient temperatures during gestation have altered phenotypes, possibly due to placental insufficiency and impaired fetal growth. Therefore, the objective of this study was to quantify the effect of maternal heat exposure during early-mid gestation, when pig placentae grow heavily, on placental and fetal development. Fifteen pregnant pigs were allocated to thermoneutral (TN; 20 °C; n = 7) or cyclic elevated temperature conditions (ET; 28 to 33 °C; n = 8) from d40 to d60 of gestation. Following euthanasia of the pigs on d60, placental and fetal morphometry and biochemistry were measured. Compared to TN fetuses, ET fetuses had increased (P = 0.041) placental weights and a lower (P = 0.013) placental efficiency (fetal/placental weight), although fetal weights were not significantly different. Fetuses from ET pigs had reduced (P = 0.032) M. longissimus fibre number density and a thicker (P = 0.017) placental epithelial layer compared to their TN counterparts. Elevated temperatures decreased (P = 0.026) placental mRNA expression of a glucose transporter (GLUT-3) and increased (P = 0.037) placental IGF-2 mRNA expression. In conclusion, controlled elevated temperatures between d40 to d60 of gestation reduced pig placental efficiency, resulting in compensatory growth of the placentae to maintain fetal development. Placental insufficiency during early-mid gestation may have implications for fetal development, possibly causing a long-term phenotypic change of the progeny.

Rumen-bypassed tributyrin alleviates heat stress by reducing the inflammatory responses of immune cells

Heat stress (HS) in summer will seriously affect the health and performance of dairy cows. To alleviate the injury to dairy cows caused by HS, we added the rumen-bypassed tributyrin to the feed. We determined whether cows were in a heat-stressed environment by testing the temperature humidity index in the morning, at noon, and in the evening. The detection of anal temperature and respiratory frequency further proved the HS state of the dairy cows. The quantificational real time PCR results showed that tributyrin could significantly reduce the relative expression of tumor necrosis factor α, interleukin 1β, and Interleukin 6. Western blot results showed that tributyrin could alleviate the lymphocyte inflammatory response by inhibiting the mitogen-activated protein kinase and nuclear factor-кB signaling pathways. To further detect the effect of tributyrin on HS in dairy cows, routine biochemical and blood tests were carried out. The results showed that the contents of aspartate aminotransferase, total bilirubin, creatinine, albumin, and globulin were significantly reduced by tributyrin. The results showed that tributyrin could significantly alleviate the liver and kidney injury induced by heat stress in dairy cows. Moreover, tributyrin could also significantly reduce the numbers of intermediate cells and increase the level of hemoglobin. Tributyrin could also improve the performance of dairy cows. These results suggested that tributylglycerol may have a positive effect on breast health of dairy cows. In conclusion, these results indicated that tributyrin could relieve HS and increase the production performance of dairy cows by reducing the inflammatory responses of lymphocytes.

Use of Different Cooling Methods in Pig Facilities to Alleviate the Effects of Heat Stress-A Review

An increase in the frequency of hot periods, which has been observed over the past decades, determines the novel approach to livestock facilities improvement. The effects of heat stress are revealed in disorders in physiological processes, impaired immunity, changes in behaviour and decreases in animal production, thus implementation of cooling technologies is a key factor for alleviating these negative consequences. In pig facilities, various cooling methods have been implemented. Air temperature may be decreased by using adiabatic cooling technology such as a high-pressure fogging system or evaporative pads. In modern-type buildings large-surface evaporative pads may support a tunnel ventilation system. Currently a lot of attention has also been paid to developing energy- and water-saving cooling methods, using for example an earth-air or earth-to-water heat exchanger. The pigs' skin surface may be cooled by using sprinkling nozzles, high-velocity air stream or conductive cooling pads. The effectiveness of these technologies is discussed in this article, taking into consideration the indicators of animal welfare such as respiratory rate, skin surface and body core temperature, performance parameters and behavioural changes.

Biology of heat stress; the nexus between intestinal hyperpermeability and swine reproduction

