Estimations suggest that 1% of cattle in the UK will experience clinical grass staggers, with up to 30% of all clinical cases resulting in death and significant direct losses. A far larger percentage of animals, including ewes, will experience sub-clinical cases that may affect overall animal performance.
Grass staggers, otherwise known as grass tetany or hypomagnesaemia, is a very real threat for suckler and dairy cows at turnout as well as ewes post-lambing. However, it is easily managed by assessing and managing the on-farm risks and farmers are urged to consider options early this year, as a result of the extreme winter weather the UK has seen and the expected rapid flush in grass growth as temperatures begin to increase.
Grass staggers is defined as a deficiency of available dietary magnesium. Magnesium is a key macro-nutrient in the diet and is essential for bone growth and maintenance, nervous system function and also as an aid to fibre digestion in the rumen.
Rapidly growing spring grass typically has a low magnesium content (0.1 to 0.2% in dry matter) which, combined with its low dry matter and rapid transit through the rumen, can result in very low levels of magnesium absorption into the animal’s bloodstream. Magnesium is predominantly stored in the bones of the animal and consequently is not readily available when dietary supply is compromised. Stock therefore rely on daily magnesium supplementation to maintain adequate blood magnesium levels at times where risk is increased such as spring, and autumn.
In addition to the low magnesium content of spring grass, a number of other dietary factors can compromise magnesium absorption in ruminants, further elevating the problem of grass staggers:
- Increased potassium levels of spring grass, possibly due to fertiliser application, can upset the sodium to potassium ratio. In turn this can lead to magnesium absorption in the animal being decreased meaning that additional sodium (salt) should be offered to help redress this ratio alongside additional magnesium.
- Dietary changes, for example, a potential imbalance between protein and carbohydrate, like that seen in spring grass, can also affect magnesium absorption.
- Metabolic stresses caused by an imbalance of minerals and trace elements can lead to a “lock up” of magnesium; again, impacting the animals’ ability to draw on the limited supply available.
- Disruptions to feed intake and therefore magnesium uptake and absorption, such as inclement weather, change of grazing pasture, transportation, stress of calving or weaning can all increase the risk of grass staggers.
To help alleviate the risk of grass staggers long fibre should always be available in the form of hay or silage, to help slow the transition of wet spring grass through the rumen. It is also essential to maintain dietary energy levels (notably starch and sugar) to help prevent excess rumen ammonia, dry matter intake, an adequate supply of minerals, trace elements and vitamins, and to also ensure a suitable supplementary sodium (salt) source is available to readdress the sodium to potassium ratio. Finally, and most importantly, it is vital to ensure stock have daily access to a suitable magnesium supplement.
Magnesium is typically an unpalatable mineral, so by presenting it in a molassed free-access lick, farmers can be assured that their stock has a reliable supplement to complement their diet. Ideally, magnesium supplements should be offered up to two weeks pre-turnout to better prepare stock for changes. Then, by turnout, they are familiar with the supplements and are not faced with a deficit.
Grass staggers is a common, well-known challenge at turnout that can be fatal, however, it’s easily avoided by predicting where the main risks are and addressing them with suitable magnesium supplements.
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