PeelBack

By Breanne Hill

Since the first equine tasted his first mouthful of roughage, grass has been a natural food source for the animal we call horse. In fact, horse owners are so comfortable with the concept of “grazing” that they use turnout time in a velvety-green pen as reward for a job well done, and they coined the term “out to pasture” as a universal reference to a horse having a happy retirement. Yes, we can just picture “Sugar” chomping away on the back forty, while a rainbow shines in the background and birds twitter in the trees. 

However, as is the case with most dream scenarios, the reality of the horse/pasture relationship is much more complicated than the perception. There are many different types of grasses and several scenarios in which these grasses can become compromised, creating roughage that has the potential to cause severe health problems if ingested by a horse.

Perhaps one of the most feared and documented among these pasture problems—especially during foaling season—is the relationship between the grass called fescue and Neotyphodium coenophialum, an endophyte fungus.

When infused with this endophyte fungus, fescue becomes a dangerous food product. In particular, it is poisonous to pregnant mares. The toxin, or alkaloids, produced in endophyte-infected fescue can penetrate a mare’s system, resulting in such complications as a prolonged gestation period, lack of milk production, stillbirths and birthing complications that may be fatal for both mare and foal. Additionally, if a foal survives a toxic pregnancy, it may be underweight with hooves and teeth that are not fully developed—all in all, a scary situation for horses and horse owners.

Until recently, there have been very few defenses to the endophyte fescue risk, but researchers at Mississippi State University are devoting their time to changing this.

Headed by Dr. Peter Ryan, an associate professor of animal and dairy science, MSU has been conducting tests on the affects of endophyte-infected fescue on all breeding stock, including stallions. Now, they believe that are getting close to developing a type of endophyte fescue that will not produce poison. They are calling the fescue “endophyte friendly,” and they’re hoping the name rings true.

ImagePretty Poison

Fescue is European in origin. It was brought to the United States in the late 1800s because of its heartiness and because of the fact that its high production rates made it less likely to succumb to instances of drought and overgrazing. Popularity of the grass boomed in the 1930s, ’40s and ’50s, due in no small part to the frenzy of replanting that occurred following the Dust Bowl years.

Unfortunately, fescue’s attractive qualities may be in direct relation to how it is affected by endophyte. Endophyte is a fungus that lives its entire life cycle inside of grass. Transmitted by seed only, it does not harm the grass, nor does it distort the plant’s appearance. In fact, it can only be detected by laboratory analysis, and some grasses, including fescue, can attribute their high-growth levels and drought and insect tolerance to endophyte.

So, what’s the harm in having endophyte-infected grass?

In the 1970s, it was discovered that, when combined with fescue, the Neotyphodium coenophialum endophyte produces alkaloids that are toxic to livestock.

The most well documented victims of endophyte fescue poisoning have been late-term pregnant mares. In these horses, the endophyte fescue alkaloids interfere with normal endocrine functions—or normal pregnancy functions.

Late-term pregnancy mares are not, however, the only types of horses that may be vulnerable to the alkaloids.

“While the endocrine disruptors (alkaloids) affect the normal functions of pregnancy, they also affect the normal levels of fertility,” Ryan says. “This means that it could also have a negative affect in the mare who is about to bred or who is in the early stages of pregnancy. It may also affect the stallion.”

Currently in the United States, the types of fescue that are vulnerable to endophyte are most prominent in the Pacific Northwest and in the Southeastern states—where there are low, damp pastures. They are also regularly found in the so-called “transition zone,” which includes Oklahoma, Arkansas, Missouri, Tennessee, Kentucky, Virginia and northern parts of North Carolina, Georgia and Texas.

“The problem with fescue is, it is very dependent on the season,” Ryan says. “If you have a very mild spring or a warm spring, or a lot of rain, the stuff grows like gangbusters, which is why it thrives where it thrives.”

Also dependent on conditions is the level of toxicity a horse can reach by eating endophyte-infected fescue.

“A lot of people want to know, ‘What is the toxic level of the infected grass?’” Ryan says. “The thing about toxic levels is they’re dependent upon how heavily contaminated your pasture is, the time of year—which is basically how much grass you have—and how long the mare is in the pasture. Usually, if the mares are out all day in the spring months, and depending on their consumption level (weight versus forage amount)—that’s how the toxicity level in horses is determined.

“With that in mind, some horses will be much more sensitive to the poisoning than others, although there is still a lot of work to be done in that area. And again, this is a big problem in the Southeastern United States.”

