All mycotoxins are produced from molds. Out of the thousands of molds that exist, only a few mold species produce mycotoxins. While greater than 300 mycotoxins have been chemically identified, the biological or medical impact of only a few mycotoxins is known.
There are two types of mold growth: field molds and storage molds. Field molds proliferate while the crop is growing in the field, and storage molds propagate during feed storage.
Field molds are an issue with cereal grain crops and, in corn, the molds Gibberella, Aspergillus and Fusarium ear rots are most common in Canada. They are responsible for producing the mycotoxins vomitoxin (DON), zearalenone, T-2 and fumonisin. Storage molds originate from soil-borne spores brought into the silo or bunk with all forages during harvest and have the environmental conditions (management) that allow them to grow in storage.
Field molds typically don’t propagate in silos, and storage molds usually don’t develop while the crop is in the field. However, mold growth also varies depending on environmental conditions and under less-than-ideal management conditions, such as low harvest moisture, poor initial packing or improper feedout techniques.
It is possible for the field mold to produce additional toxins in the storage structure when they are allowed to proliferate because of aerobic conditions.
Storage mold spores can be found in all soil types and can be picked up during growth and harvest by the crop. When harvested, the spores will remain on the crop but will need the adequate environment to grow. Even after an ideal growing season, less-than-ideal ensiling conditions can set the stage for mycotoxins to develop in silage from storage mold growth.
All storage molds require oxygen to sporulate and begin growing in silages. Therefore, you can have a high spore concentration on the crop but little to no mold growth if there is no oxygen present. Most storage molds also need a pH of 4.5 or higher except for Penicillium rouqueforti; it has the capability of growing in low-pH environments.
Typically, silage that undergoes aerobic instability is initiated by yeast in the presence of oxygen, and they consume lactic acid for substrate (energy) and, consequently, there is an increase of silage pH. This yeast activity produces the favourable environment for mold growth during feedout or the back-end fermentation.
On the other hand, the clumps of these molds frequently observed in silages were formed during the front-end fermentation, usually the result of poor packing density.
Three most common molds isolated from silages in North America include Penicillium roqueforti, Aspergillus fumigatus and Monascus ruber. Other spoilage molds include Mucor and Monila. The easiest way to differentiate these molds is by colour.
Penicillium mold
Most experts agree Penicillium is of greatest concern in ensiled forages because it is very resistant to low pH. The mycotoxins produced by Penicillium roqueforti that are harmful to cattle are PR toxin, patulin, citrinin, ochratoxin, mycophenolic acid, penicillic acid and roquefortine C.
Research studies show these toxins form at certain times during silage storage; penicillic acid can be observed after 13 days post-ensiling, while PR toxin is produced 49 days post-ensiling. This production pattern presents challenges in being able to conduct routine monitoring of toxins present in silage – along with impairing the ability of veterinarians to evaluate the actual adverse health effects in animals.
Patulin and roquefortine C are known neurotoxins, where cattle may show clinical signs of muscle weakness and lack of coordination. Discrepancies exist in ruminant studies because symptoms under in vitro conditions are produced at very high concentrations and, in the case of dairy cattle diets, the final mycotoxin concentration usually is quite low.
Further in vivo dairy cow research work needs to be conducted to determine at what patulin dosages cows will show negative effects from the toxin.
These mycotoxins also possess antimicrobial properties that impede rumen fermentation. Veterinary and nutritional consultants usually are unaware of this class of toxins because very few laboratories have developed a screen to detect these Penicillium-produced toxins. The only way to confirm the presence of these toxins is to culture the silage and make an indirect inference that patulin may be one of several storage mold-produced mycotoxins present in the silage.
Aspergillus fumigatus mold
The primary mycotoxin produced by Aspergillus fumigatus is gliotoxin. Gliotoxin in conjunction with Clostridial perfringens type A has been identified as a possible cause of hemorrhagic jejunal syndrome (HJS) in dairy cattle.
HJS is an acute disease in dairy cattle characterized by a sudden drop in milk production, abdominal pain due to obstructed bowels and anemia. Death can come within 48 hours from the onset of the syndrome. Veterinary toxicologists warn that the presence of A. fumigatus alone does not necessarily result in HJS events in dairy cattle. Many other factors come into play, including ration formulations and pre-existing sub-acute rumen acidosis events.
