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Increased global temperatures pose challenges to livestock agriculture. Domestic swine are particularly sensitive to hotter environments due to their inability to sweat, litter bearing nature, difficulty in expressing natural cooling behaviors, and intense genetic selection for production traits. Since animal welfare is central to livestock production as a matter vital to efficiency as much as ethics, developing novel traits that may be genetically related to heat tolerance may assist in improving and sustaining animal welfare. The objective of this study was to develop novel traits of behavior using an ethogram designed for efficiency in production settings, estimate the variance components, and correlate these traits with indicators of heat tolerance and maternal ability. This study considered 1,312 individual Landrace-Large White cross production sows between 6 and 19 days of lactation. Animals were housed in farrowing crates in a commercial setting in southern North Carolina in June and July of 2021, an environment susceptible to potential heat stress. These sows were subjected to a standardized procedure involving a person removing hair from both hips using an electric clipper while an observer was positioned in front of the sow to record behaviors. Scores were later applied to the variations in behavior both for changes in positions and types of vocalizations displayed by the animals during handling. Genotypes were obtained from hair follicles and captured by a 50K porcine SNP panel. Variance components for novel behavior traits were obtained using the BLUPF90+ programs and genomic relationship matrix to estimate genetic correlations of behavior with several indicators of heat tolerance and maternal ability. Heritabilities for behavior traits ranged from 0.131 for vocalization score to 0.072 for shaving time, while heritabilities for heat tolerance and maternal ability ranged from 0.15 to 0.03 for vaginal temperature and respiration efficiency, respectively. The maternal ability traits were based on the single current litter and had the lowest heritabilities ranging from 0.101 to 0.04 for number born alive and number of mummies, respectively. High and positive genetic correlations indicate a potential for coupled selection for both fewer mummified piglets and a greater number of liveborn using the behavior trait of vocalization score. These correlations between favorable maternal traits and behavior traits suggest the potential that one or more complex biological pathways exist that share relevancy between these traits. However, genetic correlations between the behavior traits and heat tolerance indicators were low to negligible, most with a magnitude falling below 0.10, revealing the need for other traits to be used as selection parameters for heat tolerance. Further studies may be able to capture additional environmental effects to improve models of behavior and create indirect measures more obtainable than direct measures of heat tolerance. [ABSTRACT FROM AUTHOR]

The effects of in utero heat stress (IUHS) range from decreased growth performance to altered behavior, but the long-term impact of IUHS on postnatal innate immune function in pigs is unknown. Therefore, the study objective was to determine the effects of early gestation IUHS on the immune, metabolic, and stress response of pigs subjected to an 8 hr lipopolysaccharide (LPS) challenge during postnatal life. Twenty-four pregnant gilts were exposed to thermoneutral (TN ; n = 12; 17.5 ± 2.1 °C) or heat stress (HS ; n = 12; cyclic 26 to 36 °C) conditions from days 6 to 59 of gestation, and then TN conditions (20.9 ± 2.3 °C) from day 60 of gestation to farrowing. At 12 wk of age, 16 IUHS and 16 in utero thermoneutral (IUTN) pigs were selected, balanced by sex and given an intravenous injection of LPS (2 µg/kg BW mixed with sterile saline [ SAL ] and injected at 2 µL/kg BW) or SAL (2 µL/kg BW). Body temperature was monitored every 30 min, and blood was obtained at 0, 1, 2, 3, 4, 6, and 8 hr following the LPS challenge. Blood samples were analyzed for glucose, insulin, non-esterified fatty acids (NEFA), cortisol, and cytokine concentrations. In addition, white blood cell counts were determined at 0 and 4 hr. Hour 0 data were used as covariates. Body temperature was increased (P < 0.01) in LPS (40.88 ± 0.08 °C) vs. SAL (39.83 ± 0.08 °C) pigs. Eosinophils tended to be decreased overall (P = 0.09; 43.9%) in IUHS vs. IUTN pigs. Glucose concentrations were reduced overall (P = 0.05; 5.9%) in IUHS vs. IUTN pigs. The NEFA concentrations tended to be greater (P = 0.07; 143.4%) in IUHS-LPS pigs compared with all other treatments, and IUTN-LPS pigs tended to have greater (127.4%) circulating NEFA concentrations compared with IUTN-SAL and IUHS-SAL pigs. Cortisol was increased (P = 0.04) in IUHS-LPS compared with IUTN-LPS pigs at 3 hr (21.5%) and 4 hr (64.3%). At 1 hr, tumor necrosis factor α was increased (P = 0.01; 115.1%) in IUHS-LPS compared with IUTN-LPS pigs. Overall, interleukin-1β (IL-1β) and interleukin-6 (IL-6) were greater (P < 0.04; 281.3% and 297.8%, respectively) in IUHS-LPS pigs compared with all other treatments, and IUTN-LPS pigs had increased IL-1β and IL-6 concentrations compared with IUTN-SAL and IUHS-SAL pigs. In summary, IUHS altered the postnatal cytokine, metabolic, and physiological stress response of pigs during postnatal life, which may have negative implications toward the innate immune response of IUHS pigs to pathogens. [ABSTRACT FROM AUTHOR]

