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Grass staggers or hypomagnesemia is the clinical condition seen when cattle have an insufficient quantity of magnesium in their blood. Whilst the body contains relatively large quantities of magnesium, animals need a constant dietary supply of magnesium in order to maintain blood levels as body stores tend to be in an unavailable form.
Typically in the early stages of the condition the cows will become agitated and twitchy, at a herd level you may notice cows kicking off units more often in the parlour. Individual cows will show a mild reduction in milk yield which will progress to signs of stiffness and muscle tremors. Untreated the condition will progress quite rapidly to the cow going down and being unable to stand, ultimately the levels of magnesium drop low within the fluid which surrounds the brain which results in fitting, coma and death.
Traditionally cases of grass staggers occur following spring turn out and often during wet weather when dietary intakes of grass drop for short periods. Staggers is also seen in the autumn months when we get a late rapid growth of grass. Despite this apparent seasonality, the risk is ever present and for herds that rely predominantly on grazed grass, staggers should be considered throughout the grazing season and preventative measures put in place in order to manage high risk times or to ensure that cows are receiving adequate magnesium in order to prevent problems from arising.
Risk factors for development of staggers
Treatment of individual animals is based around injecting magnesium sulphate (e.g. Magniject No. 9) under the skin, check the bottle for correct dosing quantities and specific directions. Magnesium must not be administered intravenously as a rapid infusion can cause heart attacks. It is crucial to ensure that this is done in a calm and stress free manner as putting the cow under more stress can lead to an increased risk of heart failure due to rapid depletion of magnesium by heart muscle. Cows should then be sat up and left quietly for a further 10-15 minutes. It is also advisable to administer calcium concurrently. Calling for veterinary assistance is also recommended as we often use sedation to calm the animals down especially when they are down and fitting. Rapid intervention is key to success.
Like other metabolic diseases clinical cases of hypomagnesemia are often just the tip of the iceberg and you are likely to have many more animals subclinically affected. We recommend taking blood or urine samples from 6 animals in the rest of the herd to build up a picture of what the herd levels are like. Excess magnesium is excreted in urine and therefore testing urine levels can be quite useful.
In terms of prevention there are several options which can be used; with the preferred choice dependent on the particular farming systems. If concentrates are being fed in the parlour or cows are being buffer fed then adding calcined magnesite (magnesium oxide) typically at a rate of 25-30g per cow per day can be used, thorough mixing should take place and all cows should have access at the same time to ensure submissive cows get adequate access. Magnesium chloride crystals can be added to water troughs, however excessive levels can lead to the water becoming bitter and cows will reduce their water intakes which we should try to avoid. It is important for this to be effective that all available water sources are treated, so if there is access to streams etc this option is not recommended. If magnesium chloride is added to water troughs then levels around 40g/cow/day are typically recommended. Water troughs should have a volume of at least 20L/cow for this option to be used successfully. Cows can be bolused with magnesium bullets to give a slow release of magnesium, however they vary in terms of daily amounts of magnesium released and how long they last for. Often multiple boluses need to be given as they typically do not release a large quantity of magnesium and hypomagnesemia can still occur in these animals if single boluses are given.
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