Glycerol may have a new use in lactating-cow rations thanks to soy biodiesel production.

During a recent study at PurdueUniversity, researchers used glycerol, a byproduct of biodiesel production, to replace corn as an energy source in lactating-cow diets.

One diet contained no glycerol. In three other diets, glycerol made up five percent, 10 percent or 15 percent of ration dry matter. The researchers replaced corn with an equivalent amount of glycerol and corn gluten feed. The latter was used to replace the protein lost when corn was removed from the diet, says Shawn Donkin, professor of ruminant nutrition and physiology at PurdueUniversity.

Overall, the study found no difference in dry matter intake or milk yield (please see the table below.) Milk composition also did not vary between treatment groups.

However, cows fed 15 percent glycerol ate less dry matter during the first week of the eight-week feeding period. This finding suggests that a gradual introduction of glycerol may be needed to help the rumen adapt to a higher feeding rate. All three glycerol feeding levels also resulted in decreased milk urea nitrogen levels. “Reduced MUN concentrations suggest improved use of dietary protein by rumen bacteria and reduced losses as ammonia,” Donkin says.

In this study, Donkin and colleagues fed food-grade glycerol, which is considered safe for animals. However, crude glycerol, which can be cheaper relative to corn, may contain higher levels of impurities. If fed, take into account the level of impurities and their energy content during diet formulation.

If you want to give it a try, replace 1 pound of corn grain with 0.86 pounds of glycerol in lactating diets, Donkin says. Remember to account for the protein lost when corn grain is taken out of the diet, he adds.

Glycerol level (percent of dry matter)

  0 5 10 15
Milk production (lb/day) 81.4 81.2 82.1 80
Feed intake (lb/day) 52.8 53.9 54.1 53

Source: 2007 Tri-State Dairy Nutrition Conference

Shawn Donkin, PurdueUniversit