ImageThe Program

The researchers at MSU recently received a call from a large Kentucky Thoroughbred Farm. The farm, according to Ryan, was reporting a high instance of early embryonic, or early pregnancy, loss in its broodmare band. Because the mares had access to the Kentucky 31 type of fescue, Ryan says he paid close attention to the complaints and has been monitoring the situation ever since.

“When you see something out of the norm, you pay attention,” Ryan says. “This wasn’t a case of late-term pregnancy loss, but a case of mares who were aborting in early pregnancy.

“That’s what I mean when I say that there is a whole lot more to the fescue problem than has yet been explored.”

MSU is doing more than its part to remedy this problem. Within its research program, there are pastures set up specifically to grow 90 percent endophyte-infected fescue. These pastures are used for research every spring during breeding and foaling season, using the program’s 50 research mares.

“In the spring season, if we’re doing our research, the mares will be out 24/7,” Ryan says. “Because of the mild climate down here, we foal our mares outside. If we’re looking for the effects of fescue on pregnancy, those mares will be out on the grass all the time. And because our pastures are 90 percent fescue, we’re working from a high-end exposure rate.”

Ryan says he is interested in every aspect of fescue consumption in equines, whether those equines are young stock, males or females. The program has even brought a few stallions into the mix to test the affects of fescue on fertility in general.

“We did a study a couple of years ago, looking at eight stallions, feeding them contaminated fescue seed,” Ryan says. “We didn’t see major changes in the reproductive functions, but we did see some neuroendocrine (the nerve cells that produce hormones) changes, and that’s very important because it has never been shown before. We’re still in the very early days of that. We have about four stallions right now.”

Although the research on the affects of contaminated fescue on horses will continue, MSU has recently turned its attention to fighting an even bigger fight—developing and endophyte that is not toxic to horses, thereby producing a new strain of endophyte-friendly fescue.

With the support of the Noble Foundation, a non-profit group devoted to agronomy research, MSU is exploring using a manmade endophyte in fescue—one that does not produce the same toxins that wild endophyte does.

“They have evaluated the new kind of culture on cattle and on sheep and have found it to be very beneficial,” Ryan says. “Pennington Seeds in Georgia has already developed one culture that a lot of cattle producers are now beginning to plant to replace the Kentucky 31, which is the most common culture that has endophyte fescue.”

Of course, trying a new manmade endophyte on cattle is one thing. Trying it on horses is another. There are great differences between the digestive systems of cattle and horses and this can make research in one species difficult to apply to the other species.

For example, when MSU attempted a new feed additive to combat fescue toxins—one that had been effective in cattle—during one of its research stints, it still lost two foals and one mare to the birth complications caused by the endophyte-infected fescue.

The problem was the amount of time that the additive spent in each type of animal’s system.

“The cow ruminates,” Ryan says. “Everything sits there and turns over, so adding an absorbing compound in the form of an additive gives them a chance to bind up and fight contamination.

“Whereas a horse’s digestive system keeps everything moving quickly. The problem we had was making available these agents in the diet consistently enough to get the same affect in horses that we were seeing in cattle.”

So, while Ryan realizes that fighting the affects of fescue in horses will likely be more difficult than in other animals, he is anxious to get the new endophyte-friendly fescue research going this spring.

“We did some trial research this last spring with a very small number of mares and it looks promising,” he says, “but it takes a while to establish the pastures, so the next two years will be crucial.

“Our pastures were first seeded during the fall of 2006, when we had such a dry spring and summer that we weren’t able to put very many mares out. But this spring and next spring, we’re going to have something between eight and 10 mares on the pastures, and we’ll foal them right out. We’ll know by the end of May how that is working.”

Until an endophyte-friendly fescue seed is approved and made available to the public, owners will continue to have to take their own precautions against the dangers of fescue. If you have had your pasture tested and know that endophyte-infected fescue is a problem, you have a few options that may help ensure your mare has a healthy pregnancy and foaling.

ImageFirst of all, be sure to remove your mare no later than day 300 of her pregnancy. From there, place her on non-fescue pasture, in a stall or in a dry lot with proper nutrition. Removing a mare from an endophyte-infected pasture may cause her to return to normal signs of pregnancy within 42 hours.

Another option may be to give her domperidone as an oral paste beginning 25 days before her foaling date. You’ll have to continue this through foaling.

Of course, the best defense with fescue is to keep your breeding stock away from it completely. If you have a pasture that is known to have endophyte fescue or that you suspect may have endophyte fescue, remove your broodmares and keep them somewhere else. And always consult your veterinarian before beginning any treatment program.

Breanne Hill is managing editor of Barrel Horse News. E-mail comments on this article to [email protected].

 

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