Heat-tolerant versus heat-sensitive Bos taurus cattle: influence of air temperature and breed on the acute phase response to a provocative immune challenge.

The difference in the acute phase response of a heat-tolerant and a heat-sensitive Bos taurus breed to a lipopolysaccharide (LPS) challenge when housed at different air temperatures (Ta) was studied. Angus (ANG; heat-sensitive; n = 11; 306 ± 26 kg BW) and Romosinuano (RO; heat-tolerant; n = 10; 313 ± 32 kg BW) heifers were transported from the USDA Agricultural Research Service SubTropical Agricultural Research Station in Florida to the Brody Environmental Chambers at the University of Missouri, Columbia. Heifers were housed in stanchions in 4 temperature-controlled environmental chambers. Initially, Ta in the 4 chambers was cycling at thermoneutrality (TN; 18.5°C-23.5°C) for a 1-wk adjustment period, followed by an increase in 2 of the 4 chambers to cycling heat stress (HS; 24°C-38°C) for 2 wk. On day 19, heifers were fitted with jugular catheters and rectal temperature (RT) recording devices. On day 20, heifers were challenged with LPS (0.5 μg/kg BW; 0 h), sickness behavior scores (SBSs) were recorded, and blood samples were collected at 0.5-h intervals from -2 to 8 h and again at 24 h relative to LPS challenge at 0 h. Serum was isolated and stored at -80°C until analyzed for cortisol and cytokine concentrations. A breed by Ta interaction (P < 0.001) was observed for RT such that the post-LPS average RT in RO heifers housed at TN was lower than the RT of all other treatment groups (P < 0.001), whereas ANG heifers housed at HS had greater post-LPS average RT than all other treatment groups (P < 0.001). In response to LPS, HS increased SBS after LPS in RO heifers compared to RO heifers housed at TN (P < 0.001), whereas HS decreased SBS after LPS in ANG heifers compared to ANG heifers housed at TN (P = 0.014). The cortisol response to LPS was greater in TN than in HS heifers (P < 0.01) and was also greater in RO than in ANG heifers (P = 0.03). A breed by Ta interaction (P < 0.01) was observed for tumor necrosis factor-α (TNF-α) concentration such that HS increased post-LPS serum concentrations of TNF-α in ANG heifers compared to ANG heifers housed at TN (P = 0.041), whereas HS decreased post-LPS concentrations of TNF-α in RO heifers compared to RO heifers housed at TN (P = 0.008). A tendency (P < 0.06) was observed for a breed by Ta interaction for IL-6 concentrations such that RO heifers had greater post-LPS concentrations of IL-6 than ANG heifers when housed at HS (P = 0.020). A breed by Ta interaction was observed for interferon-γ (IFN-γ; P < 0.01) concentrations such that HS decreased post-LPS concentrations of IFN-γ in ANG heifers compared to ANG heifers housed at TN (P < 0.001), and HS increased post-LPS concentrations of IFN-γ in RO heifers compared to RO heifers housed at TN (P = 0.017). These data indicate differences in the acute phase response between the heat-tolerant RO and heat-sensitive ANG heifers under different Ta which may aid in elucidating differences in productivity, disease resistance, and longevity among cattle breeds.