By Peter Harland
We think that forage mineral and vitamin levels will be changed in silage crops this year. The high rainfall means that forage mineral levels will be altered for some minerals. Also, due to wet ground conditions, soil contamination of forages is greater than previous years. This will mean that previous years mineral supplementation will need to be re-examined.
Selenium is one mineral that will be reduced in silages this year. Selenium availability to plants depends on rainfall; areas with high rainfall have lower forage selenium content. This is coupled with the problem that selenium can be leached from the topsoil in areas of high rainfall. Also, high rainfall leading to leached soils, resulting in low sulphur swards.
Forage mineral analysis is showing that the wet season has resulted in forages that are higher in potassium, phosphorus and magnesium content, so perhaps savings on supplementing these minerals could be achieved. Also, sodium and iodine are carried by rainfall therefore regions with high rainfall contain more of these elements. Where fields have been flooded, grass growth is slowed, which increases herbage calcium concentrations. Again savings could be made here.
High iron values are attributable to soil contamination which on some farms has been unavoidable this year and shows up on silage analysis as ash greater than 9%. In addition, herbage iron is also high in soils that are prone to water logging. Both iron and molybdenum levels increase with rainfall; these can influence copper and selenium status. Contamination of silage with soil iron and molybdenum should be taken into account when assessing their value as copper sources. In these cases cattle are likely to benefit from inclusion of a source of protected copper and selenium. Iron-rich soils are also likely to provide insufficient phosphorus, so even though phosphorus levels may be higher due to the wet year, interactions with iron may mean phosphorus is in short supply. Where animals are grazing, they cannot avoid ingesting excess iron in the soil and so they too may require mineral supplementation. A mineral analysis will tell you the status of all minerals in your forage. If it is necessary you can then feed a suitable mineral supplement or ask us to design a special mineral and vitamin based on your forage and other ingredients in the diet. Ask your rep to find out more.

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