In a market where high levels of fat on lamb carcases are not favoured, the supposition that a lamb, given adequate feeding, will grow protein preferentially to gaining lipid, holds interest. However, this idea runs counter to the evidence that body composition is not manipulable in sheep. Therefore, an experiment was undertaken to implement extreme treatments of protein and energy supply to determine to what extent the contrasting views on body composition changes in growing lambs are justified.

Seventy-two Coopworth ram lambs (mean liveweight, (LW) 30.4, s.d. 1.1 kg) were given one of the three feeds of different digestible crude protein (DCP) content at one of three allowances (ad libitum (AL), 1.2 (H) or 0.8 (L) kg/day). The feeds (H, M and L) were formulated as shown in Table 1. Feed M was a mixture of 0.55 Feed H and 0.45 Feed M. The proximate composition, measured DCP and estimated metabolisable energy (ME) content of the feeds is given in Table 1. ALH and ALM lambs were also choice-fed with ad libitum access to feed L. 8 lambs at the start of the experiment and 4 lambs per treatment at 6 and 12 weeks were slaughtered for analysis of body protein (PR), lipid (LP) and wool protein (WP).