Although minerals only account for about 5% of total ruminant nutrition they have a disproportionate role in supporting energy and protein yielding nutrients required to maintain animal health, fertility and production. Of the ninety two naturally occurring minerals in the earth’s crust, around twenty are considered to be essential for life, with fifteen described as mineral elements. To be classified as a mineral element it has to be an essential nutrient included in skeletal development, water balance, catalysing metabolic processes and cell division necessary for growth and development. In short, mineral elements can be considered to be rather like the “governor” that controls the speed of a steam engine. When minerals are in short supply the “governor” is retarded and the engine fails to operate at maximum efficiency, and so it is with livestock. The other concept important to mineral nutrition is the relationship or “balance” between elements. In terms of animal production, balancing minerals is as critical to ensuring satisfactory outcomes as overall dietary intake.
Forages exert a significant influence on the mineral composition of ruminant diets. Consequently a knowledge of the mineral status of forages is necessary when formulating balancing concentrates and supplements. This
is particularly important when grass or silage is the primary forage, due to the high variability in mineral status. Grass is a remarkable plant in that it will take up any mineral element from the soil which is in a soluble state whether it needs it or not. This action is much less pronounced in alternative forages such as maize and wholecrop silage. However, the starting point in determining forage mineral status is an analysis report, as shown here.
Forage Mineral Report
The report presents forage mineral analysis data divided into seven major minerals (calcium, phosphorus, magnesium, potassium, sodium, chloride and sulphur) and eight trace elements (manganese, copper, zinc, cobalt, iodine, selenium, iron and molybdenum). The classification of essential minerals as either “major” or “trace” is dependent on how much is needed by the animal. Major minerals are
expressed in percentages and trace elements in mg/kg. The scale of the difference between “major” and “trace” minerals is illustrated by the fact that calcium is 100,000 times higher than selenium. In addition to the fifteen essential minerals the report also includes:
- Cation-anion balance which is important for determining how much water a cow drinks and the efficiency with which
it is transferred into milk. It also provides an indication of the optimal balance between the electrolyte elements
(potassium, sodium, chloride and sulphur) which isis important for both minimising hypocalcaemia (milk fever) in
the cow at calving and also ensuring the right conditions are in place to support milk production.
- Boron is on the waiting list of being accepted as an essential trace element. While essentiality has been demonstrated in plants, no evidence has been published to show its role in farm livestock although work is in progress.
- Aluminium is included primarily as a marker for soil consumption. While not essential for cows, a high level can be potentially damaging to cow health.
- Lead is a potentially toxic element which can disrupt ruminant health and production. It tends to be an issue in those parts of the country where lead mining had historically
occurred including parts of Wales, Cumbria, Derbyshire and Cornwall.
- Relative copper antagonism is an indication of the extent to which those minerals that can “lock up” copper, such as molybdenum, iron and sulphur, combine to suppress copper uptake. This measure cannot be used for
formulation purposes but does provide a measure of the “risk” of copper “lock up”.
- Soil Contamination Index, as the name suggests, reports the level of soil that has been picked up when grass has been cut and harvested. This Index is determined by measuring titanium; which is a non-essential mineral incapable of being absorbed by the roots. Actions to minimise soil contamination of forages is important as soil can interfere with silage fermentation and introduce high levels of iron and aluminium that can be adverse to animal health.
Why have a Forage Mineral Report?
Balancing diets for minerals is as important as ensuring major nutrients (starch, protein, fats, etc.) are meeting dietary specifications. Having a Forage Mineral Report is the starting point for providing information on:
- Formulating balancing mineral supplements using a mineral formulation program, which incorporates standard mineral values for alternative forages, feed
materials and concentrates
- Determining the “pressure” on copper availability from antagonists (molybdenum, iron and sulphur), which can be incorporated into a formulation program
- Establishing the “balance” between key elements including:
• Calcium : phosphorus – important for energy utilisation
and bone development
• Potassium : magnesium – crucial for nervous health
and animal contentment
• Potassium : sodium – essential for water balance and
- How well balanced the fertiliser regime is; grass reflects lime and fertiliser levels in soil over the course of a growing season and can highlight the need for soil testing
- How healthy the soil is; soil fertility, not only measured in available nutrient levels but also in terms of biological life, is a key influencing factor in providing a sufficient and
balanced nutrient supply. When soil life is compromised by severe compaction, conditions change in the soil which allows more iron and molybdenum to be taken up. Both these elements increase “oxidative stress” in
cattle together with reducing the absorption of copper and other elements.
- What the degree of soil contamination is: as already stated, the presence of soil in silage is not desirable either from a fermentation perspective or increasing the iron level, which is a risk factor for cow health
A Forage Mineral Report provides valuable nutritional data not only for establishing the correct mineral supplementation, but also information which can improve agronomy and harvesting practices to grow more grass of better nutritional quality.