Twenty-eight lamb ewes (44 + 0.45 kg live weight) were used to study the effect of type and level of supplementation on voluntary intake of barley straw, treated with 30 g/kg of anhydrous ammonia (TS) or untreated (US) but given with urea to ensure the same nitrogen content as TS (18 g/kg DM). Each type of straw was offered ad libitum, supplemented with grass hay, rolled barley and sugar beet pulp at rates of 150, 300, 4 50 and 600 g/d, in 6 Latin Squares (4 x 4). In addition, another 2 sheep received each straw alone during the same periods. Supplements were totally consumed, except hay, which was refused in 10 - 13 and 28 - 34 per cent for US and TS, respectively.

Daily dry matter intake (DMI) of US (OMD = 0.423) and TS (OMD = 0.515) offer as sole feed were 511 ± 29.1 and 858 ± 45.2 g. As show TABLE 1, US was consumed at rates of 527, 576 and 568 g DM when supplemented with 150 g of hay, barley and sugar beet pulp, and no significant differences were found with further levels of supplementation. DMI of TS decreased linearly from 850 to 618 g/d (r = 0.75) and from 717 to 518 g/d (r = 0.63) when the level of barley and sugar beet pulp increased from 150 to 600 g/d. Substitution rates were estimated to be 0.31 and 0.27 for barley and sugar beet pulp, respectively. Decrease in TS intake when supplemented since 150 to 600 g/d of hay (720 to 605 g, respectively) were found not significative.