Environmental sensitivity exists when an environmental difference has more effect on some genotypes than on others (Falconer and Mackay, 1996). Quantifying the degree of environmental sensitivity shown by individual sires allows us to identify sires as specialists (those which rank highly in certain environments) or generalists (those which rank similarly across environments). Dairy farm environments vary enormously and this affects the production and health of the cows. The aims of this study were (1) to relate detailed survey information on farm management systems to information available at the national level to provide a definition of farm environment, and (2) to assess the effect of environment on lifespan.