By Cheryl Anderson
DTN Staff Reporter
OMAHA (DTN) -- The inclusion of distillers grain in beef rations and its growing popularity has brought with it some concerns over levels of sulfur for cattle. That was the impetus for research at Iowa State University that has examined the effect of high sulfur diets on trace mineral absorption in cattle.
Dr. Stephanie Hansen, associate professor of animal science at Iowa State University, has a background in trace mineral nutrition and was interested in looking at some of the major challenges with sulfur, especially with high levels of dried distillers grains. Since sulfur has been known to decrease copper status in cattle, Hansen said she wanted to continue to pursue those concerns.
Cattle do require some sulfur in their diets, but too much sulfur begins to affect trace mineral absorption.
"When we get into that 0.3% or greater amount of sulfur in the diet, that's when we begin to see challenges for trace minerals like copper," she said.
Some areas in the Midwest or Western U.S. have high sulfate water that can contribute to total dietary sulfur as well. However, a lot of the sulfate comes from DDG, from solubles or even from corn gluten feed.
The concerns about sulfur in DDG by nutritionists and producers are nothing new. Many ethanol plants use sulfuric acid as a cleaning agent. Unfortunately, sometimes that sulfuric acid ends up as sulfur in the resulting DDG.
"A lot of the sulfur challenges in the distillers industry are due to plant-to-plant differences in how they use sulfuric acid," Hansen said.
Most ethanol plants perform a weekly analysis of their DDG and have that nutrient/mineral composition information available to producers for protein, fiber, dry matter, and minerals.
But one of the challenges of sulfur is that the load-to-load variations, even from the same plant can be very high.
"If you are a large feedlot, there might be a pretty good variation in sulfur, even among truckloads you brought in within a certain day," she said. "And certainly if you bring in distillers from different plants, the variation in sulfur use can be very high."
So how can producers keep a handle on whether their cattle are getting too much sulfur? Hansen said she tells producer to get in the habit of grabbing a Ziploc bag-sized sample of DDG each time a load comes in and throwing it in the freezer.
"If a week later you didn't have any problems that came up from feeding that load to cattle, you can throw it away," she said. "But if something did happen, you have a sample you can send to the vet for analysis."
Hansen added that ethanol plants understand the sulfur challenge and work very closely with their merchandisers and nutritionists to mitigate risks. If a plant has performed a clean-out and know they have used sulfuric acid, merchandisers share that information to the nutritionist. That way, if a load is a little bit higher in sulfur, they can blend it down with a previous load that was lower in sulfur and lessen the risk.
Some merchandisers told DTN that it is not very common these days that there are problems with sulfur, but in the case that a high sulfur level is found, it is disclosed and sold at a discount. Others said it is sold/discounted on a case-by-case basis, but that DDG with higher sulfur content is usually not sold to cattle producers, but to swine or chicken producers. Pigs and chicken are not as affected by sulfur as cattle.
THE EFFECT OF HIGH SULFUR LEVELS
Trace minerals are important for skeletal growth, muscle growth and immune function in cattle, as well as in reproduction. The four trace minerals Hansen and fellow researchers are most interested in, in regards to sulfur, are copper, zinc, manganese and selenium.
Several trace minerals may become bound up by sulfur in the rumen so they are not available for absorption by the animal and draw down the trace mineral status of the animal over time. Those trace minerals actually form a chemical complex such as copper sulfide or zinc sulfide with the sulfur, adhering to the sulfur so the minerals are not available for absorption and pass right through the animal.
So the researchers looked at what happens with trace minerals in a low-sulfur control diet compared to a high-sulfur diet.
Although Hansen said she is really just getting started on this line of research, so far, the researchers are finding that sulfur decreases cooper and zinc status in cattle.
She added that in the end this research may also have impact on the cowherd, even though they are doing the studies with growing cattle in a feedlot.
"Even though a cow is wintered in a dry lot, she won't necessarily show signs of sulfur toxicity because she is on a high forage diet," she said. "But what you can't see is that her liver is slowly being depleted of trace minerals like copper and zinc."
But equally alarming is that calves depend heavily on trace minerals to support them when they are born.
"If we have poor trace mineral status in the cow, that's going to translate to potentially poor health in that young calf," she said. "We need to give those calves every chance we can to have a healthy start, especially when they're worth what they are today."
Hansen said she and other ISU researchers are also looking at alternate delivery forms of trace minerals that prevent harmful interactions with sulfur.
One method is to bypass the gut altogether with a product called Multimin 90, which is an injectable trace mineral that has copper, zinc, manganese and selenium in it. Researchers at ISU have done research with Multimin 90 in the past and found it quickly increases the trace mineral status of the animal. However, this will be the first time they will be using it in connection with high-sulfur diets.
"We want to see if that would be a way cattle producers or feedlot managers could overcome high sulfur in their diets and increase the animal's trace mineral status so the effect of sulfur won't be as dramatic on them," she said. "We're just going to put it straight into the bloodstream so it gets stored in the liver. Then whatever they don't need they just excrete."
The other method to be studied is using a source of trace minerals called hydroxy minerals produced by Micronutrients that don't go into the solution at the pH normally found in the rumen. These products don't release their trace minerals in the rumen, but do so later in the low pH of the abomasum, so they may not interact with the sulfur.
"If they don't go into the solution in the rumen, they still can be available for absorption in the intestine. It's like the injectable route, except we're still feeding it in the diet," she said.
Hansen said she has just gotten some funding for this line of research and will be continuing in the future.
Although the research has not been published yet, anyone interested can go to the Iowa Beef Center's website (www.iowabeef.org), which has a wealth of information on research, as well as a fact sheet about dealing with sulfur that specifically relates to distillers grains.
Cheryl Anderson can be reached at cheryl.anderson@dtn.com.
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