Unfavorable weather conditions are one of the largest constraints to maximizing farm animal productivity. Heat stress (HS), in particular, compromises almost every metric of profitability and this is especially apparent in the grow-finish and reproductive aspects of the swine industry. Suboptimal production during HS was traditionally thought to result from hypophagia. However, independent of inadequate nutrient consumption, HS affects a plethora of endocrine, physiological, metabolic, circulatory, and immunological variables. Whether these changes are homeorhetic strategies to survive the heat load or are pathological remains unclear, nor is it understood if they temporally occur by coincidence or if they are chronologically causal. However, mounting evidence suggest that the origin of the aforementioned changes lie at the gastrointestinal tract. Heat stress compromises intestinal barrier integrity, and increased appearance of luminal contents in circulation causes local and systemic inflammatory responses. The resulting immune activation is seemingly the epicenter to many, if not most of the negative consequences HS has on reproduction, growth, and lactation. Interestingly, thermoregulatory and production responses to HS are only marginally related. In other words, increased body temperature indices poorly predict decreases in productivity. Further, HS induced malnutrition is also a surprisingly inaccurate predictor of productivity. Thus, selecting animals with a "heat tolerant" phenotype based solely or separately on thermoregulatory capacity or production may not ultimately increase resilience. Describing the physiology and mechanisms that underpin how HS jeopardizes animal performance is critical for developing approaches to ameliorate current production issues and requisite for generating future strategies (genetic, managerial, nutritional, and pharmaceutical) aimed at optimizing animal well-being, and improving the sustainable production of high-quality protein for human consumption.

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.

Transcriptome analysis identifies genes and co-expression networks underlying heat tolerance in pigs

BACKGROUND

Heat stress adversely affects pig growth and reproduction performance by reducing feed intake, weight gain, farrowing rate, and litter size. Heat tolerance is an important characteristic in pigs, allowing them to mitigate the negative effects of heat stress on their physiological activities. Yet, genetic variation and signaling pathways associated with the biological processes of heat-tolerant pigs are currently not fully understood. This study examined differentially expressed genes and constructed gene co-expression networks on mRNAs of pigs under different heat-stress conditions using whole transcriptomic RNA-seq analyses. Semen parameters, including total sperm number per ejaculate, motility, normal morphology rate, droplets, and rejected ejaculate rate, were measured weekly on 12 boars for two time periods: thermoneutral (January to May), and heat stress (July to October). Boars were classified into heat-tolerant (n = 6) and heat-susceptible (n = 6) groups based on the variation of their ejaculate parameters across the two periods. RNA was isolated from the blood samples collected from the thermoneutral and heat stress periods for gene expression analysis.

RESULTS

Under heat stress, a total of 66 differentially expressed genes (25 down-regulated, 41 up-regulated) were identified in heat-tolerant pigs compared to themselves during the thermoneutral period. A total of 1041 differentially expressed genes (282 down-regulated, 759 up-regulated) were identified in the comparison between heat-tolerant pigs and heat-susceptible pigs under heat stress. Weighted gene co-expression network analysis detected 4 and 7 modules with genes highly associated (r > 0.50, p < 0.05) with semen quality parameters in heat-tolerant and heat-susceptible pigs under the effects of heat stress, respectively.

CONCLUSION

This study utilized the sensitivity of semen to heat stress to discriminate the heat-tolerance ability of pigs. The gene expression profiles under the thermoneutral and heat stress conditions were documented in heat-tolerant and heat-susceptible boars. Findings contribute to the understanding of genes and biological mechanisms related to heat stress response in pigs and provide potential biomarkers for future investigations on the reproductive performance of pigs.

Differentiating between the effects of heat stress and lipopolysaccharide on the porcine ovarian heat shock protein response1

Heat stress (HS) negatively affects both human and farm-animal health and undermines efficiency in a variety of economically important agricultural variables, including reproduction. HS impairs the intestinal barrier, allowing for translocation of the resident microflora and endotoxins, such as lipopolysaccharide (LPS), from the gastrointestinal lumen into systemic circulation. While much is known about the cellular function of heat shock proteins (HSPs) in most tissues, the in vivo ovarian HSP response to stressful stimuli remains ill-defined. The purpose of this study was to compare the effects of HS or LPS on ovarian HSP expression in pigs. We hypothesized that ovarian HSPs are responsive to both HS and LPS. Altrenogest (15 mg/d) was administered per os for estrus synchronization (14 d) prior to treatment and three animal paradigms were used: (i) gilts were exposed to cyclical HS (31 ± 1.4 °C) or thermoneutral (TN; 20 ± 0.5 °C) conditions immediately following altrenogest withdrawal for 5 d during follicular development; (ii) gilts were subjected to repeated (4×/d) saline (CON) or LPS (0.1 μg/kg BW) i.v. infusion immediately following altrenogest withdrawal for 5 d; and (iii) gilts were subjected to TN (20 ± 1 °C) or cyclical HS (31 to 35 °C) conditions 2 d post estrus (dpe) until 12 dpe during the luteal phase. While no differences were detected for transcript abundances of the assessed ovarian HSP, the protein abundance of specific HSP was influenced by stressors during the follicular and luteal phases. HS during the follicular phase tended (P < 0.1) to increase ovarian protein abundance of HSP90AA1 and HSPA1A, and increased (P ≤ 0.05) HSF1, HSPD1, and HSPB1 compared with TN controls, while HS decreased HSP90AB1 (P = 0.01). Exposure to LPS increased (P < 0.05) HSP90AA1 and HSPA1A and tended (P < 0.1) to increase HSF1 and HSPB1 compared with CON gilts, while HSP90AB1 and HSPD1 were not affected by LPS. HS during the luteal phase increased (P < 0.05) abundance of HSPB1 in corpora lutea (CL), decreased (P < 0.05) CL HSP90AB1, but did not impact HSF1, HSPD1, HSP90AA1, or HSPA1A abundance. Thus, these data support that HS and LPS similarly regulate expression of specific ovarian HSP, which suggest that HS effects on the ovary are in part mediated by LPS.

