Grass tetany can be a major problem on farms in spring and autumn. It occurs when cows have a low level of magnesium in their blood. Often, the first a time a farmer realises that his herd has a magnesium deficiency is when a dead cow is found in a field.
The tell tale signs of a death due to grass tetany are markings on the ground at the dead animals head and legs. This is as a result of an animal kicking its legs or moving its head in an aggravated fashion.
If you are lucky to catch a cow with grass tetany in time, they can show signs of being unsteady when walking, hence the term ‘grass stagger’, they may be trembling or even down and un-able to stand up.
Other signs can include lower milk yield or slow movement. Quick veterinary intercession is essential at this stage as death can result within hours.
Once a cow calves her requirement for dietary magnesium increases substantially (almost doubles). This leads to early lactation cows being at most risk. Grass tetany and milk fever can often occur simultaneously in cows that are near to calving or have recently calved. When milk magnesium concentration reduce, this can affect calcium levels and possibly increase the risk of milk fever occurring.
For this reason, a vet will normally treat a suspect cow with both magnesium sulphate subcutaneously and calcium intra-venous. In sever circumstances, a vet may choose to treat a cow with magnesium intra-venously at a very slow rate. While doing this the vet will check the heart beat of the animal. This is a practice only a vet can carry out because if it is administered to quickly, death can occur.
Factors which can increase the risk
Spring and autumn are the two main risk times for the disease. Cows that are let out to lush grass in the spring or autumn are particularly at risk, especially during cold, wet weather. A wet or cold night can lead to a reduced intake of grazed grass, which further decreases the cows’ magnesium intake leaving her at a higher risk.
Spreading high levels of nitrogen (N) or potassium (K) in spring time can also put cows at increased risk of grass tetany. If a cow’s diet has a high concentration of potassium, this has a direct effect on the absorption of magnesium from the diet.
If fields are acidic and have a low pH, this can increase the concentration of potassium in grass which can further aggravate the problem. In addition, some animals can be more susceptible than others to magnesium deficiencies as rate of absorption of magnesium can differ substantially from animal to animal.
Avoiding grass tetany
With cow values at an all time high, it is crucial that farmers should take action to safeguard their cows against the occurrence of grass tetany before clinical signs, or losses appear. When turning out freshly calved cows it is often advisable to supplement them with silage or hay and gradually increase grass intake. In addition, on cold wet nights cows should have access to shelter. If cows get cold, then their appetite will reduce and intakes will be depressed. Thus reducing the amount of magnesium ingested.
Avoid using fertilisers which contain high levels of potassium (K) during or directly before spring grazing as this can increase the level of potassium in the grass. The level of potassium in the diet can affect magnesium absorption.
Feeding concentrates or rations containing minerals will supply additional dietary magnesium to cows and may help to reduce the risk or the severity of a grass tetany problem.
However, farmers should pay particular attention to cows’ appetites while feeding concentrates. If a cow’s intake of concentrates reduces, this will leave the cow at increased risk of grass tetany. The level of minerals in many concentrates will not provide full protection against grass tetany but they can be a help to reduce the speed or impact of the disease.
Tips to reduce the risk of tetany
Blood sample cows to identify mineral levels in the bloodFeed hay or silage to cows at grassGive concentrates containing minerals to cows at grassEnsure cows are not cold and have shelter during cold wet nights (house at night with access to silage or hay) Supplement cows with a source of magnesiumPay particular attention when grazing fields that are shown to be high in K
Methods of magnesium supplementation
There are several methods of magnesium supplementation open to farmers, but care should be taken with each method.
Dusting over silage
This may only be suitable for some farmers where cows are housed at night and out at grass by day. Calcined Magnesite is the product most commonly used for this. Farmers should follow the feeding guidelines on the bag closely to ensure adequate supplementation.
However, it can be difficult to guarantee the required intake by each cow. Cow intakes should be monitored to ensure each cow is eating the required amount of minerals and is adequately protected against grass tetany.
Magnesium boluses
Magnesium bullets are given orally and provide a slow release of magnesium giving protection for 20-40 days, however the length of protection can vary depending on the product. Farmers should be aware that this method is not foolproof as cattle can cough up the bolus. If this is missed by the farmer, then they will not realise that the animal is not protected against grass tetany. Farmers should consult the instructions carefully as some products require more than one bolus.
Magnesium licks
Mineral blocks or licks containing magnesium are a popular method of supplementation. These can be placed in fields and moved easily and regularly to avoid poaching due to cattle crowding around them. These should be checked regularly and replaced as soon as eaten to ensure the cows have continuous access to magnesium supplementation.
Problems can occur as some cows may tend to eat more of the lick than others, while some cows may not eat the licks at all. Where excessive levels of magnesium are ingested by cows, scours may occur. Farmers should monitor cow’s intakes closely
Magnesium added through water
This is a quite a common practice around the country. Cows are most at risk from grass tetany during wet cold days/nights in the spring and autumn. Farmers should bear in mind that in times of high rainfall, or when grass dry matter is low appetite for drinking water may be reduced. If magnesium through water is the only source of magnesium supplementation, this may lead to an increased risk of grass tetany.
