Abstract:
3A FLUORINE ABSORPTION BY CATTLE FED ROCK PHOSPHATES CONTAINING VARIOUS CONCENTRATIONS OF ALUMINIUM AND IRON B.J. Blaney * and R.J.W. Gartner * Despite the hazards of fluorosis from feeding raw rock phosphate (Kock P) to stock, it is still useful in many short-term situations because it is cheaper and more available than defluorinated Rock P. Other widely used P supplements also have problems. Although the fluorine (F) content of superphosphate is lower than raw Rock P, it is of higher biologicai`availability. This also applies to dicalcium and monoammonium phosphate. Monoammonium phosphate has the added disadvantage that it does not supply calcium which may be limiting to 0 stock grazin, tropical grasses (Blaney, Gartner and Head 1982). Christmas Island precipitator dust has been used in Australia for many years as a livestock supplement. This is a by-product of the rock crushing process and has a relatively low F content. However, it is no longer available. To fill the gap, fertilizer manufacturers have offered a choice between batches and blends of Rock P, all with higher F contents than Christmas Island precipitator dust. As the availability of F may vary with the source of Rock P, a choice of whether there were suitable replacements should not be made upon total F alone. We speculated that the absorption of F from Rock P might be influenced by its content of aluminium (Al) and possibly iron (Fe) since Al compounds have reduced the retention of F from soluble forms of F by cattle (Hobbs and Merriman 1962). We therefore compared the.absorption of F by steers from 4 batches of Rock P in mineral balance experiments. Christmas Island precipitator dust had both the lowest F content and availability, probably because of its higher Al and Fe content, but differences between the other supplements were slight. Based on the total amount of F absorbed from similar quantities of Rock P, the fluorosis hazard would be higher with all batches of Rock P tested compared to the precipitator dust. In addition, we measured the absorption of F from Nauru Rock P both with and without the addition of 3% Al as Al sulphate. Under our experimental conditions, the Al did not decrease the absorption of F. The form of F in the supplements may be a critical factor. BLANEY, B-J., GARTNER, R.J.W. and HEAD, T.A. (1982). J. Agric. Sci. Camb. 2: 533. HOBBS , C.S. and MERRIMAN, G.M. (1962). Tenn. Agr. Sta. BuL 3% I * Department of Primary Industries, Animal Research Institute, Yeerongpilly, Qld. 4105.
