Potential For Grass Tetany

As grass begins to grow following the much-needed moisture, there is a potential for grass tetany to occur. Grass tetany is a serious metabolic disorder in cattle that is a result of two issues occurring simultaneously: 1) lactating animals have high magnesium requirements, and 2) lush, green grass is low in magnesium and unable to meet such requirements.

Grass tetany is caused by low levels of magnesium in the blood and affects lactating cows grazing lush, green grass. Magnesium requirements are high in lactating animals and increase as their milk production increases. Peak lactation in beef cattle occurs 60-80 days postpartum. Additionally, animals have a limited amount of magnesium reserves in their bodies and require a consistent intake from their diet to maintain proper blood magnesium levels, especially during these times of increased requirements.

Rapidly growing grass is low in magnesium. This problem is further complicated as the high potassium and crude protein content of the growing grass interferes with the absorption of magnesium in an animal’s rumen. Older forage is higher in magnesium content compared to new growth. Grass tetany is more prevalent when grazing areas with minimal old forage leftover from the previous year.

Onset of grass tetany can be rapid and often times the first sign may be finding animals dead with evidence of struggle. Symptoms of live animals include convulsions, weakness, disorientation, or aggression. Consult a veterinarian if you observe symptoms. Prevention of grass tetany is key. Provide a consistent supply of magnesium, which could include a salt and mineral mix or lick tubs which all are available in “high-mag” formulations.

Please contact the MSU Richland County Extension Office if you have any questions; 406-433-1206 or [email protected].