Heat stress (HS) is a multi-factorial problem that negatively affects livestock health and productivity and is closely linked with animal welfare. While HS may not be harmful when animals are able to adapt, the physiological changes that occur to ensure survival may impede the efficient conversion of feed energy into animal products. This adaptive response can be variable and is often based on previous HS exposure, genetics, species and production stage. When the heat load becomes too great for adaptive responses to compensate, the subsequent strain response causes reduced productivity and well-being and, in severe cases, mortality. The effects of HS on livestock productivity are well documented and range from decreased feed intake and body weight gain, to reduced reproductive efficiency and altered carcass composition and meat quality. In addition, researchers are beginning to elucidate the effects of prenatal HS on postnatal livestock performance and welfare. As knowledge of the negative impacts of HS on livestock performance and welfare increases, so will the development of effective mitigation strategies to support maintenance of productivity during times of high thermal heat loads and preserve appropriate animal welfare standards. [ABSTRACT FROM AUTHOR]

Study objectives were to evaluate the impact of early life thermal stress (ELTS) on thermoregulation, stress response, and intestinal health of piglets subjected to a future heat stress (HS) challenge during simulated transport. From d 7 to 9 post-farrowing, 12 first-parity sows and their litters were exposed to thermoneutral (ELTN; 25.4 ± 1.1 °C w/heat lamp; n = 4), HS (ELHS; cycling 32-38 °C w/heat lamp; n = 4), or cold stress (ELCS; 25.4 ± 1.1 °C w/no heat lamp; n = 4) conditions, and then from d 10 until weaning all piglets were exposed to thermoneutral (TN) conditions (25.3 ± 1.9 °C w/heat lamp). During the ELTS period, respiration rate, rectal temperature (TR), and skin temperature (TS) of three mixed-sex piglets per dam were monitored daily (0800, 1200, 1600, 2000 h). At 13 ± 1.3 d of age, temperature recorders were implanted intra-abdominally into all piglets. At weaning (20.0 ± 1.3 d of age), piglets were bled and then herded up a ramp into a simulated transport trailer and exposed to HS conditions (cycling 32-38 °C) for 8 h. During the 8 h simulated transport, core body temperature (TC) and TS were assessed every 15 min. After the simulated transport, piglets were unloaded from the trailer, bled, weighed, and then housed individually in TN conditions (28.5 ± 0.7 °C) for 7 d. During this time, ADFI and ADG were monitored, blood samples were taken on d 1, 4, and 7, and piglets were video-recorded to assess behavior. Piglets were sacrificed on d 8 post-simulated transport and intestinal morphology was assessed. Data were analyzed using PROC MIXED in SAS 9.4. In the ELTS period, piglet TR was increased overall (P = 0.01) in ELHS (39.77 ± 0.05 °C) compared to ELTN (39.34 ± 0.05 °C) and ELCS (39.40 ± 0.05 °C) litters. During simulated transport, TC was greater (P = 0.02) in ELHS (40.84 ± 0.12 °C) compared to ELTN (40.49 ± 0.12 °C) and ELCS (40.39 ± 0.12 °C) pigs. Following simulated transport, BW loss was greater (P = 0.01; 40%) for ELHS compared to ELTN and ELCS pigs and ADFI was reduced (P = 0.05; 28.6%) in ELHS compared to ELTN pigs. Sitting behavior tended to be increased (P = 0.06; 47.4%) in ELHS vs. ELCS or ELTN pigs. Overall, circulating cortisol was greater for ELHS (P = 0.01; 38.8%) compared to ELCS and ELTN pigs. Goblet cells per villi were reduced (P = 0.02; 20%) in the jejunum of ELHS vs. ELCS and ELTN pigs. In summary, ELHS reduced thermotolerance and increased the future stress response of piglets compared to ELCS and ELTN. [ABSTRACT FROM AUTHOR]

