Impacts of chronic and increasing lipopolysaccharide exposure on production and reproductive parameters in lactating Holstein dairy cows

Lipopolysaccharide (LPS) administration causes immunoactivation, which negatively affects production and fertility, but experimental exposure via an acute bolus is unlikely to resemble natural infections. Thus, the objectives were to characterize effects of chronic endotoxemia on production parameters and follicular development in estrous-synchronized lactating cows. Eleven Holstein cows (169 ± 20 d in milk; 681 ± 16 kg of body weight) were acclimated to their environmental surroundings for 3 d and then enrolled in 2 experimental periods (P). During P1 (3 d) cows consumed feed ad libitum and baseline samples were obtained. During P2 (7 d), cows were assigned to continuous infusion of either (1) saline-infused and pair-fed (CON-PF; 40 mL/h of saline i.v.; n = 5) or (2) LPS infused and ad libitum fed (LPS-AL; Escherichia coli O55:B5; 0.017, 0.020, 0.026, 0.036, 0.055, 0.088, and 0.148 μg/kg of body weight/h i.v. on d 1 to 7, respectively; n = 6). Controls were pair-fed to the LPS-AL group to eliminate confounding effects of dissimilar nutrient intake. Infusing LPS temporally caused mild hyperthermia on d 1 to 3 (+0.49°C) relative to baseline. Dry matter intake of LPS-AL cows decreased (28%) on d 1 of P2, then progressively returned to baseline. Relative to baseline, milk yield from LPS-AL cows was decreased on d 1 of P2 (12%). No treatment differences were observed in milk yield during P2. Follicular growth, dominant follicle size, serum progesterone (P4), and follicular P4 and 17β-estradiol concentrations were similar between treatments. Serum 17β-estradiol tended to increase (115%) and serum amyloid A and LPS-binding protein were increased (118 and 40%, respectively) in LPS-AL relative to CON-PF cows. Compared with CON-PF, neutrophils in LPS-AL cows were initially increased (45%), then gradually decreased. In contrast, monocytes were initially decreased (40%) and progressively increased with time in the LPS-AL cows. Hepatic mRNA abundance of cytochrome P450 family 2 subfamily C (CYP2C) or CYP3A was not affected by LPS, nor was there a treatment effect on toll-like receptor 4 or LBP; however, acyloxyacyl hydrolase and RELA subunit of nuclear factor kappa B tended to be increased in LPS-AL cows. These data suggest lactating dairy cows become tolerant to chronic and exponentially increasing LPS infusion in terms of production and reproductive parameters.

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 source on bioavailability of selenium, antioxidant status, and performance in lactating dairy cows during oxidative stress-inducing conditions

In the current study, we used heat stress (HS) as an oxidative stress model to examine the effects of hydroxy-selenomethionine (HMSeBA), an organic selenium source, on selenium's bioavailability, antioxidant status, and performance when fed to dairy cows. Eight mid-lactation Holstein dairy cows (141 ± 27 d in milk, 35.3 ± 2.8 kg of milk/d, parity 2 or 3) were individually housed in environmental chambers and randomly assigned to 1 of 2 treatments: inorganic Se supplementation (sodium selenite; SS; 0.3 mg of Se/kg of dry matter; n = 4) or HMSeBA supplementation (0.3 mg of Se/kg of dry matter; n = 4). The trial was divided into 3 continuous periods: a covariate period (9 d), a thermal neutral (TN) period (28 d), and a HS period (9 d). During the covariate and TN periods, all cows were housed in TN conditions (20°C, 55% humidity). During HS, all cows were exposed to cyclical HS conditions (32-36°C, 40% humidity). All cows were fed SS during the covariate period, and dietary treatments were implemented during the TN and HS periods. During HS, cows fed HMSeBA had increased Se concentrations in serum and milk, and total Se milk-to-serum concentration ratio compared with SS controls. Superoxide dismutase activity did not differ between Se sources, but we noted a treatment by day interaction in glutathione peroxidase activity as HS progressively reduced it in SS controls, whereas it was maintained in HMSeBA cows. Supplementation with HMSeBA increased total antioxidant capacity and decreased malondialdehyde, hydrogen peroxide, and nitric oxide serum concentrations compared with SS-fed controls. We found no treatment effects on rectal temperature, respiratory rate, or dry matter intake. Supplementing HMSeBA tended to increase milk yield and decrease milk fat percentage. No other milk composition parameters differed between treatments. We observed no treatment effects detected on blood biochemistry, except for a lower alanine aminotransferase activity in HMSeBA-fed cows. These results demonstrate that HMSeBA supplementation decreases some parameters of HS-induced oxidative stress.

Effects of zinc amino acid complex on biomarkers of gut integrity and metabolism during and following heat stress or feed restriction in pigs

Study objectives were to determine the effects of zinc (Zn) amino acid complex (Availa Zn, Zinpro Corporation, Eden Prairie, MN) on metabolism, biomarkers of leaky gut, and inflammation during and following heat stress (HS) and nutrient restriction. Crossbred gilts (n = 50; 50 ± 2 kg BW) were blocked by initial BW and randomly assigned to one of five treatments: 1) thermoneutral (TN) and ad libitum fed a control diet (TNCtl), 2) TN and pair-fed a control diet (PFCtl), 3) TN and pair-fed a Zn-supplemented diet (PFZn), 4) HS and ad libitum fed a control diet (HSCtl), and 5) HS and ad libitum fed a Zn-supplemented diet (HSZn). The study consisted of 3 experimental periods (P): during P1 (7 d), all pigs were fed their respective diets ad libitum and housed in TN conditions (20.84 ± 0.03 °C, 47.11 ± 0.42% relative humidity). During P2 (7 d), HSCtl and HSZn pigs were exposed to progressive cyclical HS conditions (27 to 30 °C, 41.9 ± 0.5% relative humidity), while TNCtl, PFCtl, and PFZn pigs remained in TN conditions and were fed ad libitum or pair-fed to their respective HSCtl and HSZn counterparts. During P3 (5 d; "recovery phase"), all pigs were housed in TN conditions and fed ad libitum. Pigs exposed to HS had overall increased rectal temperature, skin temperature, and respiration rate (0.33 °C, 3.76 °C, and 27 bpm, respectively; P < 0.01). Relative to TN controls, HS decreased ADFI and ADG (28 and 35%, respectively; P < 0.05), but these variables were unaffected by dietary treatment. Additionally, circulating insulin did not differ between HS and TN pigs (P = 0.41), but was decreased in PF relative to TN pigs (P < 0.01). During recovery, no differences were observed in rectal temperature or respiration rate across treatments, but HSZn pigs had decreased skin temperature relative to TN, PF, and HSCtl pigs (P < 0.01). During P3, no Zn effects were observed in production parameters; however, PF pigs had increased ADFI and ADG relative to TN and HS treatments (P < 0.01). During P3, circulating insulin was increased in pigs that were HS relative to TN and PF pigs (75%, P < 0.05). Interestingly, tumor necrosis factor alpha (TNFα) levels were decreased during P3 (P = 0.04) in Zn relative to Ctl-fed pigs. Circulating lipopolysaccharide-binding protein was not different among periods (P > 0.10). In summary, Zn reduced TNFα (regardless of HS), and the stimulatory effect of HS on insulin secretion is amplified during HS recovery.

