Pigs really are what they eat, and in many parts of the United States, they are eating diets formulated to include substantial amounts (30 to 40%) of distiller’s dried grains with solubles (DDGS). Though feeding a diet with high levels of DDGS has significant economic benefits, it also has a negative impact on carcass fat quality as measured by iodine value (IV). Strategies such as withdrawing DDGS prior to harvest, formulating diets based on iodine level targets and possibly feeding reduced-oil DDGS may help improve carcass fat quality, according to Jerry Shurson, University of Minnesota swine nutritionist.

Iodine Value

Iodine value is the most common measurement associated with pork fat quality. The higher the IV number, the greater the proportion of unsaturated fatty acids compared to saturated fatty acids. A high number means softer fat, a lower number means fat is firmer. Some research has suggested that acceptable pork fat quality can be achieved at an IV of 74 or below, though some packers prefer lower values. Some U.S. packers use IV 72 as a target, while others allow a working standard in a range of 72-74, Shurson says.

Pork producers report that some packers have imposed discounts because of soft carcass fat. Packers become concerned because fatty acid composition and soft fat impacts shelf life and consumer perception of the finished pork product.

Shurson says accurate IV levels are not always easy to obtain and may not be the best measure of pork fat quality. Fat samples from different parts of a carcass can yield different IV levels. Belly and backfat samples often show similar IV, while jowl fat tends to measure as much as two points higher in IV. “This is of concern because packer standards often do not specify the carcass location where the IV is sampled,” he says.

Measuring IV in a packing plant environment is not a practical nor a reliable undertaking at this time. Some packers monitor IV levels by sampling a representative subset of pigs on a quarterly basis. New technologies are being tested for use in the future. Currently, laboratory fatty acid analysis can take up to three days.

Even with testing constraints, IV levels are definitely on packers’ radar. Shurson says one U.S. packer has historically asked pork producers to not feed distiller’s grains at all, which means those producers will have much higher diet and production costs. Other packers have sent out letters asking for specific DDGS withdrawal periods prior to slaughter. Still other packers are imposing as much as a 25¢ discount on pork carcasses exceeding a specific IV, according to Shurson.

Pigs are What They Eat

Economics have driven up DDGS inclusion rates in swine finishing diets. DDGS have been priced at 75% to 80% of the price value of corn in recent years, with an estimated 5 million metric tons (5.5 million tons) of DDGS going into U.S. swine diets in 2011. “DDGS has approximately the same energy and higher concentrations in a number of nutrients than corn,” Shurson explains. “This means pork producers have been able to save as much as $10/pig by feeding DDGS in place of corn and soybean meal in diets.”

He has summarized research indicating carcass IV increases by approximately two units for every 10% of DDGS added to the diet.

Several factors are driving the pork fat quality concerns from feeding high DDGS diets. Corn oil is made up of polyunsaturated fatty acids, of which linoleic acid is the main culprit in causing soft fat. Corn oil is about 60% linoleic acid, thus a ration containing 30-40% DDGS with an oil content of 10-12% can have carcass implications.

Both gender and genotype contribute to the impact of DDGS on carcass IV. Leaner genetics display softer fat due to DDGS. Gilts, typically leaner than barrows, tend to have carcasses with softer fat when eating high levels of DDGS.

Withdrawal Works

There are ways to capture much of the cost savings from feeding DDGS while still meeting packer specifications. “We know DDGS withdrawal from the diet works,” Shurson says. “It is possible to obtain an iodine value of 72 when feeding barrows and gilts up to 30% DDGS with a 10-12% fat level during the grow-finish period, if producers withdraw the DDGS three weeks prior to harvest. Remember, the more corn oil pigs consume, the softer that fat can become. If you add 40% DDGS, the IV becomes higher, and a withdrawal period longer than three weeks would be necessary.”

Shurson says many producers use a step-up, step-down feeding program. Pigs may start the grower period receiving 20% DDGS, which is ramped up to 30%, then gradually reduced as pigs accumulate fat as they approach market weights. In the final finishing phase, DDGS are withdrawn or fed at a low level (i.e. 10%) prior to harvest.

Formulating for DDGS

“Withdrawal works, but you are going to be giving up some feed cost savings,” Shurson says. Some nutritionists formulate diets based on the IV product by accounting for the fatty acid composition and concentration of fats and oils to achieve a desired carcass IV. With this method, a withdrawal period may be avoided, but DDGS levels may need to be lowered to meet dietary IV.

The choice of feed ingredients is a big factor when formulating for IV level. Canadian producers with access to more competitively priced wheat and barley can feed more DDGS because those ingredients are lower in linoleic acid, for example. “It comes down to how much money producers are willing to give up in order to formulate a diet based on iodine value. It may cost as much as $2 to $4/pig in extra diet costs,” Shurson says.

Formulating diets on an IV product basis is a good, but not perfect, approach to managing diet effects on carcass fat IV. High levels of DDGS may curb feed intake and should be considered when formulating diets. Other factors influencing feed intake include pen density, genetics, pig health, season and temperature.

Extracting More Oil

A recent development in the ethanol industry is a process of extracting additional oil from DDGS for biodiesel. By the end of 2012, Shurson says up to half of the ethanol plants will be extracting more oil, with up to 75% doing so by the end of 2013. The procedure leaves varying quantities of oil in the finished DDGS product, but Shurson estimates that most of the low-oil DDGS on the market now have between 7-9% fat levels.

At first glance, this may seem to be a solution to pork fat quality challenges, but there are still a number of questions about the effect reducing oil may have on the energy content of DDGS.

“DDGS historically has the same energy as corn,” Shurson explains. “When you start pulling oil out, which is the major contributing factor to energy, you are now at an energy value less than corn. Now it becomes less economically attractive as an alternative feed ingredient for pigs.”

On the positive side, producers can feed more 7-8% oil DDGS to pigs to meet specific IV targets vs. feeding 10-12% oil DDGS, although the lower oil product will be worth less.

Shurson is currently working to summarize research investigating 11 sources of DDGS ranging in fat content from 6% up to 13%. Feeding studies were done to test metabolizable energy outcomes when pigs were fed the varying levels. The research was done to measure the impact each 1% reduction in oil contributes to the energy value of DDGS. His findings will be presented following the Midwest Section Animal Science meetings in Des Moines, IA, on March 21.

Sampling Advised

Fat levels in DDGS have always been variable, but more oil extraction adds to the variability. “Fat levels today in DDGS are going to range from as low as 3.5% up to 13%, depending upon the amount of oil that has been extracted. DDGS on the market used to range from 9% to 13% fat, so there is more spread,” Shurson says.

Shurson suggests sampling incoming batches for fat, fiber and protein. Producers who have a contract with an ethanol plant as a direct supplier should specify a minimum crude fat level they will accept.

“We don’t have national quality or composition standards for DDGS. We don’t have well-defined national standards for pork fat quality measures or iodine value in pork carcasses. There is a lot of wrestling going on to try to figure out where this is all going at the end of the day,” he summarizes. 

Lora Berg is a freelance writer from Lakeville, MN.