The ARC (1980) energy system sees growth in the single dimension of energy retention (ER) which increases, with diminishing marginal efficiency, as ME intake increases. The quantitative relationship between ME intake and ER is predicted from q, the proportion of the gross energy which is metabolisable. An experiment on growing sheep on controlled feeding of different feeds was carried out to provide data suitable for testing ARC (1980) and other energy systems.

Scottish Blackface wether sheep in single pens, entered the experiment at 25 kg liveweight (LW), when 11 were slaughtered. The remainder were allocated to 3 x 3 x 3 treatments with an intended 4 replicates per treatment. The factors were (i) feeds: feeds B, U and M shown in Table 1, (ii) levels of feeding. L, M and H where H was 936 g/d at 25 kg and was increased by 52 g/d each week, L was half H and M half-way between L and H, (iii) slaughter point, after 9 or 18 weeks, or at 40 kg liveweight.