Minerals are necessary for the formation of cells and the correct functioning of vital organs. The mineral requirements of dairy cows can be divided between (a) macro- minerals, needed in greater quantities (Ca calcium, P phosphorus, Mg magnesium, Na, sodium, Cl chlorine, K potassium and S sulphur); and (b) micro-minerals  which they need in smaller quantities (Co cobalt, Cu copper, I iodine, Fe iron, Mn manganese, Se selenium and Zn zinc). The most important macro minerals for dairy cows are sodium chloride (NaCl, common salt), calcium (Ca), phosphorus (P).

Mineral deficiencies or imbalances in fodder can cause different health, reproductive and metabolic disorders, all of which have a negative effect on productivity. Calcium and phosphorus act together with vitamin D in bone formation. A deficiency in magnesium (hypomagnesemia or grass tetany) causes a fall in production, muscular tremors and general unquiet in cows. Sodium deficiency causes a loss in appetite due to dehydration and lower production.

Copper is essential for various metabolic processes (metabolism: two conjugated processes (a) catabolism which liberates energy and (b) anabolism which uses such energy to create, for example, proteins) and when lacking animals suffer diarrhoea, unhealthy condition and their hair becomes coarse. Cobalt is an essential component of vitamin B12 and when lacking growth rates and production fall. Iodine intervenes in growth as it forms part of the thyroid hormone and, thus, has an impact on milk production. A deficiency of iodine causes goitres (enlargement of the thyroid gland), miscarriages and weak offspring. Selenium is important for reproduction and, with vitamin E, prevents formation of soft tissue. A deficiency of selenium leads to lower rates of fertility.

Examples of the mineral requirements of dairy cows*:

(i)    as % and parts per thousand (ppt) of dry matter

*     Average values are given for the reasons given above.
**   60% sown grasses, 10% Leguminosea, 30% spontaneous species

(ii) in terms of daily requirements (grams)

Again, the aim is to identify those plants in each farm’s pastureland (for grazing or as silage, hay or fresh grass) that jointly satisfy these mineral requirements. The main plants in pasturelands are grasses (Gramineae) and  those of the pea family (Leguminosae). The average mineral content of these groups of plants is:

* 60% sown grasses, 10% leguminosae, 30% spontaneous species

Examples of different types of forages:  (g/kg)

Cows on the Vista Alegre farm eating fresh grass and clover forage


It is worth noting the deficiencies that may exist in a given field (natural or sown) if not all the necessary species are present. When deficiencies are observed, such as the lack of magnesium (Mg), copper (Cu) and selenium (Se) in the pastures analysed in the Table above, they can be corrected by introducing the relevant species. Thus, members of the pea family (Leguminosae) help balance some of the deficiencies of grasses: for example, white clover has a relatively high selenium content. Other species from other families also contribute mineral elements, although in lower quantities: dandelions (Taraxacum officinale) contain calcium, iron, sulphur, manganese, magnesium, phosphorous and potassium salts; plantains (Plantago sp.) contain calcium; shepherd’s purse (Capsella bursa-pastoris) contributes iron, calcium, potassium and  phosphorus; chickweed (Stellaria media) contains copper, iron, phosphorus, calcium and potassium; and fat hen (Chenopodium alba) contributes iron, calcium, phosphorus and potassium. These plants can be found to a greater or lesser degree in grazing lands and cows only graze them occasionally. In fact, although cows may sometimes graze them, if some species are consumed in large quantities part of their content could cause health problems in cows

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