Recent research shows salt helps cattle avoid death as a result of grass tetanyWritten by Heather Smith Thomas
The cause of grass tetany or grass staggers has been poorly understood, yet annual death losses cost stockmen millions of dollars. It affects mature cattle grazing lush forage, after weather changes like freezing early spring pastures or sudden growth after rainfall following drought.
This disease is associated with magnesium deficiency, calcium deficiency and excess potassium in the blood of affected animals.
During cool, wet conditions or regrowth after frost or drought damage, sodium levels in certain forage plants plummet, while nitrogen and potassium levels spike. Recommended prevention has been supplemental dietary magnesium, and many producers feed high levels to try to prevent losses.
Standard treatment for acute cases has been to administer oral and/or intravenous magnesium.
After examining cattle lost in 2001 following spring frosts in the Midwest, Thomas Swerckzek, a veterinary pathologist in Kentucky, found clues about the cause and prevention of grass tetany.
A few years earlier, he had collaborated with William McCaw, a veterinarian working with several purebred herds, trying to find answers to some of their health problems.
When Swerckzek started looking at herds, he found one farm with very healthy Hereford crossbreds. The owner was feeding loose salt rather than mineral mixes. Most farmers in that area fed mineral mixes and salt/mineral blocks, and cattle often over-ate the mineral mixes to get the little bit of salt in them.
The farmer with the crossbred cattle had a salt house in every pasture.
“He wasn’t feeding any magnesium. He’d been in the cattle business more than 40 years and had never had a case of grass tetany,” says Swerckzek. “This was a hint that maybe it wasn’t necessary to feed magnesium to prevent grass tetany.”
Swerckzek continues, “Later, when I got several herds off the mineral mix, they quickly started to turn around. Most of the cows had been suffering from diarrhea and wasting away, and within 24 to 48 hours they improved, after giving them plain loose salt instead of mineral.”
At the time, Swerckzek was working with a herd of about 1,000 Angus and driving through that farm with the manager.
“We came across a cow that had been down for several days in spite of multiple treatments with magnesium and calcium,” he says.
Swerckzek had some sea salt and put it in front of that cow. Three hours later, she’d gotten up and wandered off before going down again. The manager put more salt in front of her.
By the next morning, she’d gotten up and rejoined the herd.
There were other cattle in the herd showing signs of grass tetany and going down.
He mentions, “I told the manager to put a handful of salt in front of them or get it into their mouths. Those cows came out of it.”
“We had massive losses in Kentucky one year due to an unusual winter with many warm spells. Grass and clover grew early. Then we had a hard freeze in April. Cattle went down by the thousands with grass tetany and bloat. People were using bloat blocks but this didn’t help because they didn’t have salt,” he explains.
“The same thing happened in 2010. We had a lot of clover, and the farmers using bloat blocks said their cows were eating them like candy, and it didn’t help. The farmers who had salt out didn’t lose cattle,” says Swerckzek.
Reasons for tetany
“The reason cows go down with grass tetany is that they are short on magnesium and calcium, but I didn’t know why salt worked,” Swerckzek says.
Then, he discovered a connection between grass tetany and nitrates.
“We’d been taught for many years that nitrate is not toxic – that nitrite is the problem. In the 1940s when nitrate was discovered as the cause of cornstalk toxicity, it was nitrites causing shortage of oxygen in the blood. But I found that nitrate is 100 times more important in grass tetany than nitrite,” he says.
The body must get rid of the nitrate, and it does this through cations, especially sodium.
“When there isn’t adequate salt in the blood, the body grabs onto the most available cation, which would be magnesium and then calcium,” he explains.
When the spike of nitrate occurs – when the cow consumes frost-damaged forage – her body immediately uses magnesium in the blood to combine with and get rid of the nitrate, which depletes the body’s magnesium, which is why the cow goes down.
“If there’s enough salt available, the body can grab onto the sodium and cows don’t go down with grass tetany or milk fever,” he says. “If they don’t have salt on the day this hits, they go down. It has to be there all the time, and it can’t be hard salt blocks because cattle can’t eat enough when they suddenly need it.”
Potassium and sodium
Another piece of the puzzle fell into place after Swerckzek found that on some farms, even though farmers supplied salt, cattle weren’t eating enough of it.
Potassium levels in grass were spiking to levels 15 times higher than normal after hard frost, especially when it was lush and highly fertilized.
“Since the cation potassium and sodium are so close together, these minerals can substitute for one another. When potassium spikes, even though cattle have salt available, they won’t eat it because the body thinks they already have enough,” he explains. “They are actually sodium-starved, but their bodies didn’t know the difference between an excess amount of potassium and too little sodium.”
The body usually has the ability to keep sodium levels within normal range, but when it drops lower, ranchers may only have a few hours before that animal dies.
“If we feed salt, however, and the animals eat it, they’ll be fine as long as they have plenty of water,” Swerckzek says.
British scientists in the 1930s noticed that salt could prevent grass tetany, but no one put it all together until Swerckzek figured it out.