Cattle of all kinds – dairy and beef – as well as other ruminant species such as goats and sheep, have a host of metabolic functions that require trace minerals. Many are required for the immune system to function properly, some are required for the proper function of enzymes, while others are critical to proper cellular function and protein synthesis. Particularly for lactating cows with high milk production or close-up cows during the transition period, deficiencies in trace minerals can impact growth, health and reproduction.
The trace minerals that receive the most attention are copper, zinc, manganese, selenium, cobalt and iodine. Although the subject of trace minerals has received extensive study for many years and many of the functions of trace minerals are well documented, there are still many aspects of trace minerals that are poorly understood, such as the symbiotic relationships that they have with one another as well as with macro minerals such as calcium and potassium. For many years, the inorganic forms of trace minerals – those bound to sulfates and chlorides – have been fed to production and companion animals. Recently, researchers have found ways to combine trace minerals to organic molecules such as amino acids. These organic trace minerals are purported to be more bioavailable than inorganic forms.
The most active area of trace mineral research with animals involves their influence on the immune system. Trace minerals are crucial for the development of an adequate immune response in cattle, especially in stressed animals. Zinc, manganese, copper and selenium are important for optimal immune function and growth in cattle, particularly when stress levels are high. Zinc plays a crucial role in stabilizing cell membranes against reactive oxygen species (ROS) that cause inflammation and signal neutrophils (white blood cells) to fight against inflammation. Zinc also contributes to the structure and function of more than 2,500 enzyme systems involved in metabolism.
Selenium helps in preventing cellular damage by inactivating ROS. Cattle with deficiencies in zinc and selenium have shown depressed white blood cell activity during inflammation. Copper also plays a role in the neutralization of inflammation, contributing to the process of destroying invading organisms that destroy cells. Less is known about the role of manganese in supporting the immune system but has been identified as necessary for synthesis of cholesterol, estrogen, progesterone and testosterone.
Trace minerals are fundamental in the structure and function of several proteins that participate in processes involved in cellular expansion as well as energy production and DNA replication. Zinc and copper play central roles in how oxygen is transferred in the bloodstream. A host of enzymes are involved with energy transfer between cells. Cobalt is needed for synthesis of vitamin B12, which is a necessary part of energy metabolism along with red blood cell formation.
Balancing dairy diets for proper levels of trace minerals can be challenging due to large fluctuations of mineral content of feeds. Some trace minerals have a relatively large margin between amounts needed to meet requirements and maximum tolerable level. Copper and selenium, on the other hand, have small margins between meeting requirements and toxicity levels. Other trace minerals such as molybdenum will be antagonistic to copper, competing directly with copper and reducing its absorption. In addition, it’s recognized that some forms of inorganic trace minerals are not absorbed in the cow and are excreted through manure and urine, releasing these unneeded elements into the environment where they have no use.
Trace minerals fed in excess of requirements may not only impede absorption of other trace minerals, but they can also be toxic. However, due to the expense of trace minerals, over-feeding in cattle diets is seldom a problem. Care must be taken even when recommended levels are being added to diets because problems may occur if the water source on a dairy has a high level of a particular mineral, which again may cause toxicity or be antagonistic to other minerals. Copper, sulfur and molybdenum, due to their atomic similarities, can impede each other’s absorption. In regions of the country where molybdenum levels are known to be elevated, copper and sulfur must be increased. Copper can also be impeded in the presence of too much iron. Selenium and sulfur can also be antagonistic to each other. Care must be taken when there are known deficiencies in soils or excessive levels of a particular mineral in water.
Trace minerals complexed with amino acids or proteins have arrived in recent years to improve their bioavailability and reduce potential for environmental pollution. Zinc complexed with the amino acid, methionine, for instance, has proven to be highly effective in providing highly bioavailable levels of zinc. A number of trace minerals are now available from commercial sources that manufacture organically complexed trace mineral products. Copper, zinc, cobalt, manganese and selenium can be purchased in complexed forms.
Research has confirmed that organically complexed trace minerals are less affected by antagonistic trace minerals. The difference in absorption and bioavailability between an inorganic form of a trace mineral compared with an organic complex is minimal when presence of other antagonist minerals is low. However, when presence of antagonists is high, organic complexes appear to have an advantage in being more highly bioavailable.
It’s widely accepted that organic complexes of trace minerals are more absorbable than their inorganic cousins – sulfates, oxides and chlorides. This makes it possible to use less trace minerals in a cow’s diet to accomplish the same effect. Due to the high cost of many inorganic trace minerals, it’s recommended that dairy diets contain a combination of inorganic and organic trace mineral sources.
By feeding a combination of organic and inorganic trace minerals nutritionist and dairy farmers will be able to meet the trace mineral requirements of their cattle when dietary levels of antagonist are high as well as when the animal is stressed. Trace mineral levels in animal waste will be reduced, risk of mineral toxicity will be reduced and animal health, growth and milk production will be improved.