EFFECT OF SEQUENTIAL IMPLANTING WITH SYNOVEX ON STEER AND HEIFER PERFORMANCE

Studies were conducted using 72 (Exp. 1) and 248 (Exp. 2) steer and he ifer calves from 1 to 2 mo of age through slaughter to determine wheth er preweaning implants affect postweaning feed conversion of cattle th at are rapidly grown and(or) finished in the feedlot. In Exp. 1, treat ments were three Synovex(R) (S) implants administered 0, 70, and 140 d postweaning (NSSS) or Synovex-C(R) (C) administered preweaning and th ree implants administered postweaning (CSSS). In Exp. 2, treatments we re no implants (NNNN), implants administered 0, 74, and 148 d postwean ing to calves that had either received no preweaning implant (NSSS), o r C (CSSS), and CSSS plus trenbolone acetate (TBA) administered with t he last S implant (CSSS-TBA). Synovex-S(R) or -H(R) implants were admi nistered postweaning to steers and heifers, respectively. Steer and he ifer calves implanted with C in the preweaning phase were 9.0 and 13.0 kg (Exp. 1) and 7.5 and 15.0 kg (Exp. 2) heavier (P < .10), respectiv ely, at weaning than nonimplanted steer and heifer calves. In Exp. 1, preweaning implant had no affect on postweaning performance or quality grade. In Exp. 2, preweaning implants (NSSS vs CSSS) decreased (P < . 10) steer postweaning gains, whereas postweaning implants (NSSS vs NNN N) increased (P < .10) DM intake; however, feed:gain ratio was not aff ected by implant strategy. Heifers in Exp. 2 that received implants ha d greater postweaning (P <. 10) DM intakes and daily gains than heifer s not receiving implants (NNNN; however, feed:gain ratios among treatm ent groups were unaffected. Using TBA as a terminal implant in combina tion with S did not affect finishing period gains, feed:gain ratios, o r carcass quality of steers or heifers compared with steers and heifer s receiving only S. Implants decreased(P < .10) quality grade and perc entage of carcasses grading Choice and Prime (Exp. 2). We conclude tha t preweaning implants had no influence on postweaning feed efficiency of cattle that are rapidly grown or finished directly after weaning.