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It is true that horses can eat fescue grass, but there are some important things to remember. Fescue is a type of grass that is often used in fields, but it can get an endophyte fungus that makes poisonous chemicals. Toxins like these can hurt horses’ health, especially pregnant mares, leading to problems like longer pregnancies, hard labor, or not making enough milk.
Endophyte-free or low-endophyte types of fescue are better for horse fields because they are safer for horses. Managing and checking the pasture on a regular basis can help make sure the forage is safe.
Tall fescue is likely what you see if you look out over your field and see bunch grass with leaf blades that are rough, flat, and ribbed on the outside. One of the most common and widely used forages in the United States is tall fescue, a hardy, productive, and adaptable cool-season grass.
More than 10 percent of the land in the U.S. is this grass, which covers about 37 million acres. About 700,000 horses graze on or eat tall fescue.
Prolonged gestation: A mare’s normal gestation lasts about 350 days. It is known that mares that eat endophyte-infected tall fescue have gestation that last two weeks or more longer than the average time for foaling, or giving birth. So far, studies have shown that a mare’s sensitivity to ergovaline (ergot alkaloid) levels that change with her surroundings may have an effect potentially impact parturition.
Dystocia: The longer gestation time seems to make dystocia problems more common, along with problems with the reproductive tract not being ready and the fetal malpresentation. Because foals are born after a longer gestation and are often rotated 90 to 180 degrees from the normal position for delivery.
Agalactia: There seems to be a link between fescue toxicity and milk production because it contains an alkaloid that lowers the production of prolactin. Prolactin is a hormone that is released late in gestation and helps the mare start producing milk. When mares graze on endophyte-infected tall fescue, their levels of prolactin are lower during pregnancy and when they give birth than when they graze on grass that is not infected.
Thickened placenta: Foals that have fescue toxicosis often look and act regularly, but they are surrounded by a placenta that is so tough that they can’t break through it on their own and die. Mares that grazed on endophyte-infected tall fescue have placentas that are thicker, redder, and heavier than mares that grazed on grass that wasn’t infected.
Mares that are pregnant aren’t the only ones who can get fescue toxicosis; their babies also have problems. Fetuses that are too weak or don’t have enough muscle mass can be problems. So can foals that are born with a septum. Septicemia is an illness of the whole body caused by bacteria in the blood. It can be partly explained by the mare’s agalactia and foals that are too weak to nurse. Foals can have big bones, be skinny, and have legs that are too long.
As far back as history goes, Kyle McLeod, PhD, associate ruminant nutrition professor at the University of Kentucky in Lexington, says that tall fescue (Festuca arundinacea Schreb.) was thought to have come to the US through meadow fescue seeds that were brought in from England until the late 1880s.
It was praised for its ability to do well and grow quickly. It was also said to be able to handle harsh weather, disease, and insects, and to handle being walked on and grazed heavily. Alta and Kentucky-31 (KY-31) were the two types that came out by the 1940s. Alta was chosen because it can survive the winter, keep growing, and stay green even when there is drought.
This variety was planted all over the Pacific Northwest and the western U.S. intermountain areas. People liked the Kentucky-31 cultivar because it could grow in a lot of different types of land and provide grazing for most of the year. A lot of KY-31 was planted in the southern U.S. for forage, to protect the land, and to cover the sides of roads. Up to now, tall grass has been found from Florida to Canada.
Tall fescue is the forage base for most animal farms, especially beef cattle, because it is high in nutrients and easy to grow.
If you take good care of fescue, according to Jim Henning, PhD, an extension forage professor at the University of Kentucky, it will produce high-quality forage with levels of crude protein (CP) and digestible energy (DE) that range from 11% to 16% CP and approximately 60 to 68% DE from vegetative to boot (the reproductive stage when the seedhead is enclosed within the sheath of the flag leaf) to mature stages of growth. Vegetative to boot is the stage of growth between germination and flowering.
Tall fescue does have some good qualities, but it also has some bad ones. According to McLeod, by the 1950s, fescue had a bad reputation for making animals—mostly cattle but also small ruminants and horses—that ate it do badly. Cattle often got a long-term illness that made them weak, especially in the summer.
During the fall and winter, some of them got lame and lost parts of their feet and tails. People also thought that not being able to shed their winter clothes, which led to heat intolerance, and lower birth rates were side effects. Mares that lived on tall grass seemed to have more foals that died or didn’t produce milk.
The word “endophyte” means “plant that lives inside another plant.” Epichloe coenophialum is the name of the fungus that lives inside the fescue plant and is poisonous. Two things about the endophyte are very useful in real life. For starters, the organism doesn’t change the way the grass grows or looks, and it takes a lab test to find out if it’s there. Second, it can only be spread by seeds. So, the endophyte is good for the plant but bad for animals that graze on it.
The toxic endophyte makes ergovaline, ergotamine, ergocristine, and lysergic acid, which are all nitrogen-containing metabolites of the plant. Ergovaline makes up 84–97% of all the ergot alkaloids that are made. Everyone’s type of horse can have problems with endophytes, but breeding mares have the worst problems.
Lea says that pregnant horses that graze on endophyte-infected fescue might carry their foals for a few weeks past their due date. This could make it hard for the foal to be born because it is so big. Mares that graze endophyte-infected grass often have placentas that are thickened and/or stay in place. Usually, the foal comes into the world properly, but he can’t get through the chorioallantois (the membrane that surrounds the foal in the placenta) because it is tough and thick.
He could therefore suffocate if the chorioallantois is not cut open right away. Mares that graze toxic endophyte-infected fescue also often have premature placental separations, which are also known as “red bag deliveries.”
