A Fresh Look at Trace Mineral Nutrition
Minerals are an essential part of nutrition and good health in all animal species. Deficiencies in minerals can lead to a host of problems, ranging from poor skeletal development and growth to poor organ and immune functions. Minerals such as sodium and potassium affect electrolyte balance and are required for proper cellular metabolism. Calcium, phosphorus and magnesium are needed for both bone formation and muscle function.
Both macro and trace mineral nutrition for cows, calves and heifers have been widely researched for many years. For instance, calcium requirements and metabolism are fairly well understood, and limestone, which is abundant, is the mineral of choice to meet calcium requirements. Potassium is seldom deficient, because forages are loaded with it. Sodium and chloride needs are easily satisfied with plain salt.
Trace mineral requirements have been more difficult to pin down, due to the fact that only "traces" are needed. Over the years, zinc, manganese, copper, selenium and cobalt have received the most attention. Trace minerals are needed in many proteins and enzymes necessary for digestion and/or cellular functions. Copper is an important part of hemoglobin. Selenium is necessary for immune function. Most feedstuffs for animals, such as grains and forages, contain minimal amounts of trace minerals. In some cases cows may have deficiencies, which can lead to metabolic problems.
Here's one of the key questions about trace minerals: In what form should they be fed to cows and heifers? Researchers have coined the terms "inorganic trace minerals" (ITM) and "organic trace minerals" (OTM). For the most part, but not exclusively, ITM are joined to another ion or molecule, such as oxygen in the case of copper oxide or sodium in the case of sodium selenite. Calcium can be joined to a sulfate molecule.
The atomic and molecular bonding of some of these compounds prevents them from being easily or readily available to the cow's digestive system. In other cases, the bonds can easily be broken in the rumen, and the free mineral ions may adversely affect rumen microbes, disrupting rumen fermentation and slowing down dry matter intakes. It's also possible that the purity - and therefore the efficacy - of ITM can be an issue.
In certain cases, there is also the problem of antagonism amongst minerals. One of the classic antagonistic relationships in ruminant nutrition is that of copper, sulfur and molybdenum. Due to a complex interaction between sulfur and molybdenum in the rumen, copper is prevented from being absorbed. Even if a milk cow diet has been formulated to contain the theoretically correct level of copper, if there are large amounts of sulfur and molybdenum in the diet, very little of the copper will be absorbed, preventing enzyme synthesis and other functions that are critical to the cow's health.
Some years ago, scientists began combining zinc, copper, manganese and cobalt with amino acids and complex sugars called polysaccharides. These chelated minerals became known as OTM, due to the fact that they were bonded with organic compounds. They must still be created synthetically, however.
Research showed that OTM were more bioavailable at a more predictable rate, thus requiring less mineral supplementation in a cow's diet. The benefits of OTM are said to be improved milk production, immune function and reproductive performance, as well as lower somatic cell counts and better feed conversion, bone growth and fiber digestion.
Selenium-yeast products are also available for more efficient selenium absorption. A process that removes a sulfur ion from a yeast cell and replaces it with a selenium ion allows for reduced use of the inorganic selenium products. Care must be taken with selenium supplementation because of FDA regulation due to toxicity concerns.
Once again, because of the complexity of understanding trace mineral nutrition, it's often difficult to tell which products or combination of products is the most effective. Results for OTM over ITM have been variable and inconclusive in some trials. If nothing else, however, the introduction of OTM to the dairy industry has reduced the levels of wasted minerals finding their way into the environment. Many nutritionists recommend a combination of both OTM and ITM in dairy diets.
Most recently, a new category has emerged, called hydroxy trace minerals (HTM). The hydroxyl molecule (OH) offers stronger bonding with certain metal ions, allowing the complex to pass through the rumen without being degraded. The complex is then broken down in the abomasum, and the mineral moves on to the small intestine, where it's absorbed and metabolized. Zinc, manganese and copper versions of HTM are currently on the market.
A challenge with both organic and inorganic trace minerals is that they can be hygroscopic, meaning they absorb water, and oxidative, meaning they can react with fats and vitamins. When these types of minerals are added to high-moisture feeds, such as corn silage and haylage, they will dissolve away, possibly reacting with the acids and vitamins in the feed mix and rendering the entire mineral pack mostly useless. The hydroxy minerals are both nonhygroscopic and nonoxidative, meaning they will stay together in a high-moisture feed mixing environment, allowing them to be more confidently delivered to the digestive tract.
As both feed costs and environmental concerns continue to challenge the dairy industry, dairy farmers must remain on the lookout for more cost-effective and environmentally friendly ways to feed cows without wasting resources or leaving mineral residues behind. At the same time, the supplementation of trace minerals cannot be ignored, due to their critical importance in milk production, reproduction, growth, immunity and overall health. Science and research are showing us that there are sensible alternatives to using the old-style inorganic mineral compounds to provide trace minerals to dairy herds. Both OTM and HTM provide purer and more stable ways to meet trace mineral requirements for dairy cows and heifers.
Note: Some information for this article was taken from the 2013 Cornell Nutrition Conference proceedings.
The author is a dairy nutritional consultant and works for Central Connecticut Cooperative Farmers Association in Manchester, Conn.