EN
Glycerol can be an efficient glucogenic substrate, if it is absorbed directly from the rumen. In that case its advantage consists in entering the neoglucogenic pathway as phosphate triose, without entering the Krebs cycle. A cow in negative energy balance activates this extra pathway, using glycerol obtained by the hydrolysis of triglycerides. This way of absorbing glycerol is superior to its fermentation in the rumen to propionates and butyrates because of the ketogenic nature of butyrates. Unfortunately, the greater part of glycerol is fermented in the rumen. The only organ where glycerol is transformed into glucose is the liver. In other organs gluconeogenesis does not occur owing to lack of an appropriate enzyme. An effective method of protecting cows against ketosis is using combinations of glycerol, propylene glycol and propioniate in a drenching form. Glucogenic substrates from this mixture are metabolized on all pathways of gluconeogenesis. In all animal species glycerol can be a good energy source, comparable with corn starch. The only disadvantage of glycerol obtained in the process of biodiesel production is its potential contamination with methanol.