Grass tetany can be a major problem on farms in spring and autumn. It occurs when cows have a low level of magnesium in their blood. Often, the first a time a farmer realises that his herd has a magnesium deficiency is when a dead cow is found in a field.
The tell tale signs of a death due to grass tetany are markings on the ground at the dead animals head and legs. This is as a result of an animal kicking its legs or moving its head in an aggravated fashion.
If you are lucky to catch a cow with grass tetany in time, they can show signs of being unsteady when walking, hence the term ‘grass stagger’, they may be trembling or even down and un-able to stand up.
Other signs can include lower milk yield or slow movement. Quick veterinary intercession is essential at this stage as death can result within hours.
Once a cow calves her requirement for dietary magnesium increases substantially (almost doubles). This leads to early lactation cows being at most risk. Grass tetany and milk fever can often occur simultaneously in cows that are near to calving or have recently calved. When milk magnesium concentration reduce, this can affect calcium levels and possibly increase the risk of milk fever occurring.
For this reason, a vet will normally treat a suspect cow with both magnesium sulphate subcutaneously and calcium intra-venous. In sever circumstances, a vet may choose to treat a cow with magnesium intra-venously at a very slow rate. While doing this the vet will check the heart beat of the animal. This is a practice only a vet can carry out because if it is administered to quickly, death can occur.
Factors which can increase the risk
Spring and autumn are the two main risk times for the disease. Cows that are let out to lush grass in the spring or autumn are particularly at risk, especially during cold, wet weather. A wet or cold night can lead to a reduced intake of grazed grass, which further decreases the cows’ magnesium intake leaving her at a higher risk.
Spreading high levels of nitrogen (N) or potassium (K) in spring time can also put cows at increased risk of grass tetany. If a cow’s diet has a high concentration of potassium, this has a direct effect on the absorption of magnesium from the diet.
If fields are acidic and have a low pH, this can increase the concentration of potassium in grass which can further aggravate the problem. In addition, some animals can be more susceptible than others to magnesium deficiencies as rate of absorption of magnesium can differ substantially from animal to animal.
Avoiding grass tetany
With cow values at an all time high, it is crucial that farmers should take action to safeguard their cows against the occurrence of grass tetany before clinical signs, or losses appear. When turning out freshly calved cows it is often advisable to supplement them with silage or hay and gradually increase grass intake. In addition, on cold wet nights cows should have access to shelter. If cows get cold, then their appetite will reduce and intakes will be depressed. Thus reducing the amount of magnesium ingested.
Avoid using fertilisers which contain high levels of potassium (K) during or directly before spring grazing as this can increase the level of potassium in the grass. The level of potassium in the diet can affect magnesium absorption.
Feeding concentrates or rations containing minerals will supply additional dietary magnesium to cows and may help to reduce the risk or the severity of a grass tetany problem.
However, farmers should pay particular attention to cows’ appetites while feeding concentrates. If a cow’s intake of concentrates reduces, this will leave the cow at increased risk of grass tetany. The level of minerals in many concentrates will not provide full protection against grass tetany but they can be a help to reduce the speed or impact of the disease.
Tips to reduce the risk of tetany
Blood sample cows to identify mineral levels in the bloodFeed hay or silage to cows at grassGive concentrates containing minerals to cows at grassEnsure cows are not cold and have shelter during cold wet nights (house at night with access to silage or hay) Supplement cows with a source of magnesiumPay particular attention when grazing fields that are shown to be high in K
Methods of magnesium supplementation
There are several methods of magnesium supplementation open to farmers, but care should be taken with each method.
Dusting over silage
This may only be suitable for some farmers where cows are housed at night and out at grass by day. Calcined Magnesite is the product most commonly used for this. Farmers should follow the feeding guidelines on the bag closely to ensure adequate supplementation.
However, it can be difficult to guarantee the required intake by each cow. Cow intakes should be monitored to ensure each cow is eating the required amount of minerals and is adequately protected against grass tetany.
Magnesium boluses
Magnesium bullets are given orally and provide a slow release of magnesium giving protection for 20-40 days, however the length of protection can vary depending on the product. Farmers should be aware that this method is not foolproof as cattle can cough up the bolus. If this is missed by the farmer, then they will not realise that the animal is not protected against grass tetany. Farmers should consult the instructions carefully as some products require more than one bolus.
Magnesium licks
Mineral blocks or licks containing magnesium are a popular method of supplementation. These can be placed in fields and moved easily and regularly to avoid poaching due to cattle crowding around them. These should be checked regularly and replaced as soon as eaten to ensure the cows have continuous access to magnesium supplementation.
Problems can occur as some cows may tend to eat more of the lick than others, while some cows may not eat the licks at all. Where excessive levels of magnesium are ingested by cows, scours may occur. Farmers should monitor cow’s intakes closely
Magnesium added through water
This is a quite a common practice around the country. Cows are most at risk from grass tetany during wet cold days/nights in the spring and autumn. Farmers should bear in mind that in times of high rainfall, or when grass dry matter is low appetite for drinking water may be reduced. If magnesium through water is the only source of magnesium supplementation, this may lead to an increased risk of grass tetany.
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