In a USDA/ARS study, pigs fed crude glycerin from biofuels plants were able to digest it efficiently, and it provided them with a supply of caloric energy that basically equaled that of corn grain. A follow-up study showed no effects on weight, carcass composition, and meat quality in pigs fed diets containing 5% or 10% crude glycerin from weaning to market weight.

In five different experiments on pigs, the diets of starter pigs and finisher pigs were fed with different levels of crude glycerin from a biofuels plant. Overall, these studies conducted by USDA/ARS animal nutritionist Brian Kerr showed that the sample of crude glycerin contained an apparent metabolizable energy (AME) concentration of 3,207 calories per kilogram (kcal/kg).

Another ARS study evaluated the use of glycerin supplements in poultry feed. Scientists used 48 egg-laying hens and 1,392 broilers in four research studies. After feeding four levels of crude glycerin to laying hens, the AME in the crude glycerin was determined to be 3,805 kcal/kg. Feed consumption, egg production, egg weight, and egg mass (calculated by multiplying egg production and egg weight) found no significant differences among the four groups. “Glycerin supplements were well utilized for egg production by the hens,” one of the researchers says.

Meanwhile, three broiler studies were conducted. In the first study, young broilers consumed either a control diet with no glycerin supplementation or feed with a 6% glycerin content. The results indicated that glycerin provided the 7- to 11-day-old broilers with an AME of 3,621 kcal/kg. Later research resulted in similar findings for older broilers. Glycerin supplements at varying levels provided 21- to 24-day-old broilers with an AME of 3,331 kcal/kg and 42- to 45-day-old broilers with an AME of 3,349 kcal/kg.

Overall, the data indicates that crude glycerin is an excellent source of energy in swine and poultry rations and can be used without harming animal performance, carcass composition, or meat quality.

“This research project has been a success so far,” according to USDA-ARS.

“But we still need additional research on how to handle glycerin as an alternative feedstuff for swine and poultry in integrated feed mills.”

ARS notes that from a nutritional standpoint, this technology can serve as an alternative dietary energy source that could result in lower feed costs. Crude glycerin does contain small amounts of methanol and salt, which could potentially limit its use as a feed supplement, however.

Additional studies might be needed to assess how much methanol livestock can safely ingest in glycerin supplements, which would help regulators refine U.S. standards for using crude glycerin in livestock feed. But as U.S. biodiesel production continues to boom, crude glycerin supplements could be a win-win situation for biodiesel producers and farmers alike, ARS says.

"Biodiesel With Benefits: Fuel for Cars and Leftovers for Livestock" was published in the April 2009 issue of Agricultural Research magazine.