Articles on forages, animals, and grazing systems
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Extension Forage Specialist
University of Kentucky
Phone: (859) 257-3358
Fax: (859) 323-1952
Grazing livestock require many different nutrients to support growth, milk production, and body tissue maintenance. Often minerals are separated into two categories. The minerals that are required in relatively large amounts are called major or macro minerals. These minerals are often listed on feed tags with a percentage sign following them. Those needed in lesser amounts are called micro, minor, or trace minerals and usually listed in parts per million (ppm).
These terms have no relationship to the metabolic importance of the specific mineral in the diet. A trace mineral can be just as important to health and performance of an animal as a macro mineral. Factors that influence the amount of specific minerals that cattle need include age, rate of growth, stage of pregnancy, and stage and level of lactation.
The essential macro minerals for beef cattle are calcium, phosphorus, chlorine, magnesium, potassium, sodium, and sulfur. The trace minerals that are needed are copper, chromium, cobalt, iodine, iron, manganese, nickel, molybdenum, selenium, and zinc. The above minerals may function as structural components of bones and teeth, electrolytes in body fluids, metabolism of nutrients, nerve conduction, reproduction, immune response, and many more functions.
Various body functions require different amounts of minerals. The daily intake of trace minerals needed for maximum immune response is greater than the amount required for optimal growth or reproduction. Cattle can have sufficient trace mineral intake to support optimal growth or reproduction. However, cattle may not consume adequate trace minerals for maximum immune function. Intake and absorption of minerals must be adequate to meet all the animal's body functions.
Although many factors affect the intake and absorption of minerals by cattle, a major factor is the mineral content of the forages they consume. The first step in developing a mineral supplementation program is to determine the feed or forage mineral content. It is important to understand that the bioavailability of minerals from forages may be low. As a general rule when figuring mineral values in forages, the suggested usefulness should be divided in half to account for potentially low bioavailability. For example if a forage has a concentration of 0.2% of X mineral, the amount of mineral absorbed would be 0.1%. Mineral supplements are calculated making adjustments for the bioavailability of the sources.
Producers should always read the mineral product label. Key things to note: target species (beef cattle, dairy cattle, etc.), mineral levels (percentage or ppm), target intake (ounces per day), feeding method (free-choice or mixing), and the ingredients or source of the minerals. Because a min-eral’s source greatly influ-ences absorption or bioavaila-bility, mineral supplements must contain sources of high bioavailability. The levels listed on the feed tag as well as the targeted intake must then be considered. There can be various mineral mix-tures with both different min-eral levels and intakes. The supplement should provide adequate intake of the vari-ous minerals to balance the supply from the forage and the animal’s needs while also being cost effective.
For further information about minerals and their functions see: Trace Mineral Supple-mentation for Kentucky Beef Cattle publication available at your local extension office or online at http://www2.ca.uky.edu/agc/pubs/asc/asc155/asc155.pdf.