Impact of environmental temperature on production traits in pigs

There is an urgent need to identify the effects of temperature on production traits. This study aimed to determine the impact of pig production in three environments (T_{°Cgrowing-°Cfattening-°Cfinishing} = T_24-24-21, T_19-19-19, and T_23-17-15) on growth curve parameters, body weight gain (DBWG), feed intake (DFI), and feed efficiency during the growing, fattening and finishing stages, and on carcass yield of primal cuts (ham, shoulder, and loin) in 158 Duroc × Iberian pigs. Maturation rate was higher in T_23-17-15 than in T_19-19-19 (P < 0.001). Pigs in T_23-17-15 reached a lower mature body weight (P < 0.05). During the growing stage, pigs in T_23-17-15 had higher DFI than those in T_24-24-21 and T_19-19-19 (P < 0.05); during the fattening stage, DFI was lowest in T_24-24-21 (P < 0.001). In the growing stage, pigs had highest DBWG in the warmest environments (T_24-24-21 and T_23-17-15) and lowest in the coldest environment (T_19-19-19; P < 0.001). Feed efficiency was highest in warmer environments (P < 0.01). Temperature T_24-24-21 favored loin yield, T_19-19-19 favored ham yield, and T_23-17-15 favored shoulder yield (P < 0.01). The results imply a favorable effect of temperature on feed efficiency, however, possible negative implications for animal health and welfare should be considered.

Effects of feeding melatonin during proestrus and early gestation to gilts and parity 1 sows to minimize effects of seasonal infertility1

This study tested whether supplemental melatonin given to mimic the extended nighttime melatonin pattern observed in the higher fertility winter season could minimize infertility during summer and fall in swine. Exogenous melatonin was fed during periods coinciding with follicle selection, corpus luteum formation, pregnancy recognition, and early embryo survival. Experiments were conducted at a commercial farm in 12 sequential replicates. In Exp. 1a, mature gilts (n = 420) that had expressed a second estrus were assigned by weight to receive once daily oral Melatonin (MEL, 3 mg) or Control (CON, placebo) at 1400 h for 3 wk starting before insemination at third estrus. In Exp. 1b, parity 1 sows (n = 470) were randomly assigned by lactation length to receive MEL or CON for 3 wk, starting 2 d before weaning. Follicles, estrus, pregnancy, and farrowing data were analyzed for the main effects of treatment, season (4-wk periods), and their interaction. Environmental measures were also analyzed for reproductive responses. In Exp. 1a, there was no effect (P > 0.10) of MEL on age at third estrus (203 d), follicle size after 7 d of treatment (5.0 mm), estrous cycle length (22.6 d), return to service (9.2%), farrowing rate (FR, 80.0%), or total born pigs (TB, 13.6). However, there was an effect of season (P = 0.03) on number of follicles and on gilts expressing estrus within 23 d of the previous estrus (P < 0.005). In Exp. 1b, there was no effect of MEL (P > 0.10) on follicle measures, wean to estrous interval, FR (84.0%), or TB (13.0). But MEL (73.5%) reduced (P = 0.03) estrous expression within 7 d of weaning compared with CON (82.0%) and season (P = 0.001) decreased FR by ~14.0% during mid summer. Also, gilts and parity 1 sows exposed to low light intensity (<45 lx) during breeding had reduced conception (-8%) and farrowing (-15%) rates, compared with higher light intensity. Similarly, high temperatures (>25 °C) during breeding also reduced gilt conception rates by 7%. Although there was clear evidence of seasonal fertility failures in gilts and sows, MEL treatment did not improve fertility in gilts and reduced estrus in parity 1 sows. It is possible that differences in lighting and thermal environments before breeding could explain the differential response to MEL in sows and gilts.

