Rapid Grass Growth Predisposing to Grass Tetany

Spring has finally arrived! It seemed like it would never come soonerthis year but we can finally see green grass growing and field work happening. With an excess of moisture over this past winter and recent warm weather, rapid grass growth has been favorable which is great for spring grazing. However, grazing of rapidly growing grasses can be concerning due to low sodium and high potassium content. Cattle andother ruminants require a sufficient Sodium:Potassium ratio of >3:1 to ensure adequate magnesium absorption from the rumen. A high protein content, particularly in fertilized pastures, can lead to elevated ammonia levels in the rumen which leads to impaired magnesium absorption. Additionally, feeding of likely marginal feeds with poor vitamin and mineral status at the tail end of the neverending winter may predispose cows to a condition called Grass Tetany. More specifically, it is a condition caused by low levels of magnesium in the blood which can be due to either reduced absorption or inadequate intake.

Animals most at risk are cows in their 2nd month of lactation and 4-7 years of age. Weather and various climate factors can also influence the risk of Grass Tetany. Pastures most at risk are tame cool season grasses,especially those that are fertilized and growing rapidly. However, native pasture can also be at risk if stockpiled grass is deficient in magnesium or has elevated potassium levels due to rapid fall growth. Not only is rapidly growing grass a concern but fast growing cereal crops are also at risk of low magnesium and high potassium, thus predisposing to Grass Tetany.

Magnesium is important for the transmission of signals from nerves to muscles as well as the transmission of signals between nerves. Affected animals, if found early in the disease process, may be seen acting uncomfortable or have muscle twitching of the head or ears. Later on,cattle may become sensitive to any intervention and may bellow or become aggressive. Animals will progress to staggering and convulsions/seizures. Often rectal temperature is increased over 40°C, and animals have an increased heart and respiratory rate. Cattle suspected to have Grass Tetany can be effectively treated early in the condition by using IV and SC injections of magnesium-containing solutions. If you suspect an animal may have Grass Tetany we encourage working with your veterinarian to confirm a diagnosis via blood sample and aid in treatment of the affected animal.

Grass Tetany cases can be avoided by supplementing cattle with salt and a high magnesium mineral prior to and during grazing of high risk forages. Using fertilizer containing magnesium or topdressing pastures with a magnesium supplement is also possible. We encourage working with your veterinarian and nutritionist to develop the right prevention plan for your herd.

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