Background
Everything was started before BC 8000-9000 by mankind who wanted to get 1-2lt cow`s milk which was produced only for her baby around mesopotamia (South East Turkey and around Syria) and North East Africa (in our century known as Sudan) . After that cattle became a tame animal followed by sheeps and goats and all other animals.

Animal Being Tamed
Civilization tried many different methods to increase daily milk production which was only 1-2kg at that time and to reach 2-3kg weight gain. Some of those methods were pure raising, relative raising, mixing the race, improved race mixed, combination of race mixed and rotated race mixed.

Importance of feeding animals
Advanced feeding and better caring for animals are essential as well as methods of domestication to increase animal production in any way (milk, meat, strength, wool)

Animals require extra nutrients such as energy, vitamin, mineral to increase 1 kg milk production or 1 kg weight gain or perfect fertility. Animals take most of the nutrients from feed. However, their mineral requirements always higher than feed.

Please see from the above table nutrient and minerals requirements of cows who produce 30-40 lt milk.

Why are trace elements important ?
Trace elements are essential components of an animal’s diet required for a range of metabolic and physiological processes. They are active role in synthesis of hormones and into the structure of some enzymes or check their functioning due to the amount of work in the ration (the animal's daily feed) must be found. Severe deficiency of one element can cause a clinical condition (e.g. Selenium and White muscle disease/muscular dystrophy; Copper and Swayback etc.). More often, the effect of a deficit is insidious, causing ill health and a loss of productivity, without obvious clinical symptoms. Marginal deficiencies affect variable numbers of stock from year-to-year. They are hard to predict and identify, but routine supplementation can be incorporated into the feeding plan. The principle of trace element nutrition should be one of prevention, rather than a response to evidence of a deficiency.