Mucor, Monila and Monascus ruber mold
Mucor and Monila do not produce any known mycotoxins. Their primary concern is reducing silage nutritional quality, bunk life and palatability. Monascus ruber usually does not present mycotoxin concerns, although researchers have isolated the citrinin mycotoxin. In monogastrics such as pigs and chickens, this mycotoxin can produce liver and kidney problems.
A common toxic effect in cows exposed to any storage-produced mycotoxins is a change in ruminal flora makeup, which alters rumen fermentation. This will affect a cow’s overall performance and efficiency in your barn. Long-term feeding of moldy silages can produce local inflammatory responses that may lead to rumenitis.
Other body systems in a cow can be affected by storage mold mycotoxins if high concentrations enter into the blood system.
If toxins are detected or highly suspected from mold identification, one must decide on a practical approach to remediation. The best options to maintain herd health include segregating spoiled feed, stimulating the immune system by increasing ration energy, protein, vitamins (A, E, B) and minerals (Se, Zn, Cu, Mn), as well as including mycotoxin-binding agents.
The most effective remedy may be the tried-and-true adage of “dilution is the solution.” Reducing the amount of feed that contains the mycotoxins in the ration will allow the overall “toxin load” the cows are eating to be lower.
Prevention of storage molds and mycotoxins
The benefit of storage molds and their mycotoxins is: Producers have control whether they have the opportunity to grow or not. To prevent molds and their mycotoxins from developing in stored silage, follow accepted production practices that preserve quality, primarily by reducing the pH level and eliminating oxygen in the feed. Accepted silage-production practices include:
- Harvesting at the proper moisture content
- Chopping uniformly at the proper length
- Filling the silo rapidly
- Packing the silage sufficiently
- Covering the horizontal silo immediately during or after filling
- Using an effective fermentation aid such as a combination of Lactobacillus plantarum and Lactobacillus buchneri inoculants
Storage size should be appropriate for the herd size to ensure daily removal of silage at a rate faster than deterioration can occur. In warm weather, it is best to remove a foot of silage daily from the feeding face of horizontal silos. Cut the feeding face cleanly and disturb it as little as possible to prevent aeration into the silage mass.
Be careful not to remove excess plastic covering from the surface during silage feedout to minimize chances of top mold activity. Feed silage (or other wet feeds) immediately after removal from storage and minimize leaving excess silage in front of the face of the bunk. Avoid feeding spoiled or deteriorated silage, as it can reduce feed consumption, fibre digestibility and production.
It has been proposed that there are no more feed toxins today than in the past; however, animals today may be consuming significantly more dry matter, resulting in greater intake of the toxin, and labs now have increased detection capabilities.
Being aware about the various types of mold and their mycotoxins is important for producers to understand. Sometimes if something is off with the cows, we can jump to the conclusion that mycotoxins are the problem.
It is very important to rule out other causes for the herd issues such as nutritional imbalances, cow comfort and environmental issues, and infectious diseases (e.g., Johnes disease, parasites, viral infections, rumen acidosis). PD
PHOTO 1: Penicillium (green/blue)
PHOTO 2: Aspergillus (yellow/green)
PHOTO 3: Mucor (white/gray fluffy)
PHOTO 4: Monascus ruber (red surrounded by white)
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Martina Pfister
- Dairy Specialist
- – Western/Central Ontario
- Dupont Pioneer – Canada
- Email Martina Pfisters
Key points to remember about mold and mycotoxins
- All mycotoxins are produced by mold, but not all molds produce mycotoxins.
- Two types of molds: Field and storage molds
- We can prevent storage molds from growing by ensiling forages using best management practices during filling, storage and feedout.
- Storage molds need oxygen to grow; most need pH of 4.5 or higher to grow except Penicillium roqueforti.
- Very few laboratories screen to detect storage molds. An alternative is to take a sample of the mold produced in storage, run a culture and then make an indirect inference about the likely presence of mycotoxins.
- Most molds identified in silages can result in lowered palatability and nutrient value.
- If a problem is suspected, a comprehensive differential diagnosis is essential – e.g., many herd problems blamed on mycotoxins turn out to be nutritional.
- Each type requires different conditions to grow. Field molds typically don’t propagate in silos, and storage molds usually don’t develop while the crop is in the field.
- The most common mycotoxins tested in a lab are vomitoxin (DON), zearalenone, T-2 and fumonisin, all of which are produced from field molds, not storage molds.
