Minerals and vitamins account for a very small proportion of daily intake in cow diets and can be overlooked due to misunderstanding the importance of adequate mineral nutrition and because of the cost of supplementation.
Beef cattle require at least 17 different minerals in their diets. Required minerals are classified as either macrominerals or microminerals based on the quantity required in the cows’ diet. Macrominerals include calcium, magnesium, phosphorous, potassium, sodium, chlorine and sulfur. Microminerals include chromium, cobalt, copper, iodine, iron, manganese, molybdenum, nickel, selenium and zinc. Mineral requirements vary depending on animal age, weight, stage of production, breed and stress level.
For the purposes of this article, we will be discussing minerals in terms of female beef animals and their needs during the specific range of just prior to calving through the breeding season.
As a general principle, when beef cows are grazing green forage during the summer months; unless a specific problem has been identified, a basic mineral supplementation strategy is more than adequate to meet mineral needs. However, once summer grazing begins to get excessively mature or pastures begin to run out and cows are moved to winter feed, adequate mineral nutrition becomes much more important. The importance of mineral nutrition during the critical stages of calving and breeding are due to the fact that not only are cows going through critical body composition changes due to calf development, lactation, and preparing to return to estrus, but they do all of this while generally being fed harvested forages of variable quality.
The biggest issue that practical nutrition for beef cows must address is mineral interactions. Minerals interact with each other in the body which can result in tying up or making other mineral elements unavailable. The interaction between calcium and phosphorous is a classic example of mineral interaction.
Calcium is the most abundant mineral in the body. Although calcium itself is rarely limiting in cow diets; maintaining an optimal 1.6:1 ratio of calcium to phosphorous in the diet may necessitate the need for supplemental calcium is some situations. Additionally, the lactation phase will increase calcium requirements of beef cows significantly, dictating the need for calcium supplementation if roughages do not supply enough.
Phosphorous needs in beef cow diets are often presented in terms of calcium to phosphorous ratio described earlier. Roughages are typically pretty low in phosphorous content, although they generally supply enough for most classes of beef cow. Drought conditions and very mature forages however, may have very low phosphorous concentrations suggesting the need for supplemental phosphorous in these situations.
In general, magnesium toxicity is not a problem in beef cattle as they can tolerate a lot of it. Magnesium deficiencies however are much more common and the results can be fatal, as with grass tetany. Heavy lactating cows on green, lush grass in the spring are most susceptible to magnesium deficiencies. Forage magnesium concentrations depend on species, soil, growth stage, season, and temperature. Legumes usually contain higher concentrations than grasses. Generally speaking, magnesium deficiencies in beef cattle are not common in Minnesota; although many producers do still make a high-magnesium mineral available to cows early in the grazing season; presumably as insurance against tetany.
Potassium is a critical mineral to the beef cow. Forages are good sources, often ranging from 1 to 4 percent potassium. Potassium content can be very high in lush pasture, potentially contributing to grass tetany. Mature and stockpiled forage contain lowered concentrations of potassium. In general, potassium supplementation of beef cows is not necessary beyond the basic oral mineral supplement.
Sodium and Chlorine
Sodium and chlorine (salt) are critical for beef cattle year-round. Cattle crave sodium and will consume more salt than needed when it is supplied free-choice. Some excess salt intake is not a problem so long as adequate water is available. Salt content of a preformulated mineral supplement is usually 10 to 25 percent of the supplement and many ranchers will provide additional loose salt to cows.
Sulfur in feedstuffs is found largely as a component of protein. In diets containing high levels of sorghum forage, mature forage, forages produced in sulfur-deficient soils, corn silage, rumen-bypass proteins, or if urea is used as a replacement for plant proteins; dietary sulfur supplementation may be increased.
Copper deficiency is best known in the cattle business for its effects on reproduction, particularly estrous cycle disruption. Copper deficiency is a widespread problem in U.S. beef herds. Additionally, copper is very susceptible to being tied up with a number of other elements in the body, namely molybdenum, sulfur, iron, and zinc, rendering copper unavailable for use by the body and the status of these elements in the body may affect copper requirements of the animal. Breed composition also affects copper requirements. Simmental and Charolais require more copper in the diet than do Angus. Copper supplementation may need to be increased by as much as 25 to 50 percent in these breeds. Forages vary widely in copper concentrations as well as concentrations of molybdenum, sulfur, iron, and zinc. Legumes typically contain higher copper concentrations than grasses. Copper is generally supplemented at 1250 ppm on a 4 oz. per day oral mineral.
Iron is a critical component of the mineral strata in beef cattle. Iron generally is not lacking in beef cattle diets, however, excessive iron can present problems. Iron depletes copper in beef cattle and can contribute to copper deficiency if copper supplementation levels are not adjusted to compensate for copper losses to iron.
Manganese is generally not a limited mineral as most forages contain adequate manganese concentrations. However, corn silage tends to be relatively low in manganese. Therefore, cows consuming corn silage as a high percentage of the diet on a dry matter basis may need to be supplemented manganese. Manganese is generally supplemented at 2000 ppm on a 4 oz. per day oral mineral.
Zinc plays an important role in immune system development and function. Zinc toxicities are not common but zinc deficiencies may impact reproductive performance and susceptibility to foot rot in some areas. Zinc concentrations in forages are very variable but generally speaking, zinc supplementation is recommended to maintain immune function. Zinc is generally supplemented at 4000 ppm on a 4 oz. per day oral mineral.
In light of all of this, it must be stated that nothing is more important than having roughages tested at fairly regular intervals throughout the winter to determine mineral availability in the diet and to ensure that your mineral package is meeting the cows’ needs for optimum production during this critical time. A good mineral and vitamin supplementation program costs between $30-$55/head/year; and with the average cost of running a cow in Minnesota nearing $900/cow/year, the mineral program is a relatively small investment. Additionally, strategic supplementation of the oral mineral program with an injectable mineral supplement may be advantageous for some at these very critical stages of production. Testing roughages regularly throughout the winter and consulting with a nutritionist to ensure you have the right mineral program for the cow herd will pay big dividends.
Visit https://extension.umn.edu/animals-and-livestock#beef or visit the University of Minnesota Beef Team on Facebook for more information.