The effect of daily slaframine injection on salivary score, feed intake, ruminal pH, and circulating concentrations of somatotropin and insulin-like growth factor I

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 microgram 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 0.01; 0.4, 3.3, and 3.7 for 0, 30, and 60 microgram of SF/kg BW, respectively), although there was a dose X day interaction (P 0.01). Injection of SF reduced DMI (P less than or equall 0.01; 6.39, 4.95, and 2.64 kg of DM/d for 0, 30, and 60 microgram of SF/kg BW, respectively). Mean ruminal pH was increased (P 0.01; 6.03, 6.42, and 6.72 for 0, 30, and 60 microgram of SF/kg BW, respectively). Steers administered 60 microgram of SF/kg BW lost weight (P