There is no reliable evidence to show that any horses have ever suffered flouride poisoning through drinking fluoridated public water, a veterinary clinical toxicologist says.
Associate Professor Cynthia Gaskill, toxicology section chief at the Veterinary Diagnositc Laboratory at the University of Kentucky, said the potential risk of fluoride-supplemented public water to horses was a topic that periodically arose.
“A casual internet search of this topic can uncover alarming reports purporting fluoride poisoning in horses from fluoridated municipal water,” Gaskill noted in the latest issue of Gluck Equine Disease Quarterly.
“These reports typically are published in non-peer reviewed sources and are missing important information necessary to confirm the diagnosis, to rule out exposure to other fluoride sources, and to eliminate other potential causes.
“A careful review of the peer-reviewed literature in reputable scientific journals showed no published reports documenting fluoride poisoning in horses due to ingestion of fluoridated public water.”
Fluoride, she said, was one of the most common elements in the environment and was found naturally in soil, rock, water, air, plants, and animal tissues.
“Volcanic rock and ash and water from deep wells or hot springs in some regions are naturally high in fluoride. Low concentrations of dietary fluoride can be beneficial to animals; excessive amounts can cause fluoride poisoning (fluorosis).
“Fluorosis can occur in any species, including horses.
“In the past, fluorosis occurred more commonly due to ingestion of forages or waters contaminated with fluoride-containing industrial waste, high-fluorine rock-phosphate supplements in animal feeds, and fluoride-containing rodenticides, insecticides, and other chemicals,” she said.
“Regulations restricting the amount of fluoride in industrial pollution, requiring de-fluoridation of rock-phosphate feed ingredients, and banning many fluoride-containing pesticides have greatly decreased the occurrence of fluorosis.
“Fluoride poisoning still occasionally occurs in areas with high volcanic activity or secondary to ingestion of fluoride-containing medications or contaminated water.
“Acute, high-dose intoxications result in severe signs and rapid death. Chronic, lower dose intoxication causes predominantly tooth and bones abnormalities,” Gaskill said.
“While small amounts of fluoride improve tooth and bone strength, excessive amounts can cause lameness, stiffness, bone thickening, pain and difficulty eating, weight loss, poor growth rates, and poor health.
“Teeth are affected during the period of tooth development, which in horses is complete before 4 to 5 years of age. Fluorotic dental lesions will not develop if animals are exposed to excessive fluoride after permanent teeth have erupted.”
Gaskill noted that public water sources were supplemented in some areas with fluoride to help prevent dental disease in humans.
“Fluoride supplementation in public water is targeted to achieve fluoride concentrations of 0.8 to 1.3 milligrams per litre. The maximum fluoride concentration permitted in public water sources by the [US] national Safe Drinking Water Act is 4 milligrams per litre.”
Gaskill noted that the maximum safe level of fluoride in water for horses had not been established.
“Published guidelines for horses are based on extrapolations from other species. In the USA, the Environmental Protection Agency recommends a maximum fluoride concentration of 2 milligrams per litre in water intended for livestock.”
She noted that in Kentucky, most horses drank fluoridated public water as their major water source, and fluorosis was not seen in this horse population.
“Studies are needed to determine safe limits of fluoride in feed and water for horses. However, evidence to date indicates that fluoride concentrations allowable in US public water systems are well tolerated by horses and do not cause fluorosis.”
Gluck’s Equine Disease Quarterly is funded by underwriters at Lloyd’s, London, brokers and their Kentucky agents.