NDSU Extension - Mercer County


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Mineral Nutrition Vital for Summer Cattle Grazing Programs

mineral nutrition, summer grazing programs

Submitted by Craig Askim, Extension Agent/Agriculture and Natural Resources

The grazing season across the county has been up and down for grass development this season. Some pasture nutrient levels are very low so a supplementation program of minerals will be needed to make sure animals are gaining weight and producing correctly. Cheating on nutrients in the summer months can cause problems such as cows not coming into heat or being open.

Proper mineral nutrition is important for optimal cattle reproductive performance, milk production, calf weight gain and a strong immune system, according to Janna Block, North Dakota State University Extension livestock specialist at the Hettinger Research Extension Center.

Required minerals for livestock are classified into two general groups: micro- and macro- minerals, based on the quantity required. Macro-minerals such as calcium, magnesium, phosphorus, potassium, sodium and sulfur are required at greater levels in the diet. Micro-minerals are needed in smaller amounts but still are important. These include cobalt, copper, iodine, iron, manganese, molybdenum, selenium and zinc.

"Forages are typically the primary mineral source for grazing livestock," Block says. "However, forages often miss the mark in meeting all mineral requirements, even during peak forage growth, when protein and energy content are high.

Commercial mineral supplements are commonly provided to make up deficiencies; however, finding the right product for a given situation is not an easy task."

Mineral Content Varies

The mineral content of forages across an individual ranch or even within a pasture can vary based on plant species, stage of maturity, soil characteristics, precipitation and other factors. Providing appropriate mineral supplements is further complicated by changing cattle requirements due to their stage and level of production, and the potential for interactions among minerals and other nutrients that may impact availability within the animal.

A large number and variety of commercial mineral products are available. Most are formulated for a certain stage of production or time of year and sometimes for a specific geographical area.

"However, these products may not be a good fit for every situation due to the factors described above," Block says. "Although it may seem like a daunting task, the best way to determine the mineral needs for an individual ranch involves testing forages, feeds and water for mineral content."

Sampling standing forage can be challenging due to the variation in species and topography in a pasture. To get an accurate representation of forages that cattle are consuming, samples should be collected in areas where cattle have been grazing for several days to a few weeks.

Select small handfuls of ungrazed plants in areas next to grazed plants. Wrap fingers tightly around the top portion of the forage and pull. Try to take grab samples that are similar in height to grazed forages.

Samples also could be clipped. However, the idea is to try to mimic grazing, and livestock do not clip all plants to the same height. Be sure to collect samples throughout the pasture to account for variation in soils types and forage species.

The mineral content of forages changes throughout the growing season. Therefore, collecting samples corresponding to peak standing crop and dormancy at a minimum would be valuable.

Standing forage samples should be air-dried before shipping to a certified laboratory. Most labs offer a package analysis that includes key minerals at a cost of about $20 to $40. Cobalt and selenium require separate analyses at an additional cost. Include crude protein and some estimate of energy (total digestible nutrients) when submitting samples to further quantify forage quality.

"Laboratory analysis of feed and water will provide an indication of the minerals available to grazing cattle," Block says. "It does not account for biological availability within the animal, which is the amount of mineral that livestock can absorb and utilize from the digestive tract."

Mineral bioavailability depends on multiple factors in the animal (stress, production level, age, breed, environment, etc.), as well as the solubility of the mineral and the presence of antagonists in the diet. In general, bioavailability of minerals in forages is assumed to be around 50%. This is an important consideration when evaluating mineral supplementation programs.

"The process of sampling and measuring mineral content is time and labor intensive," Block says. "However, it offers the potential to improve livestock performance and reduce costs by allowing producers to choose the correct mineral formulation to complement what animals are consuming and meet requirements."

She recommends additional testing of harvested forages and supplements because the amount of mineral supplied and required will change throughout the production cycle.

"Mineral nutrition is a complex issue, and there is no one solution for every operation," she adds.

For more information about evaluating your mineral program, contact your NDSU Extension county office.

Source: Janna Block, 701-567-4323, janna.block@ndsu.edu

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