Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/1996
Publication Date: N/A
Citation: Interpretive Summary: Productivity and animal well-being in the swine industry is significantly affected by neonatal mortality and morbidity. One important factor which leads to these problems is susceptibility to infections caused by bacteria and viruses. Another important factor which may contribute to neonatal mortality and morbidity is thermal environment. The objective of this study was to evaluate the effect of hot versus cold temperatures on response to infection in neonatal pigs. A portion of bacteria known as lipopolysaccharide (LPS) was injected to mimic a real bacterial infection. Body temperature was significantly elevated in the hot thermal environment. LPS injection induced fever only in piglets from the warm environment. All LPS-injected piglets developed signs of sickness (e.g., vomiting, diarrhea, lethargy, anorexia, increased sleep, and decreased general activity), and had elevated blood levels of tumor necrosis factor alpha (TNFalpha), an important response hormone of the immune system, and cortisol, a major stress hormone. There was no significant effect of thermal environment on blood concentrations of TNFalpha and cortisol, but cultures of immune cells stimulated with LPS produced significantly less TNFalpha when incubated at 41 deg C, a temperature observed during fever. These results indicate that thermal environment can have a significant impact on the response of neonatal pigs exposed to infectious disease, since the fever response is thought to help fight the disease challenge; thus providing sufficient warmth may be beneficial for disease resistance in piglets.
Technical Abstract: The main objective of this study was to evaluate the effects of thermal environment on response to an acute peripheral lipopolysaccharide (LPS) challenge in neonatal pigs. Sows with piglets were housed in either a warm (32 deg C) or cool (21 deg C) thermal environment. At 28 days of age, the piglets were injected i.p. with 150 ug/kg of E. coli LPS or with saline as a control. Rectal temperature (Tr) and signs of sickness associated with endotoxemia were monitored for 3 h post-injection. At 3 h after the injection, pigs were sacrificed, and blood samples were collected to determine serum concentrations of tumor necrosis factor alpha (TNFalpha) and cortisol. Alveolar macrophages were collected by tracheal lavage to determine in vitro production of TNFalpha. Alveolar macrophages were incubated for 24 h at 37 or 41 deg C, with or without LPS (10 ug/ml). The thermal environment had a significant effect (P = 0.0004) on Tr. The LPS injection induced a febrile response (P = 0.0078) in pigs housed in the warm environment, but not in those housed in the cool environment. All pigs injected with LPS developed signs of endotoxemia (e.g., vomiting, diarrhea, lethargy, somnolescence, anorexia, and decreased general activity). Serum concentrations of TNFalpha and cortisol were significantly elevated (TNFalpha, P = 0.003; cortisol, P = 0.0001) in pigs injected with LPS. While there was not a significant effect of environmental temperature on serum TNFalpha and cortisol levels, production of TNFalpha by LPS-stimulated alveolar macrophages was significantly reduced (P = 0.0086) when these cells were incubated at 41 deg C. These data indicate that thermal environment can have a significant impact on the response of neonatal pigs exposed to bacterial endotoxins.