Minimize fescue toxicity in cattle

Minimize fescue toxicity in cattle

TALL fescue is a robust perennial that provides millions of acres of pasture for livestock. Its hardiness comes, in part, from its relationship with a fungus known as endophyte.

Endophyte thrives on popular varieties of the grass and, in return, helps the fescue resist insects, heat and drought. It also helps the plant withstand heavy grazing. What is good for the grass, however, may be bad for the grazer.

About 8.5 million head of cattle graze on fescue, but the endophyte fungus causes fescue toxicity, diminishing growth, health and reproduction in cattle as well as horses and sheep by squeezing off the blood supply to the extremities.

Infected fescue may lead to losses of as much as $1 billion yearly due to lost bodyweight, illness and fewer pregnancies, according to beef industry estimates. Symptoms occur typically during the hot months — or "summer slump," as cattle producers call it.

Grazing fescue before it goes to seed and providing plenty of water and shade during the summer can help ranchers minimize the effects of endophyte-infected fescue forage, said Dirk Philipp, assistant professor for the University of Arkansas System Division of Agriculture.

Toxin concentrations are highest between May and October, and endophyte concentrates in the seeds.

"This means start grazing early to keep plants from going into the reproductive phase," Philipp said. "Grazing management requires diligence; given the large proportions of fescue pastures on most farms, some sort of advanced grazing management is necessary."

When cutting fescue for hay, do so before seed heads develop.

"Cutting hay will be best at the boot stage," he said. "If producers wait until June, then seeds will have already developed."

While options include re-establishing pastures into a cattle-friendly endophyte fescue, "this can be expensive and is a long-term solution that requires careful planning," he said.

In summer, when symptoms of toxicosis — including elevated body temperatures — are most likely, Philipp recommended providing sufficient amounts of water for cattle to regulate body temperatures and making sure cattle have shade in their paddocks or pastures.

"Shades can be built relatively inexpensively, or paddocks can be set up in a way that natural shade is available like large trees, high brush rows, etc.," he said.

Philipp offered other alternatives for the next few months, including:

* Establishing a summer annual grass such as pearl millet or sorghum-sudangrass to take pressure off the fescue and reduce toxicity while providing forage diversity, but watch out for high nitrate levels in pearl millet and prussic acid in sorghum-sudan species.

* Planting a summer forage crop makes economic sense because there is usually a large forage gap anyway during summer.

Philipp said another key to maintaining the health of livestock is to be sure not to over-fertilize with nitrogen, because it will increase toxin concentrations in plants. He suggested applying fertilizer based on a soil test report. Additionally, he said to be aware that excess nitrogen can also result from liberal poultry litter applications.

Clemson University researchers have been looking for ways to neutralize the effects of toxicosis on cattle, particularly bulls.

Much of the research on fescue toxicity has focused on females, which can fail to become pregnant or spontaneously abort their offspring if infected. The failure rate for cows can run as high as 35%.

Some researchers have now turned their attention to males, however, after realizing that one bull with toxicosis can have a greater impact than one cow since it can cover as many as 25 cows via natural reproduction.

"In a race that requires sprinters, these sperm were barely walkers," a researcher from Southern Illinois University said in reference to her work with infected bulls.

At Clemson, Scott L. Pratt looks at the bulls from another angle. As a molecular reproductive physiologist, Pratt focuses on the chemical molecules that deal with animals' reactions to the toxin.

Consuming infected grass and hot summer temperatures hamper the bulls' ability to maintain normal body temperatures. Particularly heat sensitive are the testicles because body temperature can affect sperm quality.

Pratt is working on finding genes and gene pathways that are affected by the toxin.

"The work we are doing to identify biochemical markers that are indicators of bull fertility may help with inconsistent breeding soundness exams, which is big problem," Pratt said. "All labs have seen mild to no effects on the exams. Bulls on toxic tall fescue will pass a breeding soundness exam but still be sub-fertile."

His work could lead to better bull management strategies to maintain bull fertility while grazing toxic tall fescue.

It would add another way to deal with fescue toxicity. Currently, a cattle producer must take his animals off an infected pasture months before breeding. There are nontoxic fescues available, but planting them requires completely replacing a pasture, which can be costly and time consuming.


Grass tetany watch

The arrival of spring means that pastures are beginning to green up and that cattle producers can soon get a break in their feed bill.

However, specialists at the University of Kentucky College of Agriculture, Food & Environment warned that this is also the time for producers to watch out for and prevent a condition called grass tetany.

"Grass tetany is also known as grass staggers, lactation tetany or hypomagnesemia," University of Kentucky extension veterinarian Michelle Arnold said. "Grass tetany is a metabolic disorder caused by reduced magnesium levels in the animals' blood."

In general, the condition affects older, early-lactation cows, but it can also affect dry cows, young cows and, in rare cases, growing calves.

"You should watch out for cattle that show symptoms such as nervousness, lack of coordination, muscle spasms and staggering. This may lead to convulsions, coma and death," Arnold explained. "If you suspect that cattle are showing signs of grass tetany, you need to contact a veterinarian, because early treatment can save animals."

While grass tetany can occur in fall and winter, it most frequently occurs in spring with young, cool-season grasses and small grains that are utilized as forage.

"This year, we have the same chance of cattle having problems with grass tetany as in previous years," said Donna Amaral-Phillips, University of Kentucky dairy specialist. "With the later start in grass growth this year, grass tetany may occur later in the spring, but a lot of it comes down to the weather as we proceed."

While there may not be a higher incidence of the problem this year, managing it may be more economically significant than in past years.

"The high value of beef cattle this year makes managing the risk of grass tetany even more important from an economics point of view," University of Kentucky beef specialist Jeff Lehmkuhler added. "Cull cows are currently in excess of $100/cwt., and feeders are around $1,000-1,200 per head. So, minimizing the risk is relatively inexpensive and definitely worth the cost."

Feeding magnesium or "high-mag" mineral supplements is the best way to reduce the occurrence of grass tetany. Most feed stores carry the supplements. Ideally, producers need to start feeding those supplements 30 days before spring grass growth. A free-choice, high-magnesium mineral with a target intake of 4 oz. should contain 12-15% magnesium from magnesium oxide.

"Obviously, prevention is the key; feeding magnesium supplements before cattle begin to graze early-spring grass will help to avoid (grass tetany) altogether," Arnold said. "Response to treatment after symptoms begin is not always good and largely depends on the time between symptom onset and treatment beginning."

Lehmkuhler added, "Reducing the risk of grass tetany in grazing cattle involves using a balanced mineral supplement offered to lactating cattle free choice. Producers must ensure that the cattle consume the mineral product at or near the suggested intake level on the feed tag. Producers should not use straight white salt during this time of the year as it reduces the intake of the complete mineral product and magnesium."

He indicated that the key to using free-choice products is to find a product that's palatable and to manage the mineral feeders to ensure that cattle have access 100% of the time.

"It is a fact that magnesium absorption is dependent upon having adequate sodium in the forestomach, but this does not preclude the necessity to provide elevated magnesium in the supplement," Lehmkuhler said.

In addition to supplementing magnesium, other management strategies include testing soil and then applying fertilizer based on the soil test results and using no more potassium than recommended. Lehmkuhler said research in Missouri has shown that phosphorus fertilization increases plant magnesium levels in tall fescue.

Producers can also graze cattle on legumes, which are high in magnesium, although their growth is often limited in early spring.

Volume:86 Issue:16

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