Trace Mineral Programs and Pasture Quality

Abstract

Pasture and supplemental feed inputs represent the lion's share of a beef producer's annual expenses and are an ideal starting place for initiating hard-nosed cost control measures. When environmental variation is combined with ever-changing animal nutrient requirements and pasture quality indices, lower feed costs represent a moving target that can only be bull's-eyed with appropriate planning and constant evaluation. An excellent starting place for many operations intent on reducing production costs is an evaluation of the existing pasture mineral supplement program.
 An understanding of mineral nutrition requires a solid appreciation of the complexities and interactions which occur between the trace elements as affected by numerous factors (such as soil and environment) and conditions (animal and microbial requirements, ruminal conditions, etc.). Consequently, no class of nutrients has caused as great a confusion among beef producers as the trace minerals. The trace mineral levels found in many commercially available supplements today is a good case in point. Unfortunately, element levels in a mineral supplement are often used as a marketing tool and usually the higher the level, the better perceived the supplement is. Meeting 100% of the animal's requirement with no consideration for the contributions from the trace elements originating from the diet or grazed forage base could potentially lead to toxic levels that create more problems than was originally intended to solve.
 Practically every recent review of trace minerals has focused entirely upon animal requirements, trace mineral antagonisms, bioavailability and the subsequent effects of deficiency (or excess) upon immunity, reproduction and performance, with very little discussion of those factors which may potentially affect trace mineral content and variation in forages. The objectives of this paper are to: 1) define the function of trace minerals in plants and how they compare to animal requirements, 2) discuss the effects of forage quality on trace element content and forage intake, 3) discuss the factors which affect absorption of trace minerals by plants, and 4) review techniques for determination of whole plant mineral status.