Re-evaluation of Phosphorus Requirements and Phosphorus Retention of Feedlot Cattle1

etal tissue growth and mineralization should improve estimation of gain requirements. Cattle have extensive ability to buffer against P deficiency through mobilization of P reserves. The buffering ability causes P requirement for growth to be less than potential retention, complicating management of P nutrition. Improved estimates of P gain requirements may reduce P over-feeding, whereas separate retention estimates will allow accurate estimation of P excretion. Cattle are thought to excrete almost all P in feces. However, cattle on very high P diets saturate the fecal P excretion route and excrete an extensive proportion of P in urine. Future research should be directed at resolving deficiencies of current P nutritional recommendations and management to reduce environmental concerns.