Potentially toxic element with acute poisoning and chronic toxicity (fluorosis) possible.
Acute poisoning is unlikely as horses rarely have access to or willingly consume fluoride compounds such as sodium fluoride formerly used to fluoridate water supplies, or sodium fluorosilicate rat poison. Signs are consistent with acute hypocalcaemia as fluorine combines with calcium in the blood. The low blood calcium causes rapid onset of excitement, seizures, irregular heart rate and sudden heart failure. Treatment if the condition is caught in time is intravenous Calcium Gluconate.
Fluorosis is most commonly caused either by consumption of fluorine contaminated rock phosphate fertilizer or artesian bore water containing high levels of natural fluoride. The problem occurs most commonly in Queensland. Water fluoride should not exceed 2mg/L. Fluorine contamination of pasture downwind of smelters has also been recorded as a cause of toxicity.
Phosphate fertilizers such as super phosphate, triple super phosphate, rock phosphate and diammonium phosphate are a potential risk as these may be used in mineral licks and blocks as a source of phosphorous. Only better quality low fluoride phosphate sources should be used for animal consumption. Contamination of drinking water by fertilizer run off is possible.
Fluoride accumulates in tissues so toxicity may result from a slow build up over time. Young growing horses are more at risk through active bone growth and tooth formation. Teeth may become pitted or wear unevenly and be softer than normal with white mottling. Disruption of bone re-modelling causes thickening of long bones with irregular bumpy surfaces, especially in the cannon bones and ribs. Abnormal posture, poor growth rate and condition may also feature. Radiography will confirm.