Grass Staggers is well recognised as a significant threat to cattle at key times of the year, despite prevention being possible it remains a common issue on farm and can cause significant losses. Grass staggers or Hypomagnesaemia is a critical emergency that can quickly result in death without prompt veterinary intervention. Furthermore, as the conditions leading up to an episode are common across all the herd, it’s not unusual for a number of animals to be affected with the associated impact on the farm. Equally significant are subclinical cases, often unrecognised, that will impact milk production, fertility, and growth, dragging down the herd’s performance. Grass staggers, is simply triggered by low blood magnesium levels. As magnesium plays an essential role in nerve and muscle function when levels drop below critical thresholds the typical signs of tremors, excitability, muscle contractions and seizures are seen.


Although Staggers can occur at any time of the production cycle, the high magnesium demands of milk production explain why it’s most frequently observed around the start of lactation. With the risks and potential cost so significant, it’s important to understand the factors that influence magnesium levels so that effective dietary precautions can be taken. Unfortunately, although there are sizeable quantities of magnesium locked up in the skeleton, this is unavailable to support blood levels. The cow must rely on the daily intake in the diet for a regular supply. This means that anything that reduces intake or interferes with absorption can quickly lead to problems.

The spring grass flush can present a particular challenge. Firstly, it tends to be low in magnesium (typically 0.1% to 0.2% DM), already starting to make levels marginal. Absorption primarily occurs in the reticulorumen and functions best when the pH is lower. The nitrogen levels in spring grass tend to raise the ruminal pH and therefore slow down uptake. Furthermore, the use of potassium fertilisers can cause further issues as potassium can interfere with magnesium absorption. The high moisture content of fresh grass can move the material through the rumen faster, reducing the time available to take up the magnesium. Inclusion of forage such as hay or straw in the diet at this time can therefore increase overall dietary fibre levels and slow transit times, this can help magnesium absorption during the spring flush.


This season’s erratic weather means it’s harder to predict conditions and their impact on magnesium levels, and what has worked on a farm in previous years might be unsuitable this year. However, the significant cost of a case of grass staggers and the impact of sub clinical hypomagnesaemia, means ensuring stock have daily access to a good quality magnesium supplement is essential in many situations.

For further Information please contact us.