Review: innovation through research in the North American pork industry

This article involved a broad search of applied sciences for milestone technologies we deem to be the most significant innovations applied by the North American pork industry, during the past 10 to 12 years. Several innovations shifted the trajectory of improvement or resolved significant production limitations. Each is being integrated into practice, with the exception being gene editing technology, which is undergoing the federal approval process. Advances in molecular genomics have been applied to gene editing for control of porcine reproductive and respiratory syndrome and to identify piglet genome contributions from each parent. Post-cervical artificial insemination technology is not novel, but this technology is now used extensively to accelerate the rate of genetic progress. A milestone was achieved with the discovery that dietary essential fatty acids, during lactation, were limiting reproduction. Their provision resulted in a dose-related response for pregnancy, pregnancy maintenance and litter size, especially in maturing sows and ultimately resolved seasonal infertility. The benefit of segregated early weaning (12 to 14 days of age) was realized for specific pathogen removal for genetic nucleus and multiplication. Application was premature for commercial practice, as piglet mortality and morbidity increased. Early weaning impairs intestinal barrier and mucosal innate immune development, which coincides with diminished resilience to pathogens and viability later in life. Two important milestones were achieved to improve precision nutrition for growing pigs. The first involved the updated publication of the National Research Council nutrient requirements for pigs, a collaboration between scientists from America and Canada. Precision nutrition advanced further when ingredient description, for metabolically available amino acids and net energy (by source plant), became a private sector nutrition product. The past decade also led to fortuitous discoveries of health-improving components in ingredients (xylanase, soybeans). Finally, two technologies converged to facilitate timely detection of multiple pathogens in a population: oral fluids sampling and polymerase chain reaction (PCR) for pathogen analysis. Most critical diseases in North America are now routinely monitored by oral fluid sampling and prepared for analysis using PCR methods.

Heat stress affects fecal microbial and metabolic alterations of primiparous sows during late gestation

Background

Heat stress (HS) jeopardizes intestinal barrier functions and augments intestinal permeability in pigs. However, whether HS-induced maternal microbial and metabolic changes in primiparous sows during late gestation remains elusive. We present here, a study investigating the fecal microbial and metabolic responses in late gestational primiparous sows when exposed to HS.

Methods

Twelve first-parity Landrace × Large White F1 sows were randomly assigned into two environmental treatments including the thermoneutral (TN) (18–22 °C; n = 6) and HS (28–32 °C; n = 6) conditions. Both treatments were applied from 85 d of gestation to farrowing. The serum and feces samples were collected on d 107 of gestation, for analyses including intestinal integrity biomarkers, high-throughput sequencing metagenomics, short-chain fatty acid (SCFA) profiles and nontargeted metabolomics.

Results

Our results show that HS group has higher serum Heat shock protein 70 (HSP70), lipopolysaccharide (LPS) and lipopolysaccharide-binding protein (LBP) levels. The gut microbial community can be altered upon HS by using β-diversity and taxon-based analysis. In particular, the relative abundance of genera and operational taxonomic units (OTUs) related to Clostridiales and Halomonas are higher in HS group, the relative abundance of genera and OTUs related to Bacteroidales and Streptococcus, however, are lower in HS group. Results of metabolic analysis reveal that HS lowers the concentrations of propionate, butyrate, total SCFA, succinate, fumarate, malate, lactate, aspartate, ethanolamine, β-alanine and niacin, whereas that of fructose and azelaic acid are higher in HS group. These metabolites mainly affect propanoate metabolism, alanine, aspartate and glutamate metabolism, phenylalanine metabolism, β-alanine metabolism, pantothenate and CoA biosynthesis, tricarboxylic acid cycle (TCA) and nicotinate and nicotinamide metabolism. Additionally, correlation analysis between significant microbes and metabolites indicated that the HS-induced microbiota shift is likely the cause of changes of intestinal metabolism.

Conclusions

Taken together, we reveal characteristic structural and metabolic changes in maternal gut microbiota as a result of late gestational HS, which could potentially provide the basis for further study on offspring gut microbiota and immune programming.

Effect of Curcumin Supplement in Summer Diet on Blood Metabolites, Antioxidant Status, Immune Response, and Testicular Gene Expression in Hu Sheep

Simple Summary

Heat stress can induce oxidative stress and has an adverse effect on the growth and reproductive performance in animals. Curcumin, a plant-derived substance, with the effect of scavenging oxidative free radicals, improving immune response and anti-apoptosis, has been widely used as a dietary supplement in the livestock industry. The present study aims to investigate the effect of a curcumin dietary supplement on the blood metabolites, antioxidant status, immune response, and testicular gene expression in Hu Sheep in summer. The results show that dietary curcumin supplementation (450 and 900 mg/per sheep daily) can promote lipid metabolism, antioxidant capacity, and immune response as well as testicular development in Hu sheep, which provides evidence for the protective role of curcumin against heat stress in sheep.

