In an experiment reported in this month's edition of the Journal of Dairy Science, researchers at Purdue University looked at the effects of glycerol, a byproduct of the biofuels industry, on feed intake, milk production, rumen volatile fatty acids and metabolic parameters in transition dairy cows. Cows were fed diets containing either high-moisture corn or glycerol from 28 days prior to calving to 56 days post-calving.
Glycerol was included at 11.5 and 10.8 percent of the ration dry matter for the pre- and post-partum diets, respectively. There was no significant difference between the treatment groups in terms of feed intake, milk production and milk composition. Glycerol has good energy value, which makes it an option for replacing some of the grain in lactating-cow diets — if the economics are right. It should be noted that the glycerol used in the Purdue study was food-grade (pure) glycerol as opposed to the crude form of glycerol or glycerin that most farms would probably use.
"Although crude glycerin contains mostly glycerol, chemical analysis is needed to identify the other components in the glycerol source if it is to be used as a feed," says Shawn Donkin, professor of animal science at Purdue.
"If the crude glycerol also contains sodium, potassium or fat, then the contributions of these to the total diet needs to be considered," he says. "Most importantly, the level of water contained in crude glycerol must be considered and is particularly critical when pricing crude glycerol relative to corn grain or other energy-containing feeds," he adds.
While this particular experiment used pure glycerol at an inclusion rate of 10.8 to 11.5 percent, the inclusion rate of crude glycerol will depend on the level of contaminants and adjustment for water content. Because crude glycerol may contain methanol and mineral salt constituents, palatability can be an issue.