Studies were conducted to evaluate the effects of delayed implanting or the use of a low-dose implant followed by a higher-dose implant in feedlot cattle. In the first study, 150 steers were allotted to 15 pens (three pens/treatment) and assigned to a nonimplant treatment (control), a single zeranol (36 mg) implant (R), or a double zeranol implant (DR) administered at the start of a 140-d finishing period, or a single zeranol implant administered at the start of an 80-d growing period, followed by a single (RR) or double (RDR) zeranol implant administered at the start of the finishing period. Steers managed under the DR, RR, and RDR implant schemes had greater (P < 0.10) finishing period gains and intakes than the control steer group. However, only DR and RDR steer groups had improved (P < 0.10) finishing period feed conversions compared with control steers. In combined growing and finishing periods, the RDR steer group displayed the lowest (P = 0.12) feed:gain ratio. In a second trial, conducted concurrently to the zeranol trial, steers that did not receive an initial implant containing 20 mg of estradiol benzoate plus 200 mg of progesterone (S) but were subsequently implanted twice, once at the start of the finishing period and again 80 d later, had a lower (P < 0.11) finishing period feed:gain ratio (6.08 vs 6.51) than steers implanted all three times. In a third trial, implanting steers with one-half S vs S, at the start of a 92-d growing period, resulted in improved (P < 0.05) gain (1.63 vs 1.54 kg/d) and feed: gain ratio (5.86 vs 6.27) in the subsequent finishing period, in which both groups received S, but not over the entire feeding period. Compared with using S alone, as a finishing phase implant, no differences were found in performance or carcass quality from using S in combination with trenbolone acetate. Delayed implanting or using a low-dose implant during an initial feeding period provides performance enhancement in subsequent feeding periods.
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