INTRODUCTION
An increasing worldwide interest in alternative fuel
sources and in a more diversified energy matrix has
provided incentives for the biodiesel industry, especially
in tropical countries with large productive areas.
Crude glycerin, composed of water, glycerol, salts, and
methanol, represents the main by-product of biodiesel
production. The pharmaceutical, cosmetic, and food industries
use purified glycerin (>95% glycerol) in several
products (Thompson and He, 2006). However, increasing
supply has outweighed these industrial demands
and the price of glycerin has fallen, opening the possibility
for its use as an alternative to conventional food
energy sources, such as corn, in the diets of livestock,
including dairy cows.