and Feed Safety by Dr Jennifer Stewart
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o different to human foods, all feedstuffs (and water and bedding) for horses can be contaminated with a variety of substances and organisms. Contamination can occur at any point from the paddock to the feed bin. Depending on the conditions during growth, harvest, storage and mixing - as well as the type of feeds and how they are provided to the horse - the level of contamination will vary between years, feed producers and the people who take care of the horses. And again as with human foods (where the concerns include salmonella food poisoning, rancid peanuts etc) - the growth of bacteria, fungi and yeasts that produce toxins can occur if environmental or storage conditions don’t support good food hygiene.
Contaminants can be: – chemical (prohibited substances, pesticides, herbicides, fertilsers, heavy metals)
Whether a fungus/mould produces mycotoxin depends on the type of mould, growing conditions, conditions during harvest, handling and storage, moisture, humidity, temperature, damage to the feedstuff, plant variety, pesticides, and geography. Feeds with more than 13% moisture are at the highest risk of mould growth and mycotoxin production. And, because mycotoxins are quite robust and hardy, they can survive food processing - so once formed in a feedstuff they will still be present in any feeds manufactured from it, including commercially prepared feeds, dried distillers grains, hay, haylage and silage.
Mycotoxin poisoning of horses has been reported in Australia, but is not common. The reasons for this include: – mycotoxins only accumulate in pasture grasses under certain conditions and most pastures are safe most of the time
– physical (stones, metal, string)
– owners are aware that feed should be stored in dry conditions and accidentally ‘spoiled’ feed must be thrown out
– biological (bacteria, moulds that produce toxic compounds called mycotoxins)
– horses are quite sensitive to ‘off ’ odours and will usually reject mouldy feed
The word mycotoxin (a poison in fungus) is derived from 2 words: ‘mukes’ – Greek for ‘fungi’ and ‘toxicum’ – Latin for ‘poison’. Fungi are part of the normal environment in crops and stored feeds, and they are everywhere – we share the world with many life-forms! There are more than 200,000 species of fungi in the environment — including mould, yeast, mushrooms, lichen and truffles. Depending on the weather and moisture levels, a single species of fungus can morph into other different species, or take on the features and behaviours of multiple types = more fun than a computer game! Over 100,000 mould species have been identified and one species can produce many different mycotoxins - and several species may produce the same mycotoxin. Mould growth and mycotoxin production are usually associated with extremes in weather conditions that cause plant stress and/or high moisture content of harvested feeds; poor storage practices; low quality feedstuffs in terms of dust, moisture and hygiene, and poor feeding practices.
– healthy horses can usually overcome the potential effects of ingesting feed containing low levels of mycotoxins
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– health problems may occur when low levels of mycotoxins are consumed over a long period All feedstuffs (including human foods) can be contaminated with mycotoxins – of which there are over 400 kinds. Mouldy, mycotoxincontaminated feeds can contain more than one mycotoxin and animals may be exposed to multiple mycotoxins. Effects are dependent on the specific mycotoxin(s), the amount and duration of exposure, and animal factors such as age, sex, reproductive status and level of stress. Most feedstuffs carry some form of unavoidable natural contamination. The challenge is to minimize any such contamination and the associated risks. Of special interest to horses are aflatoxins, fusariotoxins (fumonisin, mouldy corn disease) and mycotoxins from the ergot family produced by Claviceps spp. or other grass moulds. 11
