In three experiments with 60, 72 and 72 housed Greyface (Border Leicester × Scottish Blackface) and Suffolk × Greyface lambs on silage-based diets, a range of barley and fish-meal supplementation levels was compared. In experiment 1, six barley levels ranging from 0 to 625 glday were offered to lambs on flail-harvested and precision-chopped silages. In each of experiments 2 and 3, three levels of barley, 200, 400 and 600 g/day, were factorially arranged with four levels of fish meal, 0, 40, 80 and 120 g/day. The daily intake of flail-harvested silage was proportionately 0·76 of that of precision-chopped silage but because of a slower rate of gain the total requirement of silage dry matter (DM) per kg carcass gain was greater with flail-harvested than with precision-chopped silage. On average, over all barley supplemented diets in experiment 1, the requirement per kg carcass gain was 9·2 kg silage DM and 4·9 kg barley DM, with flail-harvested silage, compared with 8·2 kg silage DM and 3·4 kg barley DM with precision-chopped silage. Increasing barley supplementation in experiment 1 from 125 to 625 gl day reduced the silage DM requirement for carcass gain by 4·7 kg/kg increase in barley DM given. The corresponding figure over the range 200 to 600 g barley in experiments 2 and 3 was 2·6 kg silage DM per kg increase in barley DM given. The reduction in silage requirement with increasing barley was generally greater at low than at high levels of barley supplementation within the ranges examined. On silage-based diets optimum barley supplementation level was estimated to be in the region of 500 g/day.
Increasing fish-meal supplementation from 0 to 40 g/day, in experiments 2 and 3, reduced the requirement per kg carcass gain by 2·78 kg silage DM and 1·25 kg barley DM for an increase of 0·40 kg in input of fish meal DM. A further increase from 40 to 80 g/day fish meal reduced the silage DM requirement per kg carcass gain by 1·44 kg and the barley DM requirement by 0·50 kg, for an increase in input of 0·26 kg fish meal DM. A further increase to 120 g/day fish meal resulted in increases in both the silage and barley requirement per kg carcass gain. The optimum level of fish-meal supplementation was between 40 and 80 g/day and was not affected by the level of barley given.
There was evidence of an increase in carcass fat at the higher levels of gain achieved through increasing barley supplementation, but no evidence of increase in carcass fat at the higher levels of gain achieved through fish-meal supplementation.