Heat stress decreases metabolic flexibility in skeletal muscle of growing pigs

Heat-stressed pigs experience metabolic alterations, including altered insulin profiles, reduced lipid mobilization, and compromised intestinal integrity. This is bioenergetically distinct from thermal neutral pigs on a similar nutritional plane. To delineate differences in substrate preferences between direct and indirect (via reduced feed intake) heat stress effects, skeletal muscle fuel metabolism was assessed. Pigs (35.3 ± 0.8 kg) were randomly assigned to three treatments: thermal neutral fed ad libitum (TN; 21°C, n = 8), heat stress fed ad libitum (HS; 35°C, n = 8), and TN, pair-fed/HS intake (PF; n = 8) for 7 days. Body temperature (T_B) and feed intake (FI) were recorded daily. Longissimus dorsi muscle was biopsied for metabolic assays on days -2, 3, and 7 relative to initiation of environmental treatments. Heat stress increased T_B and decreased FI ( P < 0.05). Heat stress inhibited incomplete fatty acid oxidation and glucose oxidation ( P < 0.05). Metabolic flexibility decreased in HS pigs compared with TN and PF controls ( P < 0.05). Both phosphofructokinase and pyruvate dehydrogenase (PDH) activities increased in PF ( P < 0.05); however, TN and HS did not differ. Heat stress inhibited citrate synthase and β-hydroxyacyl-CoA dehydrogenase (β-HAD) activities ( P < 0.05). Heat stress did not alter PDH phosphorylation or carnitine palmitoyltransferase 1 abundance but reduced acetyl-CoA carboxylase 1 (ACC1) protein abundance ( P < 0.05). In conclusion, HS decreased skeletal muscle fatty acid oxidation and metabolic flexibility, likely involving β-HAD and ACC regulation.

Heat stress induces autophagy in pig ovaries during follicular development

Hyperthermia or heat stress (HS) occurs when heat dissipation mechanisms are overwhelmed by external and internal heat production. Hyperthermia negatively affects reproduction and potentially compromises oocyte integrity and reduces developmental competence of ensuing embryos. Autophagy is the process by which cells recycle energy through the reutilization of cellular components and is activated by a variety of stressors. Study objectives were to characterize autophagy-related proteins in the ovary following cyclical HS during the follicular phase. Twelve gilts were synchronized and subjected to cyclical HS (n = 6) or thermal neutral (n = 6) conditions for 5 days during the follicular phase. Ovarian protein abundance of Beclin 1 and microtubule associated protein light chain 3 beta II were each elevated as a result of HS (P = 0.001 and 0.003, respectively). The abundance of the autophagy related (ATG)12-ATG5 complex was decreased as a result of HS (P = 0.002). Regulation of autophagy and apoptosis occurs in tight coordination, and B-cell lymphoma (BCL)2 and BCL2L1 are involved in regulating both processes. BCL2L1 protein abundance, as detected via immunofluorescence, was increased in both the oocyte (∼1.6-fold; P < 0.01) and granulosa cells of primary follicles (∼1.4-fold P < 0.05) of HS ovaries. These results suggest that ovarian autophagy induction occurs in response to HS during the follicular phase, and that HS increases anti-apoptotic signaling in oocytes and early follicles. These data contribute to the biological understanding of how HS acts as an environmental stress to affect follicular development and negatively impact reproduction.

Physiological mechanisms through which heat stress compromises reproduction in pigs

Seasonal variations in environmental temperatures impose added stress on domestic species bred for economically important production traits. These heat-mediated stressors vary on a seasonal, daily, or spatial scale, and negatively impact behavior and reduce feed intake and growth rate, which inevitably lead to reduced herd productivity. The seasonal infertility observed in domestic swine is primarily characterized by depressed reproductive performance, which manifests as delayed puberty onset, reduced farrowing rates, and extended weaning-to-estrus intervals. Understanding the effects of heat stress at the organismal, cellular, and molecular level is a prerequisite to identifying mitigation strategies that should reduce the economic burden of compromised reproduction. In this review, we discuss the effect of heat stress on an animal's ability to maintain homeostasis in multiple systems via several hypothalamic-pituitary-end organ axes. Additionally, we discuss our understanding of epigenetic programming and how hyperthermia experienced in utero influences industry-relevant postnatal phenotypes. Further, we highlight the recent recognized mechanisms by which distant tissues and organs may molecularly communicate via extracellular vesicles, a potentially novel mechanism contributing to the heat-stress response.

Acute heat stress activated inflammatory signaling in porcine oxidative skeletal muscle

Despite well-studied clinical manifestations, intracellular mechanisms of prolonged hyperthermic injury remain unclear, especially in skeletal muscle. Given muscle's large potential to impact systemic inflammation and metabolism, the response of muscle cells to heat-mediated injury warrants further investigation. We have previously reported increased activation of NF-κB signaling and increased NF-κB and AP-1-driven transcripts in oxidative skeletal muscle following 12 h of heat stress. The purpose of this investigation was to examine early heat stress-induced inflammatory signaling in skeletal muscle. We hypothesized that heat stress would increase NF-κB and AP-1 signaling in oxidative skeletal muscle. To address this hypothesis, 32 gilts were randomly assigned to one of four treatment groups (n = 8/group): control (0 h: 21°C) or exposed to heat stress conditions (37°C) for 2 h (n = 8), 4 h (n = 8), or 6 h (n = 8). Immediately following environmental exposure pigs were euthanized and the red portion of the semitendinosus muscle (STR) was harvested. We found evidence of NF-κB pathway activation as indicated by increased protein abundance of NF-κB activator IKK-α following 4 h and increased total NF-κB protein abundance following 6 h of heat stress. Heat stress also stimulated AP-1 signaling as AP-1 protein abundance was increased in nuclear fractions following 4 h of heat stress. Interleukin-6 protein abundance and activation of the JAK/STAT pathway were decreased in heat stressed muscle. These data indicate that heat stress activated inflammatory signaling in the porcine STR muscle via the AP-1 pathway and early activation of the NF-κB pathway.

Effects of heat stress during porcine reproductive and respiratory syndrome virus infection on metabolic responses in growing pigs

Heat stress (HS) and immune challenges negatively impact nutrient allocation and metabolism in swine, especially due to elevated heat load. In order to assess the effects of HS during Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection on metabolism, 9-wk old crossbred barrows were individually housed, fed ad libitum, divided into four treatments: thermo-neutral (TN), thermo-neutral PRRSV infected (TP), HS, and HS PRRSV infected (HP), and subjected to two experimental phases. Phase 1 occurred in TN conditions (22 °C) where half the animals were infected with PRRS virus (n = 12), while the other half (n = 11) remained uninfected. Phase 2 began, after 10 d with half of the uninfected (n = 6) and infected groups (n = 6) transported to heated rooms (35 °C) for 3 d of continuous heat, while the rest remained in TN conditions. Blood samples were collected prior to each phase and at trial completion before sacrifice. PPRS viral load indicated only infected animals were infected. Individual rectal temperature (Tr), respiration rates (RR), and feed intakes (FI) were determined daily. Pigs exposed to either challenge had an increased Tr, (P < 0.0001) whereas RR increased (P < 0.0001) with HS, compared to TN. ADG and BW decreased with challenges compared to TN, with the greatest loss to HP pigs. Markers of muscle degradation such as creatine kinase, creatinine, and urea nitrogen were elevated during challenges. Blood glucose levels tended to decrease in HS pigs. HS tended to decrease white blood cell (WBC) and lymphocytes and increase monocytes and eosinophils during HS. However, neutrophils were significantly increased (P < 0.01) during HP. Metabolic flexibility tended to decrease in PRRS infected pigs as well as HS pigs. Fatty acid oxidation measured by CO2 production decreased in HP pigs. Taken together, these data demonstrate the additive effects of the HP challenge compared to either PRRSV or HS alone.

