Mineral dynamics in beef cattle diets from a southern mixed-grass prairie.

Abstract

Acute and chronic dietary deficiencies in macro and micro minerals have significant impacts on production efficiency on rangelands throughout the world. However, limited information is available on the mineral quality of diets primarily because salivary and soil mineral contamination of esophageal extrusa precludes quantitative recovery of dietary minerals. Mineral profiles of diets can be estimated indirectly, however, if forage species composition of diets and mineral concentrations of selected forages are known. The objective of this study was to utilize this approach to estimate seasonal dynamics of phosphorus (P), calcium (Ca), potassium (K), and magnesium (Mg) in cattle diets' relative requirements. Two diet selection scenarios were developed: the first, maximum mineral intake, assumed cattle consumed only live plant tissue of a forage if it was available; the second, considered minimum mineral intake, assumed cattle consumed live and dead tissue in direct proportion to their availability. Calculated concentrations of P and Ca in diets showed P concentrations were below and Ca concentrations were above their respective requirements for spring calving cows regardless of selection scenario or season of the year. However, K and Mg concentrations varied as a function of selection scenario and season of year and ranged from adequate during periods of rapid vegetation growth to marginally inadequate during periods of water (drought) or temperature (winter) induced dormancy.