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Mycotoxins may also infect pasture grasses

TAGS: Beef Dairy
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Besides endophyte-infected tall fescue, zearalenone and trichothecenes have been identified in bermudagrass pastures in southeastern U.S.

Throughout history, outbreaks of illness and disease in people and animals have occurred where the true cause was unknown, and such challenges have fueled the pursuit of identifying causal agents such as a bacteria, viruses or fungi, Biomin ruminant technical manager Paige Gott wrote in a recent post on the Biomin "Mycotoxins" blog.

Advances in knowledge and science have contributed to building tools in diagnostics, prevention and treatments that improve the ability to face such challenges, Gott said, but mycotoxins have taken longer to be understood since advanced chemistry techniques were required to detect these toxic chemicals produced by certain fungi.

Now, more than 400 mycotoxins have been identified, and more information is being uncovered about the health challenges and loss of productivity they pose in livestock, Gott said, noting that mycotoxins can cause a variety of negative effects, such as damage to the liver, kidneys and digestive tract.

Multiple factors influence how animals are affected, including the specific mycotoxin, level and duration of exposure, animal species, age and animal health status, as well as environmental factors, Gott added.

While much mycotoxin research has focused on grains, since they are food sources for people and are main ingredients in poultry and swine rations, Gott said mycotoxicoses — diseases caused by mycotoxins — occur frequently in ruminants, and this is often traced back to contamination in forages. The complex nature of ruminant diets leads to potential exposure to a broad spectrum of mycotoxins, she said.

One of the best-known forage-related mycotoxin challenges is endophyte-infected tall fescue, Gott said, because tall fescue is a hardy, cool-season, perennial grass estimated to cover more than 35 million acres of U.S. pastureland. Although tall fescue has benefits such as good yields, drought tolerance and pest resistance, she explained that toxicity issues often arise with this forage grass because it has a fungus living within the plant tissue, referred to as an endophyte. This fungus provides beneficial characteristics to the plant, but naturally occurring wild-type strains of the fungus also produce ergot alkaloids, including ergovaline, that are toxic to animals, she said.

According to Gott, additional well-known mycotoxin challenges in pasture grasses include perennial ryegrass staggers and paspalum staggers — neurologic conditions that are also linked to alkaloid toxins produced by endophytes. While death is uncommon, it can occur in severe cases or if the source of contamination is not removed, she said, adding that handling affected animals can worsen the staggers, so care is necessary when moving affected animals.

Mycotoxin challenges arising from fusarium species of molds have been reported in pasture grasses in New Zealand since studies began in the 1970s, Gott said, including identification of zearalenone (ZEN), a reproductive toxin, in pastures where livestock exhibited poor reproductive performance despite good management and adequate nutrition. Fusarium molds, as well as a mix of mycotoxins from pasture grasses, have been isolated that originated from additional countries, including South Africa and Argentina.

Gott said while grazing animals are often thought to be at low risk for mycotoxin exposure since they tend to consume relatively limited amounts of grains, a mycotoxin survey of southern U.S. pastures has identified the potential for high levels of contamination in several grasses. A variety of mycotoxins have been detected, she reported, including high levels of ZEN, type A trichothecenes (T-2 toxin and HT-2 toxin) and type B trichothecenes such as deoxynivalenol (vomitoxin), nivalenol and fusarenon X.

The pasture grass survey began in March 2016, with the majority of samples originating from Florida pastures. Initial sampling identified the potential for high levels of ZEN in bermudagrass. To date, nearly 400 pasture samples have been screened for up to 17 mycotoxin metabolites at one of two analytical laboratories, Gott said. The majority (84.7%) of samples were bermudagrass. The results are concerning, she said, since in bermudagrass samples, 68% tested positive for some level of ZEN (average of 1,718 parts per billion on a dry matter basis), and around 19% tested positive for type A trichothecenes (average of 1,226 ppb).

Observed contamination varied over time, with the highest mycotoxin levels detected during the winter months and early spring, Gott said. High variability has also been seen between pastures, with no mycotoxins detected in some pastures and very high levels occurring in others. Reproductive challenges like low conception rates and abortions, lower body condition score in dams, a reduced calf crop and decreased calf weaning weights have been reported in pastures with contamination, she noted.

Gott said the survey is an ongoing effort designed to increase the understanding of mycotoxin occurrence in pasture grasses. Additional grass species are being sampled, and the geographic area has expanded to include additional states to determine how extensive this issue is. Based on results of the three-year survey, mycotoxin contamination in pasture grasses has been both frequent and at high enough levels to warrant consideration of mycotoxins as an influential factor in the reproductive success, health and performance of grazing cattle, Gott concluded.

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