COMPUDOSE(R) - ITS EFFECTS ON THE GROWTH, OFFSPRING PERFORMANCE, LACTATIONAL PERFORMANCE, AND CARCASS CHARACTERISTICS OF HEREFORDXFRIESIAN HEIFERS AT PASTURE

This study investigated the effects of Compudose(R) on growth, lactati onal performance, carcass characteristics, and offspring performance o f HerefordxFriesian (HxF) once-bred heifers (OBH) under pastoral condi tions. Nineteen HxF heifers were implanted with Compudose 400 at 90 da ys of age (Compudose 90), 19 were implanted with Compudose 400 at 210 days of age (Compudose 210), and 19 were not implanted (control). Neit her Compudose group differed significantly in liveweight from the cont rols. However, there was a tendency for the Compudose 90 group to be s lightly heavier, and the Compudose 210 group slightly lighter, than th e controls so that the only significant differences in liveweight were between the two Compudose groups. Similarly, there were no consistent effects of Compudose on measures of body or skeletal size. The effect s of Compudose on carcass characteristics were small and related mainl y to a tendency for increased muscling. Compudose delayed conception s lightly but had no effects on calf birthweight. However, calves born t o control heifers were 15.3 kg and 16.2 kg heavier (P < 0.05) at weani ng than calves born to Compudose 90 and Compudose 210 heifers, respect ively. Most of this difference in liveweight was established by Week 4 of lactation. This implies that Compudose treatment inhibited milk pr oduction of the dams, particularly in the early part of lactation, an effect not detected by the weigh-nurse-weigh (WNW) method. Implanting heifers with Compudose at 90 or 210 days of age is unlikely to be bene ficial, both because it has little positive effect on liveweight gain or carcass characteristics and because it may inhibit lactational perf ormance.