Doctor DDGS

With ethanol plants extracting oil from DDGS, the question of how this affects feeding performance becomes paramount to the livestock and poultry industries.  University of Minnesota professor Jerry Shurson talks with Ethanol Producer Magazine about his most recent study on the growth performance from feeding reduced-oil DDGS to growing-finishing pigs, providing much-needed answers to the pork industry.

How does metabolizable energy content, specifically in swine diets, correlate with growth, carcass quality and pork fat quality? 

Metabolizable energy is the most expensive nutritional component in swine diets and represents about 70 to 80 percent of total diet cost. Pigs have daily requirements for calories (i.e., metabolizable energy or ME) that must be met for them to grow at their genetic potential and maximize the amount of muscle (pork) in the carcass at harvest. Inadequate metabolizable energy consumption causes pigs to grow slower and can reduce the percentage of lean in the carcass. Excess metabolizable energy consumption beyond that required for lean growth can lead to fatter carcasses.
The main sources of calories in feed are oil, carbohydrates and excess protein, but these are not 100 percent digestible because of their various chemical forms and the pig’s digestive processes and abilities to use them. When ingredients high in polyunsaturated fatty acids, such as distillers corn oil and DDGS, are fed, some of these fatty acids are not converted to calories, but rather are deposited in fat tissues in the body. Linoleic acid is the predominant long-chain fatty acid in corn oil that is not well-digested by the pig, and is deposited in backfat and belly fat. Linoleic acid has a very low melting point and is the primary reason that feeding diets high in corn oil causes soft pork fat.

Does less oil in DDGS mean less ME content? 

Not necessarily. Most people—including those of us doing research on this topic—reasonably assumed that removing some of the oil from DDGS would reduce the metabolizable energy content, since oil is rich in calories and taking calories out of DDGS should lead to less metabolizable energy content. However, after conducting several experiments to determine the ME content of DDGS sources with variable oil content in swine and poultry, we’ve learned that this is often not the case. From our research, we have found that some reduced-oil (e.g., 6 percent oil) DDGS sources can have the same amount of metabolizable energy as sources that contain 10 to 13 percent oil when fed to pigs and poultry. In fact, the correlation between DDGS oil content and metabolizable energy content is very low (r = 0.11 to 0.32).

Why is crude fat content a poor predictor of ME content? 

First, we know that from other experiments that we have conducted, fiber digestibility is surprisingly quite variable among DDGS sources, ranging from 23 to 55 percent. Although fiber is less digestible than other carbohydrates like starch, it can be a significant contributor of calories to the diet. Therefore, it is possible that a source of DDGS with relatively high fiber digestibility could contribute significant amounts of metabolizable energy calories in a reduced-oil DDGS source to partially make up the difference of the calories lost due to partial oil extraction. Secondly, other research studies with pigs have shown that only about 50 percent of the oil present in DDGS is digestible, compared to extracted distillers corn oil, which is over 90 percent digestible. Therefore, even those we can chemically measure the oil content in DDGS, if it is only 50 percent digestible, much of what is present is not serving as a source of calories or contributing to the overall metabolizable energy content of reduced-oil DDGS. 

What can you tell me about your most recent study?
 
It was conducted at the University of Minnesota West Central Research and Outreach Center in Morris, Minn., and involved 432 pigs with initial body weight of 57 pounds. They were fed experimental diets for about 90 days, and were harvested at 264 pounds. We used four dietary treatments in a four-phase feeding program. Dietary treatments consisted of a control corn-soybean meal diet with no DDGS; and three DDGS dietary treatments consisting of similar amounts of corn and soybean meal containing 40 percent low (6 percent oil), medium (10 percent oil), or high (14 percent oil) DDGS sources. We measured body weight and feed disappearance every two weeks during the experiment and calculated average daily gain, average daily feed intake, and gain efficiency during each two-week period and overall. Prior to harvest, ultrasound measurements of backfat and loin muscle area were obtained on each pig, and then pigs were shipped to a commercial abattoir for harvest and collection of hot carcass weight and pork fat samples at three locations. Ultrasound and hot carcass weights were used to calculate percentage of carcass lean, and pork fat samples were used to determine the effects of dietary treatment on pork fatty acid composition.

Your findings suggest low-oil DDGS has no affect on pig growth performance and improves pork fat quality. Why is this?

Correct. Overall growth rate and feed intake was not different among DDGS dietary treatments using DDGS sources containing 6, 10, or 14 percent oil. Furthermore, gain efficiency was not different between pigs fed the 10 percent and 14 percent oil DDGS diets but was slightly reduced for pigs fed the 6 percent oil DDGS diets. This means that our “best” prediction equations are accurate for estimating ME content of DDGS with oil content greater than 6 percent, but they slightly overestimate ME content of DDGS with 6 percent or less oil. This gives us confidence that we can accurately estimate ME content for many of the high and moderate oil DDGS sources in the ethanol industry. The slight reduction in gain efficiency when feeding the 6 percent oil DDGS source is not surprising in retrospect, because all of the DDGS ME prediction equations previously developed used DDGS sources that contained 6 to 14 percent oil, which was what was being produced in the ethanol industry at the time these studies were conducted. We interpret this to mean that prediction equations are most accurate for the range in nutrient content from which they were derived. Now that more ethanol plants are extracting more oil, these equations are becoming less relevant and we will need to conduct more research to develop new equations to improve our accuracy in ME estimation when evaluating DDGS sources that contain less than 6 percent oil.
We expected an improvement in pork fat quality when feeding reduced-oil DDGS sources. When you feed a diet high in polyunsaturated fatty acids as provided by corn oil in DDGS, a significant portion is deposited in body fat tissue. By reducing the oil content in DDGS, less oil is consumed by the pig, resulting in less polyunsaturated fatty acids deposited in pork carcass fat, which ultimately resulted in an improvement in pork fat quality (firmer fat). 

For pig development, what is the optimal oil percentage for low-oil DDGS? 

There is no optimal oil content for DDGS. We’ve consistently shown a poor direct relationship between oil content of DDGS and ME content.

For ethanol producers who can hit this oil percentage mark, should their product command a better price in the swine feed market? Why or why not?  

We formulate swine and poultry diets on a ME or net energy basis, as well as on a digestible amino acid and phosphorus basis—not on a “profat” or crude protein and crude fat basis, which are the traditional measures used in the commodity marketing world. Since ME content is a primary determinant of economic value of a DDGS source in a swine diet, those with a higher ME content should theoretically command a better price. From an economic point of view, our ME prediction equation could theoretically be used by DDGS marketers to establish more accurate DDGS prices based on ME content rather than profat guarantee, which is a poor descriptor of actual feeding value of DDGS sources for pigs and poultry. In addition, the ME equations can help determine which DDGS sources have higher ME value, even though purchase prices may be similar.