In a randomized complete block design with repeated measures, ruminally cannulated crossbred beef steers (n = 24; 279 +/- 3.2 kg) had ad libitum access to a 90% concentrate diet and were injected daily with slaframine dichloride (SF) at doses of 0, 30, or 60 micrograms SF free-base/kg BW. On d 1, 2, 7, 14, and 21, salivary scores were determined hourly from -2 to 8 h relative to injection (0 h), and ruminal pH was measured at 0, 4, and 8 h. Feed intake was measured daily. Serum concentrations of somatotropin (ST) were measured in samples collected at 20-min intervals from -40 min to 8 h on d 2, 7, 14, and 21, and IGF-I was measured at 8 h. Mean salivary score increased with SF injection (P < .01; .4, 3.3, and 3.7 for 0, 30, and 60 micrograms of SF/kg BW, respectively), although there was a dose x day interaction (P < .01). Injection of SF reduced DMI (P < or = .01; 6.39, 4.95, and 2.64 kg of DM/d for 0, 30, and 60 micrograms of SF/kg BW, respectively). Mean ruminal pH was increased (P < .01); 6.03, 6.42, and 6.72 for 0, 30, and 60 micrograms of SF/kg BW, respectively). Steers administered 60 micrograms of SF/kg BW lost weight (P = .02; 15.1 and -20.3 kg for 0 and 60 micrograms of SF/kg BW, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)