Abstract: Locals feed resources are prime importance for ruminants raised in the tropic particularly low-quality roughages and agricultural crop-residues. Manipulating rumen fermentation through treatment of roughage, concentrate and strategic supplementation with organic acids could improve rumen efficiency by maintaining higher pH, optimum ammonia-nitrogen (NH3-N), thus reducing methane (CH4) and increasing microbial protein synthesis and essential volatile fatty acid (VFAs), for enhancing ruminant productivity in the tropics. The manipulation of rumen efficiency through the use of organic acids especially malate with local feeds would be an advantage. Indeed, organic acids potentially provide an alternative to currently used antimicrobial compounds by stimulating rather than inhibiting specific ruminal microbial populations. At the same time, local feed resources especially cassava chip could be used effectively at high level as an energy source for ruminants especially for beef and lactating cows. More recently, the combined use of concentrates containing high level of cassava chip with supplementation of sodium dl-malate and urea could improve rumen ecology and subsequent performance in dairy steers receiving urea-treated rice straw as a roughage. In addition, the high level of cassava chip in the diet resulted in increase population of bacteria and fungi, decreasing protozoal populations, and improving microbial protein synthesis and efficient microbial nitrogen supply in the rumen. Under these circumstances, malate was also effective in reducing the drop in ruminal pH normally seen 1 to 2 h after feeding a high-grain diet and improved cows performance efficiency. In summary, supplementation of organic acid like malate with local feed resources especially cassava chip or other carbohydrate sources with high rumen degradation would be a desirable alternative because there is no risk of developing antibiotic resistance or having unwanted residues appear in either meat or milk products as well as improving ruminal fermentation efficiency and productivity in ruminants in the tropics.