Cattle at risk of low magnesium in diet with grass staggers cases on rise

Mr Ramsay explains that high levels of ammonia in the rumen, produced by excess protein in lush grass, can interfere with magnesium absorption.

Poor weather can be a stress trigger, along with low pasture covers. During periods of bad weather, cows may also eat less, resulting in a lower intake of magnesium.

When supplementing magnesium, Mr Ramsay says hi-mag rolls can be a good solution and will also provide energy when grass supplies are short. Mag buckets are an option, but be sure to allow enough buckets or blocks for the number of animals.

He adds that mineralising your own cereals can be cheaper, but wastage must be accounted for to ensure there is an adequate supply.

Other options include molasses fortified with magnesium or treating the water supply.

SAC’s top tips to avoid hypomagnesemia

• Ensure 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
  
• 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/ head/day of straw while at grass they are needing better forage to meet their needs
  
• 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
  
• 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
  
• Always take into account the risk of magnesium shortage by checking the base ration the cows are on and what is being supplied by additional supplements