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Mud Management in Horse Pens

Question:  I recently built three 14' x 65' drylots for my horses.  The soil in my area is heavy, mucky clay.  What do you recommend using as footing to ensure proper drainage and as little mud as possible?

Response:  Unfortunately, with heavy clay soil, drainage and mud is going to be a continued problem unless the drylot is renovated.   The below system, called a high traffic pad, has proven to work (tested at the Universities of Kentucky and  Vermont) and will dramatically decrease mud problems in drylots.  To install a high traffic pad:

· Remove the 8" of top soil

· Install drainpipe to direct water out of the pen.  The pipe must be sloped towards an outlet. 

· Roll out geotextile fabric.  The fabric comes in large rolls. 

· Add 4" of crushed limestone (usually 1 ½ to 1 ¾ in diameter).

· Add second layer of geotextile fabric.

· Add 4" of dirty pea stone (small gravel)

· Refresh the top layer as needed; usually once every year or two.


The estimated cost for installing a high traffic pad is about $0.80 per square foot.  In one of your 14' x 65' drylots, the cost to renovate the entire paddock will cost just under $800.  To lessen the investment, renovate one  drylot per year. 


The University of Kentucky has a factsheet further outlining the process.  It is available online at


By:  Krishona Martinson, PhD, University of Minnesota 

What can I do about off-label herbicide application?

Q: I made an application of Weed-B-Gone herbicide to my horse pasture. After application, I noticed it was labeled only for use on lawns (turf) and not horse pastures. When can I graze again?

A: It is extremely important to read the herbicide label prior to application; the label is the law. Herbicides are labeled for application to a specific site(s). Unfortunately, since Weed-B-Gone is not labeled for use in a pasture, there are two issues to consider, legality and safety.

You have made an "off-label" application, this is illegal. If the off-label application is reported to the Minnesota Department of Agriculture (MDA) (the agency charged with enforcing pesticide laws), an investigation would be opened, and there is the possibility of fines and penalties for the applicator. One benefit of involving the MDA is they take soil and plant samples to help determine when it is safe to graze. Because Weed-B-Gone is not labeled for pastures, the label does not include information on grazing restrictions.

The second issue is horse safety. If you choose not to report the off-label application, it is up to you to determine when it is safe to graze. To help determine this, look at the active and inert ingredients in the herbicide and see if they are found in any herbicides labeled for pasture use. Herbicides labeled for pasture use have information on grazing restrictions; this can be used to determine when to graze again, however, this will not ensure your pasture is safe to graze. You can also submit soil and plant samples to a laboratory for pesticide residue analysis. The herbicide manufacture might also have information related to off-label applications; a phone number is usually listed on the label.

Before a herbicide is purchased, the label should be thoroughly red and the applicator should ensure the desired application site is listed. Most herbicide labels are available online.

By Krishona Martinson, PhD, University of Minnesota

Are acorns toxic?

Q: The oak trees in my pasture have dropped thousands of acorns. I've read that acorns are toxic, what should I do?

A: Oak leaf buds and immature (green) acorn hulls are associated with horse toxicity. Mature (brown) acorns are not known to be toxic. If the acorns in your pasture are mature (brown), then there is no risk of toxicity. If the acorns are immature (green), then you must keep the horses off the pasture until the green acorns have been removed.

By Krishona Martinson, PhD, University of Minnesota

Are hybrid maples toxic?

Q: There are several hybrid maple trees being sold at Nurseries. The hybrids are half Silver Maple and half Red Maple. Have any studies been done on the toxicity of these hybrids to horses?

A: All trees in the maple family (Acer species) are considered toxic, including hybrids. However, the toxicity is only associated with wilted maple leaves (i.e. in the fall or after a storm). Assuming your horse has sufficient forage (hay or pasture), ingestion of enough wilted leaves to cause toxicity is unlikely, however, cases have occurred in the fall or during a drought when pasture forage is limited.

By Krishona Martinson, PhD, University of Minnesota

Q: I have two clients whose horses are having liver problems. Some of the light colored horses also have signs of sunburn. Their pastures are filled with alsike clover. Is the alsike clover causing this?

A: Clovers (i.e. red, alsike, and white clover) are usually considered a beneficial pasture forage. However, alsike (and other clovers) is considered toxic when infected with the mold Cymodothea trifolii that causes Black Blotch disease in clovers and legumes (i.e. alfalfa). When mold infected clovers are ingested by horses, photosensitivity (sunburn) and liver damage can occur.

To determine if your clover has Black Blotch disease, go to the lowest, wettest area of the pasture, and look at the underside of the leaves on the lower 6 inches of the clover. Look for black or brown "blotches"; like a felt tipped marker was blotted on to the leaves. Look for this on all clover species in the pasture.