Heat stress will become a more substantial issue for swine production as global temperatures continue to rise. Efforts have been made to mitigate the negative impacts of heat stress through advances in genetic selection, nutrition, precision technology, and management practices. However, heat stress is still a limiting factor to swine production that must be addressed. A key aspect to mitigating heat stress-related production losses in swine may be developing better management approaches and genetic selection techniques to improve heat stress resilience. This is especially true for heat stress sensitive populations such as gestating and lactating sows. Gestating and lactating sows are considered heat stress sensitive due to greater metabolic heat production resulting from fetal growth and milk production, respectively. Additionally, swine offspring are adversely affected by in utero heat stress, which imprints long-term negative phenotypes that reduce health and productivity regardless of environmental conditions. To address these concerns, swine producers have implemented a variety of cooling and management strategies to mitigate heat stress. However, the recommended or perceived heat stress temperature thresholds for implementation may not accurately reflect the thermal requirements of modern swine with current genetics or at variable gestation stages leading to ineffective use. As such, a re-evaluation of heat stress thresholds for modern swine is warranted. Additionally, genetic selection for productivity traits (e.g., litter sizes and lean growth) has increased metabolic heat production resulting in increased heat stress sensitivity. Therefore, the ability to perform large-scale measures of and implement heat stress tolerance traits within breeding populations may be advantageous for producers to improve heat stress resilience within their herds. Taken together, as heat stress becomes a greater issue for the swine industry, it will become increasingly important to develop sustainable approaches that improve swine heat stress resilience while maintaining or improving producer profitability. [ABSTRACT FROM AUTHOR]

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±5.9 g 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. [ABSTRACT FROM AUTHOR]