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.

Disruption of female reproductive function by endotoxins

Endotoxemia can be caused by obesity, environmental chemical exposure, abiotic stressors and bacterial infection. Circumstances that deleteriously impact intestinal barrier integrity can induce endotoxemia, and controlled experiments have identified negative impacts of lipopolysaccharide (LPS; an endotoxin mimetic) on folliculogenesis, puberty onset, estrus behavior, ovulation, meiotic competence, luteal function and ovarian steroidogenesis. In addition, neonatal LPS exposures have transgenerational female reproductive impacts, raising concern about early life contacts to this endogenous reproductive toxicant. Aims of this review are to identify physiological stressors causing endotoxemia, to highlight potential mechanism(s) by which LPS compromises female reproduction and identify knowledge gaps regarding how acute and/or metabolic endotoxemia influence(s) female reproduction.

Determining the effects of early gestation in utero heat stress on postnatal fasting heat production and circulating biomarkers associated with metabolism in growing pigs

The study objective was to characterize effects of early gestation in utero heat stress (IUHS) on postnatal fasting heat production (FHP) and blood biomarkers associated with metabolism in growing pigs. Based on previous observation of increased postnatal core body temperature set point in IUHS pigs, we hypothesized that FHP would be altered during postnatal life because of IUHS. Pregnant first-parity gilts were exposed to thermoneutral (TN; = 4; 17.8 ± 0.1°C) or heat stress (HS; = 4; cyclical 28 to 38°C) conditions from d 30 to 60 of gestation. At weaning (21 d of age), 2 median-weight male pigs (1 barrow and 1 boar) were selected from each litter ( = 8 in utero TN [IUTN] and 8 IUHS pigs) and then housed in TN conditions based on age. Blood samples were collected at 8, 9, and 10 wk of age when pigs were in a fed state to analyze thyroxine (T4) and triiodothyronine (T3) concentrations. Pigs were trained to enter an indirect calorimeter from wk 8 through 10 of life and then acclimated over a 24-h period 1 wk prior to testing. At 12 wk of age, pigs were fasted for 24 h, and then indirect calorimetry was performed on individual pigs over a 23-h testing period to determine FHP and the respiratory quotient in 3 intervals (0900 to 1700 h, 1700 to 0000 h, and 0000 to 0800 h). Body weight was determined before and after testing and was similar for all pigs ( = 0.77; 37.0 ± 0.5 kg BW). Data were analyzed using PROC MIXED in SAS 9.4. No boar vs. barrow differences were observed with any analysis. Overall, FHP per kilogram BW was greater ( = 0.03; 12.1%) in IUHS pigs compared with IUTN pigs. Fasting heat production per kilogram BW was greater ( < 0.01; 19.8%) from 0900 to 1700 h compared with 1700 to 0000 h and 0000 to 0800 h and was greater (10.9%) from 1700 to 0000 h compared with 0000 to 0800 h. The RQ did not differ by in utero treatment ( = 0.51; 0.72 ± 0.01); however, the RQ was increased ( < 0.01; 13.0%) from 1700 to 0000 h compared with 0900 to 1700 h and 0000 to 0800 h. No other FHP and RQ differences were detected. Although no in utero treatment differences were observed for T4 ( = 0.11; 52.2 ± 6.2 ng/mL), T3 was greater overall ( = 0.04; 19.5%) in IUHS pigs than in IUTN pigs. In summary, FHP and circulating T3 were increased in IUHS pigs, and this may have implications for postnatal production efficiency in pigs gestated during hot summer months.

Heat stress causes dysfunctional autophagy in oxidative skeletal muscle

We have previously established that 24 h of environmental hyperthermia causes oxidative stress and have implicated mitochondria as likely contributors to this process. Given this, we hypothesized that heat stress would lead to increased autophagy/mitophagy and a reduction in mitochondrial content. To address this hypothesis pigs were housed in thermoneutral (TN; 20°C) or heat stress (35°C) conditions for 1- (HS1) or 3- (HS3) days and the red and white portions of the semitendinosus collected. We did not detect differences in glycolytic muscle. Counter to our hypothesis, upstream activation of autophagy was largely similar between groups as were markers of autophagosome nucleation and elongation. LC3A/B-I increased 1.6-fold in HS1 and HS3 compared to TN (P < 0.05), LC3A/B-II was increased 4.1-fold in HS1 and 4.8-fold in HS3 relative to TN, (P < 0.05) and the LC3A/B-II/I ratio was increased 3-fold in HS1 and HS3 compared to TN suggesting an accumulation of autophagosomes. p62 was dramatically increased in HS1 and HS3 compared to TN Heat stress decreased mitophagy markers PINK1 7.0-fold in HS1 (P < 0.05) and numerically by 2.4-fold in HS3 compared to TN and BNIP3L/NIX by 2.5-fold (P < 0.05) in HS1 and HS3. Markers of mitochondrial content were largely increased without activation of PGC-1α signaling. In total, these data suggest heat-stress-mediated suppression of activation of autophagy and autophagosomal degradation, which may enable the persistence of damaged mitochondria in muscle cells and promote a dysfunctional intracellular environment.

Prolonged environment-induced hyperthermia alters autophagy in oxidative skeletal muscle in Sus scrofa

Prolonged heat stress represents a continuing threat to human health and agricultural production. Despite the broad, negative impact of prolonged hyperthermia little is known about underlying pathological mechanisms leading to negative health outcomes, which has limited the development of etiological interventions and left clinicians and producers with only cooling and rehydration strategies. The purpose of this investigation was to determine the extent to which prolonged environment-induced hyperthermia altered autophagy in oxidative skeletal muscle in a large animal model, serving the dual purpose of accurately modeling human physiology as well as agricultural production. We hypothesized that prolonged hyperthermia would induce autophagy in skeletal muscle, independent of the accompanying caloric restriction. To test this hypothesis pigs were treated as follows: thermoneutral (20 °C), heat stress (35 °C), or were held under thermoneutral conditions but pair-fed to the heat stress group for seven days. Upon euthanasia the red portion of the semitendinosus was collected. We found that prolonged hyperthermic exposure increased oxidative stress without a corresponding change in antioxidant enzyme activities. Hyperthermia prevented initiation of autophagy despite increased markers of nucleation, elongation and autophagosome formation. However, p62 relative protein abundance, which is inversely correlated with autophagic degradation, was strongly increased suggesting suppressed degradation of autophagosomes. Markers of mitophagy and mitochondrial abundance were largely similar between groups. These data indicate that faulty autophagy plays a key role in hyperthermic muscle dysfunction.

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.

