Fluorosis in the laying hen.

One hundred fifty Single Comb White Leghorn hens of two strains previously selected for either high eggshell strength (HES strain) or low eggshell strength (LES strain) were treated for 8 weeks with sodium fluoride added to a practical-type corn-soybean meal basal diet at 0, 300, 600, 900, or 1200 ppm. The HES strain was found to be more sensitive to fluorosis than the LES strain. High levels of dietary fluoride produced greater decreases in feed consumption, egg production, eggshell breaking strength, eggshell weight, and eggshell thickness in the HES strain than in the LES strain, despite the fact that the absolute intake of fluoride was greatest in the LES strain. Fluoride treatment significantly increased bone magnesium content in both strains and plasma phosphorus in the HES strain but did not significantly affect bone breaking strength or the concentrations of total calcium, ionized calcium, or magnesium in plasma of either strain. High fluoride treatment (1200 ppm) reduced the growth of HES progeny after 8 weeks of treatment of the hens, but LES progeny were not affected. These results suggest that the decreased sensitivity of the LES strain to fluoride may relate to its relatively greater (ca. 14%) volume of bone in which most absorbed fluoride is deposited.