For Mr Barry Garrity, Carterton dairy farmer, the spring of 1992 brought a very challenging decision-making process. A computerised simulator (model) of the physical functions of his property had been in use since October 199 1. As a high stocking rate, high performance farm the next step in improving profitability was being sought. The simulator provided a means of reviewing performance, searching out means of more efficient use of pasture and overcoming the limitations to increased production. The software (UDDER) models grass growth and animal performance for an actual season with a gross margin used to reflect the financial component. In this case base data were derived from the 1990191 season, a record year for the property. Keywords: computer, dairy farm, forecast, gross margin, model, simulator