Short-term heat stress altered metabolism and insulin signaling in skeletal muscle

Heat-related complications continue to be a major health concern for humans and animals and lead to potentially life-threatening conditions. Heat stress (HS) alters metabolic parameters and may alter glucose metabolism and insulin signaling. Therefore, the purpose of this investigation was to determine the extent to which 12 h of HS-altered energetic metabolism in oxidative skeletal muscle. To address this, crossbred gilts (n = 8/group) were assigned to one of three environmental treatments for 12 h: thermoneutral (TN; 21 °C), HS (37 °C), or pair-fed to HS counterparts but housed in TN conditions (PFTN). Following treatment, animals were euthanized and the semitendinosus red (STR) was recovered. Despite increased relative protein abundance of the insulin receptor, insulin receptor substrate (IRS1) phosphorylation was increased (P = 0.0005) at S307, an inhibitory site, and phosphorylated protein kinase B (AKT) (S473) was decreased (P = 0.03) likely serving to impair insulin signaling following 12 h of HS. Further, HS increased phosphorylated protein kinase C (PKC) ζ/λ (P = 0.02) and phosphorylated PKCδ/θ protein abundance (P = 0.02), which are known to regulate inhibitory serine phosphorylation of IRS1 (S307). Sarcolemmal glucose transporter 4 (Glut4) was decreased (P = 0.04) in the membrane fraction of HS skeletal muscle suggesting diminished glucose uptake capacity. HS-mediated increases (P = 0.04) in mechanistic target of rapamycin (mTOR) were not accompanied by phosphorylation of eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1). HS decreased (P = 0.0006) glycogen synthase (GS) and increased (P = 0.02) phosphorylated GS suggesting impaired glycogen synthesis. In addition, HS altered fatty acid metabolic signaling by increasing (P = 0.02) Acetyl-CoA carboxylase (ACC), decreasing (P = 0.005) phosphorylated ATP-citrate lyase (pATPCL) and fatty acid synthase (P = 0.01) (FAS). These data suggest that 12 h of HS blunted insulin signaling, decreased protein synthesis, and altered glycogen and fatty acid metabolism.

Short-term heat stress results in increased apoptotic signaling and autophagy in oxidative skeletal muscle in Sus scrofa

Prolonged environment-induced hyperthermia causes morbidities and mortality in humans and animals and appears to cause organ-specific injury and dysfunction. We have previously determined autophagic dysfunction and apoptotic signaling in oxidative skeletal muscle following prolonged hyperthermia. The aim of this investigation was to extend our knowledge regarding the early chronology of heat stress-mediated apoptotic and autophagic signaling in oxidative skeletal muscle. We hypothesized that 2, 4, and 6 h of hyperthermia would increase apoptosis and autophagy in oxidative skeletal muscle compared to thermoneutral (TN) conditions. Pigs were assigned to four groups (n = 8/group) and exposed to environmental heat stress (37 °C) for 0, 2, 4, or 6 h. Immediately following environmental exposure animals were euthanized and the red portion of the semitendinosus was collected. Markers of apoptotic signaling were increased following 2 h of heating but returned to baseline thereafter, while caspase 3 activity remained elevated 2-3 fold (p < .05) throughout the hyperthermic period. Heat stress increased (p < .05) markers of autophagic activation, and nucleation as well as autophagosome formation and degradation linearly throughout the heating intervention. In addition, 6 h of hyperthermia increased (p < .05) markers of mitophagy. These data suggest that apoptotic signaling precedes increased autophagy during acute heat stress in oxidative skeletal muscle.

Short-term heat stress causes altered intracellular signaling in oxidative skeletal muscle

Heat stress (HS) causes morbidities and mortalities, in part by inducing organ-specific injury and dysfunction. Further, HS markedly reduces farm animal productivity, and this is especially true for lean tissue accretion. The purpose of this investigation was to determine the extent to which short-term HS caused muscle dysfunction in skeletal muscle. We have previously found increased free radical injury in skeletal muscle following 24 h of HS. Thus, we hypothesized that HS would lead to apoptosis, autophagy, and decreased mitochondrial content in skeletal muscle. To test this hypothesis, crossbred gilts were divided into 3 groups ( = 8/group): thermal neutral (TN: 21°C), HS (37°C), and pair-fed thermal neutral (PFTN: feed intake matched with heat-stressed animals). Following 12 h of treatment, animals were euthanized and red (STR) and white (STW) portions of the semitendinosus were recovered. Heat stress did not alter intracellular signaling in STW. In STR, the oxidative stress marker malondialdehyde protein and concentration were increased in HS ( = 0.007) compared to TN and PFTN, which was matched by an inadequate antioxidant response, including an increase in superoxide dismutase (SOD) I ( = 0.03) and II relative protein abundance ( = 0.008) and total SOD activity ( = 0.02) but a reduction ( = 0.006) in catalase activity in HS compared to TN. Further, B-cell lymphoma 2-associated X protein ( = 0.02) and apoptotic protease activating factor 1 ( = 0.01) proteins were increased by HS compared to TN and PFTN. However, caspase 3 activity was similar between groups, indicating a lack of apoptotic execution. Despite increased initiation, autophagy appeared to be inhibited by HS as the microtubule-associated protein A/B light chain 3 II/I ratio and mitofusin-2 proteins were decreased ( < 0.03) and sequestosome 1(p62) protein abundance was increased ( = 0.001) in HS compared to TN and PFTN. Markers of mitochondrial content cytochrome c, cytochrome c oxidase IV, voltage-dependent anion channel, pyruvate dehydrogenase, and prohibitins 1 were increased ( < 0.05) in HS compared to TN, whereas mitochondrial biogenesis and mitophagy markers were similar between groups. These data demonstrate that HS caused aberrant intracellular signaling, which may contribute to HS-mediated muscle dysfunction.

Effects of Diet and Genetics on Growth Performance of Pigs in Response to Repeated Exposure to Heat Stress

Heat stress (HS) is one of the costliest issues in the U.S. pork industry. Aims of the present study were to determine the consequences of repeated exposure to HS on growth performance, and the effects of a high fiber diet, the genetic potential for high lean tissue accretion, and the genetic potential for residual feed intake (RFI) on resilience to HS. Barrows (n = 97) from three genetic lines (commercial, high RFI, low RFI) where subjected three times to a 4-day HS treatment (HS1, HS2, and HS3) which was preceded by a 9-day neutral (TN) adaptation period (TN1) and alternated by 7-day periods of neutral temperatures (TN2, TN3, and TN4). Body weight gain (BWG), feed intake (FI), feed conversion efficiency (FCE), RFI, and the drop in BWG and FI between TN and HS were estimated for each period, and slaughter traits were measured at the end of TN4. Commercial pigs had lower FI when fed a high fiber diet compared to a regular diet (2.70 ± 0.08 vs. 2.96 ± 0.08 kg/d; P < 0.05), while no differences were found for BWG, RFI or FCE. HS reduced FI, BWG, and FCE, increased RFI, and resulted in leaner pigs that generate smaller carcasses at slaughter. In TN, commercial pigs grew faster than the low and high RFI pigs (1.22 ± 0.06 vs. 0.720 ± 0.05 and 0.657 ± 0.07; P < 0.001) but growth rates were not significantly different between the lines during HS. Growth rates for the low RFI and high RFI pigs were similar both during TN and during HS. Pigs of interest for genetic improvement are those that are able to maintain growth rates during HS. Our results show that response in growth to HS was repeatable over subsequent 4-d HS cycles, which suggests the potential for including this response in the breeding index. The best performing animals during HS are likely those that are not highly superior for growth in TN.

Temporal proteomic response to acute heat stress in the porcine muscle sarcoplasm

Heat stress (HS) is an important topic in the swine industry, costing hundreds of millions of dollars in economic losses annually, figures that could easily rise in light of global climate change. Muscle biology during HS is particularly important given skeletal muscle's large proportion to the body and its ultimate conversion to meat. Here we report the proteomic changes that occur during acute HS (37°C and 40% relative humidity) lasting 2, 4, or 6 h in the muscle sarcoplasm of growing pigs in comparison with 6 h of thermal neutral (TN; 21°C and 70% relative humidity) conditions ( = 8 per treatment). The red and white areas of the semitendinosus muscle were used to compare the differential effects of HS on oxidative or glycolytic muscles. The results support the hypothesis of proteomic profile differences between the acute HS and TN groups. Altered abundance ( < 0.05) of several proteins occurred in as little as 2 h of HS, affecting metabolism, cell structure, and chaperone, antioxidant, and proteolytic activity. We determined that the muscle HS response is both fiber type and time specific. Overall, more differences were observed in the red semitendinosus than in the white semitendinosus, although the time point at which differences were observed varied. These data show that as little as 2 h of HS has measurable effects on muscle proteins, indicating that acute HS has the potential to impair muscle function and growth.

