Effect of the DVE and OEB value changes of grain legumes (lupin and faba beans) after roasting on the performance of lambs fed a roughage-based diet

Forty second-cross growing ewe lambs (6 months old; 35.1±1.9 kg BW) were used to study the effects of the nutritional value changes in terms of DVE and OEB (DVE — net truly absorbable intestinal protein; OEB — degraded protein balance) after dry roasting of whole lupin (Lupinus angustifolius) seeds (WLS) and whole faba (Vicia faba minor) beans (WFB) on the growth performance. Lambs were fed a fixed quantity of oat straw and alfalfa hay plus a daily supplement of either of the following: no legume seeds (CTRL), raw WLS, roasted WLS, raw WFB, or roasted WFB. Seeds were dry roasted at 150°C for 45 min. All diets were isonitrogenous (15.9% CP). In the supplemented diets, about 55% of protein was supplied by WLS or WFB protein. Diets with roasted seeds and diets with raw seeds were isoenergetic. Supplementation improved (P<0.05) ADG and gain to feed ratio, and the effect was greater in the lambs which were fed WFB than those which were fed WLS. Dry roasting of WLS and WFB tended to increase ADG (P<0.10) by 9–10 g/day and gain to feed ratio by 8 g/kg DM (P<0.10), and this effect seemed to be mainly mediated through an increase in DVE value and a decrease in OEB value of the roasted legume seeds and (or) an increase in the absorbable ruminal undegraded starch (ARUSt). The ADG predicted from AFRC [Energy and Protein Requirements of Ruminants. CAB International, Wallingford, UK, 1993, pp. 9–18] model from known intakes of DM and ME were all higher than the observed ADG. This could be because supplies of total DVE value did not meet the predicted protein requirements for support of the predicted ADG values.