By Jacquelyn Prestegaard / ASAS Communications
Outstanding advances in nutrition research continue to give livestock producers the best tools to manage their herds. Of these successful stories, research regarding sulfur metabolism in ruminants has recently been a particular focus “… primarily fueled by an increase in the S content of cattle diets due to inclusions of high S coproducts of ethanol production,” such as distillers grains with solubles, write Dr. Mary Drewnoski and colleagues in a review article appearing in the September 2014 issue of the Journal of Animal Science. The article compiles a vast array of information gained over the last 10 years concerning the impacts of high S diets in ruminants.
Sulfur-induced polioencephalomalacia, or S-PEM for short, is the primary disease associated with excess sulfur intake, and is characterized by swelling of the brain and damage to the grey matter. Even though S-PEM is mostly diagnosed postmortem, certain side effects can be observed in live animals.
“Because of brain swelling, it’s common for animals to demonstrate head-pressing against posts in their pens or become blind,” said Dr. Stephanie Hansen, coauthor and Assistant Professor at Iowa State University. “We’ve even seen animals walk in circles.”
The inclusion of ethanol coproducts in feed rations is a relatively recent practice resulting from the emergence of corn-based ethanol production. Feedstuffs such as dried distiller grains with solubles (DDGS) contain large amounts of sulfur, which poses the threat of S toxicity if fed in large amounts.
Concerns about S toxicity have long been related to high sulfate water, a problem for many locations throughout the U.S. Hansen says high-sulfate water is actually more worrisome than high-sulfate feed because sulfates in water are already solubilized and are readily available for reduction by rumen bacteria. Hydrogen sulfide is then quickly formed in the rumen, which is what causes S toxicity in the animal.
“In contrast, the sulfates found in feedstuffs may or may not be rapidly soluble in the rumen,” Hansen said. “Depending on the protein degradability by rumen bacteria, the sulfate may never break down and be released as hydrogen sulfide.”
Interestingly, most research points to eructation as the primary mechanism leading to brain damage. Rumen bacteria degrade sulfide, which is present in the rumen as hydrogen sulfide gas. When the animal belches, it breathes in the H2S, which then travels to the brain.
Fortunately, PEM can be treated if caught early. Thiamine has “nonspecific therapeutic benefits for cerebral diseases,” so it is the primary means of curing PEM.
“A high dose of thiamine will provide a quick energy boost to brain cells to reduce swelling,” Hansen said. “It’s also important to then get cattle off of the high-sulfur diet and onto a more hay-based diet until they recover.”
Brain damage is not the sole problem presented by excess dietary S. If consumed in excess, S can limit the availability of other trace minerals in the diet. For example, S reduces copper absorption through the formation of copper sulfide in the rumen. The copper is then poorly absorbed later in the intestinal tract, which can result in “a mild to severe copper deficiency,” says Hansen.
This pertains particularly to rangeland cattle, whose diets are usually high-forage, but are often “wintered” on feed containing ethanol coproducts in areas like the Midwest. While S toxicity isn’t likely in cows, excess dietary S can drain their trace mineral reserves during the winter months.
“It’s important for producers to know that decreased trace mineral status can have detrimental effects,” Hansen said. “It can result in lower calf health, calf immunity, and cow fertility.”
Other problems associated with high-S diets include reduced dry matter intake and growth, as well as negative effects on carcass quality. “The concentration of S that interferes with trace minerals is likely less than that which decreases cattle performance; however, the effect of S on trace mineral status may be more easily overcome through nutritional strategies than the negative effects of S on DMI and performance,” state the authors in the article.
There are many ways to counter and prevent S toxicity. In terms of high-S feedstuffs, good nutritional management is key. Hansen says it is particularly important for producers to “get a good handle” on the S content of their diets. Additionally, she suggests methods such as monitoring feed bunks well, feeding multiple times a day, and properly rationing of concentrates and roughage.
“Incorporating an adequate amount of roughage in the diet is very important when balancing high-S feeds,” she said. “This slows down the rate at which animals eat and also raises rumen pH. The higher the rumen pH is, the less hydrogen sulfide will be produced in the rumen.”
The review concludes that future research on the topic should focus on “antioxidants as ameliorators of S toxicity.” Hansen says she is currently working with a team researching the negative effects of S on trace mineral status in feedlot cattle.
ASAS Media Communications
ASAS Media Communications