Biological chick procedure to determine fluoride availability in sepiolite

1. A modified fluoride (F) bioassay procedure based on the method of standard additions and using chicks was tested for the determination of F availability in sepiolite. Chicks were distributed between a control group fed on a basal diet and experimental groups fed on this diet supplemented with 100, 200 or 300 mg/kg F as sodium fluoride. A further group was fed on the basal diet plus 2 g/kg sepiolite. 2. Body weight gain and food consumption during a 60 or 90 d study were similar for all treatments. 3. Ileal digestibility of F from the basal diet or from the diet supplemented with 200 mg/kg F as sodium fluoride was higher (0.907) than for chicks fed on the sepiolite diet (0.152). 4. Increases in the F contents of tibia ash were linearly related to dietary F concentration as sodium fluoride. 5. F contents of tibiae from the sepiolite group (at 60 or 90 d of age) were plotted against tibia F concentrations from groups receiving additional sodium fluoride in the diet. A weighted regression was performed. The values obtained for the relative available F from sepiolite were 0.213 and 0.150, respectively, at 60 and 90 d of age.