The project aimed to study the use of crude glycerin produced by biodiesel plants as feed for dairy cows as an alternative to reduce the use of maize, an energy source with increasingly higher international prices, and thus increase the sustainability of dairy production. Research work carried out in other countries suggests that glycerol is the main component of crude glycerin, an energetic nutrient efficiently used by ruminants. . Thus, this project considered three main strategies to address the issue. The first one, with fistulated and non-fistulated cows, studied the effect of different levels of crude glycerin in the diet on the consumption, ruminal environment (microbiota, fatty acids, and ammoniacal nitrogen), ruminal dynamics, nutrient degradability, milk production and composition and constituents of the blood. These results defined the dosage of crude glycerin to be used in the following strategy, which studied the effect of continuous consumption of crude glycerin by lactating cows during long periods and in the different stages of lactation. The effects on food consumption, milk production and composition, variation in live weight, and apparent digestibility of nutrients were evaluated. Finally, through sampling in the biodiesel plants, the crude glycerin produced in Brazil was characterized and its possible limitations for use as feed for ruminants were verified. The results indicated that glycerine can be used up to 9% of TMR (Total Mixed Ration) for dairy cows or replace up to 22% of the corn used in the concentrate formulation. Besides not affecting feed intake, milk production or composition, cows consuming glycerine gain more weight. Although not changing ruminal pH and ammonia concentration, the use of glycerine in diet impairs the ruminal degradability of the roughage present in the TMR and the ruminal population of some ciliate protozoa ( Entodinium, Isotricha and Ostracodinium). About half of the Brazilian glycerine is produced in the Midwest Region, mostly coming from soybean oil (55%) and beef lard (36%). The quality is quite variable as impurities (water + oil) varies from 6 to 46%, pH from 5 to 10 and glycerol from 60 to 88. In order to be used as animal feed, process adopted by plants must be improved aiming a final product with minimal quality requirements. Economically, the use of glycerine is recommended whenever its price is lower than corn’s. However, because it is a liquid feed, far different from those ingredients usually used in concentrate and TMR (Total Mixed Ration) formulations, its utilization implies new types of transportation, storage and handling in the industry and dairy farms.