METHODS OF MEASURING PHOSPHORUS STATUS IN SHEEP

**-t ** S. WHINERAY and B.J. THOMAS SUMMARY A series of methods for estimating the phosphorus (P) status (reserves) of sheep were compared. Inorganic P values for tarsal plasma were higher than jugular values except when P-depleted sheep were being repleted. Blood assay techniques were considered to be unsuitable for measuring P status. The most repeatable of the analytical measurements for rib bones was phosphorus expressed as mgP/mgN or mgP/gDM. The former measurement may be useful as the P and N can be measured following a single acid digestion. It may also be a sensitive index as there is evidence that the organic matrix of the bone may not be resorbed as the minerals are depleted. A rapid neutron activation analysis (NAA) technique was investigated. The metatarsal bone was irradiated for 300 s and the gamma spectrum of induced activity collected for 300 s. Using this technique, considerable depletion of metatarsal bone P was indicated in weaners fed a P-deficient diet. The NAA technique appears to have considerable potential for use as a research tool and in the field.