Partial replacement of concentrate with tomato pulp and olive cake-based feed blocks as supplements for lambs fed wheat straw

The replacement value of feed blocks tomato pulp (TP-FB) or olive cake (OC-FB) for a concentrate (wheat bran and processed barley, 1:2) was evaluated using 25 Barbarine lambs, fed wheat straw (WS) based diet, in a 75-day feeding trial followed by a total collection period (4 days adaptation and 6 days collection). Wheat straw was fed ad libitum and supplemented with (1) 500 g concentrate (control, Q; (2) 250 g C and TP-FB (TP-FB + 0.5C); (3) 250 g C and OC-FB (OC-FB + 0.5C); (4) 125 g C and TP-FB (TP-FB + 0.25C); or (5) 125 g C and OC-FB (OC-FB + 0.25C), in a randomised block design. Except control-animals, lambs had free access to feed blocks. Metabolisable energy (ME, MJ/kg dry matter [DM]) and crude protein (g/kg DM) contents of the concentrate, TP-FB and OC-FB were 13.8 and 122, 11.2 and 154, and 11.0 and 147, respectively. Tape of feed block had no effect on WS intake but increased total intake. Estimated ME intakes were 7.2, 8.5, 8.3, 8.3, and 7.3 MJ/day, respectively. Diets including FB exhibited higher digestible CP intakes than the control diet (P<0.01). Nitrogen balance ranged between 2.7 and 3.9 g/day. N retention and the efficiency of microbial nitrogen supply tended to increase with FB provision (P>0.05 and P=0.057, respectively). Compared to the control diet, FB supply had no effect on the growth rate of lambs (P>0.05). The response of lambs was in general better with diets containing OC-FB than those supplemented with TP-FB. The absence of urea and rapeseed meal in TP-FB could be among the reasons why sheep responded better to OC-FB. Feed conversion rates were higher with TP-FB diets than with OC-FB diets. Although results obtained with TP-FB were similar to those observed on lambs receiving OC-FB, the economic evaluation calls for revision of the formula of tomato-pulp-based feed blocks. Energy enrichment of OC-FB and TP-FB seems necessary for efficient utilisation of high levels of N in these feed blocks. It is concluded that OC-FB are cost-effective alternative supplements and allow farmers to reduce by 0.75 the amount of local concentrate used, while TP-FB allow a 0.5 reduction. (C) 2007 Elsevier B.V. All rights reserved.