Trichothecenes: A Complex Mycotoxin Causing Complex Issues in Cattle

Trichothecenes are a large family of mycotoxins that are produced by various species of Fusarium molds that are believed to be produced after stress conditions followed by wet weather during flowering. Most often, trichothecenes occur in field conditions prior to harvest and have been found in cereal grains, silages, by-product, dry hay, pasture grasses and other sources of feedstuffs, making trichothecenes one of the most common mycotoxins identified in cattle feeds. There have been over 200 different trichothecenes identified that are classified by their core epoxide ring structure at the 12, 13 carbon and a double bond at the 9,10 carbon positions. These two functional groups contribute to the ability for trichothecenes to inhibit protein synthesis and cause a variety of clinical issues seen in dairy and beef cattle.

Trichothecenes are further divided into 4 categories: Type A, B, C, D and differ by functional groups around the core structure previously mentioned. Within feed ingredients used for livestock, common trichothecenes analyzed include Type A trichothecenes: T-2 toxin, HT-2 toxin, neosolaniol; and Type B trichothecenes: deoxynivalenol (DON) or commonly referred to as “vomitoxin”, nivalenol (NIV), acetyldeoxynivalenol (acDON) and fusarenon X (FusX) to name a few. There are differences in toxicity reported within the type A and type B trichothences. For example, AcDON < DON < NIV << FusX and some data reporting NIV being 10 times more toxic than DON. The potency of the different trichothecenes is important in understanding and identifying outward clinical signs that are seen in cattle and associated with contaminated feed.

Since trichothecenes inhibit protein synthesis, there are many clinical signs that can be associated with cattle consuming diets contaminated by trichothecenes including:

• Feed refusal/reduced feed intake
• Diarrhea/inconsistent manure/bloody manure
• Spit out cud boluses
• Rough hair coat
• Altered rumen fermentation patterns, leading to potential alterations in milk yield and composition
• Disruption of gut wall integrity, leading to compromised nutrient absorption which can affect milk yield and composition
• Immune function may be compromised, leaving animals more susceptible to secondary infections including mastitis, metritis, and respiratory disease
• Skin/oral mucosal lesions
• Hemorrhages along the digestive tract or in other organs
• Increased incidence of metabolic disorders
• Potential negative effect on reproduction through a variety of mechanisms
• Potential role in hemorrhagic bowel syndrome (HBS)
• Death, in extreme situations

The negative effects expressed in livestock by a trichothecene challenge depend not only on the level, type, and duration of exposure, but as well as the animal's general health status, age, and species and various other stressors they may be experiencing including heat stress, overcrowding, and social/pen changes. Another important factor is if there are other mycotoxins such as zearalenone, fumonisins, aflatoxins or ochratoxin A also present within the feed. Consumption of feed contaminated with multiple mycotoxins can lead to synergistic effects. This means that the presence of more than one mycotoxin may intensify the negative effect(s) of the other mycotoxins present, leading to even poorer performance in animals than would be expected when a single mycotoxin is present.

Additional stressors animals are experiencing increase their susceptibility to the negative effects of trichothecenes as well as other mycotoxins within the diet. This may include period of stress such as near calving/onset of lactation/transition period, around weaning or transportation including the receiving period. The combination of factors may result in more pronounced effects (and at lower toxin loads) in such stressed animals. Chronic, low-level exposure to mycotoxins can negatively impact animal health and performance without causing clinical signs associated with mycotoxicoses. Additionally, it is important to keep in mind that we do see variation in contamination levels over time, so animals could be exposed to different levels of toxins, even day-to-day.

Mitigating mycotoxins in cattle diets can be a challenge as you need to identify and quantify the risk of the challenge in order to effectively reduce mycotoxin exposure and prevent negative effects. Since cattle are selective grazers and mycotoxins are not evenly distributed throughout pastures, crops, or feedstuffs, obtaining representative samples for testing may be difficult. A highly contaminated sample does not mean the entire lot of feed is bad and a ‘clean’ sample does not guarantee that all of the feed is mycotoxin-free. Although limitations exist, mycotoxin analysis of feeds can provide useful information to aid in making decisions such as to adjust the inclusion level of the contaminated feedstuff in the diet or if an in-feed mitigation product is justified.

There are a number of clay and yeast products on the market that can bind (adsorb) mycotoxins, but it is important to pair the correct product with the correct mycotoxin. For instance, the chemical and physical properties of the mycotoxin play a big role in determining whether the toxin can effectively be adsorbed by a binder. In addition, binder products vary in their composition and chemical structure, leading to variability in their effectiveness at adsorbing mycotoxins. Aflatoxins and ergot alkaloids are often sufficiently controlled by clay-type binders.

However, trichothecenes and zearalenone are poorly adsorbed and require other methods, such as detoxification through enzymatic activity which alters their chemical structure, thus preventing biological activity of the toxin in the animal. It is very important to ensure that the detoxification component is specific to the functional group and irreversible.

Additional components some products may include are plant and algae extracts that have been identified to repair and reduce damage to the liver and gut as well as provide support to the immune system. Combination products which provide activity through binding, enzymatic degradation, and protective plant and algal extracts can provide broad-spectrum mycotoxin control to combat a variety of types of mycotoxins that are frequently identified in livestock feedstuffs.

In order to manage the risk of negative effects from mycotoxins in feedstuffs, it is recommended to 1) routinely screen your feedstuffs to understand which types and concentrations of mycotoxins are present, 2) be vigilant of cattle displaying signs of mycotoxicosis (i.e., poor growth, reduced intake, feed refusals, rough hair coat, immunosuppression, reproduction issues, etc.) and 3) work with your nutritionist and veterinarian to determine if a mitigation strategy is needed.

For more information on mycotoxins, analytical services or product related questions please contact a dsm-firmenich representative.