High grain prices have dairy producers everywhere scrambling to find low-cost replacements for corn energy in rations. Glycerine (a.k.a. glycerol), a byproduct of the biodiesel manufacturing process, may just fit the bill.

“It's definitely worth taking a closer look at as it becomes more widely available,” says Mike Hutjens, Illinois extension dairy specialist. “In high-starch rations, the energy value of glycerin would be equal to corn. In haylage-based rations, it does a little better than corn grain for net-energy value.”

In a recent Purdue University study, researchers fed groups of mid-lactation cows rations with 5, 10 or 15% glycerol over a 56-day period. When they compared results to a control group, the researchers found feed intake, milk production, milk fat and milk protein were similar. Milk urea nitrogen levels were lower with diets containing glycerol and cows consuming 10 or 15% glycerol gained more weight than cows not fed glycerol.

Shawn Donkin, lead researcher in the Purdue study, notes feed intake for cows fed glycerine at the 15% level dropped off significantly compared to the other groups at the start of the study. But he attributes the drop-off to the fact that the switch-over to glycerol was abrupt.

“Cows are creatures of habit,” he says. “In a commercial dairy situation, you would gradually increase the amount of glycerol in the ration over several days, not do it all at once. In our study, we went to the full 15% level right away. The cows backed off on intake for seven days, but then they were right back on track.”

In a similar study at Ohio State University, 48 mid-lactation cows in four groups were fed 0, 5 or 10% glycerol with different concentrations of non-fermentable carbohydrates (NFC).

Feed intake, milk yield, milk protein and milk urea nitrogen were similar among groups. But milk fat percentage decreased when glycerol was added to the rations. The greatest decrease was in the group fed the ration with 10% glycerol and the highest concentration of NFC.

“Based on the results from our study, along with the work at Purdue and some other published research, we can conclude glycerol has value as a feed ingredient for dairy cattle,” says Maurice Eastridge, Ohio State dairy specialist.

Eastridge adds that glycerol, as a liquid, may help reduce sorting when fed in a TMR. He recommends that producers who feed glycerol keep levels to a maximum 10% of total ration dry matter.

“Because of variations in the manufacturing process, staying on top of the nutrient composition could pose some challenges in balancing rations,” says Eastridge. “Producers can reduce the risks some by keeping percentage levels of glycerol low.”

Hutjens warns producers considering crude glycerine as a ration replacement for corn to check:

  • Water content. Water content of crude glycerine can range from 1 to 26%, he says. “You don't want to be paying for a lot of water.”

  • Methanol levels. Due to the way it's produced, crude glycerine may have methanol levels ranging from 1 to 25%. The Food and Drug Administration has established an upper level of 150 parts per million for methanol in animal feed.

  • Other impurities resulting from the manufacturing process. Salt content in crude glycerine can be as high as 11% and as low as 2-3%. (According to German research, potassium salts and phosphates may explain the increase in salt levels.)

“With variance in the makeup of loads, it will be important for producers to have glycerol supplies analyzed by a laboratory,” says Hutjens. “You'll want to get a warranty on what you're buying and have an up-front agreement on who will be responsible for doing any testing.”

There's some disagreement among experts on how glycerol should be priced. Purdue's Donkin says even with 10% water, crude glycerine could be 20% higher priced per pound than shelled corn and still be a good buy.

“That is after any equipment costs are factored in,” he says.

Hutjens, though, says crude gly-cerin has to be cheaper than shelled corn to make it worthwhile.

“In doing the calculations,” he says, “you'll want to factor in additional labor and storage that go along with handling a liquid product. Not every dairy farm is set up with a tank for liquid feeds.”