The objective of this study consists in evaluating the sensitivity of the first part of the die grass-milk with respect to an accidental radioactive discharge. We want to know if a single uniform deposit would involve a contamination of the grazing grass identical on the scale of the own territory. The study was based on the ASTRAL model, a computer code developed by the IRSN which makes it possible to evaluate the transfer of the radionucleides in the terrestrial food chain following an accidental atmospheric emission. The way of transfer of ASTRAL on which the study focused is the transfer of the deposit to milk, via the grazing grass ingestion. The sensitivity of this way of transfer relies on several parameters: captation, yield, cows food rates and dates of setting to grass. Methodology thus consisted in regionalizing these parameters. The software STICS, developed by the INRA of Avignon was then used. This model proposes a daily follow-up of the leaf area index which has been correlated with capitation and with the production of fresh biomass (yield).