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Breeding programs have substantially improved productive and reproductive efficiency in worldwide swine populations. However, increased performance is often accompanied by reduced climatic resilience due to greater metabolic heat production. Genomic selection is an effective tool for alleviating the negative effects of heat stress, but it requires traits that effectively capture the physiological, behavioral, and morphological mechanisms regulating the heat stress response. In this presentation we will first describe the genetic background of heat tolerance based on routinely recorded phenotypes and climatic variables obtained from public-weather-station databases. There are clear genotype-by-environment interactions across environmental conditions and the definition of the critical periods for quantifying the environmental gradient directly impacts the accuracy of genomic prediction of breeding values for heat tolerance. Secondly, we will describe the genetic background of various behavioral, physiological, and morphological indicators of heat stress in maternal line pigs, including automatically recorded vaginal temperature, skin temperature measured in different body locations and times of the day, respiration rate, panting score, body condition score, hair cortisol, hair density, and ear area. We will also present recently developed indicators of climatic resilience based on variability metrics of longitudinal measurements of automatically recorded body temperature in lactating sows. These traits are heritable and can be successfully included in genomic breeding programs. Furthermore, we will discuss the transgenerational effects of heat stress in maternal-line pigs from quantitative and molecular perspectives, including an epigenomic analyses of in utero heat stress that identified over 200 genomic regions that are differentially methylated in in utero heat stressed pigs and provide results from a comprehensive biological validation study based on in-depth phenotyping of genetically divergent animals. We will also discuss key challenges and opportunities for breeding for improved climatic resilience in pigs. In summary, we will: 1) provide a comprehensive description of the environmental-gradient variables and critical periods fitted in genomic evaluations of heat tolerance; 2) describe the genetic background of various indicators of heat tolerance and climatic resilience; 3) present the accuracies of genomic predictions for each indicator trait; 5) describe key results from biological validation studies; and, 6) make recommendations for the implementation of genomic selection for improved heat tolerance in pigs [ABSTRACT FROM AUTHOR]

Gestating sows are particularly sensitive to heat stress due to their large mass and greater metabolic heat production associated with increased reproductive organ and fetal development. Unfortunately, the heat stress sensitivity of gestating sows has increased over the past decades due to genetic and genomic advances that have improved litter sizes and reproductive efficiency. When combined with the greater frequency and severity of heat waves and high temperatures, it is likely that reproductive issues associated with heat stress exposure will continue to be a concern for the swine industry. It is well understood that high temperatures pose a challenge to gestating sows and their developing offspring. Research from 50 to 60 yr ago demonstrated that heat exposure results in a decrease in viable embryos and an increase in embryonic mortality, particularly when gestating sows are subjected to heat stress in the first trimester. Additionally, late gestation heat stress exposure can increase the rate of stillborn piglets and reduce the total number of liveborn piglets. Although the reasons for these losses are multifactorial, the direct influence of maternal body temperature and total stress load on the intrauterine environment can play a significant role during these critical stages. For offspring that survive to birth, prospects for a healthy, productive, and stress-free life are at risk due to the long-lasting effects of in utero heat stress, which include greater postnatal stress sensitivity and decreased productivity. Therefore, understanding and mitigating gestational heat stress in pigs is of great importance to ensure the sustainability and profitability of swine production. [ABSTRACT FROM AUTHOR]

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

In utero heat stress (IUHS) has long-term negative-effects on pigs during postnatal life. Specifically, IUHS pigs display greater stress responses following weaning and transport and have reduced growth performance among other issues. Although efforts have been made to mitigate IUHS through management and nutrition, the use of genomic selection to improve heat stress tolerance (TOL) in gestating sows and reduce the impacts of IUHS on developing offspring has not been extensively studied. Therefore, the study objective was to determine whether genomic selection for TOL or heat stress sensitivity (SEN) in F1 gilts would impact the postnatal growth performance of IUHS piglets following weaning and transport. We hypothesized that IUHS piglets derived from TOL gilts would have improved growth performance relative to IUHS piglets derived from SEN gilts, but that overall, IUHS piglets would have reduced growth performance when compared with IUTN piglets following weaning and transport. Twenty-eight TOL (n = 15) and SEN (n = 13) pregnant gilts were exposed to either thermoneutral (TN; 17 to 20ºC; n = 7 TOL and 6 SEN) or heat stress (HS; cycling 26 to 36ºC; n = 8 TOL and 7 SEN) conditions from d 6 to 70 of gestation, and then all gilts were exposed to TN conditions until farrowing. At weaning, mixed sex piglets were selected from each litter resulting in the following treatment combinations: TOL+ in utero thermoneutral (IUTN; n = 60), TOL+IUHS (n = 60), SEN+IUTN (n = 59), and SEN+IUHS (n = 58). Piglets were then transported for 12 h to simulate commercial conditions and then group housed in 40 nursery pens (n = 6 pigs/pen) for 5 wk. All pigs were fed a standard nursery diet containing primarily corn and soybean meal and feed and water were provided ad libitum. Body weights (BW) and feed disappearance were measured on d 1, 7, 14, 21, 28, and 35 post-weaning and transport and used to calculate average daily gain (ADG), average daily feed intake (ADFI), and Gain:Feed. Data were analyzed in R using a generalized linear mixed model with pen as the experimental unit for ADFI and Gain:Feed, and individual piglet was the experimental unit for BW and ADG. Overall, IUHS piglets had a reduction (P < 0.01) in ADG (6.3%), Gain:Feed (4.4%), and final BW (2.5%) when compared with IUTN piglets. Additionally, TOL piglets had an overall improvement (P < 0.01) in ADG (6.0%), ADFI (13.6%), and final BW (3.9%), but a decrease in Gain:Feed (5.8%) when compared with SEN piglets. No genomic by in utero treatment effects were observed with any comparison. In conclusion, IUHS had a negative impact and selection for TOL had a generally positive impact on postnatal growth performance, but genomic selection for TOL or SEN did not interact with IUHS or IUTN in the F1 generation. [ABSTRACT FROM AUTHOR]

