Mycotoxins – What are they?

Myco is the Greek term for fungus and toxins mean poison and are produced in various types of fungi. Some of these fungi live inside the plant and are called endophytes. Perennial rye-grass contains endophytes which produce two very harmful myco-toxins, namely lolitrem B and ergovaline. Annual rye-grass where as it doesn’t contain the dangerous endophytes can have a highly poisonous bacteria form on the seed heads.

A toxic bacterial gall is formed and some may exude a yellow slime. Both the endophyte and bacterial gall will still be present in hay even if it has been stored for years, annual rye grass is also a nitrate accumulator.

Paspalum in Australia and New Zealand can become a dominant grass in horse sick paddocks particularly during summer and autumn when most other grasses will have browned off. Paspalum contains high mycotoxin levels in the plant close to the ground and also has a highly toxic ergot that can form on the seed heads. Both Rye grass and Paspalum are known to cause the ‘staggers’ other wise known as the rye grass staggers or Paspalum staggers.

Until recently, we horse owners didn’t take too much notice of fungi in our horses’ environment, apart from knowing not to feed mouldy hay or feed. Because they are usually invisible, and myco-toxins do not show up in blood tests, it has taken a while to make the connection between many health and behaviour problems in our horses and these insidious equine trouble-makers!! Some horse owners suspected a form of poisoning was occurring, having their soils tested for heavy metals and putting water filters on the troughs.

In 1985 the World Health Organization estimated that approximately 25% of the world’s grains were contaminated by mycotoxins. This figure has most certainly grown since then due to an increase in global import and export of grains and cereals and the changing environmental and weather patterns.

Our climate, and the generally low pH of the soils, means the conditions are frequently very favourable to the explosive proliferation of fungal spores and myco-toxins. Particularly in tropical areas where moist warm conditions are paramount. If you happen to live anywhere near any orchards you will know how often they spray for fungi. You will have seen moulds suddenly appear on horse manure from time to time or when the mushrooms appear in late autumn and early winter. Fungi love acidic conditions, so pasture fertilized with traditional super-phosphate makes an ideal environment for them.

The lifestyle of the typical horse means they spend most of the time out grazing the pasture. Consequently they are inevitably ingesting and inhaling vast numbers of fungal spores and myco-toxins 24/7. Not just at certain times of the year, but any time the conditions favour fungi!

Mycotoxins have also been directly linked to the extended gestation period for mares in foal as well as dystocia (difficulty birthing), lack of milk production, premature separation of the placenta and other placental irregularities. Weak or dead foals that may have suffered trauma or asphyxiation due to difficult birth or the foal may be weakened because of placental insufficiency.

It is no surprise that the results of the “Equine Health & Behaviour Survey” in New Zealand fit with this information. The horses with the most, and severest symptoms are invariably grazing the ‘improved’ pastures, especially the rye/clover mixes. Of these, most are also being fertilized with superphosphate.

However, there are some horses with severe symptoms that live on rye-grass pasture that hasn’t been fertilized in 10 years, and some that graze ‘low-endophyte’ pasture and still show symptoms. Thousands of horses suffer for many months of the year, from an array of the symptoms.

All of the ‘severe’ cases have exasperated owners who have spent many hundreds, sometimes thousands of dollars investigating other possible causes. They have had numerous blood-tests(which time after time come up clean or show just mild anaemia), equine practitioners of all descriptions, multiple saddle fittings and sometimes up to three new saddles, horse dentists and hoof trimmers. Finally they hear about feeding the right vitamins and minerals and a toxin-binder (a completely natural food that locks on to toxins in the horses’ intestine, prevents them from going through the intestine wall and into the bloodstream, and carries them out with the manure). Within days they are astounded at the difference in their horses!!

Due to the fact that there are hundreds of different myco-toxins lurking in and around all pasture types it is no surprise that the above scenario is very common. Feeding a toxin-binder is simple, comparatively inexpensive, and totally safe. If your horse has any of the symptoms mentioned below, it would seem logical to go down this avenue along with addressing mineral imbalances.

Signs of Myco-toxin Toxicity and/or Mineral Imbalances?

Because both these tend to happen unpredictably and simultaneously, especially coinciding with flushes of pasture growth, it can be difficult and fruitless to try and differentiate so it is best to address both issues regardless. Some mycotoxins have also been found to bind up nutrients such as magnesium.

