The level of minerals and vitamins in free-choice minerals for grazing livestock should be determined based on the following guiding principles:

Macro minerals:

• The level of P and Ca should be sufficient to avoid deficiency of these minerals. You can possibly completely refrain from supplementing with phosphorus, especially if environmental regulations require a restrictive use of phosphorus.
• The level of magnesium (Mg) should be enough to avoid grass tetany, wherefore higher contents are recommended in spring and autumn, or in other periods with low availability of magnesium.
• The level of sodium (Na) should be around 12.5% in order to ensure the control with the intake of the mineral supplement - that the animals will consume it in envisaged amounts and at the same time avoid excessive intake. Each gram of sodium is passively followed by 1.5 gram chlorine (anticipating the sodium source is normal salt - NaCl)
• The need for sulfur (S) is a gray-zone, and it is therefore neither to find exact feeding recommendations nor declared contents in mineral supplements.

Micro minerals:

• The level of trace elements should comply with the total daily needs of the animals, as body stores are practically non-existing and as the content in grass is know to be in-sufficient or in any case is unreliable.
• An exception from the above mentioned is iron (Fe), which with a high degree of certainty are found in sufficient amounts in grass, and Cu, Mn and Zn, which to some degree are found in sufficient amounts in grass.
• As some sheep breeds are especially sensitive to Cu and because the toxic level is so close to the requirement it is normally not recommended to supplement sheep with additional Cu.

Vitamins:

Grazing ruminants have no need for additional vitamins as

• they are able to convert the high content of carotene in grass and other green crops to Vitamin A;
• Vitamin D is formed in the skin of animals when the sun shines on it (due to UV-radiation of the skin); and
• there is a high content of Vitamin E in grass and other green crops.

Conclusion

In compliance with with these principles, mineral supplementation of grazing livestock - i.e. livestock without access to to other feed than grass - should as a minimum cover a percentage of the total feeding standards for mineral requirements according the table:

The difference for cattle/horses and sheep is due to the fact that sheep normally graze more marginalized areas with more atypical soil types than cattle, and because the grazing period typically is longer for sheep than for cattle and horses.

It is an elementory fact that dairy cows uses their body as an energy storage. Changes in body weight and the associated body condition scoring shows that dairy cows typically looses 10% of their body weight in the period from about 3 weeks before calving and until 3 months after calving (in addition to the weight of the fetus).

Using simple mathematics, this body weight loss can be recalculated into an average gap between feed need and feed intake of 20% for the entire period of about 100-120 days, or one third of the lactation cycle. The mentioned 20% may be 30-40% in the middle of this period, that we call the critical transition period.

The cows' metabolic ability to deposit and mobilise energy from their body, in the form of body fat, is however, to a much lower extent the case for other nutrients, including minerals, vitamins and aminoacids (protein). The skeleton and other body tissues acts to some extent as a labile storage for macro minerals, including Ca, P and Mg. However, for microminerals, mammals do not have noteworthy body stores and are dependent on stable and frequent, if not daily, supply.

Microminerals are pivotal for immune status, which again is essential for the incidence rate of diseases and for the fertility. Hence, dairy cows welfare is to a large extent dependent on a sufficient and stable intake of vitamins and minerals, expecially microminerals.

"Dairy cows should be given an extra offer of mineral feeds in the critical transition period, indicatively complying to averagely 20% of their feeding requirements for minerals and vitamins, to cover the gap between feed intake and feed need!"

It is good dairy management to ensure dairy cows extra mineral feeds in the critical transition period, and in this way to lift the herd standard compared to the general statistics that in an unmistaken way documents that disease incidences and mortality rates are far too high in this period, where, in addition, much too many cows are culled.

The need for giving dairy cows access to extra mineral feeds in the critical transition period is evident, as mentioned above. However, the use of mineral feeders for housed livestock is advantageous in any situation:

• Animals are individuals and although it is normal to group animals according age and size etc., they are never identical, and it must also be realising that the genetic productivity potential of animals in a group also is different. Giving access to extra mineral feed supplements ensures that the standard feeding of the group does not become a limiting barrier for the individual animals productivity or health.
• Saving labour: Giving mineral feed supplements as top-dressing is an extra time-consuming work routine, that can be avoided by offering free-choice mineral feed supplements in mineral feeders.
• Changed needs due to weather shifts or other are automatically adjusted by the animals themselves if they are offered free-choice mineral feed supplements in mineral feeders. A typical example is that the need for salt follows the temperature, which a standardised feeding, based on a feeding plan, does not take into consideration, and the result can be heat stress.

It is due to the large importance of minerals and vitamins for livestocks productivity, health and fertility always recommended to ensure they have an extra possibility to get their individual needs fulfilled via access to extra mineral feed supplements via mineral feeders. Mineral feeders gives possibility to use the cheapest and physiologically best types of mineral feed supplements, and they ensure that the supplements are kept clean and dry and not being polluted with dung and urine.