Abstract
Chronic heat stress in livestock diminishes growth and metabolic efficiency in part by elevating inflammatory tone. Mitigating heightened inflammation is a potential route to improve performance and well-being of finishing livestock during heat events. Thus, our objective was to determine whether supplementation of ω-3 polyunsaturated fatty acid Ca(2+) salts (ω-3 PUFA) would improve indicators of inflammatory tone in heat-stressed finishing lambs. Wethers were randomly assigned to thermoneutral conditions (pair-fed controls; 19 ºC, THI = 64; n = 12) or heat stress (39 ºC, THI = 85) for 30 d. Heat-stressed lambs received a daily oral bolus of 0.42 g/kg bodyweight of ω-3 PUFA Ca(2+) salt (Virtus Nutrition; HS+ω3; n = 11) or placebo (HS; n = 12). Blood samples were collected weekly. Plasma concentrations of the ω-3 PUFA eicosapentaenoic acid (EPA) were greater (P < 0.05) for HS+ω3 wethers (631 ± 58 ng/mL) than for controls (440 ± 32 ng/mL) or HS wethers (458 ± 39 ng/mL), whereas docosahexaenoic acid concentrations (DHA) did not differ among groups (25.8 ± 0.7 pg/mL). Circulating monocytes, which are primary mediators of systemic inflammation, were greater (P < 0.05) for HS (0.50 ± 0.02 cells/μL) and HS+ω3 (0.52 ± 0.03 cells/μL) wethers than for controls (0.45 ± 0.01 cells/μL). However, plasma TNFα was greater (P < 0.05) for HS wethers (301 ± 66 pg/mL) than for controls (178 ± 6 pg/mL) and was intermediate for HS+ω3 wethers (203 ± 10 pg/mL). Moreover, plasma IL-6 was greater (P < 0.05) for HS wethers (11.83 ± 3.01 pg/mL) than for controls (6.63 ± 0.40 pg/mL) or HS+ω3 wethers (8.01 ± 0.54 pg/mL). By d–30 of heat stress, plasma adiponectin was less (P < 0.05) for HS wethers (4062 ± 175 ng/mL) than for controls (5142 ± 196 ng/mL) and was intermediate for HS+ω3 (4555 ± 231 ng/mL). Conversely, plasma IGF-I did not differ among groups (676 ± 46 ng/mL). Semitendinosus content of the TNFα receptor, TNFR1, did not differ among groups (1.15 ± 0.49 AU), whereas content of the IL-6 receptor, IL6R, tended to be less (P = 0.06) for HS wethers (0.50 ± 0.07 AU) than for controls (0.71 ± 0.13 AU) or HS+ω3 wethers (0.86 ± 0.14 AU). Semitendinosus content of the adiponectin receptor, CDH13, tended to be less (P = 0.08) for HS (4.21 ± 0.54 AU) and HS+ω3 wethers (4.17 ± 0.45 AU) than controls (5.42 ± 0.47 AU). These findings demonstrate that daily oral ω-3 PUFA Ca(2+) salt supplementation elevates circulating ω-3 PUFA and mitigates heat stress-induced inflammatory tone.