If you find the "blotches", rotate the horses off the pasture to a shaded area to reduce the exposure to sun and potential sunburn, mow the pasture or cut it for hay; the mold can not live on dried hay. After the pasture has had a chance to regrow and dry out, you can begin grazing again.

There is research being done on rabbits in Canada demonstrating that alsike clover not infected with mold did not cause toxicity, whereas alsike clover infected with the mold did. However, this research has not been done with horses. In our experience, mold infected clover has been present in pastures of horses with photosensitivity, and we have not seen photosensitive horses in pastures of clover or alfalfa uninfected with the mold.

Because clovers tend to grow in thick bunches that promote moisture retention (most molds thrive in humid conditions), if the problems persist, you may want to consider reducing or eliminating the clover from your pasture. Broadleaf herbicides (i.e. 2-4,D) will moderately control clovers and could be used to thin stands. All herbicides do have grazing restrictions so it's important to read the herbicide label and follow all directions. Fertilizing a grass/clover pasture with nitrogen will also help the grasses better compete with the clovers. Grasses need "applied" nitrogen while legumes (i.e. clovers and alfalfa) can fix it from the environment. Not fertilizing a grass-legume mixed pasture will heavily favor the legume species and over time, the legumes will become the dominant species in the pasture. Mowing and other practices to increase air flow to the pasture should also be done to reduce the amount of moisture retained in the thick stands of clover.

By M. Murphy, DVM, PhD; and K. Martinson, PhD; University of Minnesota

Q: I have a question about our 24 year old Welsh Cob mare. We have kept her at a stable for the past 18 years. Now that we have our own farm, we are considering bringing her back to our farm to live with our other 3 equines. What concerns me is that our mare has lived the last 18 years in a paddock with very little grass and has been fed mostly baled hay. Our farm has lush pasture. I realize all horses need to be slowly acclimated to pasture in the spring or when they are introduced to a new pasture. She also had an episode of "gas" colic for the first and only time last summer. Other than the colic episode, she has never been sick or needed special treatment. What do you think?

A. You are correct, introducing her (and the other equines) slowly to the pasture is recommended (15 minutes the first day, increasing by 15 minutes each day until you reach 4-5 hours). Colic can occur for many reasons. Gas colic is often associated with feed changes or stress, so any steps you can take to minimize those two issues will be helpful if you decide to bring your mare to your farm. You might also want to consider deworming her before she goes out on the pasture to keep parasite burdens low.

Companionship will be the other key issue for her. If she is used to being with a group of herd mates, going into a group with strangers will be hard on her and consequently, her digestive tract. If she does not bond quickly with her new herd mates, keep you eyes open for a drop in appetite, depression, or manure changes that might signal an impending colic.

If she tends to be an easy keeper, you might also want to consider a grazing muzzle (or restricting grazing) to keep her from overeating in her new pasture.

Given her age, dental attention is wise, so speak to your veterinarian if she is due for her annual examination. Your veterinarian may have some other suggestions.

Finally, before turning horses out into a new pasture (regardless of the time of year), it is a good idea to check for poisonous plants and fence safety.

By Krishona Martinson, PhD, and Julia Wilson, DVM, University of Minnesota

What herbicide should I use to control hoary alyssum?

Q: We have been attempting to control weeds with frequent mowing, but now have seen some hoary alyssum and have decided to use an herbicide. We plan to use Forefront. However, upon reading the label and communications with the manufacturer, it appears that manure from horses grazing on Forefront treated pastures can only be spread in the treated pasture because it will kill broad-leaf plants. We have small paddocks and collect and compost our manure for use on our garden. It is my understanding that Forefront is very persistent and will not necessarily break down during the composting process. We also are located near a lake and designated wetland, so I am concerned about aquatic toxicity as well as impacts to amphibians. Upon review, it appeared that Stinger may be my best bet. Can you advise further?

A: Good for you for reading the label! You are correct that Forefront can persist in compost. However, if you follow the grazing restriction (time period after you apply the herbicide and before the horses can begin to graze again) on the label, you should not have these issues, but it's not guaranteed (chemical breakdown is dependent on weather and other conditions).

Stinger, Milestone, and Curtail (all commonly used herbicides for this situation) have the same potential issues (same family of herbicides). Even though these herbicides have no grazing restrictions (you should still check your specific label), we recommend at least a 7 day grazing restriction.

Hoary alyssum can be very difficult to control. The previously mentioned herbicides will work, but because of your specific issues, I'd recommend 2,4-D or Banvel. They may not give you as good of control, but you will not have the manure carry-over and compost issues to deal with. Since you can mow, I'd mow the pasture, wait about 10 -14 days (hope for some rain) and then spray the pasture. This will help achieve better control since the weeds will be younger/immature. Younger weeds are always easier to control versus mature weeds.

