When to prepare for grass tetany
March 19, 2015
Although it is still mid-March, the temperatures in South Dakota have been relatively warm and a few of the cool season grasses are beginning to green-up sooner than we expected. With that green-up and cows lactating heavily comes the concern of grass tetany, said Adele Harty, SDSU Extension Cow/Calf Field Specialist.
Grass tetany is a metabolic disorder associated with lush pastures due to low concentrations of blood magnesium, which results in nerve impulse failure in animals.
"With adequate moisture and warm temperatures, grasses begin to grow rapidly. The concern of grass tetany isn't normally seen until May, but taking steps to prevent it today will be more effective in the long run," Harty said.
How to prevent grass tetany
To ensure the proper management practices are in place to prevent grass tetany, Harty said livestock producers need first to understand the factors which play a role in it. These include:
* Low magnesium (Mg) content of rapidly growing grasses and pastures;
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* High potassium (K) content of rapidly growing grasses and pastures;
* High crude protein content of grasses and pastures;
* Bad weather, storms, stress, etc., that cause cattle to be "off feed" for 24-48 hours;
* Lactation: losses of Mg and calcium (Ca) in milk; and
* Various combinations of the above factors resulting in low blood Mg or Ca.
"The key to prevention is to be proactive," Harty said. "Measures should be taken to minimize risks associated with cows grazing lush pastures."
One long term approach she suggested is to incorporate more legumes into pasture mixes. "Legumes have higher levels of magnesium and calcium than do immature grasses resulting in a better balance across the pasture," Harty said.
If possible, she recommended that livestock producers delay the turn-out date into lush pastures until plants are 4 to 6 inches tall. "This will reduce the occurrence of tetany, in addition to giving stressed pastures a little more time to rest," she said. "The reality is that many producers need to utilize pastures when grasses begin to green-up and the risk of tetany is most prevalent."
If delayed grazing is not an option, other management tools should be utilized.
First, Harty said to always provide a high magnesium (Mg) mineral supplement or mineral mix containing at least 8-12 percent Mg. "This needs to be provided two to three weeks prior to turn-out or before tetany is likely to occur," she said.
Palatability and adequate intake can be challenging, resulting in some of the animals consuming inadequate amounts of the mineral on a daily basis. "Make sure all animals have access to the mineral supplement prior to, and while grazing, tetany-prone pastures, as this will help decrease the occurrence," Harty said.
Another potential tool is to provide hay while cattle are on lush pastures; however, cattle are not likely to eat hay unless they are forced. "Dry forages can act as carriers to provide the animals additional Mg and Ca at critical times," Harty said.
If the drinking water source can be controlled (i.e., water tanks), soluble Mg salts may be added to the water. Some examples of soluble Mg salts are magnesium acetate, magnesium chloride, and magnesium sulfate (Epsom salts). The most common form of Mg, magnesium oxide, is not soluble in water and therefore cannot be used for this purpose.
Most susceptible animals
Older, lactating cows with calves younger than two months of age have the greatest susceptibility to tetany; while steers, heifers, dry cows, or cows with calves older than four months of age are less susceptible. "Mature cows are more susceptible because they are less able to mobilize Mg from bones to maintain the necessary level in their system. Also, cows within two months after calving have increased milk production and require additional Ca and Mg," Harty said.
Harty explained that cattle will exhibit symptoms of grass tetany, but they may not be observed as death may occur relatively quickly – within four to eight hours. "An affected animal will exhibit a series of progressive signs. These include grazing away from the herd, irritability, muscle twitching in the flank, wide-eyed and staring, muscular incoordination, staggering, collapse, thrashing, head thrown back, coma, and finally death," she said.
Affected animals should be handled calmly, since sudden death can occur if animals are stressed.
There are treatment options for animals, but effectiveness depends on the clinical stage when administered, Harty explained. "If treatment is started one or two hours after clinical signs develop, the result is usually a quick recovery," she said. "Treatment is not effective if delayed until the coma stage."
Grass tetany can be treated with an intravenous dextrose-based commercial preparation of Mg and Ca purchased from a local veterinarian.
"Remember cattle are more susceptible to grass tetany in the spring, and certain weather conditions increase susceptibility," Harty said. Consider and implement prevention practices, monitor cattle for signs of grass tetany, and treat as soon as possible according to a protocol developed with a veterinarian."