The overall objective of the studies presented in this thesis was to define nutritional strategies to improve productivity of ruminants under tropical conditions. Because productivity is a function of intake of nutrients and the efficiency of their utilisation, strategies to improve these two parameters have been studied. From a review of literature, it is apparent that there has been a controversy over factors possibly associated with the low efficiency of utilisation of metabolisable energy in ruminants fed roughage-based diets. ... Results of the studies presented in this thesis indicate that bypass protein supplementation to low quality roughage (that is already adequately supplemented with RDN and minerals to eliminate rumen deficiencies), is unlikely to improve the performance of ruminants. On a very low digestibility basal diets such as barley straw, gut fill will most likely be the primary limitation to DMI once nutrient imbalances are corrected, for example by supplementation with rumen undegraded amino adds. Under tropical conditions, low productivity of ruminants is more likely to be related to low ME intake resulting from type of diet than to imbalances in absorbed nutrients.