"80% of copper deficiency in Lancashire due to molybdenum toxicity"

Sunday 13 November 2011

Twenty farmers attended November's Blackburn and Darwen Group meeting to hear speaker James Bretherton from AgScope. The topic for the evening was minerals and trace elements and understanding how the different elements work together.

Minerals were created billions of years ago during the ‘big bang’. Every farm has a different mineral status and this depends on soil type, soil pH, prevailing weather etc.

James began by commenting that such a vast subject would take weeks to cover in any detail and so he would focus on the main major minerals needed in the diet and what they are required for.

Major or micro?

Minerals can be classed as being either major or micro and this classification will affect the quantities of mineral which an animal requires in the diet. The analogy James used was that major minerals are required in quantities relative to the size of a double decker bus compared to micro minerals required in portions the size of a golf ball in relative terms. To put it another way – a bag of minerals will be made up of approximately 95% major minerals and just 5% micro minerals.

Major minerals include calcium, phosphorus and potassium whilst cobalt, copper, zinc and selenium are micro minerals or trace elements. The effects of mineral deficiency or toxicity in farm livestock are well known and can affect metabolism and water balance, for example calcium deficiency in dairy cattle can lead to milk fever.

Mineral interactions

However what is often not fully appreciated is the fact that many minerals interact together and one can affect the availability of another. A good example of this in Lancashire is the relationship between molybdenum and copper. Local soils are naturally very high in molybdenum and at certain times of the year there is excess uptake into the grass which will lock up copper, thus inducing a copper deficiency in the livestock despite the fact that there is sufficient copper in the forage. It is estimated that up to 80% of problems caused by copper deficiency in the area are actually due to molybdenum toxicity.

Measuring minerals

One way of measuring the mineral status on your farm is by having your forage (grass or silage) analysed for the mineral content. This will give a good indication of forage mineral status, although it will vary from crop to crop. Using this information it is possible to predict whether or not your livestock are likely to be supplied with all their mineral requirements by forage alone or if some form of mineral supplementation is needed.

Blood testing of stock is another option but results can be very variable and in instances such as molybdenum induced copper deficiency the results will show the animal to have sufficient copper in its system despite them showing signs to the contrary.

Potassium

Through his work James has been involved with a great deal of forage mineral testing and has seen the potassium content of forage increase quite substantially over the years. This is thought to be due to increased slurry application, particularly on dairy farms, and also better methods of application which deliver the nutrients directly to the plants.

Only apply what the soil needs

James recommended that farmers should check their soil potassium levels and if the levels in the soil are sufficient then significant financial savings can be made by reducing or omitting potassium from the artificial fertiliser you buy. Any potassium removed from the soil in the crop will be returned by the slurry so extra potassium is only really needed where arable crops are grown and completely removed from the field.

Crop minerals

Forage testing has also shown crops such as maize and wholecrop, which are often added to dairy cow diets, will only supply half of the nutrients that grass silage does. In this instance the provision of supplementary minerals is essential, particularly salt which is essential in the body for water regulation. By comparison, sugar beet is very rich in minerals particularly copper.

Deficient or not?

The modern high yielding dairy cow has a much greater mineral requirement than lower yielding breeds in the past. It is unlikely that all the cow’s needs will be met by forage so supplementation is essential to ensure that all the essential minerals are balanced.

James spoke about some signs that can be looked for in the cow which indicate mineral deficiency. Copper is of particular importance for fertility as it is needed for oestrus expression, with low levels often resulting in silent heats. A brown cast to the coat may indicate copper deficiency and subsequent fertility reduction. Another area to look at is the brisket where there are two glands, one at either side. If the glands are easily visible this is often a good sign that there is a mineral deficiency.

Conclusion

James concluded by commenting that in order to optimise production from our farmed livestock it is essential that they are supplied with the correct major and micro minerals in the correct quantities. Over-supply can be as damaging as under-supply as the interactions between the various minerals can lead to one being locked up by another and inducing deficiency. He also said that if your soil health is right, in terms of pH, aeration and structure, then the soils and the resulting forages would be more likely to supply all the minerals required.