Abstract

In summer, the high temperature affects animal growth and reproductive performance. Curcumin is a flavonoid with anti-oxidant and anti-inflammatory effects. To evaluate the effects of dietary curcumin supplement on the blood biochemical parameters and testicular gene expressions in Hu sheep in summer, a total of 144 male Hu sheep aged four months were randomly divided into three groups (Con, Cur1, and Cur2, n = 48). Sheep in Con, Cur1, and Cur2 groups were fed a basal diet supplement with 0, 450, and 900 mg (per sheep) curcumin daily, respectively. Sheep were fed for 35 days, including a pre-feed for seven days. The results showed that the supplement with 450 mg and 900 mg curcumin increased serum free fatty acid (NEFA) and glutathione peroxidase (GPX), as well as IgA and IgM. The supplement with 450 mg curcumin increased the IgG level, while the supplement with 900 mg curcumin had a lower IgG level than the supplement with 450 mg curcumin (p < 0.05). Dietary curcumin supplement increased testicular organ index, serum testosterone level, and testicular star mRNA expression (p < 0.05). Furthermore, dietary curcumin supplement linearly inhibited testicular apoptosis with increased testicular bcl-2 mRNA expression and decreased caspase-3 mRNA expression (p < 0.05). In conclusion, dietary curcumin supplement can promote lipid metabolism, antioxidant capacity, and immune response, as well as testicular development, in Hu sheep, which provides evidence of application of curcumin in sheep production.

Effects of dietary chromium propionate on growth performance, metabolism, and immune biomarkers in heat-stressed finishing pigs1

Study objectives were to determine the effects of chromium (Cr) propionate (Cr propionate 0.04%; 0.5 g/kg of feed to deliver 200 parts per billion Cr/d; KemTRACE Cr, Kemin Industries, Inc., Des Moines, IA) on growth performance, metabolism, and health biomarkers in heat-stressed and nutrient-restricted pigs. Crossbred barrows (n = 96; 105 ± 1 kg BW) were enlisted in an experiment conducted in two replicates, blocked by initial BW, and randomly assigned to one of six dietary-environmental treatments: (i) thermoneutral (TN) and fed ad libitum a control diet (TNCtl), (ii) TN and fed ad libitum a Cr supplemented diet (TNCr), (iii) TN and pair-fed a control diet (PFCtl), (iv) TN and pair-fed a Cr supplemented diet (PFCr), (v) heat stress (HS) and ad libitum fed a control diet (HSCtl), or (vi) HS and ad libitum fed a Cr supplemented diet (HSCr). The study consisted of three experimental periods (P). During P0 (5 d), all pigs were housed in TN conditions (21.3 ± 0.1 °C, 56.8 ± 0.3% relative humidity [RH]) and fed the control diet ad libitum. During P1 (5 d), pigs were fed their respective dietary treatments ad libitum and kept in TN conditions. During P2 (35 d), HSCtl and HSCr-treated pigs were fed ad libitum and exposed to progressive cyclical HS conditions (27 to 31 °C, 50 ± 0.3% RH), while TNCtl, TNCr, PFCtl, and PFCr pigs remained in TN conditions and were fed ad libitum or pair-fed to their respective HSCtl and HSCr counterparts to eliminate the confounding effects of dissimilar feed intake. Overall, HS pigs had increased (P < 0.01) rectal temperature, skin temperature, and respiration rate (0.3 °C, 3.8 °C, and 32 breaths per minute, respectively) relative to TN pigs. Overall, HS decreased ADFI and ADG (20 and 21%, respectively; P < 0.01) compared with TN controls. Final BW tended to be increased in HSCr (2.7 kg, P = 0.06) compared with HSCtl pigs. Similarly, ADG tended to be increased during P2 in HSCr relative to HSCtl-treatment (0.77 vs. 0.72 kg/d; P = 0.10). There were no effects of Cr on most production parameters, but ADFI tended to be increased in Cr relative to Ctl-fed pigs (3.19 vs. 3.09 kg/d; P = 0.08). No effects of Cr supplementation were detected on circulating glucose, insulin, NEFA, cholesterol, triglycerides, or lipopolysaccharide binding protein. However, blood neutrophils were increased in HSCr (37%; P < 0.01) relative to HSCtl pigs. In summary, these results suggest Cr supplementation may benefit growth performance during HS.

