Changes In Serum Cortisol Concentrations And Cytokine Profiles Of Growing Pigs Subjected To Low-Intensity Heat Stress

Abstract This study was to determine the impact of low-intensity heat stress on inflammatory biomarkers in serum, ileum, jejunum and lung lavage samples. Pigs (n = 64; 24.6 ± 3.7 kg BW) were housed four per pen in thermoneutral conditions (CON; 23.9°C ± 2.5°C) or constant high ambient temperatures (HS; 28.7°C ± 1.3°C) for 16 d, followed by thermoneutral conditions (24.4°C ± 1.8°C) for both groups through d 21, and subsequent heat stress (28.0°C ± 3.0°C) for both groups through d 30. Respiration rate (P < 0.01) was greater in HS than CON pigs from d 2 through d 15 (mean: 82.54 breaths/min vs. 59.26 breaths/min). HS pigs had greater cortisol concentration (40.1 ng/mL vs. 27.3 ng/mL) than CON on d 2, but lower concentrations on d 22 (32.9 ng/mL vs. 48.9 ng/mL) and d 25 (25.4 ng/mL vs. 42.0 ng/mL; treatment x day: P < 0.001). HS pigs tended to have greater serum IL1β (190.1 vs. 143.4 pg/mL; P = 0.06) and greater serum IL12 concentrations (914.9 vs. 785.4 pg/mL; P < 0.01) than CON pigs. HS pigs tended to have greater ileal mucosa IL6 concentrations than CON pigs (50.4 vs. 30.9 pg/mL; P = 0.08). Jejunal mucosa IL1α concentrations tended (P = 0.10) to be greater for CON than HS pigs (13.5 vs. 9.0 pg/mL) and CON pigs had greater jejunal IL12 concentrations (18.1 vs. 11.8 pg/mL) than HS pigs (P = 0.02). Bronchioalveolar lavage from HS pigs tended (P = 0.10) to have a greater granulocyte-macrophage colony-stimulating factor concentration (6.9 vs. 5.3 pg/mL) than CON pigs and had greater IL4 (7.7 vs. 4.2 pg/mL) and IL12 concentrations (34.8 vs. 24.5 pg/mL) than CON pigs (P = 0.01). Increased inflammatory activity and endocrine stress response occurred during low-intensity heat stress, indicating it may be more detrimental than previously accepted.