Sixty-three Friesian steers (9 mo old, 257 kg; n = 15 or 16/treatment) were employed in a 2 x 2 factorial to test
bovine growth hormone (bGH) and
estradiol (Compudose implant). Steers received daily
subcutaneous injections of vehicle or bGH (40 micrograms/kg
body weight) for 22 wk. Steers were slaughtered 8 wk after the end of bGH treatment (
wk 30). Steers had ad libitum access to silage plus a fixed amount (4 to 5.5 kg/d) of concentrate. Average daily gain (ADG) and feed conversion efficiency (FCE) improved (P less than .05) in response both to bGH and to
estradiol during wk 0 to 22. Although bGH did not affect ADG or FCE during wk 23 to 30,
estradiol improved (P less than .05) them; bGH and
estradiol appeared additive (nonsignificant interactions) during wk 0 to 22. At slaughter,
estradiol increased (P less than .05) carcass weight and carcass and leg length while decreasing (P less than .05) conformation score and percentage of kidney, knob and channel fat (KHP); bGH decreased (P less than .05) KHP. Although both bGH and
estradiol increased (P less than .01) plasma GH, their effects were not additive. Both bGH and
estradiol increased (P less than .01) plasma
somatomedin-C and decreased (P less than .01) plasma
urea nitrogen concentrations; effects were additive.
Estradiol, but not bGH, increased (P less than .05) plasma
glucose, whereas neither bGH nor
estradiol altered plasma
creatinine and
nonesterified fatty acids. In summary, both bGH and
estradiol improved growth and FCE, and their effects appeared to be additive. It is likely that some of their effects were mediated by
somatomedin-C.