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Roles for insulin-supported skeletal muscle growth

Basic principles governing skeletal muscle growth and development, from a cellular point of view, have been realized for several decades. Skeletal muscle is marked by the capacity for rapid hypertrophy and increases in protein content. Ultimately, skeletal muscle growth is controlled by 2 basic means: 1) myonuclear accumulation stemming from satellite cell (myoblast) proliferation and 2) the balance of protein synthesis and degradation. Each process underlies the rapid changes in lean tissue accretion evident during fetal and neonatal growth and is particularly sensitive to nutritional manipulation. Although multiple signals converge to alter skeletal muscle mass, postprandial changes in the anabolic hormone insulin link feed intake with enhanced rates of protein synthesis in the neonate. Indeed, a consequence of insulin-deficient states such as malnutrition is reduced myoblast activity and a net loss of body protein. A well-characterized mechanism mediating the anabolic effect of insulin involves the phosphatidylinositol 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling pathway. Activation of mTOR leads to translation initiation control via the phosphorylation of downstream targets. Modulation of this pathway by insulin, as well as by other hormones and nutrients, accounts for enhanced protein synthesis leading to efficient lean tissue accretion and rapid skeletal muscle gain in the growing animal. Dysfunctional insulin activity during fetal and neonatal stages likely alters growth through cellular and protein synthetic capacities.

A supplement containing multiple types of gluconeogenic substrates alters intake but not productivity of heat-stressed Afshari lambs

Thirty-two Afshari lambs were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments to evaluate a nutritional supplement designed to provide multiple gluconeogenic precursors during heat stress (HS). Lambs were housed in thermal neutral (TN) conditions and fed ad libitum for 8 d to obtain covariate data (period 1 [P1]) for the subsequent experimental period (period 2 [P2]). During P2, which lasted 9 d, half of the lambs were subjected to HS and the other 16 lambs were maintained in TN conditions but pair fed (PFTN) to the HS lambs. Half of the lambs in each thermal regime were fed (top-dressed) 100 g/d of a feed supplement designed to provide gluconeogenic precursors (8 lambs in HS [heat stress with Glukosa {HSG}] and 8 lambs in PFTN [pair-fed thermal neutral with Glukosa]) and the other lambs in both thermal regimes were fed only the basal control diet (HS without Glukosa [HSC] and pair-fed thermal neutral without Glukosa). Heat stress decreased DMI (14%) and by design there were no differences between the thermal treatments, but HSG lambs had increased DMI (7.5%; < 0.05) compared with the HSC lambs. Compared with PFTN lambs, rectal temperature and skin temperature at the rump, shoulder, and legs of HS lambs were increased ( < 0.05) at 0700 and 1400 h. Rectal temperature at 1400 h decreased for HSG lambs (0.15 ± 0.03°C; < 0.05) compared with HSC lambs. Despite similar DMI between thermal treatments, ADG for HS and PFTN lambs in P2 was decreased 55 and 85%, respectively, compared with lambs in P1 ( < 0.01). Although the prefeeding glucose concentration was not affected by thermal treatment or diet, HSG lambs had increased postfeeding glucose concentration compared with HSC lambs ( < 0.05). In contrast to the glucose responses, circulating insulin was influenced only by thermal treatment; HS lambs had increased insulin concentration ( < 0.01) before feeding and decreased concentration ( < 0.05) after feeding compared with PFTN lambs. Heat-stressed lambs had decreased NEFA concentration before feeding ( < 0.01) but not after feeding relative to PFTN lambs. Although this nutritional strategy did not affect ADG, the lower rectal temperature in HSG lambs indicates that dietary inclusion of a mixture of glucogenic precursors can potentially benefit animal health during HS.

Short-term heat stress alters redox balance in porcine skeletal muscle

Heat stress contributes to higher morbidity and mortality in humans and animals and is an agricultural economic challenge because it reduces livestock productivity. Redox balance and associated mitochondrial responses appear to play a central role in heat stress-induced skeletal muscle pathology. We have previously reported increased oxidative stress and mitochondrial content in oxidative muscle following 12 h of heat stress. The purposes of this investigation were to characterize heat stress-induced oxidative stress and changes in mitochondrial content and biogenic signaling in oxidative skeletal muscle. Crossbred gilts were randomly assigned to either thermal neutral (21°C; n = 8, control group) or heat stress (37°C) conditions for 2 h (n = 8), 4 h (n = 8), or 6 h (n = 8). At the end, their respective environmental exposure, the red portion of the semitendinosus muscle (STR) was harvested. Heat stress increased concentration of malondialdehyde (MDA) following 2 and 4 h compared to thermal neutral and 6 h, which was similar to thermal neutral, and decreased linearly with time. Protein carbonyl content was not influenced by environment. Catalase activity was increased following 4 h of heat stress and superoxide dismutase activity was decreased following 6 h of heat stress compared to thermal neutral conditions. Heat stress-mediated changes in antioxidant activity were independent of altered protein abundance or transcript expression. Mitochondrial content and mitochondrial biogenic signaling were similar between groups. These data demonstrate that heat stress caused a transient increase in oxidative stress that was countered by a compensatory change in catalase activity. These findings contribute to our growing understanding of the chronology of heat stress-induced intracellular dysfunctions in skeletal muscle.

Effect of heat stress on the endogenous intestinal loss of amino acids in growing pigs

Heat stress (HS) increases the death of intestinal cells in pigs, which, in turn, may elevate the endogenous intestinal loss (EIL) of proteins and AA. An experiment was conducted to analyze the effect of HS on the AA composition of intestinal endogenous proteins and the EIL of AA in pigs. Eight pigs (25.2 ± 1.2 kg initial BW) were surgically implanted with T-type cannulas at the end of the small intestine. After surgery recovery, during the subsequent 7 d, all pigs were adapted to a protein- and AA-free diet and trained to consume the same amount of feed twice a day. All pigs were housed under thermoneutral (TN) conditions (22 ± 2°C) during this time. The following day, all pigs were still under TN conditions and ileal content was collected during 12 consecutive hours, at the end of which and for the following 8 d the pigs were exposed to natural HS conditions (31 to 37°C). Ileal content was collected again on d 2 (HS at d 2 [HSd2]) and 8 (HS at d 8 [HSd8]). Body temperature (BT) was measured in another group of 8 pigs every 15 min during the whole study. The average BT at HSd2 (39.6°C) was higher ( < 0.05) compared with both TN conditions (38.6°C) and HSd8 (38.8°C), but it did not differ between TN conditions and HSd8. The AA composition of endogenous intestinal protein was not affected by HS. The EIL of Arg and His were greater ( < 0.05) and the EIL of Thr and Phe tended to be greater ( ≤ 0.10) at HSd2 than in TN conditions; the EIL of Pro was greater ( = 0.01) at HSd8. The EIL of the remaining AA was not affected by HS. Although HS increased the EIL of Arg and His within the first 2 d, it appeared that normal EIL was shortly reestablished. These data show that acute HS does not affect the AA composition of intestinal endogenous proteins in growing pigs and that the EIL of AA may not be critical in growing pigs acclimated to high ambient temperature. Nevertheless, the increased EIL of Arg and Thr at HSd2 indicate that HS might affect the integrity of the intestinal epithelium of pigs during the first day of their exposure to high ambient temperature.

