Toxic and dangerous plants.
Seen some worrying advice from people lately about horses generally avoiding them if there’s grass. My advice is to remove toxic and dangerous plants from your pasture. Some explanations below. Source is equine to equisetum, a very good page for finding out more about toxicity and our horses ....
Q: Horses generally self select and avoid toxic plants don’t they so I don’t really need to worry much do I ?
A: Noooooooooooo they don’t and yes you do need to remove them from your paddocks.
Q: But horses survive in the wild don’t they where there are toxic plants so they do avoid them?
A: Yes generally.
The following info is taken from Gen Hanson Equine to Equisetum
But .......
Horses in the wild are very different to those we have domesticated.
“In the wild
1) Foals learn from mares and older band members. Young horses mimic their elders. Negative feedback teaches adult animals that some plants cause unpleasant reactions. Avoidance of certain plants is passed down for multiple generations, with each new one learning from the last. We rarely see that type of learning in domestic situations.
2) Horses and burros in the wild have large ranges and move often; these ranges may consist of thousands of acres. The vast majority of toxic events occur from situations where pastures are degraded and forage is depleted. In the wild, animals usually have the option to keep moving in search of forage, therefore are not often forced to eat unpalatable or toxic plants in order to fill their bellies. In circumstances where wild bands are forced to remain in the same place, we begin to see illness and general poor health.
3) Eating very small amounts of toxins may help build up immunity. It is believed that animals that sample bites of various plants may be at least partially protected from toxicity later on. (This does not apply to hepatotoxins, for which toxic effects are cumulative over time.)
4) Nutrients in a widely varied diet can protect from toxicity. Research has shown that certain toxins in forage can in effect neutralize other toxins. Animals in the wild nearly never eat monocultures of one grass. Instead, they eat many different forage grasses and forbs; this diverse diet supplies many vitamins and minerals. Perennial deep-rooted plants bring nutrients from far beneath the surface up to their leaves, while pasture grasses are often species with roots that may not reach down more than several inches. Animals that can roam large ranges may ingest many probiotics that help keep the gut healthy; small pastures and hay may not provide these.
5) Animals that are fit are less likely to fall victim to plant toxicity. A life in the wild by necessity keeps horses strong and well-conditioned. Our domestic equines often don't have that level of fitness, which makes them more susceptible to things like plant toxins.
The diets of wild or feral equines vary enormously from those raised and kept in captivity, as do their grazing habits. In fact, if we were able to adopt some of their habits for our domestic equines, we would likely see an increase in health and body condition, and a decrease in toxic events.”
Other points ....
1. Horses are monogastrics and disadvantaged in regard to toxic plants. In ruminants, the rumen detoxifies plant material before it enters the gut. In horses, toxins leave the stomach and enter the gut, where the small intestine carries out much of the digestion. This means that toxins may more readily enter the blood stream without being detoxified.
There are some plants for which a mere mouthful can be deadly, as with yews (Taxus spp.) and oleander (Oleander spp.). Others like poison hemlock (Cicuta maculata) and foxglove (Digitalis spp.) required ingestion of just a pound or two before being lethal.
2. We all know that every animal is unique. They have differences in metabolism, body condition, histories, food preferences, age, physiology, and health conditions. Even color and breed can play a part.
The level of toxicity depends on many factors. Often the very young and very old are the most affected. That's also the case for those with preexisting health issues. Animals digest and metabolize feed differently, as is evident by the number of IR, EMS, and Cushing's equines.
3. One significant risk factor in the case of hepatotoxins (those that damage the liver) is a history of prior ingestion. It doesn't need to be the same plant or even precisely the same toxin. Damage from these toxins is cumulative, so it may take years to reach the toxic threshold. Equines can appear normal and healthy until the liver is 75% compromised, after which failure is rapid. It's very possible to acquire an animal with a damaged liver and not know it until at some point clinical signs appear.
It is exceedingly rare that several animals will be affected in precisely the same way by plant toxins. Those instances are usually the ones of extreme severity, where the level of toxic plant matter in hay or pasture is very high.
We also don't know what abuse or neglect in prior situations does to their well-being. It could be that deprivation of nutrients for an extended period of time predisposes them to be more susceptible to toxins later on.
4. We should never discount the possibility of plant toxicity when an equine falls ill without apparent cause or when tests are inconclusive. Always consider pastures and hay, and check them carefully. Don't assume that because only one horse is affected, toxic plants can't be the cause. If the source of toxicity is not removed, at some point it will very likely not be just one horse.
5. There are a number of toxins that don't immediately cause clinical signs, but over time, ingested amounts add up. There is a toxic threshold before which there are no signs, but when that threshold is reached, toxicity occurs. Toxins that affect the liver, primarily alkaloids, have a cumulative effect. No signs may present until the liver is 75% compromised, after which there is no recovery.
6. There are also numerous plants that aren't significantly toxic until the right set of circumstances arises. That may be a drought, a freeze, heavy rains after drought, poor forage growth one year, or a weather event that causes plant damage.
7. It really isn't a bad idea to get a blood panel done every few years, even if there are no outward signs of toxicity. It's always easier (and far less expensive) to treat disorders early and make dietary changes rather than wait until the damage is severe.
8. As mentioned earlier, the monogastric (equine) and the ruminant (other grazing animals) digestive systems vary greatly. The multi-chambered stomachs of ruminants allow for much better detoxification of plant materials, while the single stomachs of equines means that toxins are much more likely to enter the small intestine and from there, the bloodstream.
Equines actually have a much more delicate system than one would think by looking at them. They're highly sensitive to many toxins that don't affect ruminants much. They are also reactive to sudden changes in diet, sugars in forage, fiber content of forage, and molds. Anyone who has dealt with colic knows how quickly it can happen, and how insignificant the cause can seem.
9. Of course, we as equine stewards have created many of these problems. By feeding a monoculture of just one type of hay, we build guts that aren't able to tolerate a variety of feeds. There are reasons that the numbers of IR, EMS, Cushing's, and related disorders have risen and continue to rise. A diet that consists of varied grasses and forbs creates a much stronger gut than a diet of solely one type of grass. Animals that have steadily eaten just one forage species like timothy or orchard are more likely to feel the effects of even small amounts of toxic plants. As we mentioned, this is one reason wild horses don't experience toxic events like our domesticated ones do.
Conclusion
While in many ways our equines are hardy and tough animals, when it comes to their digestive systems, not so much. It's our job as their stewards to give them the best forage possible; this includes promoting a variety of grasses and forbs and limiting the presence of toxic and injurious plants.
We can't assume simply because we don't see outward clinic signs that there are no toxic agents at work. This doesn't mean that we should live in a constant state of anxiety, but it does mean that if we believe or even think our animals have been eating potentially toxic plants, we need to take the steps to protect them from toxic events.
Ignoring known toxic plants is really playing Russian roulette with our equines' health.
(Source: equine to equisetum)
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