Wheat middlings in high-concentrate diets: feedlot performance, carcass characteristics, nutrient digestibilities, passage rates, and ruminal metabolism in finishing steers.

We conducted two experiments to determine the feeding value and effects on diet digestibilities, passage rates, and ruminal metabolism of wheat middlings (WM) fed as a replacement for either the concentrate or roughage components of finishing diets of steers. In Exp. 1, 120 medium-framed steers were blocked by weight and randomly allocated to one of six treatments of high-concentrate diets: control (0%); 5, 10, or 15% pelleted WM replacing dry-rolled corn (DRC); and 5 or 10% pelleted WM replacing chopped alfalfa hay (ALF) components of the diet. Increasing WM replacement of DRC increased DMI (P < .01) and feed:gain ratio (FG; P < .05) linearly. A 9.2% increase in daily DMI and 10.1% increase in FG were observed at 15% of WM. Daily gain and final weight of the steers were not influenced by WM replacement of DRC. The WM replacement of ALF decreased (P < .01) daily DMI linearly, but it had no effect on ADG, final weight, or FG. In Exp. 2, six medium-framed steers, fitted with ruminal cannulas, were used in a 6 x 6 Latin square design with the same treatments as described in Exp. 1. Dry matter, OM, and starch digestibilities decreased (P < .01) by increasing replacement of DRC with WM, and replacing ALF increased DM and OM digestibilities linearly (P < .01). Wheat middlings could replace only up to 5% of DRC without reducing feed conversion efficiency and diet digestibilities, but complete (100%) or partial (50%) replacement of ALF increased digestibilities of DRC finishing diets.

Effects of recombinant bovine somatotropin implants on serum concentrations of somatotropin, insulin-like growth factor-I and blood urea nitrogen in steers.

Four cross-bred beef steers averaging 346 kg were used in a 4 x 4 Latin square design to determine the effect of prolonged-release recombinant bovine somatotropin (rbGH) implants on serum concentrations of somatotropin (GH), insulin-like growth factor-I (IGF-I) and blood urea nitrogen (BUN). Recombinant bGH implants of 0, 40, 80 or 160 mg were administered subcutaneously in the tailhead during the 4 trial periods. Each steer received each treatment starting at 06:00 on day 0 with 21 days between treatments. Jugular vein blood samples were collected on days 0, 1, 2 and 3 (4 day time course for GH, IGF-I and BUN) and every 15 min (GH profile) for 6 h on day 3. Serum baseline GH values were higher (P < 0.10) for the 80 and 160 mg treatments than for the control, and peak amplitude was decreased (P < 0.05) by the 40 and 160 mg treatments. There was a trend (P < 0.11) for fewer GH peaks during the 160 mg treatment. Somatotropin concentrations decreased from day 1 to day 3 (P < 0.05) in a linear manner. Serum IGF-I concentrations increased (P < 0.05) in a linear dose-dependent manner from the 0 mg to the 160 mg treatment. BUN concentrations were not significantly altered by rbGH treatment. Results from this experiment indicate that rbGH implants significantly increase serum IGF-I and GH baseline concentrations while suppressing GH peak amplitude in finishing steers.

Dose-response effects of recombinant bovine somatotropin implants on feedlot performance in steers.

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 less than .10) and feed/gain (P less than .05) in a linear dose-dependent manner. Dosage of rbST did not significantly affect (P greater than .10) ADG or final weight of the steers. Recombinant bST decreased backfat depth (P less than .10), marbling score (P less than .05), and quality grade (P less than .10) and increased yield grade (P less than .10) in a linear dose-dependent manner. Soft tissue composition of the 9-10-11th rib section was altered (P less than .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 greater than .10) dressing percentage, hot carcass weight, kidney, pelvic, and heart fat, or longissimus muscle area.(ABSTRACT TRUNCATED AT 250 WORDS)