The production of ethanol has meant many things to the petfood industry - much of which hasn't been pleasant because of the pressure it has placed on grain supplies. Okay, so a cheap dollar, high fuel costs and a few natural disasters have had their impact as well.
But, maybe there is some redemption for ethanol production that petfood companies have overlooked these last few years. Redemption in the way of an ingredient - specifically the protein-enriched, spent-fermentation co-product known as distillers dried grains with solubles (DDGS). Currently, only a few of the "value brands" of petfood are brave enough to incorporate DDGS in their formulas. Considering consumers generally have a favorable view of "green" ethanol and petfood companies have a need to recapture some lost margin encountered with rising commodity prices, it may be time for the broader industry to explore its use.
The basic steps for today's ethanol production follow the same steps as that of distilled spirits:
Grain is milled and fermented with yeast;
The alcohol is removed by distillation; and
The remaining wet residue is fed directly to livestock (predominantly cattle) or dried for use as an ingredient in the feed industry.
With DDGS, a dry milling process is used rather than a wet milling process that results in corn gluten feed or meal. Both types of processing are deployed for ethanol production, but the dry milling that results in the production of DDGS is more efficient, less capital intensive and subsequently more popular.
This means availability is not an issue. Last year, 2.3 billion bushels of grain were used in the production of ethanol with nearly one-third of the starting biomass recovered as distillers grains. In other words, over 3.5 million metric tons of DDGS was produced.
What do we know about DDGS? As it turns out, we know quite a bit about its nutrient composition, but only a smattering about its application in petfoods. Regarding nutrient composition, the theme of the day is variability. Most reference texts place protein concentration at around 27% or more. Fat, fiber and ash are also concentrated as the starch is fermented off (9.0%, 8.5%, and 4.7%, respectively; NRC, 2006). The proximate composition varies between seasons (Belyea et al., 2004) and among producers (Spiehs et al., 2002) with no established industry or regulatory standard nutrient composition.
Is now the right time for this value-based ingredient in mainstream petfood? - Greg Aldrich
Adding to this variability, not all DDGS come exclusively from corn. Other feed grains can be and are used in the production of DDGS, and the net result will be an ingredient that is somewhat reflective of the parent material. For that reason, the "predominating grain shall be declared as the first word in the name" on labels, according to the AAFCO 2006 Official Publication.
The amino acid profile differs little from that of the native grain, and the yeast fraction can contribute nearly half the amino acids. The fiber fraction is fermentable and a rich source of hemicellulose. The mineral composition is also variable with sodium content reported to fluctuate the greatest (Batal and Dale, 2003).
Work to evaluate this ingredient in petfood began nearly 50 years ago when distillers' grains were derived from the beverage and solvent industry. Since today only a small percentage of the overall DDGS supply is derived from this source, the research that was started in the late 1950s and continuing through to the 1980s doesn't completely apply. It does, however, give us some direction.
To summarize this battery of studies, the inclusion of DDGS at up to 30% of dog diets was reported to be acceptable; but, digestibility, stool consistency and palatability were measurably diminished. At intermediate levels of 9 to 16% of the diet, dry matter and energy digestibility were reported to decline 2 to 5 percentage points with an increase in stool volume. Including DDGS in diets at less than 8% did not affect dry matter or energy digestibility, alter nitrogen retention, hamper puppy performance or affect gestation or lactation. Unfortunately, no studies have been found that evaluated DDGS in cat foods.
More recent evaluations indicate that the protein quality of DDGS is superior to corn gluten meal; but this was due to a better amino acid profile rather than better digestibility (de Godoy et al., 2008). Protein utilization of DDGS, especially the digestibility of the essential amino acid lysine, is sensitive to heat damage during the drying process (Fastinger et al., 2006). This may be seen as a darkening or browning and can be a rough "eyeball" check for quality and process consistency.
DDGS are seldom, if ever, found in wet petfoods or treats, but in extruded diets may be added at 5 to 12% of the formula. At these levels, the ingredient won't have an impact on extrusion or kibble appearance versus corn or other grains as it relates to expansion or cell structure.
However, if higher inclusion levels displace grains and protein meals like soy or corn gluten meal, expansion and functionality may be compromised due to lower starch content and a decline in functional proteins. Further, the fiber fraction of DDGS may require a fine grind to prevent the kibble from having a "fuzzy" surface.
One drawback to DDGS is the potential to concentrate mycotoxins, especially given that fermentation and distilling do not destroy these mold metabolites. Nor is the ethanol industry obligated to operate under the same restrictions as the food and feed industries. In one extension report from South Dakota State University, mycotoxin concentrations for 2000 through 2007 were reported to be measurable in each testing year. Aflatoxin averaged 2.12 ppb (+/- 2.49), and vomitoxin averaged 3.62 ppm (+/- 4.12).
To put this in context, the USDA action levels for aflatoxin are 20 ppb. Vomitoxin was reported to affect palatability at levels greater than 4.5 to 7.7 ppm and cause vomiting and diarrhea at 8 to 10 ppm for dogs and cats, respectively (Hughes et al., 1999). So, while reported levels were below these thresholds, it points to the need for vigorous monitoring efforts.