MYCOTOXINS And Feed Safety by Dr Jennifer Stewart

No 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)

–physical (stones, metal, string)

–biological (bacteria, moulds that produce toxic compounds called mycotoxins)

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.

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

–owners are aware that feed should be stored in dry conditions and accidentally ‘spoiled’ feed must be thrown out

–horses are quite sensitive to ‘off ’ odours and will usually reject mouldy feed

–healthy horses can usually overcome the potential effects of ingesting feed containing low levels of mycotoxins

–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, mycotoxin-contaminated 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.

Aflatoxins are produced by the fungus Aspergillus. Acute aflatoxicosis is very rare but chronic aflatoxicosis can occur with a daily intake of 500-1000ppb of aflatoxin (Table 1.). Grain (corn, wheat, oats, sorghum, rice and barley), hay (dusty hay can have over 10 times the amount of fungal spores and allergens as good clean hay) and protein meal crops (cottonseed, copra, soybean, peanut and sunflower meal and seeds) can be affected during growth. Aflatoxins can also accumulate in stored feeds and in feed additives when conditions are favourable ie moist, warm conditions, and damaged or cracked, rolled grains. Chronic aflatoxicosis usually improves when the contaminated food has been removed from the diet. Horses are susceptible to the condition but reports of cases in Australia are not common. To reduce the risk of aflatoxicosis, feed should always be properly stored and kept dry and cool. Feed spoiled by water and uneaten dampened feeds should be thrown away. Few naturally occurring episodes of aflatoxicosis have been reported in horses.

Table 1. Australian Aflatoxin Limits (ANZFA Food Standards Code)

Aflatoxin B1 Human foods 5 ppb

Peanut butter 15 ppb

Phomopsin Human foods 5 ppb

Aflatoxin B1 Stockfeed limits:

Peanut & cottonseed meals 2000 ppb

Cattle, horse & sheep feeds 50 ppb

Dairy cattle feed 20 ppb

Grain & crushed grain 10 ppb

Duck feeds 1 ppb

Chicken feed

ppb: parts per billion or ug/kg

Infected Corn / Corn Rot

Fumonisins are a common mould of corn throughout the world. International surveys have found that there are very few instances where corn is totally free of this mycotoxin - particularly if the grains are damaged or harvested soon after rain. Infection of oats has also been reported but is extremely rare. Fumonisins can also be found in cornflour, dried milled corn fractions, dried figs, herbal tea, medicinal plants, bovine milk and others. They are extremely toxic to liver and kidneys in horses and also cause a fatal brain condition known as leukoencephalomalacia or ‘mouldy corn disease’. Outbreaks of ‘mouldy corn disease’ have been reported in horses and donkeys fed mouldy corn or commercially prepared feeds containing corn, in Australia (in 1995 an outbreak killed 3 horses), Argentina, China, Egypt, New Caledonia, South Africa and especially the USA.

Fumonisin survives the pelleting process, meaning commercial cornbased products share the same risk as corn, and dry distillers grain (DDGS) has been found to have 3 times the concentration of fumonisin as the original corn. At particular risk are damaged crops or crops that have been harvested soon after rain. Insect damage predisposes corn to mycotoxin contamination because insects damage the kernel allowing fungal colonization and they also carry them between plants and paddocks. Mouldy corn disease has no treatment apart from supportive veterinary care and removing toxic feedstuffs, but early diagnosis and treatment increases chances of recovery. There are a few reports in Australia, most notably an outbreak in 1995 that resulted in the death of three horses. Mortality due to ELEM is high and death can occur within hours or days from onset of the clinical signs. Horses seem to be among the most sensitive animal species and clinical signs are observed following exposure to >10mg/kg feed for horses, compared to 160 mg/ kg feed in pigs.

Lupinosis is caused by eating lupins that have been infected with the fungus Diaporthe toxica which thrives in warm, moist conditions and produces a mycotoxin called phomopsin. Lupins are grown mainly in Western Australia and Victoria and poisoning can occur when animals graze fungi-infected lupin stubble, or are fed lupin hay contaminated with fungi. Stubble remains toxic for several months once it has been infected. Lupinosis affects mainly sheep and has rarely been reported in horses. It is usually fatal in horses and affected animals become ataxic and sluggish, have red-brown urine and can die suddenly. The highest risk period for lupinosis is summer to autumn - especially if the weather is warm and humid - and although horses are not often grazed on lupin stubble or fed lupin hay, lupin hay is sometimes used as an alternative feed-stuff in drought times. New varieties of lupin that are resistant to fungal infection have greatly reduced the risk of this disease in Australia, so always check that horses access only fungal-resistant lupin hay or stubble.

