Physiological responses and ergot alkaloid kinetics in steers rotating grazing toxic endophyte-infected tall fescue

Abstract

Fescue toxicosis is a mycotoxin-related disease caused by ingestion of tall fescue infected with the ergot alkaloid-producing endophyte Epichloë coenophiala. Weight gain and physiological parameters related to thermoregulation are affected. Although rotational grazing might be a mitigation approach, the relationship between ergot alkaloid levels and clinical signs under such conditions remains unclear. Thus, we sought to explore how quickly clinical signs appear and resolve after exposure to toxic pastures, identify residual effects post-removal, assess environmental conditions that impair thermoregulation, and examine ergot alkaloid dynamics in biological matrices relative to onset and recovery. Steers grazed non-toxic, toxic, or endophyte-free fescue pastures. After 14 days, groups switched diets (toxic to non-toxic and vice versa). Physiological parameters and biological samples were collected. Wireless sensors monitored skin temperature and environmental conditions. Fourteen days were sufficient to induce clinical changes; rumen and urinary alkaloid dynamics preceded or aligned with their onset and recovery. While most physiological parameters recovered quickly after removal from toxic pastures, a residual effect on skin temperature, exacerbated by rain and mild heat, but not cold, persisted. Steers on toxic pastures could not dissipate heat below 18–20°C; above this, heat loss was unaffected. Rotational fescue grazing is a promising management tool, as long as thermoregulation and environmental conditions are considered.