Study on supplementing effects or feeding systems of molasses and urea on methane and microbial nitrogen production in the rumen and growth performances of bulls fed a straw diet

An experiment with growing bulls were conducted to determine the effect of supplementation of a straw (S) with 15% molasses and 3% urea as an intimate mix (UMS) on its dry matter (DM) intake and digestibility (DMD) and reduction of methane (CH4) production from fermentation in vitro of the straw. In the next experiment, the feeding of the UMS was compared with that of the feeding of molasses and urea in meals (DS) or in lick blocks (DSUMB) as supplements to straw. The UMS feeding increased daily intake of straw DM (89.5 g . kg W--0.75, p < 0.01) and digestible crude protein (DCP 333 g, p < 0.001) and nitrogen (N) balances (508 mg kg W--0.75 . d(-1), p < 0.01) of the bulls than the feeding of 'S' (65 g . kgW(-0.75), 55 g and 8.0 mg . kgW(-0.75) . d(-1), respectively). It also increased the digestibility of DM (594 g . kg(-1), p < 0.05), organic matter (OM, 641 g . kg(-1), p < 0.05), CP (619 g . kg(-1), p < 0.001) and acid detergent fibre (ADF, 773, p < 0.005). The CH4 emitted per g of DOM apparently fermented in the rumen (DOMR) was 91.0 ml in the 'S' and reduced (p < 0.05) to 61.6 ml in the UMS. The feeding of the UMS when compared with that of the DS or DSUMB also gave a higher straw intake (1.77% of live weight, LW, p < 0.01) and ADF digestibility (516 g . kg(-1), p < 0.05) than the other diets (1.52% or 1.55% LW and 472 or 490 g . kg(-1) respectively) in association with the increased microbial N yield in the rumen (14.1, 5.62 or 17.0 g . kg(-1) DOMR, respectively, p < 0.05), daily LW gains (233, 125 or 93 g, respectively, p < 0.05) and feed conversion ratios of the diets (26.0, 56.1 or 57.6 g feed/g LW gain, p > 0.05, respectively). It can be concluded that molasses and urea feeding as an intimate mix with straw (UMS) increased its digestion and intake in association with a reduced methane emissions in the rumen. When compared with that of their feeding in meals or in lick blocks as supplements to straw, the UMS gave the highest straw intake and digestion and live weight gains of growing bulls concurring the finding that the UMS system may be the best way of molasses and urea feeding to ruminants fed straws.