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SULFUR CONTENT IN FEEDS AND FORAGES IS A GROWING CONCERN

by: Stephen B. Blezinger
Ph.D, PAS

A number of years ago it was suggested by researchers that Sulfur levels in beef cattle diets could be a problem in several ways. One of these was seen in grazing cattle that consumed excessive levels of sulfur which resulted in a true sulfur toxicity, by the suppression of normal Thiamin (B-Vitamin) synthesis and by the depression of absorption of a number of trace minerals. Over recent years the focus on nutritional and physiological problems created by the intake of higher than desirable levels of sulfur has increased and today many producers are beginning to recognize a variety of these problems in their herds. Producers, nutritionists and veterinarians alike know that just as certain amounts of some minerals are needed in the diet, these same minerals can create a whole host of problems when received in excessive amounts. Sulfur is one of these minerals.

Another potential concern with sulfur intake centers around the feeding of by-products such as distillers grains, corn gluten feed and corn germ meal. Wet and dry distillers grains are by-products from the production of ethanol. Corn Gluten Feed and Corn Gluten Meal are from the production of sweeteners. Corn Germ Meal is a by-product resulting from the production of corn oil. All of these products contain a higher level of sulfur as compared to shell corn. In the milling process either before or after grinding, the corn is steeped in a liquid solution containing a high level of sulfur and thus carries the sulfur through the process. With the production of distillers grains set to increase significantly over the next few years (approximately doubling with the doubling of ethanol production) the feeding of ethanol co-products such as those listed will be promoted heavily. Researchers at Nebraska and Iowa State University are already looking at feeding levels as high as 40-50 percent in some beef finishing rations (ProBeef '07 Conference, Aimes, Iowa, September 7, 2007).

Additionally, these by-products will also find there way into numerous other applications in livestock rations, especially beef and dairy rations. This will translate into higher sulfur contents in most associated feeds and supplements. While the likelihood is good that incorporation into these diets will not create the physiological problems mentioned here and discussed at length in the following article, the possibility is very good that S levels will be high enough to depress the absorption of several of the trace minerals which could lead to suppression of performance in reproductive, immune response and growth areas. It will be very prudent to carefully monitor sulfur levels in these and other feeds and forages.

Some Discussion

Remember that sulfur (S) is an essential dietary mineral element. It is crucial for optimum rumen microbial growth and for digestion of feeds. It is a component of the essential amino acid, methionine, as well as other amino acids and is found in other compounds in the animal's body and milk. This means that like so many other nutritional components, while the appropriate amount is vital to normal performance and productivity, excessive amounts are where the problems lie.

Dietary Recommendations

The recommended dietary concentration of S is 0.15 percent of the total ration dry matter for most beef animals. Some recent research has indicated that S levels in the diet of .1 to .12 percent may be adequate. The maximum tolerable level for S is estimated to be 0.4 percent. Research reported in the Beef NRC (National Research Council) indicated that increasing sulfur levels in beef cattle diets from .12 percent to .41 percent resulted in a decrease in feed intake of 32 percent. This problem can be compounded in situations where water sources carry higher sulfate levels (5000 ppm) resulting in an overall excess in S intake. Thus it should be noted that water sources must also be monitored.

Cause for Concern

Over the last year or so several cases have been reported in both beef and dairy animals which lead veterinarians and nutritionists to suspect a potential S toxicity problem. Cattle consuming diets high in S tend to exhibit symptoms such as the following:

reduced feed intake

diarrhea

incoordination

gaunt and unthrifty appearance

Less visible symptoms include an interference with absorption of dietary copper and selenium as well as other minerals. In situations where the excessive intake become severe enough it appears that the high S intake can be related to outbreaks in polioencephalomacia (PEM), a nervous system disorder. PEM tends to occur with greater prevalence in growing or feedlot cattle.

In a case study in Michigan subclinical sulfur toxicity was suspected in dairy cows and heifers. These cattle exhibited many of the symptoms listed above although they were unable to verify the apparent toxicity clinically from abnormally high rumen or blood S concentrations. The common factor appeared to be high S (.3 to .4 percent S) in forages and rations fed to the animals for three to four months. Nonetheless, it is useful to characterize what was observed so that other producers can evaluate their feeding and forage crop fertilization programs to try to avoid potential problems that may be caused by S toxicity.

The Cause?