The effect of recovery from heat stress on circulating bioenergetics and inflammatory biomarkers

Heat stress (HS) jeopardizes animal productivity and health. The intestinal barrier is sensitive to HS and heat-induced hyperpermeability plays a key role in its pathophysiology. However, the biology of recovery following HS is less understood. Thus, study objectives were to determine the temporal pattern of metabolic, inflammatory, and intestinal histological parameters during HS recovery. Female pigs (n = 32; 19.5 ± 0.5 kg BW) were sacrificed following exposure to 1 of 4 environmental treatments: 1) constant thermoneutral (TN) conditions (TNC; 24.2 ± 0.5°C), 2) no TN recovery post HS (0D), 3) 3 d of TN recovery post HS (3D), and 4) 7 d of TN recovery post HS (7D). The HS protocol was cyclical (33.6 ± 1.8 to 37.4 ± 2.1°C) and lasted for 3 d for all HS treatments. During the 3 d of HS, rectal temperature, skin temperature, and respiration rates were increased (1.3°C, 4.8°C, and 77 breaths/min, respectively; P < 0.01) and ADFI was decreased (27%; P < 0.01) compared to TNC pigs. Skin temperature tended to be decreased 0.6°C in 3D pigs during days 1-3 of recovery (P = 0.06) and was decreased 1.6 and 0.7°C during days 1-3 and 4-7 of recovery, respectively, in 7D pigs (P ≤ 0.03) compared to TNC. Relative to TNC pigs, ADFI remained 14% decreased during days 1-3 of recovery in both 3D and 7D pigs, and 17% decreased during days 4-7 in 7D pigs (P ≤ 0.01). Plasma glucose was decreased (10%; P = 0.03) for 0D and 3D relative to TNC pigs. Circulating lipopolysaccharide-binding protein was increased in 3D and 7D vs. TNC pigs (110 and 147%, respectively; P = 0.01) and tended to increase linearly with increasing recovery time (P = 0.08). Circulating tumor necrosis factor alpha was decreased (15%) in 0D pigs and increased linearly with advancing recovery time (P < 0.01). Jejunum and ileum villus height were reduced 17 and 11% in 0D vs. TNC pigs and increased linearly with progressive recovery time (P < 0.01). Jejunum and ileum mucosal surface areas were reduced 17 and 9% in 0D pigs and remained decreased in the jejunum while the ileum recovered to TNC levels by day 3 of recovery. Relative to TNC pigs, goblet cell area was similar in jejunum and colon of 0D pigs but was reduced in the ileum of 0D pigs and in jejunum, ileum, and colon of 3D and 7D relative to TNC pigs (P < 0.01). In summary, HS has deleterious effects on intestinal morphology that seem to improve with recovery time. In contrast, feed consumption remained suppressed and inflammatory biomarkers indicative of leaky gut increased following the heat load.

A controlled heat stress during late gestation affects thermoregulation, productive performance, and metabolite profiles of primiparous sow

Heat stress (HS) alters metabolic parameters and reduces productive performance in lactating sows. However, the impact of HS on metabolomic profiles of sows during late gestation is not fully understood. We present here, a study investigating the productive performance and metabolic responses in sows when exposed to HS during late gestation. Twelve first-parity Landrace × Large White F1 sows were randomly assigned into two environmental treatments including the thermoneutral (TN) (18-22 °C; n = 6) and HS (28-32 °C; n = 6) conditions from 85 d of gestation until farrowing. Rectal temperature (RT), respiration rates (RR), and surface temperature (ST) were measured every 4 h from 0800 h to 2000 h during the 2nd week. Farrowing and litter Data, as well as duration of eating, were monitored to assess sows' productive performance. Blood biochemical parameters and urinary metabolomic profiles were measured on d107 of gestation to analyze the host metabolic responses. Our results show that HS increased RT, RR, and ST (P < 0.0001). Duration of parturition was prolonged during the delivery in HS group (P < 0.05). Piglet body weight (BW) at d 10 and weaning were reduced by 18% and 17% respectively due to maternal HS (P < 0.001). Duration of eating increased as a result of HS (P < 0.001), consistent with the significant changes observed in serum ghrelin (P < 0.05). Moreover, serum ACTH, cortisol, insulin, creatinine, and BUN saw increase as well (P < 0.05). Plasma NEFA were elevated by HS (P < 0.001). Additionally, HS elevated (VIP>1, log₂fold change>0.585, and P < 0.05) the relative concentrations of 5-aminovaleric acid, β-alanine, cysteine, isoleucine, glyceric acid, erythronic acid, mannitol, erythritol, 2-methyl-1,3-butanediol, and pantothenic acid in urine. These ten metabolites mainly affected the pantothenate and CoA biosynthesis, β-alanine metabolism, and glycerolipid metabolism in pregnant sows. In summary, our study suggests that the controlled HS during late gestation elevates thermal responses, reduces productive performance, and more importantly, enhances the catabolism of lipid and protein of first-parity pregnant sow.

