A computer program framework was established to enable a dairy herd production consultant to perform whole-herd analysis. The diagnostic process was an extensive data analysis 1) to derive key parameters related to production, reproduction, and health and 2) to produce input to a prognostic process. The prognostic process synthesized the obtained information into short- or long-term prognoses for the herd through a complex herd simulation model. Site specificity of parameter estimation and forecasting and explorability of assumptions and results were major characteristics of the approach. A user acceptance problem related to the simulation was addressed through a simultaneous process of development and validation during the introduction of the program framework into veterinary practices. The generally slow adoption of herd simulation models in extension work could be due to lack of credibility of the models. A major barrier to adoption of the current whole-herd approach may be the considerable time required to understand and use the tools properly. An example of a simulation experiment based on data from a New York dairy farm was provided, and the interpretation and practical applications of such simulations were discussed.