Mineral Nutrition in the Cow: Macro Minerals and Their Importance

Mineral Nutrition & Cow Performance
Mineral nutrition is vital to overall cow performance. Without appropriate balance of minerals, cows may not perform as desired or could exhibit detrimental effects. There is value in analyzing your mineral program to determine if modifications need to be made to improve cattle health and performance.

Minerals are divided into two groups based on the quantity of the mineral required by the cow: macro minerals and micro minerals (trace minerals). The macro minerals are required as a percent of the diet dry matter, while micro minerals or trace minerals are required in ppm (parts per million). This article will focus on macro minerals.

About Macrominerals
There are seven macro minerals that need to be analyzed and balanced within a cow’s diet. These are calcium (Ca), phosphorus (P), magnesium (Mg), sulfur (S), sodium (Na), chlorine (Cl) and potassium (K). Some of these minerals work together, while others work independently.

Calcium & Phosphorus
Calcium and P are two minerals that work hand in hand. These are the main mineral constituents in bone. In addition to their role in bone development, Ca is also important in muscle function and P plays key roles in metabolic functions throughout the body. In general, grazing cattle will have adequate Ca in forages, especially legumes such as alfalfa. On the other hand, P can be deficient in these forages and supplemental P is generally needed in forage-based diets, but how much? The key is to sample and test forages to determine mineral content and select a mineral to meet the cow’s needs. It is relatively easy to meet the requirements for Ca and P, but there is also value in ensuring the proper Ca:P ratio. The optimum Ca:P ratio based on extensive research is 1.5:1 to 2:1. The requirements for Ca and P change with animal age and stage of production. The Ca requirement for lactating cows is 0.27% and P is 0.23% of the diet dry matter. These requirements decrease in non-lactating cows.

Magnesium
Magnesium is required at 0.2% of the diet dry matter for lactating cows and only 0.12% for gestating cows. Magnesium plays a role in enzyme and nervous system function, as well as carbohydrate metabolism. It is critical that cows receive sufficient Mg when they are lactating heavily, especially grazing lush, rapidly growing pastures. Oftentimes these pastures have excess K, which inhibits Mg absorption in both the plant and animal. A high Mg mineral (8-13% Mg) should be provided to lactating cows two to four weeks prior to turn out on rapidly growing grass, to increase Mg intake to 0.25% of diet dry matter.

Sulfur
Sulfur is not typically thought to be necessary in mineral supplements, but conversely how it can cause toxicity. Sulfur is necessary in the diet for the rumen microorganisms to form sulfur-containing amino acids. There are multiple sources of S and some of these can result in toxicity, specifically high sulfate water in western South Dakota. Research conducted at the Cottonwood Range and Livestock Field Station shows that excess sulfates in water can cause polioencephalomalacia (PEM or polio) in cattle. Symptoms include blindness, difficulty walking, muscle tremors, convulsions and ultimately death. Cattle on pasture require 0.15% sulfur, but forages and water should be tested prior to adding sulfur to a mineral supplement.

Sodium & Chlorine
Sodium and chlorine work together to maintain cellular volume, pH and osmolarity of body fluids. Sodium chloride (NaCl, salt) promotes water intake. Sodium plays a role with K for nutrient transport into and out of cells and Cl is involved primarily in the production of hydrochloric acid in the abomasum (stomach) to aid in digestion. A 1300 lb cow will consume between 1 and 2 ounces of salt per day to meet requirements.

Potassium
As mentioned previously, K works with Na in the body to regulate osmotic pressure and transport nutrients in and out of cells. As the K levels increase, the Na levels will need to increase equally. Through forage analysis, K levels are adequate in most of western South Dakota. Potassium will leach out of dormant forages, therefore it may be necessary to provide a mineral supplement that contains 1% K to remedy any deficiencies.

The Bottom Line
Mineral nutrition and balance is key to animal performance and productivity. Take time to evaluate your mineral program and determine if the supplements you are using are meeting the needs of your cattle. It is often stated that a mineral is formulated for a region, but there can be significant variations in minerals from one side of your ranch to the other. It might be valuable for you to sample your forages and get a better understanding of what minerals are available in your forage and what needs to be provided in the form of a supplement.

Source: Adele Harty, South Dakota State University, iGrow