Trials were undertaken with 320 heifers in 13 groups on nine farms. Within each group heifers were allocated within matched weight pairs to treatment sub-groups at yarding. One sub-group was treated with an implant containing 200 mg Testosterone Propionate and 20 mg Oestradiol Benzoate (Synovex-H, Syntex). The two sub-groups were then reared together until slaughter or disbandonment of the group. Seven groups were sold deadweight, five of which had liveweights just prior to slaughter. Four farms sold to live auctions and weighed cattle on the day of sale. Two groups were grass finished but were weighed at turnout (Table 1).