Understanding mineral availability to dairy cows, in all stages of production, is crucial for maintaining whole farm nutrient management. Phosphorus (P) availability and utilization can be inconsistent between feedstuffs, cows and stages of production. If P is overfed on the dairy farm, environmental consequences result. Phosphorus has the potential to leach out of fields and contaminate surface and ground water. Phosphorus may be the limiting nutrient for algal growth. If this nutrient is no longer limiting and is supplied in excess of needs to surface water, eutrophication may occur. In this way over-application of manure to farm land can contribute to eutrophication, via P from field runoff. Ruminants have great potential to utilize most dietary P. From two-thirds to threequarters of phosphorus in concentrates is in the form of phytate (Common, 1940; Nelson et al., 1968b). Phytase hydrolyzes phytate to form orthophosphates, an absorbable form of P. The microbial populations within the rumen produce phytase, rendering phytate P available for the ruminant. As a cow transitions from a dry gestating period to a period of lactation, many changes occur. Nutritional demands increase and hormone levels fluctuate as gestation progresses. The cow also experiences many environmental changes from changing pens and pen mates, to a change in diet. All of these have the possibility to lead the transition cow to health stress and rumen stress. The current study was undertaken to determine the ability of the transition dairy cow to utilize phytate P. The transition period was defined as the period 14 days prepartum to 28 days postpartum. Four aspects of P utilization were investigated. An in vitro study was