Two experiments were conducted in central Vietnam to test the hypothesis that supplementation with a concentrate, comprising rice bran (45% fresh basis), maize (49%), fish meal (3%), urea (2%) and salt (1%), up to 2% of live weight (LW)/d (dry matter (DM) basis) would linearly increase digestible organic matter intake and LW gain of yellow cattle. In both experiments, there were five treatments, namely a basal diet of fresh grass fed at 1.25% of LW (experiment 1, elephant grass, Pennisetum purpureum; experiment 2, native grass) and rice straw (Oryza sativa) fed ad libitum or this diet supplemented with concentrate at about 0.3, 0.7, 1.3 or 2.0% LW. There were 4 male growing cattle per treatment in experiment 1 and 3 in experiment 2. Diets were fed for 44 (experiment 1) or 49 (experiment 2) days, with feed intake recorded daily, LW measured about weekly and digestibility measurements made over 7 days commencing on day 24 (experiment 1) or day 10 (experiment 2). The elephant grass and native grass had neutral detergent fibre (NDF) concentrations of 82 and 73% DM, and nitrogen concentrations of 1.3 and 1.8% DM, respectively. The rice straw used had a NDF concentration of 79-84% DM and nitrogen concentration of 0.8% DM. The concentrate had NDF and nitrogen concentrations of 33 and 2.8% DM. In both experiments, DM intake increased (p<0.001) linearly as the amount of concentrate consumed increased. Rice straw intake declined (p<0.001) (experiment 1: 1.24 to 0.48 kg DM/d; experiment 2: 0.95 to 0.50 kg DM/d) as concentrate intake increased. Grass intake was not significantly affected by concentrate intake in either experiment. The lowest amount of concentrate supplement increased forage intake, after which substitution rate increased as the amount of concentrate consumed increased. However, substitution rates at the highest amount of concentrate consumed were modest at 0.3 to 0.5 kg DM reduction in forage intake/kg DM supplement consumed. In both experiments, digestible organic matter intake increased linearly (p<0.001) (experiment 1: 1.16 to 2.38 kg/d; experiment 2: 1.30 to 2.49 kg/d) as the amount of supplement consumed increased, as did LW gain (experiment 1: 0.15 to 0.81 kg/d; experiment 2: 0.15 to 0.77 kg/d). This was associated with significant (p<0.01) linear increases in organic matter intake and apparent organic matter digestibility. Neutral detergent fibre digestibility declined as concentrate intake increased, but the effect was not significant (p = 0.051) in experiment 2. These results are discussed in relation to existing literature and potential to improve the profitability of cattle fattening in central Vietnam.

Increased production in smallholder beef systems requires improved forage management. Our objective was to evaluate the effects of composted cattle manure and mineral nitrogen (urea) application on soil fertility and partial nutrient balances in plots established toBrachiariacv. Mulato II in south-central coastal Vietnam from 2010 to 2013. A randomized complete block design was implemented on six farms (blocks), with five rates of composted cattle manure (0, 4, 8, 12, and 24 Mg DM/ha per yr) and three urea rates (0, 60, and 120 kg N/ha per yr) in a factorial design. Soil was analyzed before and after the experiment. Compost increased soil pH, organic matter, Ca, Mg, and Mn. The effect of compost and urea applications on postexperiment soil fertility depended on preexperiment soil fertility for K, P, S, Mg, Zn, Mn, Cu, and organic matter, suggesting that the ability to maintain soil fertility depends on the interaction between soil organic and inorganic amendments and existing soil fertility. Highest farm yields were also achieved on farms with higher preexperiment soil fertility levels. Negative partial nutrient balances for N, P, and K suggest that yields will not be sustainable over time even for the highest fertilization inputs used in this experiment.

Improved forage management can support increased production in smallholder beef systems. Our objective was to evaluate the effects of mineral nitrogen (urea) and composted cattle manure on Brachiaria cv. Mulato II yield and nutritive value in south‐central coastal Vietnam. Study design was a randomized complete block on six farms (blocks), with treatments derived from the factorial combination of five rates of composted cattle manure (0, 4, 8, 12 and 24 Mg DM ha−1 year−1) and three urea rates (0, 60 and 120 kg N ha−1 year−1), split into six yearly applications. Yield was measured from 2011 to 2013 with 36‐day average harvest intervals. Forage nutritive value was measured in September 2011 and December 2012. Highest yields were achieved when both compost and urea were applied at high rates. The initial yield and tiller responses to urea application were not sustained over the duration of the study when no compost was applied. Compost applied in isolation did not increase yield. Compost application increased ash concentration. Urea increased nutrient yield for all forage nutritive value parameters measured. Composted cattle manure combined with urea benefits grass yield, but high application rates are needed for sustained high yields on sandy soils.

An experiment was conducted in Vietnam to test the hypothesis that supplementation with cassava powder up to 2% of live weight (LW)/d (DM basis) would linearly increase digestible organic matter intake and LW gain of Laisind cattle. There were five treatments: a basal diet of elephant grass fed at 1.25% of LW and rice straw fed ad libitum or this diet supplemented with cassava powder, containing 2% urea, at about 0.3, 0.7, 1.3 or 2.0% LW. The cattle fed cassava powder at about 2.0% LW did not consume all of the supplement, with actual intake similar to the 1.3% LW treatment. Organic matter, digestible organic matter and digestible energy intakes increased (p<0.001) curvilinearly with increased consumption of cassava powder. Rice straw intake declined curvilinearly with increasing intake of cassava powder (p<0.001), and there was a small linear decline (p = 0.01) in grass intake. The substitution rate of cassava powder for forage was between 0.5 and 0.7 kg DM reduction in forage intake per kg DM supplement consumed, with no difference between treatments. Apparent digestibility of organic matter increased (p<0.001) in a curvilinear manner, while digestibility of neutral detergent fibre declined (p<0.001) in a curvilinear manner with increased consumption of cassava powder. Live weight gain increased (p<0.01) linearly with increased consumption of supplement. It was concluded that the amount of cassava powder fed should be limited to between 0.7 and 1.0% LW.