Characterization of the acute heat stress response in gilts: III. Genome-wide association studies of thermotolerance traits in pigs

Heat stress is one of the limiting factors negatively affecting pig production, health, and fertility. Characterizing genomic regions responsible for variation in HS tolerance would be useful in identifying important genetic factor(s) regulating physiological responses to HS. In the present study, we performed genome-wide association analyses for respiration rate (RR), rectal temperature (TR), and skin temperature (TS) during HS in 214 crossbred gilts genotyped for 68,549 single nucleotide polymorphisms (SNP) using the Porcine SNP 70K BeadChip. Considering the top 0.1% smoothed phenotypic variances explained by SNP windows, we detected 26, 26, 21, and 14 genes that reside within SNPs explaining the largest proportion of variance (top 25 SNP windows) and associated with change in RR (ΔRR) from thermoneutral (TN) conditions to HS environment, as well as the change in prepubertal TR (ΔTR), change in postpubertal ΔTR, and change in TS (ΔTS), respectively. The region between 28.85 Mb and 29.10 Mb on chromosome 16 explained about 0.05% of the observed variation for ΔRR. The growth hormone receptor (GHR) gene resides in this region and is associated with the HS response. The other important candidate genes associated with ΔRR (PAIP1, NNT, and TEAD4), ΔTR (LIMS2, TTR, and TEAD4), and ΔTS (ERBB4, FKBP1B, NFATC2, and ATP9A) have reported roles in the cellular stress response. The SNP explaining the largest proportion of variance and located within and in the vicinity of genes were related to apoptosis or cellular stress and are potential candidates that underlie the physiological response to HS in pigs.

Characterizing the acute heat stress response in gilts: II. Assessing repeatability and association with fertility

Mitigating heat stress (HS) in swine production is important as it detrimentally affects multiple aspects of overall animal production efficiency. Study objectives were to determine if gilts characterized as tolerant (TOL) or susceptible (SUS) in response to HS maintain that phenotype later in life and if that phenotype influences reproductive ability during HS. Individual gilts identified as TOL (n = 50) or SUS (n = 50) from a prepubertal HS challenge were selected based on their rectal temperature (TR) during acute HS. The study consisted of 4 experimental periods (P). During P0 (2 d), all pigs were exposed to thermoneutral (TN) conditions (21.1 °C). During P1 (14 d), all gilts received Matrix (15 mg altrenogest per day) to synchronize estrus, and were maintained in TN conditions. During P2 (9 d), Matrix supplementation was terminated and gilts were subjected to diurnal HS with ambient temperatures set at 35 °C from 1000 to 2200 h and 21 °C from 2200 to 1000 h. Also during P2 gilts underwent estrus detection and artificial insemination. During P3 gilts were housed in TN conditions for 41 d at which they were sacrificed and reproductive tracts were collected. During the last 2 d of P1 and throughout the entirety of P2, TR and skin temperature (TS) were recorded. During P2, SUS had increased TR relative to TOL pigs during P2 (0.27 °C; P < 0.01). Overall, uterine wet weight, ovarian weight, corpora lutea (CL) count, and embryo survival were 5.6 ± 0.1 kg, 21.6 ± 0.3 g, 17.8 ± 0.3 CLs, and 79 ± 2%, respectively, and not influenced by prepubertal HS tolerance classification (P ≥ 0.37). Tolerant gilts had a longer return-to-estrus (6.1 vs. 5.5 d, respectively; P = 0.01) following altrenogest withdrawal and tended to have larger CL diameters (10.3 vs. 10.1 mm; P = 0.06) compared to SUS gilts. Fetal weight (25.4 vs. 23.6 g; P = 0.01) and fetal crown-rump length (74.8 vs. 72.8 mm; P < 0.01) were higher in gilts previously classified as SUS compared to those previously classified as TOL. Additionally, neither litter size nor the number of fetuses detected as a percentage of ovulations was influenced by classification. In summary, SUS gilts had a shorter return-to-estrus, increased fetus size, and tended to have smaller CL diameters compared to TOL gilts. Additionally, SUS gilts also retained their inability to maintain euthermia postpubertally relative to TOL gilts. In conclusion, there appeared to be little reproductive advantage of maintaining a lower TR during HS.

