Initial research conducted at the University of Minnesota indicates crude glycerol can be used to supply energy in lactating sow diets. However, producers need to pay close attention not only to how the glycerol has been handled, but also to salt concentration and methanol content when determining if the ingredient is practical for feeding on a regular basis.
Glycerol is a liquid byproduct of the biodiesel refining process. During biodiesel production, 100 lb. of a fat source, such as soybean oil, is combined with 10 lb. of methanol plus a catalyst, such as sodium hydroxide or potassium hydroxide. The reaction produces 100 lb. of biodiesel and 10 lb. of crude glycerol. Hydrochloric acid is added to neutralize the catalyst remaining in the crude glycerol.
An estimated 450 million gallons of biodiesel were generated in the United States in 2007. “If you do the math, that comes up to about 148,000 tons of crude glycerol available last year,” says Lee Johnston, swine nutritionist at the University of Minnesota's (UM) West Central Research and Outreach Center. “Potential U.S. glycerol production could be about 740,000 tons. There should be a fair bit of this material available that could possibly be used in livestock production.”
According to Johnston, human endurance athletes, particularly those performing under heat stress conditions, use glycerol mixed with water to hyper-hydrate their bodies prior to competition. Glycerol helps improve their water balance by decreasing urine output, which is thought to enhance performance.
Research results indicate rats consuming glycerol have higher blood glucose levels. Since glucose is a precursor of lactose, and lactose is an important driver of milk production, researchers wondered if sows and their litters would benefit if the lactating sows were fed diets containing crude glycerol, particularly when the potential for heat stress is high. They speculated that glycerol's role in water balance may help lactating sows cope with the stress of producing milk during hot weather.
A glycerol trial was designed using 345 mixed-parity sows. Sows were fed corn-soybean meal-based diets containing 2.5% choice white grease. Diets were formulated to 0.9% standardized ileal digestible lysine.
The diets contained treatment levels of 0, 3, 6, or 9% crude glycerol. Researchers used a crude glycerol formulation containing 86.1% glycerol, 6% salt and less than 100 ppm methanol.
“This high salt content (of the glycerol) allowed us to remove all of the supplemental salt in the 6% and 9% diets,” Johnston explains. Supplemental salt was reduced to 0.15% in the 3% glycerol diet.
Sows were fed the experimental diets when they entered the farrowing room on Day 109 of gestation and continued through to Day 19 of lactation, when litters were weaned. The study was conducted from July through November.
The researchers found inclusion of up to 9% crude glycerol had no significant effects on sow weight or backfat loss, litter size or weight at weaning. There were no differences in post-weaning return to estrus.
Sows consumed about 13.4 lb. of feed/day while receiving the 3% glycerol diet. Sows receiving the 6% glycerol diet ate about 12.2 lb./day, while the 9% glycerol group consumed around 12.8 lb./day.
The difference in feed consumption in the 6% glycerol group puzzled researchers. “We could not see an obvious explanation for the sows on the 6% glycerol diet consuming less feed,” he states. Overall, results of the study suggest lactating sows fed diets containing up to 9% crude glycerol perform similarly to sows fed a standard corn-soybean meal control diet.
Watch Salt, Methanol
Johnston cautions producers that the salt content of glycerol can vary greatly. Research conducted by Brian Kerr, Agricultural Research Service animal scientist at Iowa State University, indicated glycerol salt content ranged from 2% to 10% in test samples.
The National Research Council (NRC) says a pig can tolerate up to 8% dietary salt if adequate water is available.
Methanol content in the glycerol may be a little more problematic. Johnston says the residual methanol content can range anywhere from less than 100 ppm up to as high as 3,200 ppm. The toxicity of methanol to pigs is not well established. A Food and Drug Administration (FDA) regulation allows up to 150 ppm of methanol in the crude glycerol fed to livestock.
Johnston and research colleagues Sarah Schieck, Jerry Shurson, Sam Baidoo and Brian Kerr continue to analyze glycerol's role in helping lactating sows cope with heat stress.