Early spring weather creates grazing concerns

“Worrisome,” is the word Isaac Swortzel, of Suffangus Farm in Greenville, Va., used to describe the rapid early growth of forages brought on by an unusually warmer and wetter winter.
The vigorously growing grass in late February and into March is causing Swortzel and other farmers to wonder what the next few weeks will bring.
One of Swortzel’s concerns is that his cattle could develop grass tetany, a metabolic disease involving magnesium deficiency in ruminants usually occurring after the animals have grazed on pastures of rapidly growing grass.
Magnesium uptake in the plant cannot keep up with plant growth and therefore doesn’t get to the animal.
“Grass tetany is a condition that occurs when magnesium levels in the blood and spinal fluid become too low to support normal bodily functions.” Sarah Potts, dairy and beef Extension specialist with the University of Maryland, wrote in an Extension article. “The occurrence of grass tetany is often isolated to the springtime when cattle are grazing primarily lush, rapidly growing perennial pasture.”
Tom Stanley, Virginia Cooperative Extension farm management agent in the Shenandoah Valley, said most of the region had five or more days in February where temps were 15 degrees or more above normal and adding rains to the equation has made for good conditions for rapid forage growth in some areas.
“Looks like west central Virginia got more precipitation in February than the coast,” he said. “That makes sense when we see the pattern of storms has been for them to track up the Ohio Valley so the farther east the location, the less precipitation.”
According to Potts, magnesium is classified as a macromineral that is required by the body in relatively larger amounts than other minerals for several metabolic functions, including nerves and muscles in the body.
“Magnesium deficiency can progress rapidly and quickly become life-threatening if not addressed,” she said. “Early signs include nervousness, reduced feed intake, and muscle twitches, particularly around the face and ears. In the early stages of magnesium deficiency, animals may also walk with a stiff gait or stagger. Animals with advanced magnesium deficiency will lay out on their side with their head extended and have convulsions. “Death is likely if treatment is not administered within four to eight hours of symptom onset.” 
Prevention is the best approach when it comes to managing grass tetany and a combination of mineral supplementation and pasture management can help mitigate risk, according to experts. However, even with the best prevention plan, producers should work with their veterinarian to develop a protocol to treat cases of grass tetany that emerge during the season, Potts added.  
Potts said the most common strategy is to provide mineral supplement of magnesium in the diet.
During the high-risk period for grass tetany, 0.6 ounce of magnesium per head per day is recommended to help prevent magnesium deficiency. 
If supplementing with magnesium oxide is 1 ounce per head per day is necessary to meet this recommendation as it is about 60-percent magnesium. It should also be fed with Swortzel said he is working to manage the growth with selective grazing to keep the grass of from heading too early.
Potts entire article is available at https://extension.umd.edu/resource/grass-tetany.