Bovine calves as ideal bio-indicators for fluoridated drinking water and endemic osteo-dental fluorosis

Relative susceptibility to fluoride (F) toxicosis in the form of osteo-dental fluorosis was observed in an observational survey of 2,747 mature and 887 immature domestic animals of diverse species living in areas with naturally fluoridated (>1.5 ppm F) drinking water. These animals included buffaloes (Bubalus bubalis), cattle (Bos taurus), camels (Camelus dromedarius), donkeys (Equus asinus), horses (Equus caballus), goats (Capra hircus), and sheep (Ovis aries). Of these mature and immature animals, 899 (32.7 %) and 322 (36.3 %) showed evidence of dental fluorosis with varying grades, respectively. Their incisor teeth were stained with light to deep brownish color. On clinical examination, 31.2 % mature and 10.7 % immature animals revealed periosteal exostoses, intermittent lameness, and stiffness of tendons in the legs as signs of skeletal fluorosis. The maximum susceptibility to fluoride toxicosis was found in bovines (buffaloes and cattle) followed by equines (donkeys and horses), flocks (goats and sheep), and camelids (camels). The bovine calves were found to be more sensitive and highly susceptible to F toxicosis and revealed the maximum prevalence (92.2 %) of dental fluorosis. This indicates that bovine calves are less tolerant and give early sign of F poisoning (dental fluorosis) and therefore, they can be considered as bio-indicators for fluoridated water as well as for endemicity of osteo-dental fluorosis. Causes for variation in susceptibility to F toxicosis (fluorosis) in various species of domestic animal are also discussed.