Fescue-associated oedema of horses grazing on endophyte-inoculated tall fescue grass (Festuca arundinacea) pastures.

The research article discusses a new form of toxicity called equine fescue oedema that affects horses grazing on endophyte-inoculated tall fescue grass, which may be caused by the pyrrolizidine alkaloid, N-acetyl norloline.

Overview of the Research Study

• The study is centered around identifying and describing a new form of toxicity known as equine fescue oedema that has been observed in horses grazing on endophyte-inoculated tall fescue grass. Its symptoms include depression, reduced appetite (inappetence), and swelling beneath the skin (subcutaneous oedema) in the head, neck, chest, and abdomen regions of the affected horses.
• The research took place in Australia on six different farms, where 48 out of 56 horses showed signs of this toxicity, and four deaths were recorded. All horses affected were grazing on a type of Mediterranean tall fescue grass that contained the endophyte—Max P or Max Q.

Role of Albumin and Endophyte

• It was noted that the affected horses had very low plasma albumin values. Albumin is a protein in blood plasma that regulates the oncotic pressure of blood. A low albumin level might explain some of the symptoms such as subcutaneous oedema.
• The endophytes Max P or Max Q, present in the tall fescue grass, are established as likely contributors to the toxicity. Endophytes are fungi that live inside plants and often produce alkaloids that have been associated with toxicity in grazing animals.

The Probable Cause of Toxicity

• The researchers hypothesized that equine fescue oedema may be caused by a pyrrolizidine alkaloid known as N-acetyl norloline produced by the Max P endophyte.
• Pyrrolizidine alkaloids are secondary plant compounds that have been implicated in causing terminal liver damage in humans and livestock when consumed in large amounts.

Significance of Stated Findings

• The findings provide an important insight into a new form of toxicity that affects horse populations grazing on specific types of fescue grass. This understanding could inform strategies to prevent and treat this toxicity in the future.
• The identification of the potential cause—The pyrrolizidine alkaloid—suggests a direction for further research. Additional studies could investigate this compound’s exact role in inducing toxicity and explore potential mitigation strategies.