In the last 10 years, the use of corn grain for feed has been reduced by nearly 30 percent. The emphasis on corn for fuel instead of feed has driven up the competition for corn grain and corn silage. The reality of the future is that less corn and silage and more corn co-products will be available for use in cattle diets. Producers have had to seek out new uses for co-products from corn processing industries and will continue to have to do so.
However, shifting our feeding focus to co-products presents some challenges for producers. Whether it’s corn gluten feed, corn gluten meal or distillers grains, these co-products all add excess protein and sulfur to the diet. In the case of distillers grains, there can be additional fat added to the diet as well.
One of the first challenges associated with feeding co-products is excess dietary protein. Excess protein can be used as an energy source. Most of the amino acids are glucogenic, meaning if they are fed in excess, they get converted to glucose, or energy, for cattle. However, overconsumption of protein also comes at a cost.
While too much protein in a diet can decrease feed intake, it must also be excreted by the cow. Excess dietary protein, or nitrogen (N), is excreted in urine and feces. Protein is excreted as urea in urine, and early work suggested the production cost of overfeeding protein was due to this conversion of N to urea.
However, more recently, the increased cost of excess dietary protein has been attributed to the increased tissue size necessary to break down the excess protein. Perhaps more importantly, as we move toward an increasingly environmentally conscious society, more than 50 percent of the protein in distillers grains escapes ruminal fermentation.
Some of this is digested in the small intestines and can be beneficial to cattle, but what is not used is excreted and volatilized as ammonia, which accounts for more than 90 percent of the N lost from manure.
In confinement barns that may not be as well-ventilated, this represents an animal comfort and health concern, but there is also the chance that feeding excess N may invite the government to impose stricter environmental regulations on animal agriculture.
Fat can be another big issue for dairy producers in regards to production. Increasing intake of plant-based fats can limit milk fat synthesis. Milk fat depression occurs because dietary unsaturated fats decrease rumen fiber degradation.
Fortunately, this problem was limited to distillers grains and not corn gluten feed or corn gluten meal (distillers grains contain the 10 percent-plus fat, dry matter basis, versus about 2.5 to 3 percent fat in corn gluten feed and corn gluten meal).
Although it was originally, and logically, assumed that all the fat in distillers grains would come from corn oil, and therefore behave like corn oil, the fat in wet distillers grains has been evaluated and appears to be less available in the rumen than fat from corn oil, suggesting it could have less impact on milk fat synthesis.
Furthermore, many ethanol plants that manufacture distillers grains are now pulling the fat out of distillers grains to sell as another value-added co-product. These new products are referred to as “low-fat” distillers grains.
Low-fat distillers grains vary in fat content but range between 5 to 8 percent fat typically, compared to the “traditional-fat” distillers grains, which could have as much as 12 or 13 percent fat. An analysis of one’s distillers grains will quickly reveal if the plant used has reduced the fat.
The final challenge with feeding corn co-products is the sulfur (S) concentration. Elevated dietary S can depress intake and cause polioencephalomalacia because it increases ruminal hydrogen sulfide gas concentrations. More recently, the S concentrations in corn co-products have been linking to another pressing issue in our industry: ruminal acidosis.
In 2011, researchers reported a direct correlation between ruminal pH and hydrogen sulfide gas concentration and suggested the link between these two is the use of sulfuric acid in the ethanol production process. These researchers postulate that the acidity, not the S alone, is responsible for reductions in beef cattle performance.
While these researchers fed diets containing little fiber, the direct link between acidity, fiber digestibility and corn co-products can be alarming for all cattle producers. Fortunately, the effectiveness of buffering the acidity through alkali treatments of co-products has been demonstrated to improve ruminal pH and fiber digestibility. However, this emerging research needs to be further validated in dairy cattle.
One of the more alarming issues with the acidity-S discussion is its variability. Because co-products are really waste products of ethanol, there is currently no regulation on maximum S they can contain.
Sulfur values have been reported of as much as 1.2 percent of the distillers grains dry matter and pH values as acidic as 3.2 (think of good silage in comparison, around pH 4.5 or so). In short, knowing the S concentrations in co-products is a critical step in diagnosing potential intake reductions and other performance-related issues that may arise.
The new understanding of acidity in co-products and the conversion of many ethanol plants to create low-fat distillers grains are all good changes for the dairy industry in terms of its ability to take advantage of co-products.
The addition of corn stover to the list of available co-products to feed for energy has been one more recent change on the co-product scene. Corn stover is the mature plant, harvested after corn grain; therefore, it does not compete with the grain yield for ethanol, like corn silage.
Because it is a mature, poor-quality forage though, the feeding value of corn stover is quite poor. So historically it was used as bedding or maybe ground to add some bulk to dry cow rations. Now, recent research has shown that the digestibility of corn stover can be increased by treating it with CaO.
This process involves grinding the corn stover, wetting it to 50 percent dry matter and then adding 5 percent CaO (dry matter basis). The “treated” corn stover must sit for at least one week before feeding to allow the chemical reaction to be effective.
The process of treating corn stover is not without labor and effort; therefore, its feeding value must be further validated for this co-product to be efficacious in dairy cattle rations.
The good news is research is emerging daily with new ways for producers to face the challenge linked with feeding co-products. PD
Tara Felix has a Ph.D. in ruminant nutrition from Ohio State University and is currently employed in a research/teaching position with the University of Illinois in Urbana.
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