Impact of heat stress during the follicular phase on porcine ovarian steroidogenic and phosphatidylinositol-3 signaling

Environmental conditions that impede heat dissipation and increase body temperature cause heat stress (HS). The study objective was to evaluate impacts of HS on the follicular phase of the estrous cycle. Postpubertal gilts (126.0 ± 21.6 kg) were orally administered altrenogest to synchronize estrus, and subjected to either 5 d of thermal-neutral (TN; 20.3 ± 0.5 °C; n = 6) or cyclical HS (25.4 - 31.9 °C; n = 6) conditions during the follicular phase preceding behavioral estrus. On d 5, blood samples were obtained, gilts were euthanized, and ovaries collected. Fluid from dominant follicles was aspirated and ovarian protein homogenates prepared for protein abundance analysis. HS decreased feed intake (22%; P = 0.03) and while plasma insulin levels did not differ, the insulin:feed intake ratio was increased 3-fold by HS (P = 0.02). Insulin receptor protein abundance was increased (29%; P < 0.01), but insulin receptor substrate 1, total and phosphorylated protein kinase B, superoxide dismutase 1, and acyloxyacyl hydrolase protein abundance were unaffected by HS (P > 0.05). Plasma and follicular fluid 17β-estradiol, progesterone, and lipopolysaccharide-binding protein concentrations as well as abundance of steroid acute regulatory protein, cytochrome P450 19A1, and multidrug resistance-associated protein 1 were not affected by HS (P > 0.05). HS increased estrogen sulfotransferase protein abundance (44%; P = 0.02), toll-like receptor 4 (36%; P = 0.05), and phosphorylated REL-associated protein (31%; P = 0.02). Regardless of treatment, toll-like receptor 4 protein was localized to mural granulosa cells in the porcine ovary. In conclusion, HS altered ovarian signaling in postpubertal gilts during their follicular phase in ways that likely contributes to seasonal infertility.

Effects of heat stress and insulin sensitizers on pig adipose tissue

Heat stress (HS) negatively impacts several swine production variables, including carcass fat quality and quantity. Pigs reared in HS have more adipose tissue than energetically predicted, explainable, in part, by HS-induced hyperinsulinemia. Study objectives were to evaluate insulin's role in altering fat characteristics during HS via feeding insulin-sensitizing compounds. Forty crossbred barrows (113 ± 9 kg BW) were randomly assigned to one of five environment by diet treatments: 1) thermoneutral (TN) fed ad libitum (TNAL), 2) TN and pair-fed (TNPF), 3) HS fed ad libitum (HSAL), 4) HS fed ad libitum with sterculic oil (SO) supplementation (HSSO; 13 g/d), and 5) HS fed ad libitum with dietary chromium (Cr) supplementation (HSCr; 0.5 mg/d; Kemin Industries, Des Moines, IA). The study consisted of three experimental periods (P). During P0 (2 d), all pigs were exposed to TN conditions (23 ± 3 °C, 68 ± 10% RH) and fed ad libitum. During P1 (7 d), all pigs received their respective dietary supplements, were maintained in TN conditions, and fed ad libitum. During P2 (21 d), HSAL, HSSO, and HSCr pigs were fed ad libitum and exposed to cyclical HS conditions (28 to 33 °C, 58 ± 10% RH). The TNAL and TNPF pigs remained in TN conditions and were fed ad libitum or pair-fed to their HSAL counterparts. Rectal temperature (TR), respiration rate (RR), and skin temperature (TS) were obtained daily at 0600 and 1800 h. At 1800 h, HS exposed pigs had increased TR, RR, and TS relative to TNAL controls (1.13 °C, 48 bpm, and 3.51 °C, respectively; P < 0.01). During wk 2 and 3 of P2, HSSO pigs had increased 1800 h TR relative to HSAL and HSCr (~0.40 and ~0.42 °C, respectively; P ≤ 0.05). Heat stress decreased ADFI and ADG compared to TNAL pigs (2.24 vs. 3.28 and 0.63 vs. 1.09 kg/d, respectively; P < 0.01) and neither variable was affected by SO or Cr supplementation. Heat stress increased or tended to increase moisture content of abdominal (7.7 vs. 5.9%; P = 0.07) and inner s.c. (11.4 vs. 9.8%; P < 0.05) adipose depots compared to TNAL controls. Interestingly, TNPF pigs also had increased adipose tissue moisture content and this was most pronounced in the outer s.c. depot (15.0 vs. 12.2%; P < 0.01) compared to TNAL pigs. Heat stress had little or no effect on fatty acid composition of abdominal, inner, and outer s.c. adipose tissue depots. In summary, the negative effects of HS on fat quality do not appear to be fatty acid composition related, but may be explained by increased adipose tissue moisture content.