title: The effects of heat stress and plane of nutrition on metabolism in growing pigs.
abstract: Heat stress (HS) jeopardizes pig health, reduces performance variables, and results in a fatter carcass. Whether HS directly or indirectly (via reduced feed intake) is responsible for the suboptimal production is not known. Crossbred gilts (n = 48; 35 ± 4 kg BW) were housed in constantly climate-controlled rooms in individual pens and exposed to 1) thermal-neutral (TN) conditions (20°C; 35% to 50% humidity) with ad libitum intake (n = 18), 2) HS conditions (35°C; 20% to 35% humidity) with ad libitum intake (n = 24), or 3) pair-fed [PF in TN conditions (PFTN), n = 6, to eliminate confounding effects of dissimilar feed intake (FI)]. Pigs in the TN and HS conditions were sacrificed at 1, 3, or 7 d of environmental exposure, whereas the PFTN pigs were sacrificed after 7 d of experimental conditions. Individual rectal temperature (Tr), skin temperature (Ts), respiration rates (RR), and FI were determined daily. Pigs exposed to HS had an increase (P < 0.01) in Tr (39.3°C vs. 40.8°C) and a doubling in RR (54 vs. 107 breaths per minute). Heat-stressed pigs had an immediate (d 1) decrease (47%; P < 0.05) in FI, and this magnitude of reduction continued through d 7; by design the nutrient intake pattern for the PFTN controls mirrored the HS group. By d 7, the TN and HS pigs gained 7.76 and 1.65 kg BW, respectively, whereas the PFTN pigs lost 2.47 kg BW. Plasma insulin was increased (49%; P < 0.05) in d 7 HS pigs compared with PFTN controls. Compared with TN and HS pigs, on d 7 PFTN pigs had increased plasma NEFA concentrations (110%; P < 0.05). Compared with TN and PFTN controls, on d 7 circulating N(τ)-methylhistidine concentrations were increased (31%; P < 0.05) in HS pigs. In summary, despite similar nutrient intake, HS pigs gained more BW and had distinctly different postabsorptive bioenergetic variables compared with PFTN controls. Consequently, these heat-induced metabolic changes may in part explain the altered carcass phenotype observed in heat-stressed pigs.
authors: Department of Animal Science, Iowa State University, Ames, IO 50011, USA.
authors: S C
authors: SC
authors: Pearce
authors: N K
authors: NK
authors: Gabler
authors: J W
authors: JW
authors: Ross
authors: J
authors: J
authors: Escobar
authors: J F
authors: JF
authors: Patience
authors: R P
authors: RP
authors: Rhoads
authors: L H
authors: LH
authors: Baumgard
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001774:Blood Chemical Analysis / Q000662:veterinary; D004591:Electrophoresis, Polyacrylamide Gel / Q000662:veterinary; D004734:Energy Metabolism; D005247:Feeding Behavior; D005260:Female; D005786:Gene Expression Regulation; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D018869:Heat-Shock Response; D006706:Homeostasis; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D009752:Nutritional Status; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D034421:Sus scrofa / Q000235:genetics / Q000254:growth & development / Q000502:physiology*
chemical_list: D018840:HSP70 Heat-Shock Proteins; D009124:Muscle Proteins