EFFECTS OF ANABOLIC-STEROIDS ON NITROGEN-METABOLISM AND GROWTH OF STEERS FED CORN-SILAGE AND CORN-BASED DIETS SUPPLEMENTED WITH UREA OR COMBINATIONS OF SOYBEAN-MEAL AND FEATHERMEAL

The objectives of these experiments were to examine whether N retentio n and feedlot performance by steers administered estradiol 17-beta (E( 2)) alone (metabolism study) or in combination with trenbolone acetate (TAB; feedlot study) could be enhanced by increasing dietary ruminal escape protein. For the metabolism study, 16 Angus steers (average wei ght = 308 +/- 5 kg) were used in a randomized block design experiment having a 2 x 4 factorial arrangement of treatments. Main factors were E(2) administration and supplemental CP source. Steers were fed diets based on corn silage and corn (60:30 DM basis) and were supplemented w ith urea or three combinations of soybean meal (SBM) and feathermeal ( Fth). Combinations and SBM and Fth (SBM:Fth) provided 75:25, 50:50, an d 25:75 of supplemental CP on a N basis. Estradiol 17-beta increased ( P <.05) N retention and decreased (P < .05) plasma urea N concentratio ns. Total tract N digestion decreased linearly (P <.05) as the proport ion of Fth in the diet increased. However, N retention increased linea rly(P <.05) with increased Fth. A CP source x E(2) interaction (P <.05 ) was observed for N retention because retention increased linearly wi th increasing dietary Fth in cattle receiving E(2) but was unaffected (P >.05) in control steers. A growth study was conducted using 128 cro ssbred steers (400 +/- 19 kg) that received no implant or a combinatio n of E(2) (Synovex(R)) and TBA (Finaplix-(R)). Steers were fed diets c ontaining 75% high-moisture corn, 15% corn silage, and 10% supplement (DM basis) for 84 d (heavy replicate) or 124 d (light replicate). Supp lemental protein was provided by urea or combinations of SBM and Fth. Implantation improved (P < .05) growth rate and efficiency of growth. Feeding higher Fth resulted in linear (P <.10) and quadratic (P <.10) improvements in gain and efficiency. However, no interactions (P >.45) between implant and protein source were observed. Feeding higher rumi nal escape protein may enhance the growth of implanted cattle but this relationship is likely impacted by animal growth potential, basal die t fed, and choice of supplemental protein.