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Stock on flooded grassland may need additional mineral supplementation

Livestock farmers in areas affected by flooding and waterlogging this winter are being advised to check mineral levels in forages to avoid problems with deficiencies or imbalances when feeding these forages this year. Farmers Guardian reports.


Following a record-breaking wet winter, farmers in many parts of the country are struggling to get to grips with the financial cost of flooding, especially as getting animals out to grazing early will be essential to help reduce production costs.

While problems such as increased poaching risks are highly visible, Rosie Miller, ruminant nutritionist with Trouw Nutrition GB, warns of a hidden problem.

She says: “Flooding can have a significant impact on mineral content and balance of pasture. Grazed grass is at best a variable source of minerals, with levels directly dependent on the mineral content of soils.

“Typically, some minerals will be in short supply, giving rise to potential deficiencies, while some can be present at high levels and be antagonistic to other minerals.”

Minerals and vitamins are involved in core body functions, including metabolism, enzyme function, nutrient utilisation, reproduction and cell repair.

A deficiency or toxic level of any mineral will potentially compromise a number of metabolic functions and reduce performance from grazing, so Ms Miller says it is vital to ensure the correct levels are fed.

“All farmers are aware of the problem of staggers, which are caused by magnesium deficiency, but there are other less well-known problems.

“Fresh grass is often high in iron and molybdenum which actively lock up copper, making it unavailable to the cow.

“Copper deficiency can lead to poor conception rates, so diets may need supplementation.”


Miss Miller explains there are three specific reasons why flooding and waterlogging can compromise mineral supply. The first is in affected fields, levels of mineral leaching can be higher, resulting in poorer soil mineralisation.

At the same time, damage to soil structure will reduce the ability of roots to absorb nutrients from soil. Combined, these may lead to lower forage mineral levels in grazed or conserved forages.

She says: “In addition, farms may suffer the effects of an increased level of heavy metals, which are antagonists to more favourable metals, due to soiling of grassland, caused by flooding and soil run-off.

“Many fresh grass samples analysed, from pastures which were flooded in previous years, show elevated levels of mineral elements such as iron, molybdenum and aluminium, all of which can cause problems.”

Ms Miller says if farmers take prompt action, it will be possible to identify any problems and take action to prevent performance, health and production being affected.


She advises farmers to have grazed grass analysed for mineral content as soon as possible, explaining a mineral assay is the only way to understand mineral levels in grazing and the precise risks stock may be exposed to.

The aim must be to understand the specific problem and then target supplementation from the most cost-effective solution.

She says: “Using the analysis, it will be possible to supplement diets precisely to supply the right minerals in the most appropriate form, addressing specific problems which will vary from species to species.

“Furthermore, it is essential to ensure legal maximum levels are not being exceeded.

“However, farmers should avoid blanket increases in mineral levels, as this can result in feeding minerals above the required level, which can just push up costs and make issues with antagonism worse.


“The most cost-effective approach will be accurate supplementation based on the analysis of forage mineral levels and a mineral assessment of the whole diet.

“For example, while cutting back on buffer feeds and parlour concentrates will reduce costs, this also reduces opportunities to provide effective mineral supplementation.

“A short-term gain in reduced costs will soon be wiped out if fertility suffers or conditions such as mastitis and lameness, both of which are related to mineral deficiencies, increase.”

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Potential problems with flooded grazing

Dairy cows

  • Calcium and phosphorus deficiency can be a problem, leading to increased incidence of milk fever, while low phosphorus can impair fertility; aluminium on contaminated fields can lock up phosphorus
  • Low zinc levels can affect foot and udder health
  • Iodine, selenium and copper can all be low in grazing produced from flooded pasture, leading to weak calves, increased retained cleansings and cell counts
  • High molybdenum, sulphur or iron levels can reduce copper availability, leading to generally poorer performance

Sucklers and growing cattle

  • High dependence on grazing and low supplementation with concentrates increases risk of problems from flooded pastures
  • The effect of low phosphorus on fertility will affect profitability of suckler enterprises
  • Reduced magnesium in grass can increase staggers risk
  • Iodine, selenium and copper can be low, causing problems in cows and growing cattle
  • Cobalt deficiencies can reduce growth rate in growing cattle due to energy shortfall



  • Particular attention must be paid to mineral balance, due to variable concentrate feeding to ewes in late pregnancy and early lactation
  • Hypocalcaemia at lambing can be a major issue if grazing is low in calcium and magnesium and supplementation is not formulated to balance forages
  • Cobalt deficiency in ewes will reduce lamb liveability, with lambs being slower to stand and suckle
  • Calcium and phosphorus deficiency in lambs will reduce skeletal growth
  • Cobalt deficiency will slow growth rates
  • Selenium deficiency in ewes can increase lamb mortality associated with hypothermia and reduce healthy muscle development


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