Influence of Sulfur Content of Distiller’s Grains and Potential Risk of Polioencephalomalacia in Dairy Cattle (Benjamin Wenner, Michigan State University)
Introduction
With the increasing supply of distiller’s grains (DGs) in the United States as ethanol plants expand and increase production, the opportunity to use DGs as a low-cost feedstuff source for dairy cattle is apparent. According to legislation passed by the U. S. Congress in 2005, total ethanol usage in fuels by 2012 is to exceed 7.5 billion gallons (1). Considering that ethanol is roughly equal to the quantity of DGs produced, this also means that approximately 7.5 billion ‘gallons’ of DGs will be available as feedstuffs (1). With this enormous supply of byproducts, it is an opportunity for the livestock industry to make use of the byproducts as a low-cost feedstuff and better incorporate it into the diets fed in the future.
Accompanying the increase in DGs availability is a wide variation in the nutrient content of actual product being marketed by ethanol plants. An example is the wide range in concentrations of S in the feedstuff. Excessive S, contributed from DGs, may raise the S concentration in rations and exceed the requirement of dairy cattle.
Hydrogen sulfide has been considered a potential cause of polioencephalomalacia (PEM) in cattle and therefore is a concern with the variations in S content among DGs byproducts from assorted ethanol plants (2, 3, 4). Additionally, S intake can be further increased by elevated concentrations of S and sulfate in drinking water. This could have a cumulative effect resulting in greater concentrations of S-containing compounds in the body (5).
The goal of this paper is to implicate high S concentrations in DGs byproducts in the incidence of PEM via hydrogen sulfide production in the rumen. Further, this paper will attempt to provide a better understanding of this relationship and also how the prevention of S-induced PEM is possible for the future. Sulfur is an essential mineral element for dairy, but it also can be highly toxic. Awareness of the variation in S content of DGs byproducts should lead to greater accuracy in ration formulation and feeding models resulting in healthier cattle, reduced risk of PEM from S and greater milk production.
S in DGs
According to the Distiller’s Grains Technology Council, the S content as a percentage of dry matter (%DM) in distiller’s dried grains with solubles (DDGS) is 0.38% (6). While this may be an industry average, the actual analyzed concentrations apparently vary quite a lot from 0.38%, and are often considerably greater.
Reviewing a 2008 Distiller’s Grain Byproducts Handout of analyses of byproducts from ethanol plants solely within the state of Michigan, it is striking how great the disparity in S content can be from one sample to the next. Sulfur content ranges from 0.58% to 1.01% DM among all of the products and in the same ranges for DDGS products specifically (7). In another sampling, S values ranged up to 2% of DM (8). With a total dietary maximum established by the NRC (2001) at 0.4% of dietary DM, it is easy to see how much the concentration of S in DGs byproducts might impact the total quantity of S content of the diet and the amount of S fed (3, 5, 8, 10).
There are a plethora of listed reasons why DGs byproducts have such large S concentrations. Corn itself contains S and through the fermentation process as starch is converted to alcohol (ethanol) the remaining S in corn grain is concentrated in the byproduct (9). Additionally, the bacteria used in fermentation are a part of the final product and also are concentrated, adding S to the final byproduct (9). Acids, for example mainly sulfuric acid, are added to the fermentation process to stabilize the pH and will add to the S content (10). Even the water used in the local area might contribute differing quantities of S to the production and when the systems are cleaned the cleaning agents used are commonly sulfuric acid-based which ends up in the DGs (10).
How Sulfur Affects Cattle
Sulfur is listed as a dietary essential mineral element. It is a constituent of some amino acids used to manufacture the proteins used in everyday life functions. Bacteria in the rumen are able to utilize S regardless of the chemical form consumed because there are certain species with specific capabilities for this purpose (3).
However, S can reach toxic concentrations in the body. The NRC (2001) listed the maximum dietary limit at 0.4% of DM and the requirement is set at 0.2% of DM in order to avoid toxic concentrations (11). When reaching concentrations over the maximum limit, animals run the risk of lung and brain damage, loss of mobility or even death due to S toxicity from hydrogen sulfide originating in the rumen. One of the most common forms of S toxicity is polioencephalomalacia (PEM). PEM occurred at a significantly higher rate once S content was over 0.56% of the diet (12). This disease is a result of brain degeneration and therefore its clinical symptoms include loss of motor control, depressed appetite, depressed bodily functions, inability to stand and death. It is not always fatal, but damage may be permanent.
Originally, PEM was designated specifically as a result of thiamin deficiency and even to this day thiamin deficiency is the leading cause of PEM (3). It was thought after some experiments seemed to support it, that there seemed to be an interaction between thiamin and S (in the form of hydrogen sulfide) which resulted in PEM cases. Recently, it was found that S, independent of thiamin, is the second most important factor in PEM, and cases have been reported of PEM occurring entirely without thiamin deficiencies due to high concentrations of hydrogen sulfide (2, 3).
