Page 155 - Fundamentals of Air Pollution

IV. Effects on Animals 123

Chronic fluoride toxicity (fluorosis) is the type most frequently observed
in cattle. The primary effects of fluorides in cattle are seen in the teeth
and bones. Excessive intake weakens the enamel of developing teeth; the
initially dulled erupted teeth can develop into soft teeth, with uneven
wearing of molar teeth. Characteristic osteofluorotic bone lesions develop,
causing intermittent lameness and stiffness in the animal. Fluoride content
of the bone increases with dosage despite excretion in urine and feces.
Secondary symptoms include reduced lactation, nonpliable skin, and dry,
rough hair coat. As shown in Fig. 8-4, the fluoride ingestion level correlates
with the fluoride content of bones and urine as well as incisor teeth classifi-
cation (18),
Tolerance of animals for fluorides varies, dairy cattle being most sensitive
and poultry least (Table 8-3). Fluorosis of animals in contaminated areas
can be avoided by keeping the intake levels below those listed by incorporat-
ing clean feeds with those high in fluorides. It has also been determined

Fig. 8-4. Effects of fluoride on 4-year-old dairy cattle.