We consider joint production and disaggregation in the dairy sector by specifying a disaggregation routine that nests a standard Global Trade Analysis Project (GTAP) model and a model built on a SplitCom disaggregation as special cases. We show that disaggregation and joint production can have a large influence on simulation results. In a detailed application, we consider the removal of US tariffs on New Zealand dairy products. Disaggregation of the dairy sector results in a welfare gain nearly twice as large as when dairy products are included in a single sector. Our preferred aggregation and production specification for dairy commodities generates results that differ from those produced by standard approaches.