Effects of long-term administration of pituitary-derived bovine growth hormone and estradiol on growth in steers.

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Abstract
Sixty-three Friesian steers (9 mo old, 257 kg; n = 15 or 16/treatment) were employed in a 2 × 2 factorial to test bovine growth hormone (bGH) and estradiol (Compudose implant). Steers received daily subcutaneous injections of vehicle or bGH (40 μg/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 < .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 < .05) them; bGH and estradiol appeared additive (nonsignificant interactions) during wk 0 to 22. At slaughter, estradiol increased (P < .05) carcass weight and carcass and leg length while decreasing (P < .05) conformation score and percentage of kidney, knob and channel fat (KHP); bGH decreased (P < .05) KHP. Although both bGH and estradiol increased (P < .01) plasma GH, their effects were not additive. Both bGH and estradiol increased (P < .01) plasma somatomedin-C and decreased (P < .01) plasma urea nitrogen concentrations; effects were additive. Estradiol, but not bGH, increased (P < .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.

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