Experimental rayless goldenrod (Isocoma pluriflora) toxicosis in horses.

This research aims to understand the harmful effects of rayless goldenrod (Isocoma pluriflora) toxicity in horses. Initial findings reveal that extended exposure to various doses of benzofuran ketones (BFK) present in rayless goldenrod can lead to significant health complications in horses, such as myocardial disease, implying the need for further investigation to identify the specific toxic elements and their long-term effects.

Introduction to the Study

• The experiment was designed to explore the impact of the rayless goldenrod plant (Isocoma pluriflora) on horses. This plant, commonly found in the southwestern United States, has been known to sporadically poison horses and other livestock. The toxic properties of the plant are believed to be attributed to benzofuran ketones (BFK).
• Although theorized, the direct cause-and-effect relationship between rayless goldenrod consumption and its specific health impact has previously remained undocumented. Thus, the study attempted to reproduce the toxicity scenario under controlled conditions, detailing its effect on horses with known BFK concentrations.

Experiment and Findings

• Four horses were fed increasing amounts of rayless goldenrod over a period of 14 days, with dosages corresponding to approximately 0, 10, 30, and 60 mg BFK/kg body weight (BW).
• The horse that received the highest dosage (60 mg BFK/kg BW) began showing signs of illness after seven days. Symptoms included depression, reduced appetite, dehydration, trembling, and muscle fatigue. The horse also exhibited increased enzyme activity in the serum, evidenced by elevated levels of CK, AST, ALT, and LDH, along with a rise in cardiac troponin I concentration, indicating heart damage.
• The affected horse also showed decreased endurance, reluctance to exercise on a treadmill, and prolonged heart rate recovery following exercise. This horse had to be euthanized on day 10 due to its deteriorating condition. The post-mortem examination revealed extensive myocardial degeneration and necrosis, fibrosis, mineralization, and muscle damage.
• The horse that received the 30mg BFK/kg BW dosage also showed myocardial changes, but these were less severe and occurred over a longer duration, suggesting that the toxicity might be cumulative and long-term exposure to lower doses could also lead to harmful effects.
• No adverse symptoms were observed in the horses subjected to the control dose (0 mg BFK/Kg BW) and the 10 mg BFK/kg BW dose.

Implications and Future Work

• The research indicates that horses are particularly susceptible to myocardial disease caused by rayless goldenrod poisoning, and elevated cardiac troponin I levels may serve as a useful diagnostic marker for such poisoning.
• However, the specific BFK responsible for inducing myocardial toxicity and the precise influence of dosage and duration on the poisoning need to be further investigated.