Response: It is common for horses to be exposed to city water while at suburban show and event venues. We know that horses are less susceptible to fluoride toxicity than cattle or sheep. Maximum dietary allowance of fluoride for horses is believed to be 40 ppm (mg/kg) in dry matter intake and 4 to 8 mg/liter in drinking water. The suggested maximum dietary allowance is substantially higher than normal fluoridation levels for municipal water supplies, which is 0.5 to 1.0 mg/liter of water. Cities monitor fluoride levels very closely in municipal water supplies. Most horses will drink approximately 40 liters of water (10 gallons) daily, or about 20 to 40 mg of fluoride. Keep in mind, horses can have up to 40 mg/kg of fluoride which translates into 18,000 mg of fluoride daily for a 450 kg (1,000 pound) horse.
There have been reported cases of fluoride toxicity; however, these cases have been from industrial pollution/contamination or from the use of rock phosphate sources that have not been de-fluorinated.
By: Roy Johnson, MS, Cargill Animal Nutrition