Effect of implant sequence and dose on feedlot cattle performance

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 < .10) finishing period gains and intakes than the control steer group. However, only DR and RDR steer groups had improved (P < .10) finishing period feed conversions compared with control steers. In combined growing and finishing periods, the RDR steer group displayed the lowest (P = .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 < .11) finishing period feed:gain ratio (6.08 vs 6.51) than steers implanted all three times.(ABSTRACT TRUNCATED AT 250 WORDS)