Further investigation of equine fescue oedema induced by Mediterranean tall fescue (Lolium arundinaceum) infected with selected fungal endophytes (Epichloë coenophiala)

AIMS: To determine if equine fescue oedema (EFO) induced by grazing Mediterranean-type tall fescue (Lolium arundinaceum) infected with selected endophytes (Epichloë coenophiala) could be prevented by treatment with the corticosteroid, methylprednisolone, and antihistamine cetirizine, and to determine concentrations of lolines, specifically N-acetyl norloline (NANL), in grasses grazed by horses that did and did not develop EFO. METHODS: Four horses were grazed on AR542-infected Mediterranean tall fescue pasture(from Day 0) for 7 days prior to being subjected to euthanasia. Two of these horses were treated with 250 mg methylprednisolone and 300 mg cetirizine hydrochloride every 12 hours orally from Days 0–7. I Two more horses grazed meadow fescue (Festuca pratensis) infected with the naturally-occurring, common endophyte (Epichloë uncinata) for 21 days before euthanasia. All horses were observed closely for signs of EFO, and blood samples were taken daily for measurement of concentrations of total protein (TP) in serum. Following euthanasia post-mortem examinations were conducted on all horses. Pasture samples of meadow fescue and Mediterranean tall fescue from the current study, and endophyte-infected Mediterranean tall fescue a from previous study, were analysed for concentrations of lolines using gas chromatography. RESULTS: By Day 7, the treated and untreated horses grazing AR542-infected Mediterranean tall fescue all developed signs of EFO, and concentrations of TP in serum of all horses were <45 g/L. No signs of EFO were observed in horses grazing meadow fescue and concentrations of TP remained above 60 g/L. Necropsy showed marked oedema and eosinophilic inflammation in the intestines of all horses grazing Mediterranean tall fescue. In the sample of meadow fescue, concentrations of total lolines and N-acetyl norloline (NANL) were 2,402 and 543 mg/kg, respectively. In the samples of Mediterranean tall fescue, concentrations of total lolines were 308, 629 and 679 mg/kg, and concentrations of NANL were 308, 614 and 305 mg/kg. CONCLUSIONS AND CLINICAL RELEVANCE: In horses grazing Mediterranean tall fescue infected with the AR542 endophyte, treatment with methylprednisolone and cetirizine did not prevent development of EFO. Results of pasture analysis indicated that lolines or NANL are unlikely to be the causative agent of this disease.