Perennial ryegrass staggers and paspalum staggers are sometimes seen in horses grazing pasture containing perennial ryegrass or paspalum. There have been reports of cases in Australian horses in temperate areas where perennial rye grass is the dominant pasture species and it can also occur from ryegrass hay and ryegrass seed screenings. The fungus (Neotyphodium lolii) invades perennial rye grass, where it produces a toxin called lolitrem B. Clinical symptoms include muscle twitching and tremors, swaying and convulsions, which increase with stress or exercise. The risk to horses is injury caused by uncoordinated movements and affected horses should be kept in a quiet, safe area; veterinary attention should be sought and in severe cases the horse may receive fluids and other medications. The clinical signs of a lolitrem intoxication are completely reversible and once removed from the contaminated feeds, animals generally recover within 5 days. The risk of ryegrass staggers is low in Australia. It can be reduced by not allowing pastures to be overgrazed — mycotoxin concentrations are highest at the base of the plants — slashing paddocks before heading; planting new ryegrass varieties that contain no fungi or fungi that produce only low levels of mycotoxin, and keeping an eye on horses during summer and autumn, especially if rain causes a flush of growth. Affected horses usually appear normal except for sudden episodes of trembling, incoordination, panic and collapse. Horses should be removed from the pasture, kept in a quiet place and veterinary treatment with fluids and therapy may be required.

Claviceps purpurea (ergot) | moederkoren (nl) is an ergot fungus that grows on the ears of rye and related cereal and forage plants. Highly toxic fungus | All species

Diaporthe phaseolorum var. sojae damage to soybean Glycine max en.wikipedia.org/wiki/Diaporthe#/media/ File:Diaporthe_phaseolorum_var._sojae

Paspalum can be infested with claviceps as can other pasture grasses and grain crops including ryegrasses, cereal rye, phalaris and paspalum. Paspalum staggers produces signs that are identical to the signs of perennial ryegrass staggers. The risk of ryegrass or paspalum staggers in Australia is low and good grazing management can help reduce the risk. Pastures should contain a mix of grass types and should not be grazed close to the ground. New varieties of perennial ryegrass are available which contain no-endophyte or low mycotoxin-producing endophyte. Paspalum pastures should be inspected for Claviceps paspali infection before the introduction of horses. Watch for symptoms during the high-risk period of summer to autumn. This is especially important if pasture has been grazed low, or if summer rains have produced a flush of perennial ryegrass.

Pregnant mares and foals are sensitive to low concentrations of claviceps and other fungal mycotoxins on grasses and cereal grains. Cases have also occurred in mares fed oats contaminated with claviceps-infected ryegrass seeds and in mares grazing Neotyphodium infected tall fescue. Signs include dystocia, prolonged gestation, reduced milk production and weak foals. Case reports are uncommon in Australia. Management includes preventing late gestation mares from grazing endophyteinfected pastures or feeding endophyte-infected grains or hay. Removal of pregnant mares from endophyte-infected pasture 60 to 90 days before the expected foaling date has been recommended to prevent these symptoms.

The complete elimination of mycotoxins from the food chain is extremely difficult. Methods to inhibit mould growth and remove mycotoxins include ammonia, bleach, binders, bentonite, botanicals (such as mustard, green garlic, cinnamon bark, peppers, cloves, thyme, green tea and honey), pasteurisation, peroxide, polishing, milling, fermentation, formaldehyde, irradiation, ozone, roasting, caustic soda and chicken intestinal microbes. Some work on some mycotoxins. Activated carbon (charcoal) has produced variable binding results and yeast cell walls have some effect in binding aflatoxin.

Adsorbents bind the mycotoxins to their surface so that they cannot damage the intestine or be absorbed. This includes several different clays and zeolites. From data in other species, to be effective, they must be consumed at a rate of approximately 1 to 2% of the diet. A horse consuming 10 kg of food per day would need to eat 100 grams per day as a minimum. Charcoal is also an effective adsorbent and isolated cell walls from Saccharomyces yeast also adsorb mycotoxins. There is no universally effective adsorbent. Digestive upsets can be a sign of mycotoxin intakes, and can also put the horse at higher risk of effects from mycotoxins. Supplementation with Saccharomyces cerevisiae yeast (Yea Sacc) may help, since this strain’s cell wall can adsorb mycotoxins.

Microscopic image of growing molds/fungus/spores 3d

Fungus ( Aspergillus – fumigatis)

Aspergillus mold

However, it is not known if it also can biologically inactivate them. Dosage for an anti-mycotoxin effect is also unknown but the digestive enhancing dose is 46 billion organisms/day.

Drought and insect damage are most important in causing mould and mycotoxin formation in the field. Storage conditions are also critical to preventing mould growth and mycotoxin production in harvested feedstuffs. Grain should be stored below 15% moisture. Seasonal peaks in aflatoxin content can occur in drought years and in particularly wet harvest seasons. Optimizing the conditions of feed production and storage (including straw as bedding material) is essential for horses health and performance. The application of sound hygiene practices in feed production and storage as well as feeding can help to minimize feed hygienerelated problems.

ABOUT THE AUTHOR Dr Jennifer Stewart (BSc, BVSc, PhD, MRCVS, Dip BEP AAIM) is an equine veterinarian with over thirty five years of experience. She is also a consultant nutritionist and has formulated feeds, custom mixes and supplements for leading international horse feed manufacturers in Australia, India, Ireland, Japan, New Zealand, Philippines, South Africa, Thailand, Turkey and the UAE. Dr Stewart is passionate about equine nutrition and it’s role in the management, treatment and prevention of many equine diseases and she is committed to bringing ‘science to the feed bin’. www.jenquine.com