PSI-1 - Effects of in utero heat stress on the circulating cytokine response of F2 generation pigs genomically selected for heat stress sensitivity or tolerance and given a lipopolysaccharide challenge

Abstract: Previous research demonstrates that in utero heat stress (IUHS) increases the circulating cytokine response of pigs subjected to a lipopolysaccharide challenge during postnatal life relative to in utero thermoneutral (IUTN) exposed pigs. Therefore, the study objective was to determine whether genomic selection for improved heat stress tolerance (TOL) could mitigate this negative effect in IUHS pigs. Because greater maternal body temperature may directly contribute to IUHS phenotypes in pigs, we hypothesized that IUHS offspring derived from TOL dams would have a reduced inflammatory response to an innate immune challenge relative to those derived from heat stress sensitive (SEN) dams. Twenty-eight pregnant F1 generation gilts (Large White x Landrace) divergently genomically selected to be TOL (n = 14) or SEN (n = 14), were bred to TOL or SEN boars (Landrace) and then exposed to thermoneutral (TN; n = 13; 17.5 ± 2.1°C; n = 7 TOL and 6 SEN gilts) or heat stress (HS; n = 15; cyclic 26-36 °C; n = 7 TOL and 8 SEN gilts) conditions from gestation d6-65. On d71, all pregnant gilts were exposed to TN conditions (20.9 ± 2.3°C) until farrowing. At 12 wk of age, each pig had a jugular catheter placed, and then pigs were given either a 1 mL injection of sterile saline (SAL) or lipopolysaccharide (LPS; 2 ug/kg weight). Pigs were assigned to 1 of 8 treatment groups (n = 3 gilts and 3 barrows per treatment): IUHS+TOL+LPS, IUHS+TOL+SAL, IUHS+SEN+LPS, IUHS+SEN+SAL, IUTN+TOL+LPS, IUTN+TOL+SAL, IUTN+SEN+LPS, and IUTN+SEN+SAL. Rectal temperatures were taken in 30 min intervals throughout the 8h LPS challenge. Blood samples were obtained via the jugular catheter immediately prior to LPS and SAL injections (0 h), and then at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, and 8 h. Blood samples were analyzed to assess pro- and anti-inflammatory cytokines (IL-1α, IL-1β, IL-1RA, IL6, IL8, TNFα). Individual pig was considered the experimental unit for all analyses. Rectal temperatures were greater (P < 0.01) in pigs given LPS (40.24 ± 0.07°C) versus SAL (39.61 ± 0.07°C). All measured cytokines were greater (P < 0.01) in pigs given LPS versus SAL, regardless of in utero or genomic treatment. A decrease (P = 0.04; 60.4%) in TNFα concentrations were observed in IUHS+SEN given LPS when compared to all other treatment groups provided LPS. An overall decrease (P < 0.01) in IL-1α (28.2%), IL-1β (34.2%), and IL-6 (50.6%) was observed for TOL versus SEN pigs. In utero HS pigs tended to have greater (P = 0.08; 31.7%) IL-8 when compared to IUTN pigs. In summary, although some interactions between IUHS and divergent genomic selection were observed for TNFα, most cytokine differences were driven by the main effect of divergent genomic selection.