Recent analysis from surveys of dairy farms has shown that despite large increases in production, the productivity gains on these farms have been modest. Productivity gains are important for farm viability, farmers have made production gains through adoption of technologies and increases in scale. This long-term farm case study of an irrigated dairy farm over a 40-year period provides an in-depth analysis of system changes and management complexity. Detailed records of milk production, herd, farm area and infrastructure, water use, supplementary feed, and labour were collected and pasture consumption was estimated. Changes in milk production were analysed in relation to individual resources, particularly farm inputs. Increases in production were associated with the use of more resources, including cows, land, water, fertiliser, feed and labour. However, measures of partial productivity indicated that that there has also been a trend towards more efficient use of these resources. This long-term study can provide an insight into production impacts from changes in farm resource use and illustrates the short and longer term impacts of changes to farming systems.