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Grazing and toxic plants

From: Stacey

Hi Jessica. Now that Spring is here and wild flowers and plants are coming up all over the place, it would appear that horse owners could never be too cautious about letting their animals eat whatever they find. There is a particular weed which came in rampant this year in and around the Tucson area and our horses love it! We, fortunately, knew ahead of time that this wasn't harmful to them but watch them when they graze these weeds and there are other weeds mixed in, but they just naturally pass over the other weeds.

We are so cautious with our domesticated animals. My question is, do horses in the wild have an instinct for good versus toxic plants or perhaps an intolerance to those that are toxic? I mean, they obviously aren't grazing in a cultivated pasture.

Many thanks again for your consideration and expertise.

Stacey H.

Hi Stacey! What an interesting subject this is. Horses in general do seem to have a good instinct for choosing the "healthy" vs the "unhealthy" plants that make up their forage. They'll choose the most nutritious and healthy forage first, then work their way down through the less nutritious and healthy forage until they reach the plants that are really dangerous. At that point, they will usually leave the plants alone - unless they are starving, or unless the plant has suddenly appeared in their field and they are curious.

It's difficult to compare wild and domesticated horses, though, for many reasons.

Wild horses are out all the time, taking their chances with whatever forage is available to them. Like domesticated horses, wild horses will eat good plants first and toxic plants last - but like domesticated horses, wild horses WILL eventually eat toxic plants if the good plants are gone. When a wild horse makes a mistake and eats something toxic, it dies, and nobody knows about it. When a domesticated horse eats something toxic, it will be noticed - either before it dies, or when it has died.

Domestic horses exist in a wide variety of situations. They don't all have full-time pasture - some have only half-time pasture or part-time pasture, and some have no pasture at all. Many horses get a few minutes of hand-grazing after a ride if their owners have time, and no other "pasture time" at all. The less time a horse has in pasture, the more likely it is to grab mouthfuls of anything green it sees on the trail... and sometimes the results are not good.

Even domesticated horses that live in pastures all the time rarely live in "natural" pastures. Our pastures are often quite artificial. Since farm-owners have to maintain pastures, and most pastures are less than huge, the pastures are tilled, seeded, sometimes fertilized and/or overseeded, watered during the dry season, etc. Horses are often kept off the pastures entirely during the wet season so that the pastures can become or remain grassy - and not turn into giant mudlots that will later turn into giant drylots!

Because of the way we plant and manage pastures, most pastures are very limited in the types of forage that they offer horses.

Horses like dandelions, for instance - and so do many humans. ;-)

I once spent several days following my horses around just so see what they did and what they ate, and it was very interesting. Horses eat the most palatable forage first. Given a choice, they'll first consume the new, green shoots close to the ground - then they will eat the longer grasses, they they will eat the more palatable weeds, and finally, when everything else is gone, they will eat whatever is left. Unless they are desperate, they won't eat the long, tall grasses that grow in their "bathroom" area - and that is why it's important to clean out and mow paddocks and pastures regularly. It's quite possible to fool yourself about how much sustenance your horses can derive from a small pasture if you don't realize what those areas of tall grass represent.

We have to guard our horses against toxins because we don't want our horses to become ill or to die. It's that simple. In the wild, horses can eat toxic plants and die - that's part of nature. Nature is concerned only with the life and preservation of the SPECIES - the individual, any individual, is unimportant. We, on the other hand, are very concerned with the health and welfare and life and preservation of the one horse, or the two or ten individual horses, in our care. To nature, any given horse is expendable. To a horse-owner, an individual horse is unique and irreplaceable.

If a wild horse eats a toxic plant and dies, there is rarely anyone around to mark the event, and the other horses move on. If a domesticated horse eats a toxic plant and dies, someone is bound to notice, and circumstantial evidence or the results of a necropsy will show whether the horse ate too many acorns, or a large branch of wilted red maple leaves, or a small mouthful of yew, or... Also, horses in the wild are not likely to run across yew hedges, or have access to vast amounts of acorns.

Domestication has certain drawbacks. We provide our horses with limited space containing a limited amount of nutritious forage, then wonder why the horses eat the top board of the fence or the bark of the pasture trees. We try to keep our pastures in grass, but which grasses? There may well be nutrient requirements that we can't meet by letting the horses graze a pasture consisting of only two or three grasses of our choice.

We also choose the grasses for their looks (bluegrass) and for their strong root systems (essential for overcrowded small areas) and so on. Fescue is great, but many people won't grow it because of worries about endophyte-infested fescue causing problems in pregnant mares.

Wild horses don't have to deal with these limitations - they stay on the move, have access to many different sorts of grasses and plants, and never reach the point at which the grass is completely grazed down or full of dung. On the other hand, they DO experience times when there is little or no forage of any kind available, and they become thin and weak in conditions that, if duplicated in a pasture (heavy snow, no grass) would simply mean that the horse's owner would say "The pasture's getting low on grass" and then toss a bale of hay over the fence every morning. Domestication has its advantages, too. ;-)

One thing we can do for our pastured horses is to give them more variety in their diet. We can do this by varying the grasses we grow, and/or by adding pasture herbs to the fields. There are companies offering special mixes of pasture herbs and grasses that can be scattered either in the field (plants with strong root systems) or along the fenceline (plants with more delicate root systems).

No matter what we do, though, we still have to patrol our pastures and fields, and be sure that they are free from toxic plants - and from branches of toxic plants that may have blown in from elsewhere. A bored or curious horse may well take a few bites of whatever happens to be in the field, and if the "whatever" is cuttings from someone's Japanese yew, that bored and curious horse will soon be a dead horse.

There are other risks too - if you identify a toxic weed in your fields, be careful how you get rid of it. Round-Up or similar products are popular, but you'll need to be quick to remove the dead weeds after using Round-Up, as it actually seems to make the dead weeds MORE palatable and attractive to the horses! So if you find something in your field that you don't want there, either remove it manually or kill it and then remove it manually. It's really just a matter of using your common sense. If you usually turn your horses out early in the morning, wait a little longer on mornings after a storm, and walk the pasture yourself before turning the horses out. That way, if you find anything, whether it's a branch of red maple with wilting leaves that you need to remove or a broken section of fence that you need to repair, you won't have any unpleasant surprises later in the day.


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