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Rapid expansion of fuel ethanol production has made available abundant supplies of distiller’s grains with solubles, which are well-suited as a substitute for cereal grains in finishing cattle diets. Several recently reported experiments have revealed that feeding distiller’s grains may have adverse effects on carcass value as a result of the tendency to produce carcasses with lower quality grades and(or) higher yield grades. The effects on quality grade have been most evident in flaked grain diets, but effects on yield grade are more-or-less independent of the type of grain that is fed. This may be a result of substituting starch as an energy source with non-starch carbohydrates, fats, and proteins when cereal grains are replaced by distiller’s grains. Researchers at Texas A&M University have proposed that the accumulation of intramuscular fat (i.e., marbling) may be influenced by the presence of energy substrates that yield glucose, as it appears that glucose may be the preferred energy source for the fat-producing cells that are located in this region of the muscle tissue. Starch is the primary energy substrate in grain, and when it is digested in the intestine it yields large quantities of glucose. This is not the case when distiller’s grains are substituted for starch-based feeds.
The manner in which grains are processed before feeding also has a significant impact on the proportion of starch that is converted to glucose. It is well-documented that steam flaking results in extensive digestion of starch within the rumen compared to dry rolling. Dry-rolled corn is less extensively digested in the rumen, thus allowing for increased starch supply to the intestine. This increases glucose absorption from the small intestine, which is believed to be directly tied to the synthesis of intramuscular fat. It is conceivable that partial substitution of steam-flaked corn with dry-rolled corn would increase glucose supply for intramuscular fat deposition, thus compensating for the reduced digestion in the rumen and improving quality grade when distiller’s grains are added to the diet.
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