Performance and digestibilities of beef cattle fed diets supplemented witheither soybean meal or roasted soybeans and implanted with synovex

Two 160-d feedlot experiments, each consisting of 20 Angus-Hereford steers (216 +/- 5 kg BW, Exp. 1; 258 +/- 5 kg BW, Exp. 2) and 20 Angus-Hereford he ifers (208 +/- 5 kg BW, Exp. 1; 236 +/- 5 kg BW, Exp. 2), were used to inve stigate the effects of supplementing diets with either roasted soybeans (RS B, roasted at 127 degrees C for 10 min) or soybean meal (SBM) and implantin g or not implanting with an estrogenic growth promoter (SYN; Synovex-S, 20 mg of estradiol benzoate plus 200 mg of progesterone or Synovex-H, 20 mg of estradiol benzoate plus 200 mig of testosterone) on performance. The cattl e were fed a basal diet of 15% orchardgrass silage, 15% corn silage, and 70 % corn-based concentrate. Treatments were 1) no SYN and fed a SBM-supplemen ted diet, 2) no SYN and fed a RSB-supplemented diet, 3) SYN and SBM, and 4) SYN and RSB. Cattle in the SYN groups were reimplanted at 80 d. Four addit ional Angus-Hereford steers were used in a digestion and nitrogen balance e xperiment conducted during the first half of Exp. 1. For the total 160-d fe edlot experiments, DMI for RSB compared with SBM was lower (P < .01; 8.5 vs 9.2 kg/d, SEM = .07) and ADG/DMI tended to be higher (P < .10; 165 vs 157 g/kg, SEM: = 1.3). Final BW of steers fed RSB was similar (P > .10) to that of steers fed SBM (473 vs 478 kg, SEM = 5.6), as was ADG (1.39 vs 1.43 kg/ d, SEM = .02). Dry matter intake for SYN-implanted steers was higher(P < .0 1) than for steers not implanted (9.2 vs 8.5 kg/d). Likewise, final BW (491 vs 460 kg) and ADG (1.49 vs 1.33 kg/d) were higher (P < .01), and ADG/DMI (166 vs 157 g/kg) tended to be higher (P < .10), for SYN-implanted steers t han for steers not implanted. During the more rapid muscle growth period(0 to 80 d), DMI for RSB compared with SBM was lower (P < .01; 7.8 vs 8.6 kg/d , SEM = .07) and ADG/DMI was similar (P > .10; 181 vs 172 g/kg, SEM. = 1.8) . Dry matter intake for SYN-implanted steers was higher (P < .05) than for steers not implanted (8.4 vs 8.0 kg/d), as was ADG/DMI (P < .01, 182 vs 171 g/kg). During this more rapid growth period, the supplement x implant inte raction for ADG was significant (P < .05; 1.35, 1.36, 1.59, and 1.44 kg/d f or Treatments 1, 2, 3, and 4, respectively, SEM = .04). There were no diffe rences in digestibilities or N balance. The results suggest that there is n o improvement in performance under feedlot conditions when RSB replaces SBM in the diet of beef cattle, and, in young cattle, RSB may reduce the respo nse expected by an estrogenic growth promoter.