Dietary organic zinc attenuates heat stress-induced changes in pig intestinal integrity and metabolism

Dietary zinc (inorganic and organic or zinc AA complex forms) is essential for normal intestinal barrier function and regeneration of intestinal epithelium. Given that heat stress (HS) exposure can negatively affect intestinal integrity and caloric intake, possible nutritional mitigation strategies are needed to improve health, performance, and well-being. Therefore, our objective was to evaluate 2 dietary zinc sources and reduced caloric intake on intestinal integrity in growing pigs subjected to 12 h of HS. A total of 36 pigs were fed 1 of 2 diets: 1) a control diet (CON; 120 mg/kg of zinc from zinc sulfate) or 2) 60 mg/kg from zinc sulfate and 60 mg/kg from zinc AA complex (ZnAA). After 17 d, the CON pigs were then exposed to thermal neutral (TN) conditions with ad libitum intake (TN-CON), HS (37°C) with ad libitum intake (HS-CON), or pair-fed to HS intake under TN conditions (PFTN); the ZnAA pigs were exposed to only HS (HS-ZnAA). All pigs were sacrificed after 12 h of environmental exposure, and blood and tissue bioenergetics stress markers and ex vivo ileum and colon integrity were assessed. Compared with TN-CON, HS significantly ( < 0.05) increased rectal temperatures and respiration rates. Ileum villus and crypt morphology was reduced by both pair-feeding and HS. Both PFTN and HS-CON pigs also had reduced ileum integrity (dextran flux and transepithelial resistance) compared with the TN-CON pigs. However, ZnAA tended to mitigate the HS-induced changes in ileum integrity. Ileum mucin 2 protein abundance was increased due to HS and pair-feeding. Colonic integrity did not differ due to HS or PFTN treatments. Compared with the HS-CON, HS-ZnAA pigs tended to have reduced blood endotoxin concentrations. In conclusion, HS and reduced feed intake compromised intestinal integrity in pigs, and zinc AA complex source mitigates some of these negative effects.

Effects of acute heat stress on lipid metabolism of bovine primary adipocytes

Heat stress (HS) affects numerous physiological processes including nutrient partitioning and lipid metabolism. Objectives of this study were to evaluate how acute HS affects lipid metabolism in subcutaneous adipose tissue of dairy cattle. Adipose tissue biopsies were performed on Holstein cows for bovine primary adipocyte isolation and cultured at either 42°C (HS) or 37°C (thermal neutral, TN). Adipocytes were incubated with increasing isoproterenol (ISO), and with increasing concentrations of insulin in the presence of ISO to evaluate changes in lipolysis. Incorporation of radioactive acetate into lipids was measured as an indicator of lipogenesis. Abundance and phosphorylation of several lipolytic and lipogenic proteins were also measured. Adipocytes exposed to HS had an elevated maximal response to ISO and were more sensitive to lipolytic stimulation by ISO compared with cells cultured at TN. Thermal treatment did not affect the antilipolytic effects of insulin in the presence of ISO. Lipogenesis measured as acetate incorporation was not altered by HS, but a temperature by insulin interaction was observed for the regulation of acetyl CoA carboxylase, such that the presence of insulin resulted in a reduction in phosphorylation of acetyl CoA carboxylase in adipocytes cultured at TN but not HS conditions. Results of this study demonstrate that acute HS has a direct effect on the regulation of lipolysis and the rate-limiting enzyme of lipogenesis in isolated bovine adipocytes.

In utero heat stress increases postnatal core body temperature in pigs

In utero heat stress (IUHS) negatively impacts postnatal development, but how it alters future body temperature parameters and energetic metabolism is not well understood. Future body temperature indices and bioenergetic markers were characterized in pigs from differing in utero thermal environments during postnatal thermoneutral (TN) and cyclical heat stress (HS) exposure. First-parity pregnant gilts ( = 13) were exposed to 1 of 4 ambient temperature (T) treatments (HS [cyclic 28°C to 34°C] or TN [cyclic 18°C to 22°C]) applied for the entire gestation (HSHS, TNTN), HS for the first half of gestation (HSTN), or HS for the second half of gestation (TNHS). Twenty-four offspring (23.1 ± 1.2 kg BW; = 6 HSHS, = 6 TNTN, = 6 HSTN, = 6 TNHS) were housed in TN (21.7°C ± 0.7°C) conditions and then exposed to 2 separate but similar HS periods (HS1 = 6 d; HS2 = 6 d; cycling 28°C to 36°C). Core body temperature (T) was assessed every 15 min with implanted temperature recorders. Regardless of in utero treatment, T increased during both HS periods ( = 0.01; 0.58°C). During TN, HS1, and HS2, all IUHS pigs combined had increased T ( = 0.01; 0.36°C, 0.20°C, and 0.16°C, respectively) compared to TNTN controls. Although unaffected by in utero environment, the total plasma thyroxine to triiodothyronine ratio was reduced ( = 0.01) during HS1 and HS2 (39% and 29%, respectively) compared with TN. In summary, pigs from IUHS maintained an increased T compared with TNTN controls regardless of external T, and this thermal differential may have practical implications to developmental biology and animal bioenergetics.

Twelve hours of heat stress induces inflammatory signaling in porcine skeletal muscle

Heat stress causes morbidity and mortality in humans and animals and threatens food security by limiting livestock productivity. Inflammatory signaling may contribute to heat stress-mediated skeletal muscle dysfunction. Previously, we discovered increased circulating endotoxin and intramuscular oxidative stress and TNF-α protein abundance, but not inflammatory signaling following 24 and 72 h of heat stress. Thus the purpose of this investigation was to clarify the role of inflammatory signaling in heat-stressed skeletal muscle. Crossbred gilts (n = 8/group) were assigned to either thermal neutral (24°C), heat stress (37°C), or pair-fed thermal neutral (24°C) conditions for 12 h. Following treatment, animals were euthanized, and the semitendinosus red (STR) and white (STW) were recovered. Heat stress did not alter inflammatory signaling in STW. In STR, relative heat shock protein abundance was similar between groups, as was nuclear content of heat shock factor 1. In whole homogenate, relative abundance of the NF-κB activator inhibitory κB kinase-α was increased by heat stress, although abundance of NF-κB was similar between groups. Relative abundance of phosphorylated NF-κB was increased by heat stress in nuclear fractions. Activator protein-1 (AP-1) signaling was similar between groups. While there were few differences in transcript expression between thermal neutral and heat stress, 80 and 56% of measured transcripts driven by NF-κB or AP-1, respectively, were increased by heat stress compared with pair-fed thermal neutral. Heat stress also caused a reduction in IL-6 transcript and relative protein abundance. These data demonstrate that short-term heat stress causes inflammatory signaling through NF-κB in oxidative, but not glycolytic, skeletal muscle.