Mares that graze endophyte-infected fescue make less or no milk and colostrum (first milk that is high in antibodies). Colostrum may have smaller amounts of the antibody immunoglobulin G (IgG), and foals born to mares that graze toxic endophyte-infected fescue may not absorb as much IgG.
Scientists aren’t sure how these reproductive issues in mares happen exactly, but they do know that the ergot alkaloids bind to dopamine (D2) receptors and make the body make too much of it. In 2000, Marc Freeman, PhD, and his colleagues in the Department of Biological Sciences at Florida State University in Tallahassee did research that showed mares that grazed endophyte-infected fescue had significantly less prolactin in their blood and agalactia. Prolactin is a hormone that is needed for the last stages of labor.
Suppressing the hormone progesterone is another thing that can lead to a prolonged gestation. Progesterone levels should rise about two weeks before foaling, but mares that eat grass that is infected with endophytes have lower progesterone levels.
Coleman says that grazing endophyte-infected tall grass doesn’t seem to have as much of an effect on other types of horses. In one study at Auburn University, researchers looked at how yearlings that grazed endophyte-infected fescue grass grew and changed.
A group at the University of Georgia looked at the growth and development of yearlings that ate tall fescue hay that was infected with endophytes in another study. Neither group of researchers found big differences between horses that ate fescue and controls in terms of their usual daily gains or wither heights.
A group from Missouri State University looked at performance horses that were fed endophyte-infected fescue seed mixed in with their grain. The infected fescue did not have a big effect on the parameters that were tested. Lea says that vasoactivity (the ability to make blood vessels narrow or widen) of ergot alkaloids has been studied by researchers at the University of Kentucky. Even though they saw vasoconstriction, with ergovaline being the most vasoactive ergot alkaloid, the horses didn’t seem to be harmed on the outside.
In terms of management, what can farmers do to keep broodmares from getting sick from tall fescue? Coleman and Lea both agree that managing the field is the best thing to do.
The first step is to be sure that the field is infected and to find out how bad it is. Contact your county’s Cooperative Extension office to find out specifics about how to sample, how much it will cost, and how it needs to be shipped. However, here are some general rules for collecting samples:
How often to try. Samples should be taken after the plant has been growing for at least a month; this is the best time to find any endophytes that are there.
Collection – Pick out plant stems that are at least 1/8 inch thick. These are called tillers. Cut at the soil’s surface with a razor or sharp knife, being careful not to cut stems that have seedheads. To get a good picture of the field, pick at least 10 to 20 tillers at random from every five acres.
Storage – Put samples in a strong box sealed with plastic and put a cold pack inside. Then, take the box to a county extension office or send it overnight express to a testing lab. Put samples in the fridge to make sure they stay good.
Results – The report you get will tell you what percentage of the tillers you sent in had the endophyte on them. Some labs in the U.S. also measure the amount of ergovaline present.
Lea says that ergovaline levels change with the seasons and closely follow the cool-season growth curve of tall fescue, with spring and fall being the peak times. Some farms, though, don’t test for ergovaline levels. The Horse Pasture Evaluation program at the University of Kentucky has been collecting data for 15 years. Lea’s team has used that data to create a relative risk scale (ergovaline wasn’t tested or wasn’t tested during the normal months) to help breeders decide how to handle the grazing of late-term mares.
Endophyte production of ergovaline is what causes problems in broodmares, so knowing how much ergovaline the mare is taking in will give you more information to help you handle her better. Researchers have found that pregnant mares that eat fescue with more than 300 parts per billion (ppb) of ergovaline show signs of fescue poisoning.
Most publications on extension, on the other hand, say that 200 ppb should be used as the threshold number. Based on the amount of ergovaline in a mare’s whole food, the University of Kentucky team has set risk levels for mares that are very far along in their pregnancy.
Lea says that most fields are not made up of only tall fescue. Mares like to eat other grasses and beans that grow in pastures, which lowers the amount of ergovaline that is actually there. You can figure out how much ergovaline is in the land by guessing how many other grasses or legumes are there.
Coleman says that pregnant mares should not be in any grass or hay that has endophyte-infected tall fescue 60 to 90 days before they foal. You could move mares to a drylot where they can get the nutrients they need from hay and concentrate, or to a field using forage plants other than endophyte-infected tall fescue. Researchers and agronomists think this is the safest way to avoid problems with toxins.
To keep mares with a moderate to high risk of agalactia and dystocia from happening, you can give them domperidone, a drug that helps the body make normal amounts of prolactin and progesterone. Domperidone should be given every day for 30 days before the foal is born. The fescue plants will stay young and in the vegetative state as long as the field is grazed or mowed.
Coleman stresses how important it is to not graze the grass too much because the endophyte is at the base of the plant, near the seedheads. Lea says, “Don’t let the horses graze on grass that is less than 3 inches tall.”
Adding other grasses and legumes to a field can also help thin out tall fescue that has been infected with endophytes. Mares will not eat tall fescue if they can get something better. This is because it is not the tastiest grass. With this plan, the health and production of your pasture will also get better.
Even though it’s pricey, killing sick stands and planting new ones might be the best way to handle the situation. Lea says that tall grass comes in three main types:
Due to the widespread use of tall fescue as a field grass in the U.S., it is almost impossible to completely remove the risk of toxicosis in broodmares. To stay away from fescue toxicosis, you need to know about the plants in your field. Find out when ergovaline levels will be high and pick the best ways to handle the situation to keep broodmares safe.
