DDGS: Nutrient profiles, variability

By P.H. Robinson

 

Nutrient profiles of ethanol industry byproducts aren’t new. What is new is that they’re ration inclusion rates are higher. 

 

 

Previously, I discussed the production and physical characteristics of some new dried distillers grain (DDG) products (“DDGS: It’s a new generation”, September 2013 issue of DairyBusiness West). In this article, I’ll address nutrient profiles and their variability.

 

Nutrient analysis

The nutritional attributes of corn, wheat, barley and rye are well known. Thus, the primary by-products of those grains from ethanol production should be what we’d expect from de-starched grain. What is “new” about DDGS as livestock feedstuffs is that, in contrast to the past where DDGS might comprise 2% -3% of the dry weight of animal diets, producers are now interested in feeding DDGS at much higher levels. 

Nutritional research of feedstuffs has historically been driven by practicality. Thus, of the research completed on the nutritional value of DDGS prior to ~1995, virtually none examined high dietary inclusion levels, mainly because it wasn’t considered practically important. Nevertheless the nutritional attributes of the protein, fiber, non-structural carbohydrates and minerals in corn grain were generally well understood and, in general, animal feeding industries moved quickly to utilize DDGS when they became available in larger quantities in the early 2000s. 

From a nutritional perspective, it’s common to be more concerned about feed nutrients present at high levels, since deficient (relative to animal needs) nutrients can generally be supplemented, but they cannot be “unsupplemented” if provided in excess of an animal’s need or human desire. 

For example, a nutrient which can be a problem due to its high level in corn-based DDG by-products, especially to lactating ruminants, is corn oil. Present in conventional DDGS at about 11% of DM, a 10% dietary inclusion in a lactating cow diet would deliver a little over 1% of dietary DM as corn oil, or about 0.7% of diet DM as C18:2 and C18:3 fatty acids. When fed at high levels to lactating cows, especially diets which create a low rumen pH, these fatty acids can spill over to create  an undesirable rumen bacterial pathway which can inhibit milk fat synthesis.

 

Nutrient variability

Nutrient levels in feedstuffs are never exactly the same among production processes, facilities with the same production process, within production facilities, among loads and even within loads. 

In addition, what is claimed to be “nutrient variability” may partly be sampling and/or nutrient analysis variation. Heterogeneous feeds (such as pomaces, pulps and forages based on multi-source materials) and analytes   with higher analytical variation will tend to have more measured “variation,” even when there may be very low real variation. In general, homogeneous feeds such as grains and protein meals based on single-source materials will have lower variability than heterogenous materials.

From a diet formulation perspective, variability in feed ingredient profiles is seldom directly considered, although it may be considered indirectly by fixing lower inclusion rates of feedstuffs known to be more variable. 

In this context, DDG by-products generally would not be considered to have high nutrient variability, since few risk factors exist. For example, in general, the grain source is consistent and the processes used to ferment its starch to ethanol are large scale and highly automated. In addition, the drying process is generally tightly controlled to prevent heat damage. As all DDG by-products have a fine particle size, they tend to flow smoothly and mix easily, making it relatively simple to collect a representative sample. If this sample requires sub-sampling at a laboratory before grinding prior to chemical analysis, its small particle size creates little chance of non-representative sub-samples.

However, it is clear DDG production facilities use different processes to create distillers dried grains with solubles (DDGS), wet DGS (WDGS), high protein distillers dried grains (HPDDGS) and low fat distillers dried grains (LFDDGS), which will lead to differences in nutrient profiles among production facilities. 

Based on samples of various feeds collected over a three-year period from commercial dairy farms throughout California, the variability of conventional DDGS is similar to protein sources such as canola meal, with one exception: the co-efficient of variation (CV) for its organic nutrients is <10%. In contrast, a group of DDGS samples collected from a single DDGS production facility had substantially lower nutrient CV’s than the DDGS collected from commercial dairy farms. However, in general, DDGS is a feedstuff with low variation in its important nutrients, and its upper constraint in diet formulation should not be impacted to a substantive extent by this variation. 

 

Conclusions

Ethanol by-products contain nutrient profiles consistent with their base grain, and those nutrients have relatively low variation relative to similar feeds.

 

P.H. Robinson is a Cooperative Extension Specialist responsible for dairy cattle nutrition and nutritional management. He can be reached via phone: 530-754-7565; email: phrobinson@ucdavis.edu.

• Fnd additional articles by Robinson at http://animalscience.ucdavis.edu/faculty/robinson/Articles/FullText/FeedstuffEvaluation.htm.