Skeletal muscle and hepatic insulin signaling is maintained in heat-stressed lactating Holstein cows

Multiparous cows (n=12; parity=2; 136±8 d in milk, 560±32kg of body weight) housed in climate-controlled chambers were fed a total mixed ration (TMR) consisting primarily of alfalfa hay and steam-flaked corn. During the first experimental period (P1), all 12 cows were housed in thermoneutral conditions (18°C, 20% humidity) with ad libitum intake for 9 d. During the second experimental period (P2), half of the cows were fed for ad libitum intake and subjected to heat-stress conditions [WFHS, n=6; cyclical temperature 31.1 to 38.9°C, 20% humidity: minimum temperature humidity index (THI)=73, maximum THI=80.5], and half of the cows were pair-fed to match the intake of WFHS cows in thermal neutral conditions (TNPF, n=6) for 9 d. Rectal temperature and respiration rate were measured thrice daily at 0430, 1200, and 1630 h. To evaluate muscle and liver insulin responsiveness, biopsies were obtained immediately before and after an insulin tolerance test on the last day of each period. Insulin receptor (IR), insulin receptor substrate 1 (IRS-1), AKT/protein kinase B (AKT), and phosphorylated AKT (p-AKT) were measured by Western blot analyses for both tissues. During P2, WFHS increased rectal temperature and respiration rate by 1.48°C and 2.4-fold, respectively. Heat stress reduced dry matter intake by 8kg/d and, by design, TNPF cows had similar intake reductions. Milk yield was decreased similarly (30%) in WFHS and TNPF cows, and both groups entered into a similar (-4.5 Mcal/d) calculated negative energy balance during P2. Insulin infusion caused a less rapid glucose disposal in P2 compared with P1, but glucose clearance did not differ between environments in P2. In liver, insulin increased p-AKT protein content in each period. Phosphorylation ratio of AKT increased 120% in each period after insulin infusion. In skeletal muscle, protein abundance of the IR, IRS, and AKT remained stable between periods and environment. Insulin increased skeletal muscle p-AKT in each period, but the phosphorylation ratio (abundance of phosphorylated protein:abundance of total protein) of AKT was decreased in P2 for TNPF animals, but not during WFHS. These results indicate that mild systemic insulin resistance during HS may be related to reduced nutrient intake but skeletal muscle and liver insulin signaling remains unchanged.

Hormonal and metabolic responses to upper temperature extremes in divergent life-history ecotypes of a garter snake

Extreme temperatures constrain organismal physiology and impose both acute and chronic effects. Additionally, temperature-induced hormone-mediated stress response pathways and energetic trade-offs are important drivers of life-history variation. This study employs an integrative approach to quantify acute physiological responses to high temperatures in divergent life-history ecotypes of the western terrestrial garter snake (Thamnophis elegans). Using wild-caught animals, we measured oxygen consumption rate and physiological markers of hormonal stress response, energy availability, and anaerobic respiration in blood plasma across five ecologically relevant temperatures (24, 28, 32, 35, and 38° C; 3-hour exposure). Corticosterone, insulin, and glucose concentrations all increased with temperature, but with different thermal response curves, suggesting that high temperatures differently affect energy-regulation pathways. Additionally, oxygen consumption rate increased without plateau and lactate concentration did not increase with temperature, challenging the recent hypothesis that oxygen limitation sets upper thermal tolerance limits. Finally, animals had similar physiological thermal responses to high-temperature exposure regardless of genetic background, suggesting that local adaptation has not resulted in fixed differences between ecotypes. Together, these results identify some of the mechanisms by which higher temperatures alter hormonal-mediated energy balance in reptiles and potential limits to the flexibility of this response.

Insulin: pancreatic secretion and adipocyte regulation

Insulin is the primary acute anabolic coordinator of nutrient partitioning. Hyperglycemia is the main stimulant of insulin secretion, but other nutrients such as specific amino acids, fatty acids, and ketoacids can potentiate pancreatic insulin release. Incretins are intestinal hormones with insulinotropic activity and are secreted in response to food ingestion, thus integrating diet chemical composition with the regulation of insulin release. In addition, prolactin is required for proper islet development, and it stimulates β-cell proliferation. Counterintuitively, bacterial components appear to signal insulin secretion. In vivo lipopolysaccharide infusion acutely increases circulating insulin, which is paradoxical as endotoxemia is a potent catabolic condition. Insulin is a potent anabolic orchestrator of nutrient partitioning, and this is particularly true in adipocytes. Insulin dictates lipid accretion in a dose-dependent manner during preadipocyte development in adipose tissue-derived stromal vascular cell culture. However, in vivo studies focused on insulin's role in regulating adipose tissue metabolism from growing, and market weight pigs are sometimes inconsistent, and this variability appears to be animal, age and depot dependent. Additionally, porcine adipose tissue synthesizes and secretes a number of adipokines (leptin, adiponectin, and so forth) that directly or indirectly influence insulin action. Therefore, because insulin has an enormous impact on agriculturally important phenotypes, it is critical to have a better understanding of how insulin homeostasis is governed.

Effects of in utero heat stress on postnatal body composition in pigs: I. Growing phase

Environmentally induced heat stress (HS) negatively influences production variables in agriculturally important species. However, the extent to which HS experienced in utero affects nutrient partitioning during the rapid lean tissue accretion phase of postnatal growth is unknown. Study objectives were to compare future whole-body tissue accretion rates in pigs exposed to differing in utero and postnatal thermal environments when lean tissue deposition is likely maximized. Pregnant sows were exposed to thermoneutral (TN; cyclical 15°C nighttime and 22°C daytime; n = 9) or HS (cyclical 27°C nighttime and 37°C daytime; n = 12) conditions during their entire gestation. Twenty-four offspring from in utero TN (IUTN; n = 6 gilts and 6 barrows; 30.8 ± 0.2 kg BW) and in utero HS (IUHS; n = 6 gilts and 6 barrows; 30.3 ± 0.2 kg BW) were euthanized as an initial slaughter group (ISG). Following the ISG, 48 pigs from IUTN (n = 12 gilts and 12 barrows; 34.1 ± 0.5 kg BW) and IUHS (n = 12 gilts and 12 barrows; 33.3 ± 0.3 kg BW) were exposed to constant HS (34.1 ± 2.4°C) or TN (21.5 ± 2.0°C) conditions until they reached 61.5 ± 0.8 kg BW, at which point they were sacrificed and their whole-body composition was determined. Homogenized carcasses were analyzed for N, crude fat, ash, water, and GE content. Data were analyzed using PROC MIXED in SAS 9.3. Rectal temperature and respiration rate increased (P < 0.01) during postnatal HS compared to TN (39.4 vs. 39.0°C and 94 vs. 49 breaths per minute, respectively). Regardless of in utero environment, postnatal HS reduced (P < 0.01) feed intake (2.06 vs. 2.37 kg/d) and ADG (0.86 vs. 0.98 kg/d) compared to TN conditions. Postnatal HS did not alter water, protein, and ash accretion rates but reduced lipid accretion rates (198 vs. 232 g/d; P < 0.04) compared to TN-reared pigs. In utero environment had no effect on future tissue deposition rates; however, IUHS pigs from the ISG had reduced liver weight (P < 0.04; 17.9%) compared to IUTN controls. In summary, postnatal HS reduced adipose tissue accretion rates, but IUHS did not appear to impact either lean or adipose tissue accretion during this specific growth phase.

