Beef farmers urged to use magnesium after grass staggers rise

Beef farmers are being warned about the risk of grass staggers, which is caused by a lack of magnesium, after an increase in cases have been reported in Scotland.

Poor weather conditions, lush autumn grass and high potash levels are all risk factors, with lactating cows, older cows and cows under nutritional stress most at risk.

See also: Advice on feeding suckler cows at different stages of production

Robert Ramsay, SAC Consulting’s senior beef consultant, said: “While it is common practice with set-stocked spring-calvers to receive supplementary feeding, including a high magnesium mineral in the autumn, producers who have recently changed to paddock grazing have been concentrating on maximising output from grazed grass. 

“This year, grass covers are good on these systems and supplementary feeding may seem unnecessary. However, advice to producers is to use magnesium licks/buckets and make sure your stock have access to them at all times, particularly when turning cattle into a new paddock of lush grass.”  

Risk factors for grass staggers (hypomagnesemia)

  • Poor weather conditions can be a stress trigger. Low pasture covers and poorer weather can also mean cow weights fall dangerously low by not eating enough.
  • Lush grass in autumn can be low in magnesium and has a high passage rate, so less magnesium is absorbed. Magnesium is absorbed in the rumen and it is also thought that high rumen ammonia levels – due to excess protein in lush grass – can interfere with magnesium absorption.
  • High potash levels in grazing grass can antagonise magnesium absorption.

Magnesium targets

Mr Ramsey said farmers should target an overall intake of 25g magnesium/day. Grass can be variable but, on average, has about 1.6g magnesium/kg of dry matter (DM) – so if a cow eats 10kg DM (around 50kg grass), this is 16g of magnesium.

This may be adequate under normal conditions, but if she eats less or there are antagonists to absorption, it will not be enough and staggers risk is high. Straw has less than half the magnesium of grass and silage.

Farmers can mitigate the risk of grass staggers by managing nutrition and stress. This includes:

  1. Ensuring cows are eating enough so they are not in negative energy balance and, hence, low magnesium and under additional metabolic stress. The less stress, the better – extra care is needed when cows are handled, and calves weaned.
  2. If grass is below 6cm, cows must be supplemented for energy as well as for magnesium. This can be from silage, hay or straw. Remember straw is very poor for magnesium and low in energy. If spring-calved cows are eating more than 5kg a head a day of straw while at grass, they are needing better forage to meet their needs.
  3. Avoid periods where intakes may be lower than required, then suddenly change – for example, rotational grazing taking residuals too low to meet nutritional needs for the time of year then moving to a lush paddock or overnight with no feed then a move in the morning.
  4. Observe cow behaviour and spot the risk factors. For example, cows standing around the gate or sheltering from weather for long periods without eating. Look at the amount of grass available and if they are going to realistically meet their daily requirements from this grass.
  5. Always consider the risk of magnesium shortage by checking the base ration the cows are on and what is being supplied by additional supplement.

How to supplement magnesium in the ration

  • High magnesium rolls – easy to feed on the ground. Normally 1kg supplies a full daily magnesium requirement (check with supplier), and around 10MJ energy, which is important when grass supplies are short.
  • Mineralising your own cereals – cheaper but need to account for wastage and the possibility of losing mineral when feeding on the ground – 100g a head of 25% magnesium mineral required.
  • Liquid molasses fortified with magnesium – harder to regulate intakes.
  • High magnesium buckets or free access mineral – aim for around 20% magnesium in buckets and 25% magnesium for powdered minerals. The downside is you are relying on all cows taking the mineral – ensure good access to minerals/enough buckets are put out for the number of cows.
  • Treating water supply – not as effective at grass, takes managing and shouldn’t be relied on.