The potential of diets, based on maize silage (M), non-bird-resistant grain sorghum silage (NBRGS), bird-resistant grain sorghum silage (BRGS) and forage sorghum silage (FS), in different proportions with concentrate for each silage, was evaluated for the finishing of weaner lambs. On a dry basis the ratios of silage: concentrate were 70: 30, 60:40, 50:50, 40: 60 and 30: 70 respectively for each of the silages. The concentrate mixtures were composed of different quantities of maize meal and soya-bean oilcake meal in order to balance the crude protein contents of the different diets used from weaning to 35 kg live weight and from 35 kg live weight to slaughter at 140 and 110 g/kg respectively.
Better apparent digestibilities of dry matter, crude protein and acid-detergent fibre as well as food conversion to live weight were found for diets with M or NBRGS as roughage sources compared with those with BRGS and FS as roughage sources. At the lower levels of concentrate inclusion in the diets the dressing proportions, carcass grades and food conversion to carcass weight for the diets with M and NBRGS as roughage sources were also better than were those with BRGS and FS as roughage sources. Although higher levels of concentrate inclusion in the diets to a large extent rectified these biological disadvantages of the diets based on BRGS and FS, they will also cause a rise in the price of the diet.