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 feathermeal2

Abstract

The objectives of these experiments were to examine whether N retention and feedlot performance by steers administered estradiol 17-β (E₂) 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 weight = 308 ± 5 kg) were used in a randomized block design experiment having a 2 × 4 factorial arrangement of treatments. Main factors were E₂ administration and supplemental CP source. Steers were fed diets based on corn silage and corn (60:30 DM basis) and were supplemented with urea or three combinations of soybean meal (SBM) and feathermeal (Fth). Combinations and SBM and Fth (SBM:Fth) provided 75:25, 50:50, and 25:75 of supplemental CP on a N basis. Estradiol 17-β increased (P < .05) N retention and decreased (P< .05) plasma urea N concentrations. Total tract N digestion decreased linearly (P< .05) as the proportion of Fth in the diet increased. However, N retention increased linearly (P < .05) with increased Fth. A CP source × E₂ interaction (P < .05) was observed for N retention because retention increased linearly with increasing dietary Fth in cattle receiving E₂ but was unaffected (P > .05) in control steers. A growth study was conducted using 128 crossbred steers (400 ± 19 kg) that received no implant or a combination of E₂ (Synovex^®) and TBA (Finaplix-S^®). Steers were fed diets containing 75% high-moisture corn, 15% corn silage, and 10% supplement (DM basis) for 84 d (heavy replicate) or 124 d (light replicate).(ABSTRACT TRUNCATED AT 250 WORDS)