Published online by Cambridge University Press: 02 September 2010
An experiment has been carried out to examine the effects of implantation with hormonal growth promoters on the response in the performance of castrated male cattle (steers) to protein supplementation of a silage-based diet. The treatments consisted of grass silage offered ad libitum and supplemented with 2·7 kg per head daily of either a low protein (LP, 114 g crude protein per kg dry matter (DM)) or a high protein (HP, 206 g crude protein per kg DM) concentrate. Half of the animals, given each of the two concentrates were implanted with 20 mg oestradiol plus 200 mg progesterone and 300 mg trenbolone acetate at the beginning of the experiment and after 77 days, while the remainder of the animals received no implant, giving four treatments in a 2 × 2 factorial design. Sixty-four British Friesian and Simmental cross steers which were initially 426 (s.e. 3·5) kg live weight were used. The treatments were imposed for 157 days. The silage used was well preserved and of high digestibility. For LP and HP concentrates given to non-implanted animals and LP and HP given to implanted animals respectively silage DM intakes were 5·7, 5·8, 6·3 and 6·6 (s.e. 0·18) kg/day; live-weight gains 0·96, 0·92, 1·22 and 1·33 (s.e. 0·045) kg/day; carcass gains 0·58, 0·53, 0·78 and 0·81 (s.e. 0·024) kg/day; carcass subcutaneous fat depth 6·0, 6·5, 5·8 and 5·5 (s.e. 0·35) mm; areas of m. longissimus dorsi 69·1, 58·5, 69·6 and 74·7 (s.e. 1·91) cm2 and marbling scores 3·0, 3·6, 3·3 and 3·1 (s.e. 0·25). It is concluded that protein supplementation of well preserved grass silage produced a marginal increase in the performance of implanted finishing steers but did not affect carcass fatness. With non-implanted steers protein supplementation produced a marginal depression in performance and increased carcass fatness.