In the world of alternative feed ingredients, crude glycerin (also called glycerol) is still a “newbie” compared to the ubiquitous dried distillers’ grains with solubles. However, just like DDGS, this biofuels co-product offers pork producers yet another choice to mull over with their feed supplier and swine nutritionist, as they continue to seek cost-effective solutions to high input costs.

There are currently 171 biodiesel plants in the United States, with an annual production capacity of 2.24 billion gallons of biodiesel. So, the supply is growing. Each gallon of biodiesel generates about 0.66 pounds of crude glycerol.

Brian Kerr, a research scientist with USDA’s Agricultural Research Service in Ames, Iowa, has been involved with much of the research related to crude glycerin’s potential use in swine rations. “Although crude glycerin possesses energy, it’s roughly the same as that found in corn. So from a nutrition standpoint, we are mainly replacing energy from corn in the diet. Think of it as liquid starch.”

This oily liquid offers some dust-prevention abilities, but beyond that how does it benefit your pigs? Kerr explains crude glycerin works much like other energy-rich ingredients. It gets calories into the diet in an efficient way, which in this case involves using less corn. Pigs can absorb up to 97 percent of it for glucose conversion, making it a unique way to achieve the caloric value desired in swine diets.

Trials Validate Interest

To investigate the metabolizable energy content of crude glycerin, Kerr led a team of IowaStateUniversity researchers who conducted five experiments in 2008 involving both weaned and finishing pigs. The researchers used crude glycerin obtained from AGP in Sergeant Bluff, Iowa.  The facility uses soy oil as its initial feedstock, which is 87 percent glycerin; the remainder consists of methanol, water, sodium chloride, ash and total fatty acids. Using a corn/soybean meal-based diet, researchers fed pigs feed with 0 percent, 5 percent, 10 percent or 20 percent crude glycerin.

In the weaned pigs, investigators found the metabolizable energy of crude glycerin — the energy the pig can use — declined as glycerin supplementation increased. The estimated metabolizable energy values were 3,601, 3,239, and 2,579 kilocalories per kilogram of crude glycerin for 5 percent, 10 percent and 20 percent inclusion, respectively. However, when the researchers removed the 20 percent level from the results, the data were more consistent, showing a metabolizable energy value of 3,463 kilocalories per kilogram.  In contrast, the finishing-pig results were consistent, showing no effect of crude glycerin inclusion level on metabolizable energy determination.

What’s this mean to you? Kerr says, “Overall, these results illustrate the energy value that glycerin has for pigs at various stages, and it shows the need for producers to know what these values are.”

University of Minnesota researchers looked at glycerol effects in lactation-sow diets. The key point of interest is that glycerol can influence the water balance of athletes, “so it seemed logical to investigate it for lactating sows,” says Lee Johnston, University of Minnesota swine nutritionist. After all, sow’s milk is about 80 percent water.

The Minnesota study involved 345 mixed-parity sows. The corn/soybean meal-based diets contained 0 percent, 3 percent, 6 percent or 9 percent crude glycerol. The various lactation dietary treatments began on the 109th day of gestation when the sows entered the farrowing house. Until farrowing, the sows were restricted to 5 pounds of feed per day. After farrowing they had ad libitum access to their assigned experimental diet.

What the researchers found was that crude glycerol levels up to 9 percent had no significant effects on sow weight, backfat loss, litter size, weight at weaning or wean-to-estrus interval for sows that displayed estrus by the 10th day after weaning, Johnston notes.

Just like any other co-product, you should be aware that a wide variation in the end product can exist. “Glycerin can be almost a clear liquid or as dark as molasses,” Kerr says. He cites purity, source of initial feedstock used in the biodiesel process and the amount of fatty acids present as reasons for variations in the product’s color and handling characteristics. In recent tests involving 12 different sources of crude glycerin, he found energy levels varied greatly due to these differing compositions of crude glycerin.

Don’t let production variation deter your own investigation into using crude glycerin. According to Kerr’s research, a 5 percent inclusion rate can save approximately 6 percent in dietary corn and 50 percent of sodium chloride. At 10 percent inclusion, the figures move up to a 16 percent corn savings and 90 percent sodium chloride savings. However, such savings would be partially offset because of the extra soybean meal needed at 5 percent and 9 percent, respectively.

Practical Considerations

Is there an optimum level of glycerin in diets? Kerr says the industry is still experimenting, but it’s somewhere between 5 percent and 10 percent. In reviewing literature available to date, he says, “Levels up to 10 percent appear to have no effect on market pig performance, carcass composition or meat quality.”

Depending on your feed storage and handling equipment, feeding even 10 percent crude glycerin can pose difficulties. Glycerol weighs 10.4 pounds per gallon, whereas vegetable oil weighs about 7.7 pounds per gallon. Glycerin’s inherent oily nature can lead to feed-flow issues after it’s incorporated into the feed. “In our research, diets containing 8 percent to 9 percent crude glycerol exhibited some initial problems with bridging in bulk storage bins,” Johnston says, “but flow was easily established.”

Storing crude glycerin on the farm means treating it like you would oil or, if there is a high level of fatty acids in the product, treating it like animal fat. In Kerr’s experience, a glycerin product with approximately 85 percent purity means it acts like a heavy, oily liquid. However, if fatty-acid content is moderately high, it can be more of a solid substance. It also responds to temperature, as it becomes thicker during the winter months. “But it does not freeze,” Johnston adds.

For those wishing to give it a try, Kerr advises starting at no more than a 5 percent inclusion rate. Maybe even as little as 2 percent inclusion would be prudent, especially if you have fears of handling or storing the product.

Aside from the challenges in handling, glycerin poses another critical issue — methanol. This unwanted byproduct is utilized in the biodiesel process and is not completely removed from the crude glycerin product. It is closely regulated by the federal government because of its potentially toxic effects, which can cause blindness, organ damage and even death. While toxicity levels for pigs are not well established, researchers have tested very high levels (for example, dietary levels at 640 parts per million and 1,000 ppm) without negative tissue effects. So, while feeding methanol to a pig’s toxicity level is highly unlikely, you do need to know that your supplier is in compliance with the established methanol limit of 150 ppm.

Another factor to consider involves salt concentrations. Sodium hydroxide or potassium hydroxide are used in converting fats or oils to biodiesel and glycerol. Glycerol carries some unused catalysts which further convert to sodium chloride or potassium chloride during a neutralization process. As a result, salt concentrations in crude glycerol can range from 2 percent to 10 percent. The NRC’s maximum tolerable salt level is 8 percent, provided pigs have an adequate drinking-water supply. “These high salt levels must be considered when formulating swine diets,” Johnston says. This may mean reducing or eliminating supplementary salt and certainly ensuring access to water.

From an input-cost perspective, crude glycerin prices vary just like other ingredients, largely based on local supply and demand. Lately, it has averaged 5 cents per pound in many locations of the United States. As with any co-product, proximity to a supplier is a key to making it an economically viable option for swine diets.

There’s also competition for this biofuels byproduct. Glycerol is used to moisten, sweeten and preserve food; it’s used in cosmetics, pharmaceuticals, paper manufacturing and much more.

But Kerr adds, “We may have less corn available for feeding pigs in the future, but we have no shortage of alternatives to consider. It’s about knowing what each is worth to the pig and the producer.”