Animal Science, Department of
Department of Animal Science: Faculty Publications
Accessibility Remediation
If you are unable to use this item in its current form due to accessibility barriers, you may request remediation through our remediation request form.
Document Type
Article
Date of this Version
2004
Citation
The Professional Animal Scientist 20 (2004):319–329
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.