11 May 2018
By Dr Mark Little MVB CertDHH PhD MRCVS
After the long winter, it is good to see cattle grazing in the fields. However, there are reports of cow deaths due to grass staggers. What is grass staggers and how can we prevent it?
What is Grass Staggers?
Grass staggers, also known as Grass Tetany, is a metabolic disease caused by a low blood magnesium concentration. Veterinary surgeons may call this hypomagnesaemia, hypo (low) magnesaemia (blood magnesium).
Cattle with grass staggers are often found dead, possibly with the soil around their feet disturbed due to paddling or seizures. If caught in time, affected cows may be twitching (especially around the head), uncoordinated, staggering, nervous, collapsed and convulsing. It is important to keep cows with grass staggers calm as excitement can trigger a seizure.
Although magnesium is stored in the body, predominately in bones, there is little mobilization or control mechanisms and consequently, blood magnesium concentrations are essentially dependent on daily dietary intake. In the adult cow, the majority of magnesium absorption occurs in the reticulum, rumen and omasum. There is a small amount of absorption in the large intestine.
Cold and wet spring weather may disrupting grazing patterns and decrease intakes of grass and therefore magnesium. Grazing in poor weather also increases stress levels, which decrease blood magnesium concentrations. In spring, lush young pastures may be low in magnesium, or high in potassium and nitrogen, which reduces the absorption of magnesium.
Lush pastures are also low in fibre, which increases the rate of passage through the rumen, reducing time for magnesium absorption.
Young grass, particularly those that fertilized with nitrogen, have a high fermentable protein content. This leads to an increased rumen ammonia concentration, which impairs magnesium absorption.
As volatile fatty acids (VFA) provide the energy for active transport of magnesium across the rumen wall, magnesium absorption improves with increasing amounts of readily degradable carbohydrate.
Rapid treatment is essential with an injectable solution of magnesium under the skin in the area behind the shoulder and over the ribs. The high magnesium solution should not be administered intravenously as this can cause fatal disruptions to heart rhythms. Your veterinary surgeon may administer a small amount of magnesium mixed into a calcium solution (and a sedative drug if needed) by slow intravenous injection while listening to the heart.
The administration of magnesium will raise the blood magnesium for a short period, therefore it is essential to continue to supplement magnesium to grazing cows.
Providing some shelter from the wind and rain will help alleviate stress, while supplementary feed will increase the supply of magnesium. A source of long fibre will slow rumen transit times, which increases magnesium absorption.
Cattle require 30 grams of magnesium daily, which equates to 60 grams of calcined magnesite. This can be provided through magnesium licks, water delivery methods, boluses and compound feed.
Compound feed is particularly good as it supplies additional magnesium and also the energy (VFA) needed for magnesium absorption.