Toxins are ones that have been ingested with pasture or feed
(They generally respond to a toxin-binder or removal from pasture)

Mineral imbalances are complex and it is important to consider the inter-relationship of them all. Excess of potassium and deficiency of the macro-minerals such as Calcium and Magnesium and sodium have very serious consequences. They require urgent attention in the short term in the form of appropriate supplementation. Horses kept on a dry lot or stabled will also require vitamin and mineral supplementation.

Meanwhile if your horse exhibits any of the following then it is highly likely he is ‘affected’ by his diet, in particular the grass he is eating.

Often starts with:

  • General ‘tetchiness’, an unwillingness to be touched, or tensing up and reacting when touched, especially around chest and thorax
  • Appears somewhat ‘stiff’, stepping short behind

This can then cause:

  • Cinchiness/girthiness, not standing for saddling/mounting
  • General crabbiness when ridden, pinning ears, swishing tail etc.
  • Tightness, tenseness, impulsiveness, wanting to run off
  • Can’t use your legs, reaching around to bite the girth when ridden

Progresses to:

  • Touchy around ears, difficulty with bridling
  • Flings off suddenly when haltering
  • Sore across the loins
  • Uncharacteristic bucking when first moves off with girth tightened
  • Excessive aggressiveness towards you or other horses (viciously biting you, attacking, Hounding other horses, you think they’re a ‘rig’)
  • Excessive herd bound behaviour (eg screaming maniac, irrationally attached to another horse)
  • Can exhibit both these previous two ‘opposite’ behaviours concurrently!!
  • Bucking (quite violent and “out of the blue”)
  • Bolting off in short bursts
  • ‘Nutty’ or ‘ballistic’ behaviour


  • Excessive spookiness/alertness
  • Shies away when approached, hard to catch
  • ‘Spaced out’, ‘wired’, ‘not there’, hallucinating
  • Eyesight seems to be affected, can’t judge jumps
  • Overly claustrophobic, extremely sensitive to noise (reluctant to ride close to the arena wall, rushes off the float etc)


  • Heavy on the forehand, stumbling over nothing
  • Standing ‘base-wide’
  • Difficulty backing up, out of floats etc
  • Discomfort walking downhill
  • Slightly drunk or ‘zonked’ looking
  • Uncoordinated movement, staggering
  • Giving out in the hind-quarters, laying down a lot in the paddock
  • Dragging back feet, reluctant to go forward,
  • Reluctant to canter, won’t canter

Heat stress:

  • Instantly overheats when you put the rugs on
  • Running madly around paddock for no reason (while other horses aren’t)
  • Slamming into fences/gates
  • Excessive sweating, white sweats, smelly sweats,
  • Sweating in unusual places, eg on top of rump, patches on upper neck
  • General agitation
  • Fence walking


  • Like a bug has flown up their nose, can be worse on sunny days
    head twitch


  • Jerky upward action of the hind limbs


  • When autopsy shows hind gut necrosis due to vaso-constriction of blood supply to the intestine


  • Raging seasons, not cycling properly
  • Difficulty getting in foal
  • Abortion
  • Prolonged gestation
  • Reduced milk production
  • Weak suckling by foal


  • Chronic dull/rough coat
  • Won’t put on weight, looks wormy but not, no top-line
  • Bloated or ‘potty’ belly, looks fat but neck and rump are normal or thin
  • Consistently small, frequent manure
  • Scours/diarrhoea
  • Lifeless eyes, dull, nobody home – glazed eyes
  • No energy, lethargic
  • Falling asleep on their feet (like narcolepsy)

Grasses that can harbour myco-toxins:

  • Perennial Rye Grass
  • Clover
  • Paspalum
  • Bermuda Grass (couch)

Make it your business to be able to recognize these grasses. When not in seed, the rye-grass is characterized by a narrow, dark green leaf, that is shiny on the back. Some species of paspalum have a purple tinge around the edge of the broad leaves.

Clover is 1/3 higher in sugar and starch than grass. All rye-grasses are high sugar grasses therefore even when they have had the endophytes removed as in low or zero-endophyte strains they are still not suitable for horses.

Toxin-Binders Explained

A toxin-binder helps to protect the horse from the toxins which can cause ill-health. It is NOT a cure. The yeast cell wall extract provides lots of ‘sites’ for toxins in the feed to latch onto and takes them out with the manure. Sometimes, when the climate favours proliferation of fungi, or grazing very short grass close to the roots, or when seed heads are present, the toxin-binder has its work cut out and you will need to up the dose, feed morning and night or completely remove the horse from pasture until the horse ‘cleans out’ and comes back to normal.

Horses do not become ‘immune’ to the toxin-binder because it does not enter their bloodstream.