Nutritionists at the University of Minnesota are studying a new byproduct — and it's not distiller's dried grains with solubles (DDGS).

Corn-based condensed distiller's solubles (CDS) is another ethanol waste product that may have benefits similar to DDGS. Both contain yeast and residual yeast metabolites that may aid the pig's immune system and help avoid enteric problems.

In the United States, CDS is produced from putting the thin stillage, or syrup, through an evaporator to remove some of the water before it gets blended back with the coarse solids fraction to make DDGS.

As Figure 1 shows, DDGS is the bulk of what is available to the feed industry, explains University of Minnesota swine nutritionist Gerald Shurson. The CDS is about 70% water, which is sometimes sold to local cattle feeders. In Ontario, Canada, several hog farms are feeding the product in liquid grow-finish feeding systems.

Unidentified Growth Factors

CDS was first referenced as being fed to pigs back in the mid-1940s and '50s. Researchers observed that it improved growth above its perceived nutritive content, and attempts have been made to extract the unidentified growth factors ever since.

Those growth factors may be related to the yeast component of condensed distillers, says Jeff Knott, a former University of Minnesota graduate student. Knott's Ph.D. work investigated the nutritional value of yeast byproducts from ethanol; he reported his findings at the Minnesota Nutrition Conference last fall.

Yeast cells have many biologically and potentially immunologically important parts that include beta-glucans, mannan-oligosaccharides, chitin and proteins. Extracts from yeast cell contents include nucleotides, glutamate and other amino acids, vitamins and trace minerals.

Nucleotides are important for maintaining the cellular immune response and for development of intestinal tissues and the immune system, says Knott. Between 20-25% of the protein in yeast cells are nucleotides and antioxidants.

CDS Spray-Dried

The high water content of CDS poses a problem for the ethanol industry because of the difficulties of drying it to more than 50% dry matter.

But the University of Minnesota has developed a patent-pending process for drying CDS and its fractions. This spray-drying technology turns CDS into a dry powder that is 98% dry matter. It prompted Knott and Shurson to take another look at CDS as a source of unidentified growth factors in diets for early weaned pigs.

They conducted a series of trials to study effects of feeding spray-dried corn distiller's solubles and its two subfractions, yeast cream and residual solubles. The yeast cream came from CDS, which was centrifuged to separate high fat or the lipid fraction. This fraction was originally thought to contain residual yeast cells. The remaining product was called residual solubles.

Knott and Shurson looked at the effects of those three fractions on energy and nitrogen balance, growth performance, gut morphology, serum IGF-1 (insulin-like growth factor) concentrations and acute-phase protein responses in early weaned pigs. Diets were compared to diets containing spray-dried porcine plasma and/or carbadox.

Knott used 63 crossbred barrows weaned at 17 days of age in his studies. They were housed in individual stainless steel metabolism crates and fed one of seven diets: negative control (NC); 15% spray-dried distiller's solubles (DS); 7.5% spray-dried yeast cream (YC); 15% spray-dried residual solubles (RS); 55 ppm carbadox (AB); 6% spray-dried porcine plasma (animal protein) (PP) or 55 ppm carbadox with 6% spray-dried porcine plasma, which was the positive control (PC).

All diets contained corn, soybean meal, 20% lactose, 12.5% oat groats and 11% fishmeal. The diets with porcine plasma contained 12.5% soybean meal; the rest contained 22.5%. All diets were formulated to provide 1.60% total lysine, 3440 kcal/kg of metabolizable energy, 0.87% calcium and 0.80% phosphorus.

Byproducts vs. Carbadox

Results from the first study suggest that pigs fed diets containing distiller's solubles byproducts will have similar growth performance compared to pigs fed the negative control and carbadox diets. However, the pigs had poorer average daily gain and feed intake compared to pigs fed diets containing porcine plasma and the combination of plasma and carbadox.

Although growth performance during the initial 10 days postweaning was poorer, the higher digestible and metabolizable energy concentrations in the DS and RS diets may lead to improved energy utilization compared to pigs fed diets containing porcine plasma and YC. The spray-dried byproducts were highly digestible, but provided lower performance than carbadox and PP diets. The trend was for PP diets to have higher average daily gain.

In a second trial, including blood parameters, Knott found that the diet with residual solubles showed the best gut health response. Villi height was increased in the small intestine along with the villus height:crypt depth ratio (VCR) in the upper 25% of the small intestine.

“This really interested us,” he says. “Villi were shorter for carbadox-fed pigs, which suggests that villi were eroded off. It would not have the absorptive capacity. That suggests greater intestinal health and potentially greater nutrient absorptive capacity compared to pigs fed the diet containing carbadox.”

The bottom line is that the distiller's residual solubles fraction may contain significant amounts of “unidentified growth factors.”

The improvement in gut health, however, did not result in improvements in immune response, as measured by acute-phase proteins, IGF-1 or growth performance, compared to pigs fed diets containing porcine plasma or carbadox and porcine plasma.

The spray-dried distiller's solubles and associated fractions evaluated in these studies can be used effectively in Phase 1 starter diets, Knott concludes.

Shurson notes that the university hopes to license the spray-drying process. He sees CDS as having potential in complex Phase 1 or Phase 2 diets. “There appears to be a growth advantage later in the nursery from a carryover effect,” he says. The health status of the pigs may have been too high in Knott's trials, he adds, and they're not sure pigs were fed long enough to see any potential advantages from feeding the spray-dried distiller's products.

Antibiotic Alternative?

“We don't know if it's the combination of nucleotides, beta glucans (which are carbohydrates) and antioxidants that are providing protection to the intestine. All have positive benefits in pigs and humans,” adds Shurson. “We hope to isolate, concentrate and measure those components to see if there is an impact.

“There's also a lot of interest in Asia and Europe on fermentation byproducts due to metabolites from the process that may have biological activity,” he points out. “Producers are anxiously waiting for CDS because there are no fermentable corn-based products in those countries. They look at CDS as an alternative to antibiotics.”

There's no end in sight to DDGS production from ethanol, adds Shurson. Production has doubled in three years to 7.7 million tons. And the trend is continuing. “What this does is give ethanol plants and the feed industry another byproduct option to consider, which appears to have nutritional and immune system benefits for pigs.”

Shurson sees a market for CDS in nursery diets, poultry, pet foods and aquaculture. “The best place to use expensive products that are highly digestible is the nursery,” he notes. “If CDS can be dried economically, it will become of higher value. Right now, there is a limited market in the U.S. for CDS because of its high water content. Transportation costs are too high.”