What are mycotoxins?

A concise definition of a mycotoxin is "substances metabolised by certain fungi (moulds), which grow naturally on a wide variety of raw plant materials" or "toxic, secondary metabolites of low molecular weight produced by naturally occurring fungi."

A more extensive definition is that they are toxins produced by organisms of the fungus kingdom, which includes mushrooms, moulds and yeasts. Fungi are found almost everywhere in extremely small quantities because they reproduce by spores that are mircoscopically small that spread very easily. Most fungi are aerobic (they need oxygen to live), they consume organic matter and are found wherever humidity and temperature are suitable for their growth.

Mycotoxins themselves are invisible to the naked eye but the fungi that produce them are, on the whole, unmistakable. Moulds produce mycotoxins either as defence mechanisms, and/or to help colonisation of their host organism. They are a natural means by which moulds increase their competitiveness in their environment. Moulds occur throughout our environment and therefore so do mycotoxins.

It is evident, therefore, that in poorly made silages, for example ones that are not rolled and consolidated sufficiently well, fungi will thrive producing mycotoxins during their life cycle. There are literally hundreds of different types of mycotoxins and it is believed that there are more yet to be identified.

Which crops are affected by mycotoxins?

Moulds or fungi, depending on the prevailing conditions of temperature, water and oxygen levels can affect all crops, growing or stored.

Stored grass crops can be affected by moulds or fungi and this is usually apparent when the pit or bale is opened. Penicillium moulds are of greatest concern post-harvest and in particular P. roqueforti. It will survive at low pH and is often the dominant mould on silage clamps, with an estimated 80% of all silages in Europe believed to be contaminated to some degree.

The infections can be seen with the naked eye, though, the metabolised mycotoxins cannot. Loose bales of silage or hay or poorly compacted clamp silage are all forage crops open to infection. Hay stored in damp conditions can also become infected.

Correctly compacted silage and hay kept in the dry are less likely to get infected and those crops treated with a preservative when being made have a better than even chance of remaining clean. Straw made or stored damp will be easily colonised by fungi that grow on the bales and these can also be a source of mycotoxins. Dry feeds should be kept away from moisture and vermin, since any damage, even in storage, can allow mould growth to occur, especially in warm, damp conditions.

Despite all the best measures being taken, once the feeds are mixed together and air introduced, feeds can heat up in the feed trough. If this happens, try to feed smaller meals more often or consider a buffered propionic acid or inoculant to help keep the mix cool.

For instance crimped grain is a crop that will resist fungal or mould attack, the crimping process involving the use of liquid preservatives or bacterial inoculants that produce lactic acid to preserve the grain. This is all common sense. Regardless of the risk of mycotoxin contamination, feeds and forages cost money and should be stored effectively.

Where do we find evidence of mycotoxin poisoning?

All creatures, including ruminants, are susceptible to mycotoxin poisoning. In severe cases mycotoxin poisoning can lead to death.

Diagnosing mycotoxin poisoning is a problem because it can present in many different ways. Sometimes the illness may be slight and does not cause any great concern while at other times it can be dramatic depending on the number, type or combinations of mycotoxins involved.

However, recent research has identified a number of areas where mycotoxin poisoning can be identified in different classes of ruminants.

Although most research work has concentrated on the dairy cow, these organisms can also severely affect all beef cattle, calves, ewes and lambs and have a dramatic, negative, effect on farm incomes.

What do mycotoxins do?

In the dairy cow the effects could be manifested as:

  • Depressed milk yield
  • Loose dung or scouring
  • Reduced butterfat content
  • Increased cell count
  • Poor fertility or signs of oestrus
  • Variable feed intakes
  • Acidosis-like symptoms

Beef animals and calves demonstrate:

  • Reduced feed intakes
  • Poor growth rates
  • Calves fail to grow-on (do) post weaning

In sheep observations could include:

  • Poor or variable feed intakes
  • Abortions
  • Ewes selecting straw bedding in preference to silage
  • Twin Lamb disease

In all stock a healthy rumen has an ability to protect against low levels of some mycotoxins, but not all, and the situation can be complex when the animal is challenged with different or high levels of mycotoxins.

Overall, ruminants will react in similar ways to mycotoxin poisoning and along with all those identified above some of the examples below can also be evident to a greater or lesser extent.

  • Overall lethargy and general poor performance without any alternative explanation
  • Impaired immune function leading to a greater risk of disease
  • Antibiotics and drugs have little effect in controlling the problem
  • Poor rumen function
  • Muscle tremors
  • Bloody faeces
  • Stock that are ill at ease

Many of these examples can be indicators in other on farm problems but the fact that mycotoxins could be the causative factor can brought into the discussion along with examination of the dry fodder, silage and hay as well as the bedding.

It is easy to ignore bedding but, as we all know, cattle and sheep always eat some of the straw used as bedding. Also, while they lie on infected bedding, stock can absorb mycotoxins when they breathe or lick themselves.

Which type of farm is affected by mycotoxin poisoning?

Any farm can suffer from the effects of mycotoxin poisoning that will influence the overall income.

Beef and sheep producers have mostly ignored the implications of mycotoxin poisoning, largely because no one has bought it to their attention, while many dairy farmers are aware of the consequences of this type of poisoning as researchers and nutritionists have focused on this part of the industry.

The beef and sheep industries can suffer severe losses from mycotoxin poisoning, with animals failing to mature to their potential or animals dying for unknown reasons but most of the farms involved fail to correctly identify the problem. This is where the on-farm advisor can help.

Often the beef and sheep farms are the ones where silage is made later in the year as one crop. The grass can be dryer and harder to compact in pit or bale and when preservatives are not used moulds and fungi can easily develop. Damage to the plastic wrap on big bales, caused during handling or by vermin in the stack, can also let moulds to penetrate and allow mycotoxins to build up.

How do we prevent mycotoxins doing what they do?

Mycotoxins can be a product of poor practices on-farm, often forced upon stock farmers due to the prevailing weather conditions during harvest. Trying to avoid their production can be difficult but in the main:

  • Try to avoid ensiling mature, dry forages that are difficult to pack
  • Clean silage clamps prior to use and seal them promptly on the day they are filled
  • Inspect bag or pit plastic for holes regularly and seal any promptly with proper tapeUse six layers of wrap on baled forages instead of four
  • Use an effective forage additive to promote the production of lactic acid
  • Clean feed stores and discard contaminated crops or feed.
  • DO NOT FORGET mould will develop on old feed cake or other concentrates stored in poor conditions.