This paper presents details of a knowledge based system (KBS) X-Breed that was built to help Livestock Advisory Officers deliver expert advice on crossbreeding beef cattle to clients in temperate and subtropical Australia. The KBS is made up of six knowledge sources. Of these, five knowledge sources represent the knowledge of a well bounded sub-domain relevant to crossbreeding beef cattle (e.g. selecting a crossbreeding system, selecting a terminal sire, selecting first cross females for breeding) and the sixth knowledge source represents the pasture quality domain. The knowledge sources are integrated into an advisory system through a blackboard architecture. Problems pertaining to reasoning about the timing of events concerning livestock relative to events concerning pasture development are addressed in the context of the pasture quality knowledge source. Case studies are presented.