A model to predict kidney and liver cadmium concentrations in grazing animals

Cadmium (Cd) accumulation in the kidneys and liver of older grazing animals is a major concern in New Zealand and Australian agriculture. Use of phosp hate fertilisers containing high Cd concentration is the main cause of this accumulation. A simple mathematical model running in a user-friendly compu ter package was developed to predict annual accumulation of Cd in kidneys a nd liver of animals grazing pastures of known herbage Cd concentration and phosphate fertiliser history. Results from the model showed that kidney and liver Cd concentration of sheep were most sensitive to fertiliser Cd conce ntration, moderately sensitive to pasture ingestion rate, and least sensiti ve to soil ingestion rate. The model was validated using kidney Cd data from a farmlet-scale sheep-gra zing trial. Kidney Cd concentrations predicted by the model were strongly c orrelated with measured mean kidney Cd concentrations. The relationship bet ween the measured and predicted Cd concentrations is not statistically diff erent from the 1:1 relationship indicating that the model can explain the v ariation in the measured mean kidney Cd concentration.