Deficiencies in certain minerals can have adverse effects on herd health

As the season changes from summer to fall, livestock nutrition experts recommend producers consider a slight modification to their mineral program. It’s suggested producers incorporate a mineral supplement that’s high in magnesium, during certain times of the year. 

This is particularly important for cows that have just calved in the fall or spring and are grazing on cool season forages.  These animals are more susceptible to grass tetany, a condition caused by a lack of magnesium in the blood.

The magnesium deficit occurs due to several factors. First, a cow that has recently calved has a higher demand for magnesium due to her body using the magnesium in lactation. Cows have a greater need for magnesium during the early stages of lactation. 

Additionally, rapidly growing fall and spring pastures create an environment unconducive for magnesium absorption. “The cool season grasses with that lush growth in the spring, and under certain conditions in the fall, have low magnesium and high potassium,” Beth Kegley, Ph.D., cattle nutrition expert and professor, with the University of Arkansas, explained. 

The elevated levels of potassium in the grass hinder a cow’s ability to absorb magnesium. 

“When cows eat that grass, potassium directly interferes with magnesium absorption,” Kegley stated.

If the magnesium level in a cow’s blood falls too low, then they may come down with grass tetany. “Grass tetany is an acute magnesium deficiency,” Kegley explained. 

The symptoms of grass tetany include muscle spasms, staggering, agitation and convulsions. Once symptoms start, there is little time for producers to save the animal. “It’s a condition that occurs very rapidly in a cow. So, producers will very commonly find a dead cow from grass tetany,” Kegley added.

If producers catch the symptoms quickly, they can treat the cow following the recommendations of their veterinarian. Most commonly, the treatment consists of high doses of magnesium given orally or intravenously. 

Producers must act quickly to have a chance to save the animal. “Cows don’t linger for days with this,” Kegley said. “You have to catch it and treat it within hours, not days.”

The best defense against grass tetany in a herd is providing a mineral mix that contains a high magnesium content. Cattle do not build up a store in their body of magnesium, they need to consume it every day. 

Not only does the high magnesium mineral mix need to be regularly available to fall and spring calvers, but producers should monitor the herd’s intake to make sure all their animals are eating the mineral. 

Kegley recommends producers provide a consistent supply of free choice mineral, year around, to keep cattle in optimal health. “There is more problem with sporadically giving mineral, than worrying about changing to a certain type of mineral,” Kegley explained. “Cattle need these minerals every day, so ideally these cattle would always have a free choice mineral available.”

Nutrition experts recommend keeping an eye out to determine if cattle are consuming too much or too little mineral. If they are consuming more than they should, move the mineral feeder away from areas where the cattle congregate, eat and drink. If they are not eating enough mineral, then move the mineral closer to water, shade or areas where the herd tends to linger. 

During hot, dry conditions when forage is brown and crispy, cattle tend to consume less mineral. At these times, producers may want to consider moving the mineral feeder to areas where cattle will be more likely to ingest the supplements. 

Currently, most of the forage in the Ozarks contains decreased nutrient levels. “The grass right now that is dry and not growing is lower in potassium, phosphorus and magnesium,” Kegley said. “So, it is important to have mineral out at this time because the forage does have fewer of those major minerals that cows need.”

Lastly, livestock specialists discourage producers from offering a separate mineral feeder containing solely white salt. Some cattle will only consume the white salt, therefore forgoing the commercial mineral. If producers plan to use white salt, experts recommend combining it with a mineral mix and feeding it all together.


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