This paper deals with the economic analysis and management implications of extending lactations in specialised dairy cows. The main conclusion from this study is that in the two dairy farm cases that have been investigated in depth, the use of extended lactations to achieve efficient herd reproduction is highly likely to give greater profit than alternative systems that could be implemented. This conclusion holds even after allowing for less than total persistency of cows embarking on extended lactations. The overall outcome of a change from having only 10-month lactations to having some cows in the herd milking for extended lactations is determined by the complex interactions of all of the major input, output, cost and income factors at work in a dairy system. The likely net effects of adopting the extended lactation innovation in a dairy system has to be estimated for each unique farm system, with particular attention paid to the skills and aspirations of the people who operate the system.