Re-evaluation of Phosphorus Requirements and Phosphorus Retention of Feedlot Cattle |
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| Institution: | 2. University of Idaho Custer County Extension, Challis 83226;3. University of Idaho Idaho County Extension, Grangeville 83350;4. University of Idaho Bannock/Bingham County Extension, Blackfoot 83221;6. University of Idaho Owyhee County Extension, Marsing 83639;5. University of Idaho Lehmi County Extension, Salmon 83467;11. Furst-McNess Company, Rexburg, ID 83440;12. Micronutrients USA LLC, Jerome, ID 83338 |
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| Abstract: | Phosphorus requirement recommendations for cattle are important for preventing over-feeding of P and excessive P excretion. Improved precision in managing P nutrition can reduce feedlot waste management concerns. Current beef recommendations (NRC, 1996) fail to account for absorption coefficient variation related to P source, whereas dairy recommendations (NRC, 2001) change absorption coefficients with P source. Maintenance and BW gain requirements for absorbed P do not represent underlying relationships. Maintenance P requirements reflect endogenous P loss arising from failure to reabsorb salivary P. Basing maintenance requirements on saliva P secretion and re-absorption rates should improve precision of maintenance requirement estimates. Gain requirement recommendations are from limited body composition data and relate P requirements to protein retention. However, metabolism and BW gain studies show uncoupled N and P retention. With extensive deposition of body P into skeletal tissues, basing gain requirements on skeletal 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. |
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