Tall fescue (Schedonorus arundinacea), a widely utilized cool-season perennial grass, plays a significant role in beef and dairy cattle production due to its adaptability and resilience (White et al., 1992). However, ergot alkaloids, particularly ergovaline, pose a substantial risk to cattle health and productivity. This article explores the importance of understanding and managing the risks associated with ergot alkaloids in tall fescue for cattle.

Benefits and Hazards of Tall Fescue

Tall fescue's popularity stems from its durability and ability to thrive under various environmental conditions. It covers approximately 35 million acres across the United States (Gott et al., 2018), providing essential forage for cattle. One key reason for its hardiness is its symbiotic relationship with the fungal endophyte Neotyphodium coenophialum. This endophyte enhances the grass's drought and disease tolerance of the grass but also produces ergot alkaloids, including ergovaline, leading to a condition known as fescue toxicosis (Aiken and Strickland, 2013; Gott et al., 2018).

Impact on Livestock Health and Performance

Ergovaline, a potent vasoconstrictor found in tall fescue, causes several detrimental symptoms in cattle, collectively known as fescue toxicosis. Symptoms include increased body temperature, labored breathing, excessive salivation, and exacerbation of heat stress (Strickland et al., 2011; Klotz, 2015). The animals also exhibit a dull and rough hair coat, poor growth, weight loss, and decreased weaning weights (Burns and Chamblee, 1979; Gott et al., 2018).

Cattle grazing on ergovaline-infected fescue consume less feed and experience slower weight gain, negatively impacting their overall productivity. For example, cows grazing on toxic tall fescue during late gestation show lower body weight gain and reduced milk production than those on non-toxic varieties (Adams et al., 2018). 

One of the most severe consequences of ergovaline toxicity is "fescue foot," which causes lameness and gangrene in the extremities due to restricted blood flow (Garner and Cornell, 1978; Cornell et al., 1982). This condition harms the animals' well-being and leads to economic losses due to decreased productivity and increased veterinary costs (Gott et al., 2018). 

Furthermore, a study found that chronic exposure to ergot alkaloids from endophyte-infected tall fescue reduces the diameter of arteries and veins serving the ovary and uterus during critical times in the estrous cycle (Poole et al., 2018), potentially compromising the animal reproductive performance.

Research Findings on Mycotoxin Contamination

A comprehensive survey analyzed 40 samples collected from Kentucky and Georgia between August 2017 and January 2018. The results revealed that type B trichothecenes and zearalenone could co-contaminate tall fescue with ergovaline. This co-contamination raises concerns about the combined toxic effects on livestock.

The study found that 57.5% of the samples contained type B trichothecenes, 27.5% contained zearalenone, and 100% of the screened samples contained ergovaline. The mean ergovaline concentration in the samples was 410 parts per billion (ppb), significantly above the risk threshold of 200 ppb (Gott et al., 2018). These findings highlight the frequent co-contamination of Fusarium mycotoxins with ergovaline, emphasizing the need for continuous research to understand the combined toxic effects and improve management strategies.

Management Strategies for Mitigating Risks

Several agronomic practices can help mitigate the effects of tall fescue toxicosis, such as feeding supplements, rotating cattle to warm-season forages in summer, reducing alkaloid concentration by making hay, and adding clovers or other forage species to dilute toxins (Kallenbach, 2015). Rotational grazing and interseeding pastures with non-toxic forage species can help dilute the ergovaline concentration in the diet. Planting endophyte-free or novel endophyte tall fescue varieties can significantly reduce the risk of ergovaline toxicity while maintaining the benefits of the grass (Aiken & Strickland, 2013; Kallenbach, 2015).

Regular testing of forage for mycotoxin levels can help make informed decisions regarding feed management. Awareness of seasonal variations in ergovaline content can aid in planning grazing and feeding schedules. Fescue toxicity tends to be more severe in late spring and summer, making it essential to adjust management practices during these periods (Gott et al., 2018).

Conclusion

Tall fescue remains a valuable forage resource for the beef and dairy cattle industry. However, ergovaline and other mycotoxins pose significant challenges that require proactive management. Producers can safeguard cattle health and optimize productivity by understanding the risks and implementing effective strategies. Continued research and monitoring are essential to provide a clearer picture of mycotoxin prevalence and seasonal variations and to explore the synergistic effects of multiple mycotoxins on cattle health.