Published Wednesday, 16th October 2019 in SAC Consulting news
In the last week, there has been a large increase in cases of hypomagnesemia (Grass Staggers) in beef cows.
SAC Consulting, part of Scotland’s Rural College (SRUC), has now issued advice to farmers to combat the problem, which is caused by a lack of magnesium.
Experts warn that lactating cows, older cows and cows under nutritional stress are most at most at risk.
Magnesium is not stored in the body and a daily dietary intake is required and there can be various reasons why cows fall dangerously low in magnesium:
- Poor weather conditions, like we have had of late, can be a stress trigger. Low pasture covers and poorer weather also can mean cows fall dangerously low by not eating enough
- Lush grass in autumn can be low in magnesium and have 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 also interfere with magnesium absorption
- High potash levels in grazing grass can antagonise magnesium absorption
It is likely that a combination of the above reasons will contribute to clinical cases. A good target is an overall intake of 25g/day of magnesium. Grass can be variable but on average has around 1.6g magnesium per kilogram of dry matter so if a cow eats 10kg of dry matter (around 50kg of 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.
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.”
A guide to additional magnesium supplementation to the base ration:
- Hi Mag rolls, normally 1kg supplies a full daily Magnesium requirement (check with supplier) these are easy fed on the ground. 1kg will also supply around 10 MJ of energy which is important when grass supplies are short.
- Mineralising your own cereals, cheaper but need to account for wastage when feeding on the ground and possibility losing mineral on the ground – 100g/head of a 25% magnesium mineral required.
- Liquid molasses fortified with magnesium – harder to regulate intakes
- Hi Mag buckets or free access mineral – aim around 20% mag in buckets and 25% mag for powdered minerals. 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, shouldn’t be relied on.
Nutritional and stress management as an aid to mitigating the risk of Grass Staggers:
- 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
- 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
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