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

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

The study objectives were to test the hypothesis that heat stress (HS) during gestational development alters postnatal growth, body composition, and biological response to HS conditions in pigs. To investigate this, 14 first parity crossbred gilts were exposed to one of four environmental treatments (TNTN, TNHS, HSTN, or HSHS) during gestation. TNTN and HSHS dams were exposed to thermal neutral (TN, cyclical 18–22°C) or HS conditions (cyclical 28–34°C) during the entire gestation, respectively. Dams assigned to HSTN and TNHS treatments were heat-stressed for the first or second half of gestation, respectively. Postnatal offspring were exposed to one of two thermal environments for an acute (24 h) or chronic (five weeks) duration in either constant TN (21°C) or HS (35°C) environment. Exposure to chronic HS during their growth phase resulted in decreased longissimus dorsi cross-sectional area (LDA) in offspring from HSHS and HSTN treated dams whereas LDA was larger in offspring from dams in TNTN and TNHS conditions. Irrespective of HS during prepubertal postnatal growth, pigs from dams that experienced HS during the first half of gestation (HSHS and HSTN) had increased (13.9%) subcutaneous fat thickness compared to pigs from dams exposed to TN conditions during the first half of gestation. This metabolic repartitioning towards increased fat deposition in pigs from dams heat-stressed during the first half of gestation was accompanied by elevated blood insulin concentrations (33%; P = 0.01). Together, these results demonstrate HS during the first half of gestation altered metabolic and body composition parameters during future development and in biological responses to a subsequent HS challenge. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Excessive heat exposure reduces intestinal integrity and post-absorptive energetics that can inhibit wellbeing and be fatal. Therefore, our objectives were to examine how acute heat stress (HS) alters intestinal integrity and metabolism in growing pigs. Animals were exposed to either thermal neutral (TN, 21°C; 35–50% humidity; n = 8) or HS conditions (35°C; 24–43% humidity; n = 8) for 24 h. Compared to TN, rectal temperatures in HS pigs increased by 1.6°C and respiration rates by 2-fold (P<0.05). As expected, HS decreased feed intake by 53% (P<0.05) and body weight (P<0.05) compared to TN pigs. Ileum heat shock protein 70 expression increased (P<0.05), while intestinal integrity was compromised in the HS pigs (ileum and colon TER decreased; P<0.05). Furthermore, HS increased serum endotoxin concentrations (P = 0.05). Intestinal permeability was accompanied by an increase in protein expression of myosin light chain kinase (P<0.05) and casein kinase II-α (P = 0.06). Protein expression of tight junction (TJ) proteins in the ileum revealed claudin 3 and occludin expression to be increased overall due to HS (P<0.05), while there were no differences in claudin 1 expression. Intestinal glucose transport and blood glucose were elevated due to HS (P<0.05). This was supported by increased ileum Na+/K+ ATPase activity in HS pigs. SGLT-1 protein expression was unaltered; however, HS increased ileal GLUT-2 protein expression (P = 0.06). Altogether, these data indicate that HS reduce intestinal integrity and increase intestinal stress and glucose transport. [ABSTRACT FROM AUTHOR]

The study objective was to evaluate the impact of electronically controlled cooling pads on physiological measurements of heat stress during early lactation. Twelve sows (d 3 to 11 of lactation) were provided with a specially designed cooling pad. Sows randomly received no cooling (CONTROL, n=6) or pads set to flush 2L cool water every 30s when aluminum plate reached 29.5°C (TREAT, n=6). Respiration rates (RR), rectal temperatures (RT) and skin temperatures (ST, 15 cm posterior to the ear) were recorded daily (0700 and 1500 h) for seven days of early lactation. Feed intake (DFI) was measured daily at 0700 h. RR, RT, and ST were fitted to a model that included the effects of day, time, parity, cooling pad treatment, and interactions. DFI was fitted to the same model, excluding time of day. For RR: treatment, day, time, treatment by day, treatment by time, and day by time interactions were significant (P< 0.0004, CONTROL=49, TREAT= 30). Pad treatment had greater impact on RR during the first two days of the trial when the temperature was greater (32°C maximum CONTROL mean=66 vs. TREAT mean=30) than the following five days: 42, and 30 respectively). There was greater treatment impact on RR at 1500 versus 0700 h (0700 h: CONTROL= 35, TREAT= 25; 1500 h: CONTROL= 61, TREAT= 36). For RT: treatment, day, time, parity and interaction of day by time were significant (P< 0.01, CONTROL= 37, treat= 35.). For ST: treatment, day, time, parity and the interactions of time by parity, treatment by time, and day by time were significant (P< 0.0006, mean CONTROL=36.5, TREAT= 35.1). For DFI: day and the interaction of day by treatment were significant. The difference in feed intake between treatments increased as day increased. The use of electronically controlled cooling pads reduced measures of heat stress in early lactating sows. [ABSTRACT FROM AUTHOR]