Study eliminates factors in low amino acid digestibility in DDGS

By Holly Jessen | March 14, 2012

Compared to corn, dried distillers grains with solubles has a low and variable digestibility of amino acids, nutrients which swine and poultry need. Although that has generally been pinned on syrup balls or heat used in the drying process, researchers from the University of Illinois, Urbana, and the University of Minnesota did a study of growing pigs that eliminated syrup balls as a suspect for low amino acid digestibility.

The results of the study were published in the Journal of Animal Science. In order to determine if amino acid digestibility issues were associated with the solubles or syrup balls formed in DDGS, five ingredients were evaluated, including DDGS, intact syrup balls, ground syrup balls, liquid condensed solubles and pulse-dried thin stillage, all produced at the same ethanol plant.

Researchers noted that batches of DDGS can contain variable amounts and sizes of syrup balls, said Juliana Soares-Almeida, who worked on this study as part of her master’s study in animal science at University of Illinois. “Our concern was that the presence of syrup balls could contribute to the low and variable amino acid digestibility in DDGS,” she told EPM.

Laboratory results of seven samples of DDGS showed the amount of syrup balls ranged from zero to 20 percent. Those DDGS samples were used in a previous study of the amino acid bioavailability in chicks, which revealed that DDGS with greater amounts of syrup balls demonstrated low lysine availability for chicks. The researchers of this study, however, noted that there were no measurements of amino acid digestibility of syrup balls in pigs or what would happen if the syrup balls were ground up.

In the end, researchers found that, for growing pigs, digestibility of amino acids were not negatively affected by the presence of syrup balls in DDGS. Although preliminary results showed syrup balls were hard and insoluble in different solutions, it didn’t end up being a problem because the pigs studied were able to digest and absorb the amino acid in both ground syrup balls and liquid condensed solubles similarly to DDGS. “The fact that DDGS has lower and variable digestibility compared to corn may be explained by various reasons such as application of severe and variable heat, greater concentration of dietary fiber, low lysine concentration, and others but not by the presence of variable amounts of syrup balls,” the study said. Still, Soares-Almeida cautioned that variability in particle size in syrup balls is an issue to watch and perhaps study further.

Heat, however, did negatively impact the digestibility of the amino acid lysine. “When intact proteins are heated in the presence of reducing substances, lysine is usually damaged more extensively than other [amino acids] because its free amino group is available to participate in the Maillard reaction,” the study said.

Finally, there was a separate issue with the digestibility of another amino acid, methionine, in the liquid condensed soluables. “We don’t know what the reason is but we know that it was not the heat since the solubles were removed before the drying process and the heating process usually impacts lysine the most,” Soares-Almeida said. The study hypothesized, but did not experimentally verify, that the proteins in liquid condensed solubles are more complex and less digestible than other corn proteins.