Observations on the development of the febrile response to pyrogen in newborn pigs

The febrile response of newborn pigs to exogenous pyrogen injection was investigated. Lipopolysaccharides (LPS, E. coli) were injected intravenously into the superior vena cava of 1-30-day-old piglets. All the experiments were carried out in littermates half of which were injected with pyrogen and half with pyrogen-free saline. Newborn pigs did not develop a febrile response from 1 to 4 days of age; however, when the animals were 5 days old exogenous pyrogen determined a typical monophasic febrile response. A second intravenous injection of pyrogen into newborn pigs (1 day old) 24 h after the first did not raise body temperature. It is suggested that newborn pigs behave like the newborn of other mammalian species regarding endotoxin-induced thermogenesis.