Mineral Minutes: How much copper do I need in my free choice mineral?

The copper content of forages is usually insufficient to meet needs, and there are often other minerals that interfere with the absorption of copper. Molybdenum and sulfur are two minerals that act as antagonists, tying up copper and making it unavailable to the animal. This means that only looking at the copper content in the forage will not give you an accurate understanding of the amount of available copper or how much supplemental copper is needed. One must also look at the sulfur and molybdenum content as well. Although variable, vegetative pasture in North Western NE, the Sandhills, and South Central NE, contains enough sulfur and molybdenum to make the majority (95%) of copper in pasture unavailable for absorption. Thus at a minimum, supplementation of the full requirement (1300 ppm in a 4 oz. mineral) is often needed to meet needs. In Eastern NE, the Mo content of vegetative pasture appears to be less resulting in 65 to 90% of the requirement needing to be supplemented (1000-1200 ppm in a 4 oz mineral). There can be significant variation in mineral content of forages by location and management thus testing can be beneficial to refine supplementation. One should also keep in mind that water can also be a source of sulfur and if the water source is high in sulfate then additional supplemental copper will be needed. Due to the higher sulfur content of distillers and corn condensed distillers solubles (often called syrup) extra copper may also be needed when feeding diets containing significant amounts of these products. In high sulfur and molybdenum situations a 4 oz. mineral may need to contain up to 2500 ppm of Cu.
Thanks to the Iowa Beef Industry Council for sponsoring this series!