As Brazil increases its production of biodiesel, so does the production of glycerin, a by-product with a high energy value. At the same time, corn, the main energy component in concentrated feeds, in addition to being the ingredient that most increases feed costs, tends to become less available in the market due to its use in the production of alcohol in Europe and the United States. Glycerol, the main component of glycerin, has already been used in some countries, mixed with concentrate for lactating cows. The use of glycerin as an additive in corn silage can be an alternative to increase the energy supply of diets. Glycerin, when mixed with the chopped corn plant up to 15% (base of natural matter) during its ensiling, increased the dry matter content of the final product without interfering with the quality of the silage fermentation. Although the presence of glycerin in the silage increases the dry matter intake and the milk production of the cows, it compromises their fat percentage, meaning that there is no difference in terms of PLC (milk production corrected for 3.5% fat). The use of glycerin-added corn silage as a single roughage in a total ration for cows reduced, on average, 14% of diet efficiency. The use of glycerin as an additive in corn silage, although effective in maintaining the quality of fermentation and increasing the dry matter intake of cows, has reduced the efficiency with which the diet is transformed into milk.