What are mycotoxins?
Mycotoxins are toxins produced by moulds and fungi that can be found on fresh pasture grasses and hay, or even on commercial feed items that have been improperly stored. Virtually any feed item can potentially be infected by mycotoxins. It is possible for some feeds to contain multiple species of fungal toxins that may interact; the overall toxicity could then increase to a greater extent than with individual separate mycotoxins.
How do mycotoxins affect horses?
Fungal endophytes can be present on pasture grasses such as tall fescue and perennial ryegrass, and have been found to cause vasoconstriction of the palmar artery. As arterial vasoconstriction has been associated with laminitis, protecting the horse from exposure to alkaloid endophytes may play an important part in keeping horses sound. See the link below under the ‘Recommended Reading’ heading, summarising the study, "Vasoconstriction in horses caused by endophyte-infected tall fescue seed is detected with Doppler ultrasonography," published in April 2013 in the Journal of Animal Science.
Other forms of mycotoxin poisoning can be very serious, even resulting in the death of the horse. A wide range of clinical symptoms in horses vary from a subtle hindlimb ataxia, to obvious signs including respiratory, gastrointestinal, neurological, and reproductive problems.
Some common mycotoxins are shown on the chart below:
Is there any way to protect horses from mycotoxins?
Ensuring that all feeds are completely free of mycotoxins is very difficult, and is often no fault of the feed producer. Contamination can occur after harvesting or shipping if ideal clean, dry, storage conditions are not maintained. The harmful effects of mycotoxins may be reduced when toxin-binders are added to each feed. The toxin-binders work by attaching to the mycotoxins in the horse’s gut so they cannot be absorbed; they are then harmlessly excreted.
Some research has been done which found that glucomannan polymer was able to prevent toxicity from fumosarium toxins and ergot alkaloids as it has a naturally high affinity and capacity for binding to mycotoxins. It has been used extensively throughout most livestock industries; it is inexpensive, safe, and can be added to feeds daily.
Yeast Cell (Saccharomyces Cerevisiae)
The yeast cell wall comprises between 35% to 40% of the total yeast cell
Glucomannan polymer is produced from the cell walls of inactivated baker’s yeast (Saccharomyces Cerevisiae) which has been grown by non-alcohol fermentation. The yeast cell walls are ruptured, extracted by centrifuge and then washed, dried and pasteurised. The yeast cell wall comprises between 35% to 40% of the total yeast cell.
The outer yeast cell wall provides mannan proteins, often referred to as mannanoligosaccharides or MOS. Mannan cannot be digested by the animal, therefore it is available as a prebiotic nutrient for the beneficial bacteria or flora in the gut. The good flora then grow rapidly in the gut, providing the animal with an improved defence against harmful bacteria. A Prebiotic can be described as a biological agent that stimulates preventative activity within the gut of an animal.
The inner yeast cell wall provides B-glucan complex carbohydrates that have a naturally high capacity for adsorption of mycotoxins. Mycotoxins and harmful bacteria enter the animal’s gut and then attempt to bind to sugar compounds on the cells lining the gastrointestinal tract, an ideal location for subsequent colonization and reproduction. The binding process can be diverted away from the GI tract lining by the presence of glucomannans which attract and bind with the toxic substances. The glucomannans and their toxic load are then harmlessly expelled by the gut along with normal waste material.
‘Mycoglannan’ is a brand of glucomannan polymer manufactured in Europe and sold in Australia. The recommended dosage rate is 20g per day. As the product is non-toxic, many horse owners have found it helpful to give their horses double that amount (or even more) at high-risk times of the year such as during cool, damp conditions which are favoured by most fungi. Mycotoxin contamination of pasture is less likely during hot, dry summer weather conditions.
Fungal mycotoxins are thought to be the cause of some cases of photosensitisation in horses.
The photodynamic pigments present within the fungal mycotoxin are ingested by the horse from pasture grasses or contaminated hay or feed. The pigments are absorbed through the gut wall, enter the boodstream and circulate to the skin where they are exposed to UV light in areas of thin, non-pigmented skin such as muzzle and pasterns. The pigments react to the UV light by fluorescing which causes oxidative damage to the cells of the skin.
The resulting sores are painful, often being mistaken for sunburn. Greasy-heel and mud fever may also be caused by photosentisation.
Molds and Mycotoxins In Horse Feed: Basic Facts
H.V.L.N. Swamy, DVM, PhD November 11 2010, Article # 17233
Karen Briggs, August 01 2002, Article # 3695
New Tool Detects Effects of Endophytic Alkaloid Consumption
Kristen M. Janicki, MS, PAS MAY 19, 2013
Poison Plants in the Pasture
D. Bennett, PhD
Photosensitization in the Horse
Heather Smith Thomas, Jul 01, 2005
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