Oestradiol 17β (Compudose-365 ) is widely used as a growth promoter in steers and the daily gain response is well known. However, for bull beef production the efficiency of the hormone implant is not so well researched, particularly in Great Britain, where there is not yet a product licence for use in bulls. Work in the U.S.A. has shown that Oestradiol 17β implants in bulls stimulate daily gain and improve carcass shape, but at the same time increasing subcutaneous fat levels (Johnson et al, 1984). The trial described here was designed to study the effect of Oestradiol 17β under a range of farm conditions in Great Britain.

Sixteen groups of bulls on 14 farms, totalling 450 bulls, were selected. Fourteen of the groups were wholly British Friesian, the remainder Friesian/Holstein or Limousin cross. The bulls were weighed at 3-4 months of age and paired by weight. One of each pair was implanted subcutaneously in the ear with a silastic rubber implant containing 45 mg Oestradiol 17β (Compudose-365, Elanco Products Ltd.). The bulls were weighed after three and six months (mean 108 and 180 days respectively), and about half were weighed within four days of slaughter (mean 222 days).