Cow Mineral Nutrition: Macro Minerals and Their Importance

By: Adele Harty, SDSU Extension Cow/Calf Field Specialist

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 Macro Minerals
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 AND 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 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 a 1400 lb lactating cows is 0.30% and P is 0.20% of the diet dry matter. These requirements decrease in non-lactating cows.

MAGNESIUM
Magnesium is required at 0.20% of the diet dry matter for lactating cows and 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 if they are 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 onto rapidly growing grass, to increase Mg intake to 0.25% of diet dry matter and prevent grass tetany.

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 SDSU Cottonwood 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. Many forages contain adequate sulfur to meet requirements and there is sulfur in the water, it will have an additive effect. If sulfur levels in the total diet exceed 0.30%, cattle can start to experience negative effects on health and performance.

SODIUM AND 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. Cattle have a taste for salt and a 1400 lb cow will consume between 1 and 2 ounces of salt per day to meet requirements. Various factors affect salt intake and it is key to have plenty of fresh water available at all times.

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, with the 1400 lb lactating cow having a requirement of 0.70% of diet dry matter and most forages samples having close to 2% K. 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. There is great value in sampling forages when cattle care grazing them to get a better understanding of what minerals are available in the forage. Water also plays an important role in mineral status, so sampling water is important when determining what needs to be provided in the form of a supplement.

For more information on mineral programs or custom mineral formulations for your ranch, contact Adele Harty at 605-394-1722.

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