Some industry professionals have described distillers’ dried grains with solubles as the biggest change in feeding livestock and poultry since soybean meal was introduced several decades ago.  Whether or not you agree, there’s no doubt that DDGS is having a major impact — both positive and negative — on pork production.

Since DDGS is a relatively new feed ingredient being added to swine diets in large quantities (30 percent to 40 percent), it’s become an easy target to blame for a variety of evolving pig health and performance problems. DDGS use has dramatically increased over the past 10 years, predominantly because of rapid increases in supply and availability, as well as an opportunity to substantially reduce diet cost by replacing some of the corn, soybean meal and inorganic phosphate in swine diets.

During the past few years, swine veterinarians have reported observations of what some perceive as an increasing trend of mulberry heart disease in nursery pigs.  MHD is a classic nutrient-deficiency disease caused by inadequate vitamin E and/or selenium in swine diets. It most commonly causes sudden death of fast-growing nursery pigs within a few weeks after weaning.  However, there are no published data indicating that MHD is increasing in U.S. swine herds, nor are there any clear trends from University of Minnesota and Iowa State University Veterinary Diagnostic Laboratory reports over the past five years. But that does not mean it is or is not a concern.

Why is DDGS Being Targeted?

Recent University of Minnesota research evaluated the level of lipid peroxidation and sulfur in DDGS sources from 31 ethanol plants across the Midwest. The sulfur concentration and lipid peroxidation levels varied widely among sources, but on average, DDGS had much greater levels of both oxidized lipids and sulfur compared to a corn reference sample.  It’s well known that DDGS contains high levels of linoleic acid, a long-chain polyunsaturated fatty acid that’s easily oxidized.  Several published research studies have shown that feeding oxidized fats or oils to pigs reduces growth performance.  Therefore, when the pig’s antioxidant capacity is diminished by feeding diets high in oxidized lipids or polyunsaturated fats, there may be an increased need to supplement antioxidants, such as vitamin E.  Finally, sulfur has been shown to interfere with selenium utilization, which could further reduce the pigs’ metabolic oxidation status.

To determine if these nutritional characteristics of DDGS are contributing to MHD, we evaluated the worst-case scenario by feeding diets containing DDGS with the highest oxidized lipids and sulfur levels. If there is a connection, then we wanted to know whether increasing dietary vitamin E levels above the pig’s requirement would overcome these effects.

Testing the Theory

Sows were fed fortified corn/soybean meal-based diets or diets including DDGS (40 percent in gestation and 20 percent in lactation) for three parities.  Litters from the third parity were weaned and fed one of three nursery diets over a seven-week period: 1) a corn/soybean meal diet (no DDGS), 2) a corn/soybean meal diet containing 30 percent DDGS, and 3) a corn/soybean meal diet with 30 percent DDGS and 5x the National Research Council-recommended vitamin E level (1998). 

Pig diets were fed in a three-phase feeding program. Vitamin E (dl-a-tocopheryl acetate) was supplemented at 66 IU per kg in the sow diets and at NRC-recommended levels (11.3 to 14.4 IU per kg), or 5x the NRC-recommended level (56.6 to 72.2 IU per kg) in the pig diets, with the dietary level decreasing in each phase. Diets contained similar but adequate concentrations of selenium (0.3 ppm), supplemented as sodium selenite. A total of 31 DDGS sources throughout the Midwest showed that one source among these had high levels of oxidized lipids as well as sulfur content, compared with others, and much higher levels than typically found in corn. The DDGS source used in the sow diets had moderate levels of lipid oxidation and sulfur, whereas the DDGS source used in the nursery diets had the highest sulfur and oxidized lipid content.

Feeding high levels of this highly oxidized, high-sulfur DDGS source to nursery pigs did not result in MHD. No heart lesions were detected when evaluated histopathologically.  Including DDGS in sow diets slightly reduced the selenium status of pigs and sows and resulted in minor reductions in the pigs’ pre-weaning vitamin E status. (See graph on page 24.) These effects did not persist after weaning, when MHD is often observed.  Other metabolic antioxidant compounds (glutathione concentration of liver and glutathione peroxidase activity of pig serum) were not affected by feeding DDGS.  When DDGS was included in nursery diets neither pig antioxidant status nor growth performance were affected.  There was no difference in pig mortality among dietary treatments.

Regardless of the diet, vitamin E concentration of the pigs’ serum dropped dramatically in the first weeks after weaning.  This may be due to metabolic oxidative stress after weaning or it may be due to inadequate antioxidant protection from the chemical form of vitamin E supplemented in the nursery diets (dl-a-tocopheryl acetate). Although dl-a-tocopheryl acetate is the most common form of vitamin E added to swine diets, other chemical forms or commercially available synthetic antioxidants may be more effective in minimizing metabolic oxidative stress post-weaning. 

However, when diets were supplemented with vitamin E at 5x the requirement, the pigs’ antioxidant status improved at the end of the nursery period. (See graph above.)  Regardless, high DDGS levels can be fed to pigs and sows without the risk of developing MHD or reducing pigs’ antioxidant status post-weaning. 

Why Doesn’t DDGS Cause MHD?

In another recent University of Minnesota study, feeding the same highly oxidized, high-sulfur DDGS source to nursery pigs resulted in an increase in liver glutathione concentration, as well as an increase in serum glutathione peroxidase activity and vitamin E concentration, but serum TBARS (an indicator of metabolic lipid oxidation) was not affected.  There also was an increase in serum concentrations of methionine and taurine (both strong sulfur-containing antioxidants) and an increase in sulfur retention when pigs were fed DDGS diets. 

These results indicate that feeding DDGS appears to improve the pig’s metabolic oxidation status, because sulfur is an integral component of glutathione, and the increased levels of these sulfur-containing antioxidants likely counteracted or masked any effect of oxidized lipids in the DDGS diets, leading to a sparing effect on vitamin E.

DDGS IN SOW DIETS HAD LITTLE EFFECT

In the study, pig diets were fed in a three-phase program. Vitamin E (dl-a-tocopheryl acetate) was supplemented at 66 IU per kg in the sow diets and at NRC-recommended levels (11.3 to 14.4 IU per kg), or 5x the NRC-recommended level (56.6 to 72.2 IU per kg) in the pig diets, with the dietary level decreasing in each phase. Diets contained similar but adequate concentrations of selenium (0.3 ppm), supplemented as sodium selenite.

A total of 31 sources of distillers’ dried grains with solubles throughout the Midwest showed that one source among them had high levels of oxidized lipids as well as sulfur content, compared with others, and much higher levels than typically found in corn. The DDGS source used in the sow diets had moderate levels of lipid oxidation and sulfur, whereas the DDGS source used in the nursery diets had the highest sulfur and oxidized lipid content.

Shown here is the effect of the sow’s diet on vitamin E and selenium concentrations on the pre-weaned piglets' serum level and sow milk.  Including DDGS in sow diets resulted in only minor reductions in the vitamin E and selenium status of their pigs during lactation.