What is the evidence on growth-promoting implants in beef cattle and recommended implant strategies?

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Growth-promoting implants consistently improve feedlot performance across all major production metrics. Compared to non-implanted cattle, implants increase dry matter intake by 4.2%, final body weight by 5.3%, average daily gain (ADG) by 12%, gain-to-feed ratio by 8.7%, hot carcass weight by 6.2%, dressing percentage by 0.3%, and longissimus muscle area by 5.3%. The tradeoff is a significant reduction in marbling score and a 7.7% increase in liver abscess prevalence. 3 Implant strategy selection hinges on production phase, sex class, and days on feed. For finishing steers fed 280 days, a single extended-release implant containing 200 mg trenbolone acetate (TBA) and 40 mg estradiol 17β administered at day 60 or day 80 post-arrival produces gain-to-feed ratios superior to day-0 administration or a reimplant program (Revalor-IS followed by Revalor-XS), while also reducing the proportion of steers treated once for bovine respiratory disease compared to day-0 and reimplant groups. 2 Steers implanted at day 0 or on a reimplant program had greater dry matter intake than delayed-implant groups, but inferior feed efficiency. 2 Fat thickness, marbling, and estimated empty body fat all differ by implant timing, confirming that timing influences carcass composition beyond growth alone. 2 Recent FDA guidance now restricts reimplantation: a maximum of 2 implants can be used during finishing, and reimplantation within the same production phase is prohibited unless specifically stated on the implant label. Delaying a single extended-release implant 60–80 days after arrival is a viable strategy to comply with these guidelines without sacrificing growth performance or carcass quality in long-fed steers. 210 For moderate versus aggressive reimplant programs in finishing steers, implant potency has a measurable but modest effect on ADG. An aggressive strategy (Revalor-IS 80 mg TBA / 16 mg estradiol followed by Revalor-200 200 mg TBA / 20 mg estradiol) produced an ADG of 1.72 kg/day ver