The role of minerals in animal health
10/06/2011 12:00:00 AM
Dr Colin Trengove
Minerals have an essential role in livestock diets and mineral deficiencies can have devastating consequences on animal and human health.
Minerals have three major roles in animals. They:
- Provide structural material to bones and connective tissue;
- Allow electrical impulses to be transmitted across nerves;
- Act as catalysts involved in the numerous physiological processes such as DNA replication, digestion, immune function, endocrine synthesis, neurological activity, energy storage and release, muscle contraction and numerous other functions.
As a consequence, mineral deficiencies can have devastating consequences on animal and human health. For example, magnesium alone is responsible for 100 enzymatic reactions in the human body. Zinc accounts for another 200 and a deficiency of only these two minerals can account for 300 physiological malfunctions.
The availability of nutrients in appropriate quantities is a major factor determining the health of grazing livestock, but is often poorly understood or appreciated. At least 15 minerals are essential to animals. The major elements obtained from the atmosphere are carbon (C), hydrogen (H), oxygen (O) and nitrogen (N). The major nutrients obtained from the soil are calcium (Ca), chlorine (Cl), phosphorus (P), magnesium (Mg), potassium (K), sodium (Na), and sulphur (S). Essential trace elements obtained from the soil include cobalt (Co), copper (Cu), iron (Fe), iodine (I), manganese (Mn), selenium (Se), zinc (Zn) and molybdenum (Mo).
Minerals in plant and animal health
Most of the 16 nutrients are regarded as essential for plants and animals. Animals have an additional requirement for iodine (I2) and fluorine (F). Most plants have little or no requirement for Na, Cl, Se, I and Co – except for the Co required by rhizobia for N fixation. Plants have a higher requirement for K, Fe and Ca (legumes) and a lower requirement for Cu than animals. Other mineral requirements are similar which means that both pasture and animals can benefit from these nutrients applied as solid or foliar fertiliser.
The critical nutrient levels for plant growth are sometimes lower than the minimum levels required for animal diets. It is therefore possible for plants to be growing perfectly normally, but to contain suboptimal levels of nutrients for grazing livestock. Conversely, high levels of certain nutrients in plants, for example Mo, Se, nitrite (NO2) and nitrate (NO3) can be toxic to animals without harming plant growth.
Investigation of production and disease
Advisors to the grazing industry are often only consulted when livestock production is already compromised and then focus on blood analysis for Cu, Co, Se and sometimes Zn to examine mineral intake. The commonly recognised mineral deficiencies and disease syndromes in livestock at pasture are associated with the major elements Ca, P, Mg, Na, S and trace elements Co, Cu, I, Mn, Se and Zn. Excessive intake of minerals such as Cu, Mo, Fe, S, Na, Se and fluorine (F) can also affect livestock productivity as much as deficiency in these minerals.
Comprehensive soil and pasture tests are available that provide an estimate of the availability of the 15 essential nutrients in the diet. The nutrition of grazing animals is a complicated interaction of soil, plant and animal. An example is if Cu deficiency is present in livestock, but pasture Cu is high (> 10ppm DM), there is no benefit in applying Cu as fertiliser as an antagonism with Mo, S or Fe must be occurring. Direct Cu supplementation to the animal is indicated in this instance. Alternatively, Cu fertiliser may be the cheapest and most effective option to treat Cu deficiency in livestock if pasture Cu is relatively low (< 7 ppm DM). In practice if the pasture Cu:Mo ratio is above 3:1, then livestock are not at risk to Cu deficiency.
Macro and trace elements provided in a balanced diet are fundamental to livestock health and productivity. The most comprehensive approach to herd production & preventative health will include the use of soil and plant analyses as a means of monitoring these nutrients in conjunction with tests on blood, liver, milk, urine, faeces, grains, conserved feeds and water as appropriate. The livestock owner and consultant equipped with this information as well as their knowledge of season, pasture availability, grazing management and the class of stock is then able to make strategic production and management decisions with a high degree of confidence.