We find that in most cases the culprit are forages containing high levels of S. Very aggressive fertilization with S as ammonium sulfate was implicated as the cause of the high S content of home-grown forages. At least in the areas of the farms discussed, a big push by commercial fertilizer companies for aggressive S fertilization began in 1996 in much of the U. S. and before that in other parts of the country, particularly the south. Laboratory analyses of 97 samples collected by a professional nutrition consultant from forages grown in 1996 and 1997 showed that samples from about 45 percent of farms had S contents 1.5 to 3 times higher than comparable forages grown in 1994 and 1995 when typical values ranged from 0.10 to 0.28 percent, before the emphasis on S based nitrogen sources. Because of the concern, the immediate practical strategy in operations with these types of forage assays was to replace or dilute the high-S forages with forages or feeds containing less S. When this was done the problems disappeared. Furthermore, lactating cows in these herds did not exhibit similar abnormal signs, presumably because their diets were sufficiently diluted with low S-containing feeds; total dietary S was 0.20 to 0.24 percent, dry matter basis. The high S content of forages and the reduction in abnormal signs of animals when the high-S forages were replaced by lower S-forages certainly point to possible S toxicity.

Sulfur Toxicity

The majority of S research has been done with feedlot beef cattle, Holstein steers, sheep with a lesser emphasis on dairy cattle. However, there is no reason to believe that S toxicity would not occur in pregnant dairy heifers and lactating cows if dietary S concentrations were high enough. As we discussed earlier the main visual signs are incoordination, muscle twitching, and diarrhea, and in severe cases head pressing, staggering, blindness, animals going down, and death. Sulfur toxicity is caused by microbial conversion of sulfate to hydrogen sulfide in the rumen. With excessive dietary S, high ruminal sulfide production results. The sulfide is absorbed into blood and is highly toxic. This condition affects the central nervous system. As mentioned before a specific condition, dietary sulfate-induced polioencephalomalacia, has been documented as a form of subacute hydrogen sulfide toxicity.

When drinking water is high in S (e.g., greater than 200 parts per million [ppm]) and dietary S is 0.16 percent (as recommended) the risk of toxicity may increase, especially in hot weather when water intakes increase. For example, if a cow consumed 15 gallons of water with 200 ppm S and ate 26 lb of dry forage (0.16 percent S) daily, her total S intake would be 11 grams from water plus 19 grams from feed, or 0.26 percent of total dietary dry matter. If S content of water was 400 ppm and S contribution from feed was still 19 grams, total dietary S intake would be 0.35 percent. Both S in feed and water should be accounted for when determining dietary S concentration, and the potential for toxicity. In many situations it is beneficial to test the mineral content of ground water sources to determine if the potential for a problem such as this exists. Many parts of the United States are characterized by high S levels in the soil. This is further aggravated by S based fertilization and also the S output by many lignite coal-burning power plants. In the south I strongly recommend evaluating forages for S content. To verify S concentrations in feedstuffs, analysis by wet chemistry is recommended. Book values of S content or analysis by near infrared reflectance spectroscopy (NIRS) should not be trusted. Most feed analysis laboratories can provide S concentration values determined by wet chemistry.

Other Nutritional Considerations

High dietary S also can cause problems for animals if dietary copper and (or) selenium concentrations are deficient. Dietary concentrations of these elements also should be reviewed if dietary S is in excess (e.g., greater than 0.20 percent of dietary dry matter). As discussed earlier high S levels can depress absorption of Cu, Se as well as other trace minerals. Over time this can cause a depletion of these traces in the blood and the liver leading to a wide variety of production and health losses.

Sometimes supplementation of S in nutritional programs is needed to meet requirements. Elemental S (flowers of S), though inexpensive, has very low bioavailability, and does not help much to meet the animal's requirement. Better choices are sulfate salts of calcium, magnesium, potassium, sodium, or ammonium.

Dietary nitrogen-to-sulfur ratio of 12-to-1 is adequate to maintain maximum feed intake of lactating cows, as long as the protein requirement is met.

Summary

Sulfur content of diets for beef cattle should range between 0.1 and 0.2 percent, depending upon production status. Higher concentrations are cause for concern. Forages with high S content can cause health problems in cattle consuming those feeds. Agronomist recommend a plant tissue level of 0.2 percent for optimum forage production. Recognizing that this is on the upper end of the beef animal requirement range it is important to be very judicious when selecting mineral products and other feed supplements for your herd. A careful review the S content of all forages, feeds and supplements can offset many health issues and save a lot of trouble and expense.

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 352-3475 or by e-mail at sblez@verizon.net. For more information please visit www.blnconsult.com.

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