Mineral Nutrition Vital for Summer Cattle Grazing Programs
Required minerals for livestock are classified into two general groups: micro- and macro- minerals, based on the quantity required. Macrominerals such as calcium, magnesium, phosphorus, potassium, sodium and sulfur are required at greater levels in the diet. Microminerals 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.”
Participants in an NDSU and South Dakota State University Extension program titled “Mineral Nutrition for Livestock Producers” collected approximately 50 forage samples during the 2017 and 2018 growing seasons. These samples were sent to a certified laboratory for mineral analyses.
Results showed that nearly all of the samples were deficient in copper (less than 10 parts per million [ppm]). Less than 20% of the samples contained enough zinc to meet requirements (30 ppm). More than 98% of the samples would meet calcium requirements for lactating cows (recommended levels of 0.28% to 0.58%); however, only 8% of the samples would meet phosphorus requirements (recommended levels of 0.22% to 0.39%).
In addition to mineral deficiencies, forages can contain excess levels of certain minerals that may reduce the availability of other minerals to the animal when present in high amounts. Iron levels greater than 250 ppm, the level at which iron can interfere with copper availability, were found in 45% of the samples submitted through the mineral program. More than 12% of the samples contained potentially toxic levels of iron (greater than 500 ppm). Molybdenum, another potential copper antagonist, was found at levels greater than 2 ppm in 60% of the samples.
Although not an extensive data set, these numbers indicate several mineral deficiencies and antagonists that could impact livestock production and performance if producers don’t provide proper supplementation.
Get Your Forage Tested
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
“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.
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.