PHYSIOLOGICAL-RESPONSES TO REPEATED ENDOTOXIN CHALLENGE ARE SELECTIVELY AFFECTED BY RECOMBINANT BOVINE SOMATOTROPIN ADMINISTRATION TO CALVES

The study determined 1) whether the pretreatment of calves with recomb inant bovine somatotropin (bST, sometribove) would alter the change in packed cell volume (PCV), rectal temperature (RT), and the plasma con centrations of Ca2+, Fe2+, glucose (G), urea N (PUN), nonesterified fr ee fatty acids (NEFA), albumin (ALB), and blood cell populations after endotoxin challenge (EC) and 2) whether the natural development of ph ysiologic tolerance to repeated EC was affected by bST. Twelve steer b eef calves were assigned to either control (-bST) or +bST treatment in equal numbers. Calves were injected intramuscularly with either HCO3- -buffered saline or bST (0.1 mg/kg) daily for 5 d. On Day 6, the first EC was administered (Escherichia coli, 055:B5, 0.2 mu g/kg, intraveno us bolus in pyrogen-free saline). Saline or bST injections were contin ued from Day 7 up to the repeat of EC on Day 11. RT and PCV were measu red hourly through 12 and 6 hr, respectively. Jugular blood was obtain ed at 0, +1, 2, 3, 4, 6, 8, 12, and 24 hr relative to each EC. bST had no effect on the increase in RT, the hyperglycemic phase of the G res ponse, the biphasic change in Fe2+, or increases in NEFA and PUN. PCV increased after each EC only in -bST. The mean decrease in G during th e hypoglycemic phase was less in +bST. Hypocalcemic responses were sig nificantly less in +bST. ALE concentrations decreased after each chall enge; the response was unaffected by bST. CD2(+), CD4(+), and CD8(+) T -lymphocyte populations were unaffected by bST and EC. Overall, the ma gnitude of change in all plasma variables was less after the second EC compared with the first, either in terms of magnitude or duration. Th e data suggest that the treatment of calves with bST diminishes the ma gnitude of hypoglycemic, hypocalcemic, and PCV changes after EC and do es not compromise fever response, changes in blood cell populations, o r tolerance to repeated EC.