1. Introduction
The world demand for livestock product, especially meat and milk, has been increasing annually due to a high rate of population and economic growth and improved standard of living (Leng, 1991; Delgado et al., 1999), especially in developing countries. In Thailand, one of the strategies to improve animal productivity and efficiency is to increase the efficiency of utilization of low quality forages, crop residues and high potential local feed resources through appropriate feed supplementation, thereby balancing the supply of nutrients to the animal.