POOR weather conditions, lush grass growth and high potash levels are being blamed for a recent spike in hypomagnesemia cases in beef cattle.
SAC Consulting warns cows which are most at risk of developing the disorder are lactating cows, older cows and cows under nutritional stress.
Magnesium is not stored in the body and must therefore be available daily in the diet. The target for daily intake is about 25g/day. The levels of magnesium provided by grass can be variable but on average it contains about 1.6g/kg dry matter. 50kg of fresh weight grass would provide about 16g of magnesium. However there are several factors which can impact the absorption of magnesium.
Robert Ramsay, SAC senior beef consultant says: “This year grass covers are good on paddock grazing systems and supplementary feeding may seem unnecessary. However advice to producers is to use magnesium licks or buckets and make sure stock have access to them at all times.
He says this is particularly important when turning cattle onto new paddocks with lush grass. Lush grass in autumn can be low in magnesium and its fast rate of passage through the animal means there is less time for absorption.
High levels of ammonia in the rumen, produced by excess protein in lush grass, can also 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, SAC 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.
If 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.
1. Ensure that 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/head/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 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