Feedlot Performance and Carcass Characteristics of Feeder Lambs Implanted and Re-implanted with Zeranol

Abstract

One hundred-twenty Rambouillet feeder lambs (Mean BW = 29.5 kg) were used to compare the effects of double and single implanting with Zeranol hormonal implants on lamb performance and carcass characteristics.  Lambs were randomly assigned to three treatments: no implant (treatment 1), single implant (treatment 2), and double implant (treatment 3).  On d 0, lambs in treatments 2 and 3 were implanted.  Lambs in treatment 3 were re-implanted on d 56.  Lambs were weighed every 28 d and slaughtered at 120 lb BW.  Backfat thickness, leg circumference, hot carcass weight, USDA yield and quality grades were recorded, dressing percentage and calculated yield grade (CYG) were calculated.  Treatments 2 and 3 had higher (P < 0.05) ADG than non-implanted lambs on d 28, 56, 84, and overall.  Days on feed and feed to gain ratio were lower (P < 0.05) for implanted lambs than non-implanted lambs.  Treatment 3 lambs had a lower (P < 0.05) dressing percentage and a lower (P < 0.05) percentage of choice grade carcasses and higher (P < 0.05) percentage of no grades.  Treatment 2 and 3 wether lambs had a higher (P < 0.05) value and profit margin than implanted ewes and control lambs.