Technical grade glycerol

When manufacturing biodiesel an interesting by-product appears: glycerol . This product could very easily be used as a feed ingredient. Here’s some ideas how to deal with glycerol in feed in the future.

In the manufacture process of biodiesel, of which EU guidelines ask for a 5.75% addition to regular fuel by 2010, triacyl-glycerol from vegetable oils reacts in the presence of sodium hydroxide (a catalyst) with methanol and yields 90% methyl esters of fatty acids and 10% glycerol.

The latter comes in the form of a by-product, usually of 80% purity (technical grade glycerol), that is predicted to become available in increasingly large quantities as a feed ingredient. Technical grade glycerol (85-88% dry matter) is a yellowish brown, viscous liquid with a sweet/salty taste.

It contains 14.6 Mj/kg metabolisable energy, about 12-15% water and around 5-8% salt. It is hydroscopic, remains in good condition for up to one year in storage, and it does not require heating for ease of handling during the winter because of its high sodium content.

But, special attention should be given to mineral (sodium) and electrolyte balance of feeds containing technical grade glycerol. During feed processing, technical grade glycerol acts as a pellet and dust binder, it imparts a sweet taste to feeds, and it can be mixed up to 10% in complete feeds without problems.

Feeding up to 10% technical grade glycerol in growing finishing pigs as a replacement of cereal energy sources has resulted in comparable performance and slightly improved carcass characteristics (less dripping and water loss).

Nevertheless, recent evidence suggests that 5-6% dietary pure glycerol (6.25-7.5% technical grade glycerol) may be reaching the upper limit of the organism to metabolise this nutrient, as evidenced by increasingly higher urinary losses of glycerol with increasing dietary concentrations.

To this effect, the use of technical grade glycerol in nursery diets should be limited to no more than 6% until further research clearly indicates otherwise.

 

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