Study maps metabolic effects of toxic tall fescue in steers

A new Frontiers in Veterinary Science paper offers a closer look at how toxic endophyte-infected tall fescue affects beef steers at the metabolic level during fall rotational grazing. The study found that steers exposed to toxic fescue developed a distinct metabolomic profile marked by reduced lipid metabolism and increased amino acid and carbohydrate pathway activity, with most changes resolving after the animals were moved off toxic pasture. (frontiersin.org)

That finding builds on a long-running concern in cattle production: fescue toxicosis caused by ingestion of tall fescue infected with the ergot alkaloid-producing endophyte Epichloë coenophiala. Tall fescue remains one of the most heavily used forages in the United States, particularly in beef systems, which is why even modest production losses matter at scale. Prior research has shown that toxic fescue exposure can impair productivity, alter thermoregulation, and interact with environmental stressors such as heat and humidity. (frontiersin.org)

In the new study, 18 steers grazed toxic, novel-endophyte, or endophyte-free fescue pastures. After 14 days, groups switched, so animals moved from toxic to nontoxic pasture and vice versa. Researchers collected urine, saliva, plasma, rumen fluid, and feces, then used untargeted high-resolution metabolomics and targeted volatile fatty acid analysis to map metabolic changes. They found that total and individual volatile fatty acids in rumen fluid rose during toxic fescue exposure and returned to baseline after removal. Discriminative analyses showed exposed steers had a clearly different metabolome, while animals previously exposed to toxic pasture later resembled steers that had never been exposed. (frontiersin.org)

The pathway-level findings were especially notable. According to the paper, beta-oxidation, fatty acid metabolism, and arachidonic acid metabolism shifted downward in toxic-fescue steers, while aromatic amino acids such as tyrosine and tryptophan, branched-chain amino acids, vitamin B6 pathways, and carbohydrate pathways including gluconeogenesis shifted upward. The authors also identified discriminatory metabolites including tyramine, methyltyramine, methoxytyramine, and dopamine. They detected clavine alkaloids and lysergic acid derivatives in most matrices, but not plasma, and said those compounds rose and fell within about two days of exposure or removal. The authors concluded that the principal detected ergot alkaloids were clavine-type alkaloids and simple lysergic acid amides rather than ergopeptines, suggesting substantial biotransformation in the animal. (frontiersin.org)

The work also fits with the group’s recent 2025 Toxins paper on fall-grazing steers, which found that even low ergot alkaloid-producing toxic fescue altered metabolomic profiles more clearly than microbiome structure and was associated with effects on thermoregulation, behavior, and weight gain. Earlier studies in Scientific Reports similarly linked toxic tall fescue grazing to broad metabolomic disruption and increased susceptibility to environmental stress. Taken together, the research points toward a recurring pattern: the metabolic consequences of toxic fescue may be detectable before or alongside more visible production losses. (doaj.org)

Why it matters: For veterinarians and allied cattle-health professionals, this study strengthens the case that fescue toxicosis is not just a vascular or performance problem, but a multi-system metabolic disturbance. That has practical implications for herd investigations when pet parents—more accurately here, cattle producers and caretakers—report poor gain, heat intolerance, or vague performance issues in animals on tall fescue. The apparent reversibility after pasture removal is encouraging, but it also underscores the value of early recognition, forage testing, pasture renovation strategies, and consideration of nontoxic or novel-endophyte alternatives where feasible. Because the metabolomic signal appears to shift energy use away from lipids and toward amino acids and carbohydrates, it may also help explain why exposed cattle can underperform even when gross clinical signs are subtle. (frontiersin.org)

No outside expert quote tied directly to this new paper was readily available in the sources reviewed, but the broader literature reflects continued interest in identifying biomarkers and management interventions for fescue toxicosis. Prior authors have suggested that metabolome-microbiome signatures could eventually support more targeted diagnostics or therapeutic strategies, especially as climate and seasonal stress compound disease expression in grazing systems. That’s an inference drawn from the direction of the published work, rather than a formal consensus statement. (nature.com)

What to watch: The next step will likely be validation, specifically whether these metabolomic markers can be translated into field-useful tools for earlier detection, monitoring response to pasture changes, or comparing risk across toxic, novel-endophyte, and endophyte-free systems. (frontiersin.org)