Bacteria in the rumen of a dairy cow take up S from the feed and convert it the H2S (hydrogen sulfide). The bacteria respire anaerobically and during this process produce electrons through oxidative reactions. These electrons reduce many compounds, including sulfate (SO4-2) which is a typical form of S in feedstuffs and water. Sulfur in the body eventually finds itself in one of two compounds: hydrogen sulfite and hydrogen sulfide. The sulfide itself absorbs quickly through the rumen wall and travels through the blood stream to interfere ultimately with central nervous tissue (3).
The ruminal production of H2S is directly linked to the amount of dietary S (3, 13). Because S is an essential mineral element as well for the microbes within the rumen, H2S must be accepted as a necessary product of ruminants. The problem lies with the fact that as a ruminant produces increasing amounts of H2S, this H2S must be released through belching, which in turn travels to the lungs. This results in lung damage and possible in brain damage as H2S in the blood increases and negatively impacts the central nervous system (3).
Additionally, S reducing bacteria appear to respond positively to additional S and increase their ability accordingly to reduce sulfate in the rumen (3). Also, the concentration of sulfate in drinking water may contribute positively to the production of H2S and the resulting S toxicity (2).
While not always viewed as an important issue in dairy production, PEM can have devastating impact on herds in production (list References). Hundreds of animals from single herds have died or been adversely affected by S toxicity when dietary concentrations were as low as 0.45% and as high as 0.91% of dietary DM (3). In 2006, 256 cattle in one case study on two ranches exhibited signs of PEM after being fed barley sprouts as a feedstuff. The total S concentration in the diet was 0.45% and out of 5,050 cattle 256 died or were slaughtered due to PEM (14). Even drinking water with a concentration equivalent to 0.67% DM intake in a 1997 study resulted in blindness with a total PEM incidence of 0.88% (3).
Preventative Measures
Prevention of S-induced PEM is challenging due to the sudden and unexpected nature of the illness and death that can strike animals. It is most important to be aware of the composition of feedstuffs and the actual concentration of S in a ration. It is important to be aware that the S concentration in DGs is hard to predict. Precautions should be to limit the amount of potential S intake to prevent toxicity, while still supplying the requirements.
Assuming that a plant with acceptable sulfur concentrations in their byproducts has been identified, one approach to greatly improve consistency of ration S content is to establish a relationship with that specific ethanol plant and to contract for delivery from that location only. Distiller’s grains byproducts still vary immensely even within a plant due to inconsistent production patterns. However, combining regular laboratory analysis of the feedstuff into a ration formulation can be an effective method for monitoring the amount of S consumed in the diet (9).
Considering that S content of most feedstuffs is within the realm of NRC (2001) requirements, it is my suggestion that in order to prevent PEM from DGs byproducts the DGs concentration be kept at or below 20% of the total ration on a DM basis. This allows for safety in the chance of temporary elevation of S concentrations in the DGs byproducts being fed.
Assume, for example, the feed ration without DGs byproducts was at a 0.25%, dry basis S. Then if 20% of the ration DM is replaced with DGs with S concentrations of 0.50%, 0.75% and 1.0% would result in total feed concentrations of 0.30%, 0.35% and 0.40% of DM respectively. When feeding at 25% of the ration DM at concentrations of 0.50%, 0.75% and 1.0% would result in total feed concentrations of 0.31%, 0.38% and 0.44% of DM respectively. Alternatively, at 30% fed of DM, DGs byproducts with concentrations in DM of 0.50%, 0.75% and 1.0% would elevate total feed concentrations of S to 0.33%, 0.40% and 0.48% of DM respectively. This concentration of S in the total ration can be hazardous as already shown and therefore to ere on the side of safety by feeding no more than 20% of DM with DGs byproducts helps to ensure the health of the dairy cattle.
Also, it was shown that the quantity of hay in a ration can alter the concentration of H2S in the rumen. With increasing consumption of alfalfa or grass forage, H2S concentrations produced in cattle significantly decreased (12). Despite the fact that roughage is provided in the diet already, adding more hay could significantly reduce the potential for PEM in diary cattle. Alternatively, this is not necessarily a positive solution to the issue of H2S production because it will also reduce the milk yield in a dairy herd.
Conclusion
Distiller’s grains are a source of energy and essential nutrients for dairy cattle. However, they also may be high in S content and overfeeding of S can lead to toxicity and PEM. Although S is an essential element, it must be limited to avoid the real risk of PEM in dairy cattle. This can be accomplished by regular analysis of feedstuffs received from specific producer(s) of DGs to try to ensure consistency. Additionally, following a safe limit of no more than 20% distillers grains combined with adequate forage in the diet can greatly reduce the risk of PEM.
References:
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5. Beede, D. 1999. Excess Dietary Sulfur: A Problem? Michigan Dairy Review.
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11. National Research Council. 2001. Nutrient Requirements of Dairy Cattle. 7th revised edition. Nat. Acad. Sci., Washington, DC.
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