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Time to be vigilant for grass tetany

Most mid-season flocks are currently lambing or at the point of lambing, so farmers need to be vigilant for different diseases such as grass tetany, writes Marion Fox, B&T Drystock Adviser, Galway/Clare Regional Unit.

Bad weather, especially very wet spells similar to what we have experienced in recent weeks, affects the utilisation and intake of grass and the ability of the ewe to absorb nutrients from grass.

Rapid grass growth and high potash levels in excess of 70 kg/ha in springtime reduces magnesium absorption. Stress due to disease, weaning and malnutrition makes the ewe more susceptible.

At this time of year, there will be pressure to get ewes and lambs out to grass. Grass tetany can cause big losses on many sheep farms, so you need to be aware of the factors, treatment and ways to prevent it on your farm.

A lot of grass has accumulated on farms over the winter providing good quality grass for ewes and lambs. Farmers need to monitor grass supplies closely as the ewe’s requirements increase rapidly before and after lambing and grass supplies can be quickly depleted.


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The symptoms if seen are excitability, twitching, nervousness, staggering, collapse, convulsions with frothing at the mouth, coma followed by death.


Grass tetany is caused by a magnesium deficiency which if not treated, is life threating. Poor weather conditions, grass scarcities, high soil potash levels and stress can trigger the condition.

To prevent grass tetany, ewes should be supplemented with between 3-5g of magnesium daily, protection will occur one or two days after supplementation has started and will last for one to three days after supplement has ceased.

This supplementation is in the form of high mag mineral buckets, concentrate supplementation, where the concentrate contains calmag (5-10kg/tonne), high-mag bullets and pasture dusting. You need to be careful with males with magnesium to avoid urinary calculi.


Affected ewes can be treated with 100ml of warm magnesium sulphate injections under the skin (five or six locations) and can save the ewe if it is caught early.

Protected urea:

Some farms may have had the opportunity to apply fertiliser in the last couple of weeks, but it is important that you try and get some early Nitrogen out where conditions allow.

Protected urea is a urea fertiliser treated with a urease inhibitor, making urea safe from ammonia – N volatilisation loss which is the problem with ordinary urea. The Urea inhibitors that are currently registered are NBPT, 2- NPT and NBPT + NPPT. 

When farmers are purchasing protected urea, they should make sure that the bag or label should state ‘urea with urease inhibitor’ and also the type of fertiliser used.

Teagasc research has shown that urea protected with a urease inhibitor consistently gives the same yield as CAN.

Protected Urea costs 82c/kg N , therefore, it is important to get it out as soon as possible if soil temperature, ground conditions and weather forecast allows. The soil temperature needs to be 5.5°C upwards. The recommended rate for the first application is 23 units/ac or half a bag. The effects are not immediate, so it is important to apply in time provided ground conditions are suitable.

In the second application, 20 plus units should be applied in late March/early April. Compound fertilisers should be used where the soil fertility needs to be addressed.

Protected urea is safe to use throughout the growing season in the straight N slots in a fertiliser programme giving reliable yield, reduced emissions and is cost-efficient.

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