By Krishona Martinson, PhD, University of Minnesota

Q: Is there any danger in horses grazing frosted pastures in the fall? If so, how long would you wait?

A: Some deciduous leaves can be deadly after a frost or after they have wilted due to broken branches, fall leaf shed or storm damage. Leaves of greatest concern for horses are wilted maple and prunus species, including chokecherry, ornamental almond, and cherry trees. Horse owners should identify all such seasonally toxic trees on the property, and keep horses from their fallen or frost damaged leaves for at least 30 days. Even though these leaves are not commonly eaten, horses can accidentally ingest them, especially if hungry or bored.

Cyanide toxicity can also be an issue after frost. There are no reports of toxicity of horses grazing frost damaged grass, alfalfa, or clover. However, frost damaged pasture forages can have higher concentrations of sugars, leading to an increase in potential for founder and colic. To reduce the chance of adverse health effects, it is recommend that horse owners wait up to a week before turning horses back onto a pasture after a killing frost.

By Krishona Martinson, PhD, University of Minnesota

Can I feed both alfalfa hay and alfalfa pasture?

Q: What is your opinion on feeding both alfalfa hay and alfalfa pasture for horses?

A: Forage (hay and/or pasture) should be the backbone of a horse's diet, with at least half of the diet being some type of forage. Alfalfa is an excellent forage for most livestock, but the forage quality of good alfalfa hay and pasture exceeds the nutritional needs for most horses.

The average adult horse (lightly worked or ridden) needs about 10% crude protein in their diet. The crude protein in most good quality alfalfa hays and pastures vastly exceeds 10%. Although feeding excess protein to horses does not result in any short term health problems, it can lead to strong smelling urine (a concern if the horses are stalled in a barn) and can contribute to weight gain. If buying hay, hay with higher protein levels usually demands a higher price. Numerous horse owners are paying a premium for protein that is not needed by their animals.

Alfalfa hays and pastures also have higher digestible energy (DE) compared to grass hays and pastures. DE is used to balance the energy portion of a horse's diet. Feeding alfalfa hay and pasture to the average horse will most likely result in significant weight gain. Horse health problems tied to excessive weight gain include Cushings, metabolic syndrome, laminitis or founder, and insulin resistance. The potential for excessive weight gain is the major drawback for feeding a high quantity of alfalfa to horses. Mares that are lactating or in late term gestation, or horses that are in an intensive training program would most likely benefit from adding some alfalfa to their diet because of the increased energy.

Calcium (Ca) and Phosphorus (P) is critical to bone and tissue formation in horses. For the average adult horse, the Ca:P ratio should be between 3:1 to 1:1. A benefit of having alfalfa as part of your forage is that alfalfa hays and pastures tend to have higher calcium levels relative to phosphorus, and have higher Ca levels than most grass hays and pastures. It is important to have your forage and grain tested to ensure the Ca:P is adequate and never inverted, especially in young, growing foals.

Not only will horses likely gain weight on pastures with a high quantity of alfalfa, but there are also pasture management practices to consider (i.e. no chemical weed control options) when alfalfa is included in pasture mixes. Horses are selective grazers. Some research studies have shown that horses prefer alfalfa over grasses in a pasture. In a mixed grass - alfalfa pasture, horses will actually choose to continuously graze the alfalfa, while leaving the grasses. However, most varieties of alfalfa will not withstand continuous grazing causing it to be short lived in a pasture. To extend the life of alfalfa in a pasture, choose a variety that is recommended for grazing. Be sure to rest the pasture and allow regrowth of both alfalfa and grasses.

Bottom line, alfalfa is an excellent forage, but should not be fed as the sole forage or in high quantities to the average adult horse because of the potential for excessive weight gain and the negative health effects tied to weight gain. Feeding alfalfa (not usually as the sole forage, but in higher quantities) can be useful for classes of horses that require additional energy, including lactating mares and horses in intensive training programs.

By K. Martinson, PhD, University of Minnesota

Should I keep my horses on pasture in the winter?

Q: Is it recommended to keep horses on pasture once the ground has frozen and there is snow cover?

A: We do not recommend keeping horses on pasture over winter. There is minimal nutritional value in the dormant/dead grass and legumes. Hoof traffic and continuous grazing can cause considerable damage, which can results in weak plants or bare spots in the pasture the following spring and summer. Also, some poisonous plant skeletons, like white snakeroot, can remain above the snowline, tempting horses to ingest them. During winter months, keep horses in a safe area where they are fed hay, have water and shelter. As a guideline, turn horses back into the pasture the following spring after the pasture dries out and grasses and forages are between 6 - 8" tall.

By Krishona Martinson, PhD, University of Minnesota

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