Dose-response effects of recombinant bovine somatotropin implants on feedlot performance in steers
Dalke, B.S. | Roeder, R.A. | Kasser, T.R. | Veenhuizen, J.J. | Hunt, C.W. | Hinman, D.D. | Schelling, G.T.
One hundred twenty crossbred beef steers averaging 377 kg were used in a 2 X 4 factorial experiment to determine the dose-response effects of recombinant bovine somatotropin (rbST) implants on growth performance and carcass characteristics. The implant dosages were 0 (sham), 40, 80, or 160 mg/wk administered s.c. in the tailhead region on a weekly basis throughout the experiment. The steers were fed a high-concentrate diet, which contained either a degradable (DP; soybean meal) or an escape (EP; corn gluten and blood meal) protein source. No dietary protein effect or dietary protein X rbST level interactions were detected. Recombinant bST decreased both DMI (P < .10) and feed/gain (P < .05) in a linear dose-dependent manner. Dosage of rbST did not significantly affect (P > .10) ADG or final weight of the steers. Recombinant bST decreased backfat depth (P < .10), marbling score (P < .05), and quality grade (P < .10) and increased yield grade (P < .10) in a linear dose-dependent manner. Soft tissue composition of the 9-10-11th rib section was altered (P < .01) by rbST administration in a linear dose-dependent manner. The percentage of protein in the rib section was increased by 9.4% and fat was decreased by 11.8% at the 160 mg/wk rbST level compared with the sham-implanted steers. Recombinant bST did not affect (P > .10) dressing percentage, hot carcass weight, kidney, pelvic, and heart fat, or longissimus muscle area. Serum insulin-like growth factor I (IGF-I) concentrations in the steers exhibited a linear response to dosage of rbST (P < .01). These data indicate that rbST is an efficacious method of improving feedlot performance and partitioning nutrient deposition in feedlot steers.
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