Effects of in utero heat stress on postnatal body composition in pigs: II. Finishing phase

The detrimental effects of heat stress (HS) on animal productivity have been well documented. However, whether in utero HS interacts with a future thermal insult to alter tissue deposition during the finishing phase of pig growth is unknown. Study objectives were to compare the subsequent rate and quantity of whole-body tissue accretion in pigs exposed to differing in utero and postnatal thermal environments. Pregnant sows were exposed to thermoneutral (TN; cyclical 15°C nighttime and 22°C daytime; n = 9) or HS (cyclical 27°C nighttime and 37°C daytime; n = 11) conditions during their entire gestation. Twenty-four offspring from in utero TN (IUTN; n = 6 gilts and 6 barrows; 62.4 ± 0.7 kg BW) and in utero HS (IUHS; n = 6 gilts and 6 barrows; 61.9 ± 0.8 kg BW) were euthanized as part of an initial slaughter group (ISG). After the ISG, 48 pigs from IUTN (n = 12 gilts and 12 barrows; 66.1 ± 1.0 kg BW) and IUHS (n = 12 gilts and 12 barrows; 63.4 ± 0.7 kg BW) were exposed to constant HS (34.4 ± 1.8°C) or TN (22.7 ± 2.5°C) conditions until they reached 80.5 ± 1.5 kg BW, at which point they were sacrificed and their whole-body composition was determined. Homogenized carcasses were analyzed for N, crude fat, ash, water, and GE content. Data were analyzed using PROC MIXED in SAS 9.3. Rectal temperature and respiration rate increased during postnatal HS compared to TN (39.6 vs. 39.3°C and 92 vs. 58 breaths per minute, respectively; P < 0.01). Postnatal HS decreased (P < 0.01) feed intake (2.13 vs. 2.65 kg/d) and ADG (0.70 vs. 0.94 kg/d) compared to TN conditions, but neither variable was influenced by in utero environment. Whole-body protein and lipid accretion rates were reduced in HS pigs compared to TN controls (126 vs. 164 g/d and 218 vs. 294 g/d, respectively; P < 0.04). Independent of postnatal environments, IUHS reduced future protein accretion rates (16%; P < 0.01) and tended to increase lipid accretion rates (292 vs. 220 g/d; P < 0.07) compared to IUTN controls. The ratio of lipid to protein accretion rates increased (95%; P < 0.01) in IUHS pigs compared to IUTN controls. In summary, the future hierarchy of tissue accretion is altered by IUHS, and this modified nutrient partitioning favors adipose deposition at the expense of skeletal muscle during this specific phase of growth.

Acute Heat Stress and Reduced Nutrient Intake Alter Intestinal Proteomic Profile and Gene Expression in Pigs

Heat stress and reduced feed intake negatively affect intestinal integrity and barrier function. Our objective was to compare ileum protein profiles of pigs subjected to 12 hours of HS, thermal neutral ad libitum feed intake, or pair-fed to heat stress feed intake under thermal neutral conditions (pair-fed thermal neutral). 2D-Differential In Gel Electrophoresis and gene expression were performed. Relative abundance of 281 and 138 spots differed due to heat stress, compared to thermal neutral and pair-fed thermal neutral pigs, respectively. However, only 20 proteins were different due to feed intake (thermal neutral versus pair-fed thermal neutral). Heat stress increased mRNA expression of heat shock proteins and protein abundance of heat shock proteins 27, 70, 90-α and β were also increased. Heat stress reduced ileum abundance of several metabolic enzymes, many of which are involved in the glycolytic or TCA pathways, indicating a change in metabolic priorities. Stress response enzymes peroxiredoxin-1 and peptidyl-prolyl cis-trans isomerase A were decreased in pair-fed thermal neutral and thermal neutral pigs compared to heat stress. Heat stress increased mRNA abundance markers of ileum hypoxia. Altogether, these data show that heat stress directly alters intestinal protein and mRNA profiles largely independent of reduced feed intake. These changes may be related to the reduced intestinal integrity associated with heat stress.

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

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

Heat stress increases insulin sensitivity in pigs

Proper insulin homeostasis appears critical for adapting to and surviving a heat load. Further, heat stress (HS) induces phenotypic changes in livestock that suggest an increase in insulin action. The current study objective was to evaluate the effects of HS on whole-body insulin sensitivity. Female pigs (57 ± 4 kg body weight) were subjected to two experimental periods. During period 1, all pigs remained in thermoneutral conditions (TN; 21°C) and were fed ad libitum. During period 2, pigs were exposed to: (i) constant HS conditions (32°C) and fed ad libitum (n = 6), or (ii) TN conditions and pair-fed (PFTN; n = 6) to eliminate the confounding effects of dissimilar feed intake. A hyperinsulinemic euglycemic clamp (HEC) was conducted on d3 of both periods; and skeletal muscle and adipose tissue biopsies were collected prior to and after an insulin tolerance test (ITT) on d5 of period 2. During the HEC, insulin infusion increased circulating insulin and decreased plasma C-peptide and nonesterified fatty acids, similarly between treatments. From period 1 to 2, the rate of glucose infusion in response to the HEC remained similar in HS pigs while it decreased (36%) in PFTN controls. Prior to the ITT, HS increased (41%) skeletal muscle insulin receptor substrate-1 protein abundance, but did not affect protein kinase B or their phosphorylated forms. In adipose tissue, HS did not alter any of the basal or stimulated measured insulin signaling markers. In summary, HS increases whole-body insulin-stimulated glucose uptake.

Environmental heat stress modulates thyroid status and its response to repeated endotoxin challenge in steers

The objective of this study was to evaluate in cattle, the effects of acute exposure to a heat stress (HS) environment on the status of the pituitary (thyrotropin, TSH)-thyroid (thyroxine, T4)-peripheral tissue T4 deiodination (type 1 5'-deiodinase [D1]; triiodothyronine [T3]; reverse-triiodothyronine [rT3]) axis, and the further response of this pituitary-thyroid-peripheral tissue axis (PTTA) to perturbation caused by the induction of the proinflammatory innate immune state provoked by the administration of gram-negative bacteria endotoxin (lipopolysaccharide [LPS]). Ten steers (318 ± 49 kg body weight) housed in controlled environment chambers were subjected to either a thermoneutral (TN: constant 19°C) or HS temperature conditions (cyclical daily temperatures: 32.2°C-40.0°C) for a total period of 9 d. To minimize the effects of altered plane of nutrition due to HS, steers in TN were pair-fed to animals in HS conditions. Steers received 2 LPS challenges 3 d apart (LPS1 and LPS2; 0.2 μg/kg body weight, intravenously, Escherichia coli 055:B5) with the first challenge administered on day 4 relative to the start of the environmental conditioning. Jugular blood samples were collected at 0, 1, 2, 4, 7, and 24 h relative to the start of each LPS challenge. Plasma TSH, T4, T3, and rT3 were measured by radioimmunoassay. Liver D1 activity was measured in biopsy samples collected before the LPS1 (0 h) and 24 h after LPS2. Before the start of LPS1, HS decreased (P < 0.01 vs TN) plasma TSH (40%), T4 (45.4%), and T3 (25.9%), but did not affect rT3 concentrations. In TN steers, the LPS1 challenge decreased (P < 0.01 vs 0 h) plasma concentrations of TSH between 1 and 7 h and T4 and T3 at 7 and 24 h. In HS steers, plasma TSH concentrations were decreased at 2 h only (P < 0.05), whereas plasma T3 was decreased at 7 and 24 h (P < 0.01). Whereas plasma T4 concentrations were already depressed in HS steers at 0 h, LPS1 did not further affect the levels. Plasma rT3 concentrations were increased in all steers at 4, 7, and 24 h after LPS1 (P < 0.01). The patterns of concentration change of T4, T3, and rT3 during LPS2 mirrored those observed in LPS1; the responses in plasma TSH were of smaller magnitude than those incurred after LPS1. The LPS challenges reduced (P < 0.01) hepatic activity of D1 in all animals but no differences were observed between steers subjected to TN or HS environment. The data are consistent with the concept that acute exposure of cattle to a HS environment results in the depression of the pituitary and thyroid components of the PTTA, whereas a normal capacity to generate T3 from T4 in the liver is preserved. The data also suggest that LPS challenge further suppresses all components of the PTTA including liver T3 generation, and these PTTA perturbations are more pronounced in steers that encounter a HS exposure.

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

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