Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Animal Science

First Advisor

Zachary Smith


bedding, estradiol, implant, maintenance coefficient, trenbolone acetate


Three randomized complete block design feedlot experiments were conducted over the course of two years. Two experiments were conducted to investigate the effect of bedding use in confined beef steers. The third experiment evaluated the effects of implants containing increasing doses of trenbolone acetate (TBA) and estradiol benzoate (EB) in confined beef steers. Experiment 1 used Simmental × Angus steers (n = 240; initial body weight (BW) = 365 ± 22.5 kg). Experiment 2 used newly weaned Charolais × Red Angus steers (n = 162; initial BW = 278 ± 13.4 kg). Steers were allotted to 1 of 2 treatments: 1) no bedding (NO), or 2) 1.8 kg (Exp. 1) or 1.0 kg (Exp. 2) of wheat straw (as-is basis) bedding/steer·d-1 (BED). In Exp. 1 and Exp. 2 data were analyzed as a randomized complete block design with pen serving as the experimental unit for all analyses. In Exp.1, applying bedding improved (P ≤ 0.01) dry matter intake (DMI), gain:feed (G:F), and average daily gain (ADG). Bedding reduced (P = 0.01) the estimated maintenance coefficient (MQ). Dressing percentage, rib fat, marbling, and yield grade were increased (P ≤ 0.03) in NO. Bedding resulted in an increase (P = 0.01) in serum insulin-like growth factor I (IGF-I). In Exp. 2, a tendency (P = 0.06) for increased DMI for NO was noted. Bedding improved G:F (P = 0.01). MQ was elevated (P = 0.03) for NO and NO had an increase (P = 0.02) in serum concentration of urea-N (SUN). An increase (P = 0.01) in serum non-esterified fatty acid was noted for NO. These data indicate that bedding application should be considered to improve growth performance and feed efficiency by reducing maintenance energy requirements in beef steers during the feedlot receiving and finishing phase. In experiment 3, yearling Simmental × Angus crossbred beef steers (n = 240; allotment BW = 365 ± 22.5 kg) from a South Dakota auction facility were transported 117 km to Brookings, SD and used in a randomized complete block design feedlot study to evaluate the effects of implants (both from Zoetis, Parsippany, NJ) containing increasing doses of TBA and EB administered 124 d prior to harvest have on finishing phase growth performance, carcass characteristics, and serum concentrations of urea-N (SUN) and insulin-like growth factor I (IGF-I). Thirty pens (10 pens/treatment) were assigned to 1 of 3 treatments: 1) negative control given no implant (NI); 2) a steroidal implant containing 100 mg TBA and 14 mg EB administered subcutaneously in the center one-third of the ear on d 1 (Synovex Choice, Zoetis, Parsippany, NJ; CH); 3) a steroidal implant containing 200 mg TBA and 28 mg EB administered subcutaneously in the center one-third of the ear on d 1 (Synovex Plus, Zoetis; PL). Cattle were fed for 124 d post-implantation. Steers were fed a common diet throughout the study. Treatment effects were evaluated by the use of orthogonal polynomials. Pen was the experimental unit for all analyses; an α of 0.05 determined significance. There was a quadratic effect (P = 0.01) on carcass adjusted final BW. Increasing doses of TBA and EB resulted in a linear increase for both ADG (P = 0.01) and DMI (P = 0.02). A quadratic effect on G:F was observed (P = 0.01). No quadratic (P ≥ 0.40) or linear (P ≥ 0.14) effects were observed for dressing percentage, rib fat (RF), calculated yield grade, or marbling scores. A quadratic increase (P = 0.01) in hot carcass weight (HCW) and a linear increase (P = 0.01) in ribeye area (REA) was detected. No significant implant × day interaction (P ≥ 0.09) was noted for serum concentrations of urea-N or IGF-I. Implants decreased (P = 0.01) circulating SUN compared to NI. Serum concentration of IGF-I was increased (P = 0.04) in implanted steers compared to NI steers. In yearling crossbred beef steers the use of steroidal implants containing a combination of 100 mg TBA + 14 mg EB or 200 mg TBA + 28 mg EB increases growth performance, HCW, and REA at equal RF accumulation without detriment to marbling score compared to non-implanted steers.

Library of Congress Subject Headings

Beef cattle -- Housing.
Beef cattle -- Growth.
Beef cattle -- Carcasses.
Acetates -- Physiological effect.
Estradiol -- Physiological effect.
Estradiol benzoate -- Physiological effect.



Number of Pages



South Dakota State University


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