The maternal response to heat stress (HS) has detrimental effects on swine offspring in the form of in utero heat stress (IUHS). Long-term effects of IUHS include reduced postnatal growth performance and lean muscle deposition. As such, developing mitigation strategies that reduce IUHS is essential to maximize economic return. Therefore, the study objective was to investigate whether genomic selection for HS tolerance (TOL) or HS sensitivity (SEN) would impact the postnatal growth of IUHS and in utero thermoneutral (IUTN) pigs from birth to market. We hypothesized that the IUHS pigs born to TOL dams would have improved growth relative to IUHS pigs born to SEN dams, but overall, IUHS pigs would have reduced growth compared with IUTN pigs. Pregnant gilts (n = 15 TOL and 13 SEN) were exposed to thermoneutral (TN; 17-20ºC; n = 7 TOL and 6 SEN) or heat stress (HS; cycling 26 to 36ºC; n = 8 TOL and 7 SEN) conditions from d 6 to 70 of gestation, and then all gilts were exposed to TN conditions until farrowing. Thirtysix offspring (barrows) were selected to represent each possible treatment combination: TOL+IUTN (n = 9), TOL+IUHS (n = 9), SEN+IUTN (n = 9), and SEN+IUHS (n = 9). Barrows were group-housed and fed a corn-soybean based diet that was provided with water ad libitum. Body weight (BW) of all barrows was measured at d 1, 21, 28, 35, 42, 49, 56, 84, 105, 126, 147, 168, and 189 of life to evaluate growth from birth (d 1) to market (d 189). Data were analyzed using the PROC GLIMMIX procedure of SAS with pig as the experimental unit and random effects being pen and litter. Body weights for each treatment group were fitted to a generalized Michaelis-Menten (GMM) function using the Nonlinear MIXED procedure of SAS with pig specific random effects for mature BW. On d 1, 126, and 168, IUHS pigs tended to have reduced BW (P < 0.10; 1.19 ± 0.07, 58.37 ± 4.94, 91.18 ± 7.26 kg, respectively) when compared with IUTN pigs (1.32 ± 0.07, 68.95 ± 4.94, 106.25 ± 7.26 kg, respectively). Overall, final BW was reduced (P = 0.04) for IUHS (111.08 ± 7.91 kg versus IUTN (128.79 ± 7.91 kg) pigs, and estimated days to a market weight of 125 kg tended to be greater (P = 0.06) for IUHS (219.8 ± 10.8 d) versus IUTN (188.1 ± 10.21 d) barrows. The GMM model predicted that IUHS+TOL and IUTN+TOL barrows had different shaped BW growth curves with decreased age to achieve one-half of their predicted mature BW than IUHS+SEN and IUTN+SEN barrows. In conclusion, IUHS resulted in reduced growth rates overall; however, TOL improved some aspects of growth [ABSTRACT FROM AUTHOR]

Heat stress (HS) decreases lactation output in sows due to an attempt to reduce metabolic heat production. However, this negatively affects litter growth performance. Therefore, the study objective was to determine whether electronically controlled cooling pads (ECP) would improve indirect measures of lactation output (e.g., total heat production [THP]) and litter growth performance in HS exposed sows. Over two repetitions, 12 multiparous (2.69 ± 0.85) lactating sows (265.4 ± 26.1 kg body weight [BW]) and litters were assigned to either an ECP (n = 3/repetition) or a non-functional ECP (NECP; n = 3/repetition) and placed into farrowing crates within indirect calorimeters from days 3.7 ± 0.5 to 18.7 ± 0.5 of lactation. Litters were standardized across all sows (11.4 ± 0.7 piglets/litter), and sows were provided ad libitum feed and water. All sows were exposed to cyclical HS (28.27 ± 0.26 °C nighttime to 33.09 ± 0.19°C daytime). On days 4, 8, 14, and 18 of lactation, indirect calorimetry was performed on each individual sow and litter to determine THP and THP/kg BW0.75. Body temperature (TB) was measured hourly using vaginal implants, and respiration rate (RR; breaths per minute [bpm]) was measured daily at 0700, 1100, 1300, 1500, and 1900 h. Sow feed intake (FI) was assessed daily. Litter weights were obtained at birth, on days 4, 8, 14, and 18 of lactation, and at weaning. Data were analyzed using PROC GLIMMIX with sow and/or litter as the experimental unit. An overall decrease (P < 0.01; 25 bpm) in RR and maximum daily TB (P = 0.02; 0.40 °C) was observed in ECP vs. NECP sows. An increase in THP (P < 0.01; 20.4%) and THP/kg BW0.75 (P < 0.01; 23.1%) was observed for ECP when compared with NECP sows and litters. Litter average daily gain and weaning weight were increased (P < 0.05; 25.0 and 19.2%, respectively) for ECP vs. NECP litters. No FI differences were observed (P = 0.40) when comparing ECP (5.66 ± 0.31 kg/d) and NECP (5.28 ± 0.31 kg/d) sows. In summary, ECPs improve litter growth, thermoregulatory measures, and bioenergetic parameters associated with greater milk production in lactating sows exposed to cyclical HS. [ABSTRACT FROM AUTHOR]