Tall fescue, a nutritious, cool-season perennial grass, is the most widely grown forage in the U.S. Ninety percent of it carries a fungus that makes it resistant to heat, drought and insects.
Unfortunately, these fungus-infected plants create problems for the livestock that consume it. The problems include reduced heat tolerance, lowered rates of weight gain, milk production and fertility, and sometimes loss of feet, ears or tails in cold weather. All in all, it adds up to millions of dollars in losses annually for the U.S. industry.
In northern climates, some producers are replacing infected stands with fungus-free varieties. But farther south, this isn't always an option because non-infected fescue has less survivability and costs more to maintain. As a result, it's often easier to try to live with the fungus by minimizing the problems of “fescue toxicosis” (see sidebar) in cattle.
Don Spiers, a University of Missouri-Columbia associate professor of animal science, is among the folks on the leading edge of finding those solutions. His areas of study include the possibility that some animals are more sensitive than others to the toxins.
“Some producers tell us they don't have a problem anymore with fescue toxicosis because they got rid of the animals that were sensitive to it,” Spiers says. “We've been trying the last couple years to identify an animal model for use in our research that will reliably show sensitive and insensitive animals. So far, we haven't identified it.”
Spiers says researchers would like to know if such a genetic difference exists. If so, the next step would be to identify the responsible genes and remove them from the population.
“At this point, we don't see a genetic relationship,” Spiers says.
Some folks claim certain heat-tolerant animals do better on infected fescue, he adds, and studies comparing Brahman to Angus — both grazing the same fungus-infected fescue — have been conducted. Such studies, however, are complicated by the fact that heat-tolerant animals like Brahman are less stressed at a set temperature than might stress Angus cattle.
“If Brahman are comfortable at that heat, they won't be affected. So when we're talking about an animal that is sensitive or insensitive to fescue, it may be that we're talking about an animal that's just sensitive or insensitive to a certain level of heat,” Spiers explains.
Meanwhile at the University of Arkansas, plant scientists are trying to develop a fescue infected with a different type of fungus that doesn't produce the toxins that adversely affect grazing animals.
“When we talk about these toxins, we're usually referring to those produced by the symbiotic relationship between the fescue and the fungus, not by just the fungus itself. It's the relationship with the plant that results in the release of these toxins,” Spiers says.
It's for that reason that Spiers and his team recommend to producers that they keep fescue pastures grazed down so that cattle aren't consuming the plant's seed head, where the toxin concentrates.
“Either rotate the animals to keep the fescue grazed down, or mow the pasture before letting animals into it, if the plants are getting too high,” Spiers says.
Research is also underway to find compounds already on the market that might prove helpful in the battle against fescue toxicosis. One such product of promise is ivermectin, a broad-spectrum parasiticide from Merial.
“We received some suggestions from producers, and some hints from other researchers, that maybe ivermectin works, so we've done some control studies in environmental chambers with rats and cattle where we've tested the effects of ivermectin,” he says.
In cattle, the bolus form of ivermectin has been used. Placed in the animal's stomach, the bolus releases ivermectin continuously for 120 days, Spiers says.
“Thus far, we've only tested the boluses in short-term studies, but it does seem to improve the feed intake, and body temperature doesn't seem to get quite as high,” Spiers says. “Ivermectin affects a part of the nervous system that we believe might be impacted by these toxins, but this is just preliminary work. We're not recommending it to producers.”
Meanwhile a group led by Vivian Allen at Texas Tech is looking at the potential benefits of feeding seaweed compounds to reduce problems of fescue toxicosis. The group recently published four papers on the subject in the Journal of Animal Science.
Spiers says Missouri has done some research in this area as well. Their control studies show seaweed does appear to reduce body temperature in the animals exposed to heat stress, with or without fescue toxicosis.
“The problem we have is that many of these compounds are not on the market yet, so to get them into the hands of producers you have to find a company to buy into the project and produce the compound, and that may take 10 to 15 years.
“Hopefully, we can find available compounds that have already been approved by FDA for use in animals. That's one reason we are looking at ivermectin — it's been approved and it's fairly safe. We need something that doesn't run a risk of overdose for the animal, with a lot of flexibility at the upper level.”
Heather Smith Thomas is a freelance writer from Salmon, ID.
The Fescue Riddle
The fescue problem goes back to the 1940s when “Kentucky 31” was first released, says University of Missouri animal scientist Don Spiers. The fungus, which is most concentrated in the seed head of the grass plant, wasn't identified until 1977, however.
Spiers says “fescue toxicosis” is a general term that lumps together all the problems associated with the fungus. It's a multi-million dollar annual problem for beef producers.
The summer condition is called “summer slump” or “summer toxicosis.” Symptoms include decreased growth rate, feed intake and milk production, as well as rough hair coat and poor reproductive performance.
Decreased blood prolactin causes the decrease in milk production, while decreased blood circulation in the skin causes the increase in body temperature, Spiers says. That increase may be what produces many of these other signs of fescue toxicosis, as well.
“We don't usually see the increase in body temperature and other symptoms until the animals are heat stressed. Seldom do we see signs of fescue toxicosis when animals are in a neutral, comfortable environment,” Spiers says. “The biggest reason for the increase in body temperature is a reduced flow of blood to the skin; the animals just can't get rid of the heat.”
Spiers says people confuse fescue toxicosis with fever. But in fescue toxicosis, the body isn't creating heat as in a fever condition; it just can't get rid of heat.
Fescue foot is the winter problem. Affected animals suffer necrosis (death) of the tissues in the tail, ears and feet; some to the point that they eventually fall off. The tissue dies due to reduced blood flow, which starves those areas of nutrients.
“The primary toxin we look at is ergovaline. It's one of a number of toxins classified as ergot alkaloids. You find different ones in different situations. The class of toxins involved in fescue toxicosis is produced by the fungus in combination with the fescue,” he says.
While Spiers says ergovaline is the toxin usually used in fescue toxicosis experiments, some of the other ergot alkaloids may also be important.
Check out: beef stocker USA www.beefstockerusa.org