Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Animal Science

First Advisor

Joseph P. Cassady

Second Advisor

Kristin E. Hales


cattle, fedlot, frame size, growth, implants


The growth promoting activity of implants have been documented. However, stage of growth in which the implant is administered may alter growth performance and carcass traits. An experiment was conducted to examine the effects of administering a conventional implant (Synovex C; SYN-C), or an extended-release combination implant (Synovex One Grass; ONE-G) to suckling steer calves on weaning weight, post-weaning growth performance, and carcass characteristics. Suckling steer calves were either not implanted (NONE) or were implanted with SYN-C or ONE-G. Steer calves were predominantly 30 to 60 d of age when implants were administered. Steers were weaned 176 d post-suckling implant administration. Weaning weight was greater for steers implanted with SYN-C compared to NONE (285 vs 291 ± 1.1 kg; P = 0.04), and greater for steers implanted with ONE-G compared to SYN-C (291 vs 297 ± 1.1 kg; P = 0.02). Steers were used in a 44-d receiving experiment, fed a common diet, and no implants were administered. No differences in receiving-phase growth performance were observed (P ≥ 0.57). At the conclusion of the receiving experiment, NONE and ONE-G steers were used in a backgrounding and finishing experiment. All steers were implanted with 14 mg estradiol benzoate and 100 mg trenbolone acetate on d 49 and 28 mg estradiol benzoate and 200 mg trenbolone acetate on 129 and were fed for a total of 211 d. Steers implanted with ONE-G during the suckling-phase were heavier than NONE steers at the onset of the backgrounding-phase (334 vs. 323 ± 0.9 kg; P < 0.01). By d 129 there were no differences in body weight (P = 0.98). No difference in cumulative dry matter intake (DMI) was observed (P = 0.26). On a cumulative carcass-adjusted basis NONE steers had greater gain-to-feed (G:F) than ONE-G steers (0.186 vs 0.174 ± 0.0035; P = 0.04). Steers implanted with ONE-G had a larger ribeye area than NONE steers, despite being implanted similarly in the feedlot (91.32 vs. 88.19 ± 0.893 cm2; P = 0.05). No differences were observed for other carcass characteristics or Quality Grade (P ≥ 0.24). Percent empty body fat at harvest was not different for NONE and ONE-G steers (P = 0.45). The ONE-G implant is labeled for 200 d of implant coverage (FDA, 2014). To evaluate the potential anabolic effects of ONE-G in the feedlot, we chose not to re-implant steers until 226 d post-suckling implant administration. Therefore, steers implanted with ONE-G steers did not have continuous exposure to an active implant. Differences in early growth performance may be a consequence of discontinuous exposure to anabolic agents. Administering ONE-G during the suckling-phase did not diminish carcass quality. Future research should evaluate implant strategy options to follow ONE-G in suckling calves. Two experiments were conducted to evaluate potential interaction of frame size (FS) and implant status in calf-fed steers. Steer calves from the same 2 sources were used in each experiment and were managed similarly from weaning to study initiation. Steers were the product of a 50-d calving season, so it was assumed differences in FS were reflected in weaning weight (WW). Smaller-framed (SM) and larger-framed (LG) steers were identified from tails of the WW distribution. Within each FS group, steers were implanted with 20 mg estradiol benzoate and 200 mg progesterone (SS) or 14 mg estradiol benzoate and 100 mg trenbolone acetate (CH) on d 1 (Exp. 1), and nonimplanted (NI) or implanted with SS on d 2 (Exp. 2). In both experiments, all steers were terminally implanted with 24 mg estradiol and 120 mg trenbolone acetate on d 84 and fed for 161 (Exp.1) and 168 d (Exp.2). No FS × implant interactions were observed in either experiment (P ≥ 0.08). In both experiments LG steers had heavier body weights (BW), HCW, and BW adjusted to 28% empty body fat (AFBW), greater average daily gain (ADG), DMI, and feed:gain (FG) than SM steers (P ≤ 0.02). No differences were evident in marbling score or Quality Grade distributions between SM and LG steers (P ≥ 0.13). In Exp. 1, no differences in growth performance, carcass traits, AFBW, or calculated FS were observed for steers initially implanted with SS or CH (P ≥ 0.12). In Exp. 2, steers implanted initially with SS had heaver final BW, greater ADG and DMI (P ≤ 0.01), and no difference in FG (P = 0.78) than NI steers. Steers initially implanted with SS had heavier HCW (P < 0.01), but no other differences in carcass characteristics were observed (P ≥ 0.23). Additionally, steers implanted with SS tended to have heavier AFBW (P = 0.07) and greater calculated FS (P = 0.05) than NI steers. Steers of different FS responded similarly to implants while in the feedlot. Previous exposure to implants did not alter the response to the terminal implant. Estradiol implants increase the FS of steers; however, when similar doses of estradiol are compared, trenbolone acetate does not further increase FS.

Library of Congress Subject Headings

Beef cattle -- Growth.
Beef cattle -- Behavior.
Beef cattle -- Carcasses -- Quality.
Hormones in animal nutrition.



Number of Pages



South Dakota State University

Included in

Beef Science Commons



Rights Statement

In Copyright