Fever response of sheep to endotoxin is not affected by steroids or pregnancy status : a dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science (Honours)

Abstract

To examine possible changes in immune function, corticosteroids, progesterone and pregnancy effects were examined using Escherichia coli lipopolysacchmide (LPS) induced febrile responses in Coopworth ewes. An initial dose response study showed that 200 ng/kg lwt was a sufficient dose of LPS to induce febrile responses ( defined as an increase in rectal temperature exceeding 0.7 °C in 4 hours) in sheep.

Dexamethasone trimethly acetate, prednisolone sodium succinate, and cortisol sodium succinate treatments (n = 8) were found to have no effect (p > 0.05) on changes in mean rectal temperature, plasma glucose or plasma iron concentrations. In contrast, the non-steroidal anti-inflammatory drug, flunixin meglumine suppressed (p < 0.001) the increase in rectal temperature recorded from cortisol-treated or control sheep (n = 8), but had no effect on plasma glucose concentration. In an initial trial, progesterone treatment (n = 8) elevated rectal temperature above (p < 0.001) that of LPS-treated control sheep (n = 8) and increased (p < 0.01) plasma glucose concentration, where the control group had a corresponding decrease. However in a second progesterone trial no such differences between the progesterone-treated and control groups (n = 8) were recorded, thus discounting the initial results for this steroid.

Pregnancy status had no effect on febrile responsiveness to LPS challenges in mid-pregnancy, late-pregnancy, the periparturient period, or lactation. However, there appeared to be a time-of year effect on febrile responsiveness, with the mid-pregnancy challenge producing a higher fever (p < 0.001) than successive challenges. Plasma glucose concentration was lower (p < 0.05) in the pregnant group (n = 12) than in the non-pregnant group (n = 9) at the late-pregnancy challenge, probably indicating metabolic differences between pregnant and non-pregnant ewes at this time. It was concluded that corticosteroids have no effect on LPS induced fever, or plasma glucose and iron concentrations and that fever is not suppressed in the periparturient ewe.