MYCOTOXINS

The knowledge of and on mycotoxins has increased exponentially in the past decade.

For the reader of this article who needs further in-depth information please refer to “Mycopedia -the technical reference book for in feed mycotoxin contamination.” In the more than 300 pages there are over 1000 referenced publications.
This short article will attempt to summarise the mycotoxin problem in South Africa with special reference to pork production. Producers can by reading this article attempt to introduce practices to minimize the negative effects of mycotoxins on their production systems.

Definition and symptoms

• Mycotoxins are toxic products formed by fungi that colonize crops in the field or after harvest and thus pose a potential threat to human and animal health.
• There are numerous species of mycotoxins with each type causing specific symptoms.
• All farm animals are affected with swine being the most susceptible.
• A mycotoxin affected diet may lead to substantial economic losses.
• The most common symptoms are feed refusal, poor feed conversion, reduced daily gain and immune suppression. This results in an increased susceptibility to disease. There is interference with fertility.
• There are also residues in animal tissues, especially the body fat.
• All the organs of the body are affected.
• We are also aware of a potentiated effect with a combination of toxins. 

 

Types of mycotoxins

• There are several hundreds of mycotoxins. The most common referred to in the swine industry are aflatoxins, ochratoxins, fumonisins, zearelenones and tricothecenes. 
• Polycontaminations (more than one mycotoxin) are common.

 

Control of mycotoxins

• The first approach to control mycotoxin contamination in feed is to prevent the formation of mycotoxins ahead of the feed mill. It however has limited efficacy.
• Once the feed becomes contaminated with mycotoxins, the elimination of mycotoxins is almost impossible.
• Mycotoxins are chemically and thermally stable, meaning that the common feed processes are not efficient to remove mycotoxins.
• Extrusion processing at temperatures greater than 150°C are needed to give a good reduction of zearalenone and fumonisins, a moderate reduction of aflatoxins and a variable to low reduction of deoxynivalenol. 
• Removing kernels with extensive mould growth, broken kernels, and fine materials by sieve cleaning significantly lowers total mycotoxin contamination. It is however possible that a large amount of the total feed can be rejected resulting in economic losses.
• The use of an effective mycotoxin binder is common strategy in South Africa.

 

The use of mycotoxin binders

• There are more than 120 mycotoxin binders registered in South Africa for animal use.
• Mycotoxin binders are registered under Act36/1947 as a Zootechnical additive in animal feeds and should have a V registration number.
• Pork producers should be hesitant to use an unregistered product.

 

The attributes of a mycotoxin binder

• The most common strategy for reducing an animal’s exposure to mycotoxins is to decrease mycotoxins bioavailability by incorporating various mycotoxin-detoxifying agents in the feed, which targets a reduction of mycotoxin uptake and distribution to the blood and target organs.
• Depending on their mode of action, these feed additives may act by reducing the bioavailability of the mycotoxins (adsorbing agents also called binding agents, adsorbents, binders) or by degrading them into less toxic metabolites (bio-transforming agents).
• The most common binders are activated charcoal and clays. 
• Activated carbon, also called activated charcoal, is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions.
• Mycotoxin-adsorbing agents are large molecular weight compounds that are not digested by the animals and end in the faeces.
• Silicate minerals are the most frequent mycotoxin adsorbing agent in the market. There are numerous clays, and they differ in their fineness of grind, the type of clay, their adsorbant capability and ease of mixing. They can be either phyllosilicates (smectites) or tectosilicates (zeolites), the latter having a limited efficacy compared to phyllosilicates and particularly smectites (Lemke et al., 2001
• Adsorbing agents must be able to bind mycotoxins in contaminated feed without dissociating along the gastrointestinal tract of the animal.
• Organic adsorbing agents such as yeast cell walls are also frequently used. They are popular for their ability to complex with some mycotoxins without reducing the bioavailability of other feed nutrients. They are mostly composed of polysaccharides (beta-glucans and mannan oligosaccharides MOS).
• FOS and MOS are often also used as pro and prebiotics.
• A great number of microorganisms have some capacity to degrade or detoxify some mycotoxins into non-toxic metabolites. These are the so-called enzymes that can detoxify certain mycotoxins. Many enzymes originate from bacteria.
• The use of algae has also been incorporated into certain binders. Algae mimic the work of modified smectites.
• Certain other products have over the years gained acceptance by including them into the mycotoxin neutralising package. These are immune stimulants, such as polyphenols; liver support or hepatotropic agents, milk thistle or sylamarium comes to mind; the addition of sweeteners can be added to stimulate appetite. The addition of yeasts/MOS and FOS and algae extracts complete the picture. Polyphenols are reducing agents, and we think of vitamin C and vitamin E and certain caretonoids. They are referred to as antioxidants.
• The binding of all mycotoxins and especially DON is imperative. Not every product has an equal binding capacity. Certain consultants combine different products. This practice is often frowned upon by the primary manufacturer.

 

The diagnosis of mycotoxicosis

• In many instances consultants will offer an opinion that mycotoxins are the cause of the poorer than expected zootechnological performance.
• The opinion will be based on the exhibition of clinical symptoms.
• Feed testing remains an important factor in confirming the presence of mycotoxins. It is important to remember that mycotoxins occur in pockets or hot spots within the feed.   Sampling methodology is therefore very important.
• The use of blood tests “mycomarkers’ confirms the presence of toxins in the body. This recent innovation from the Belgian company Innovad is revolutionary and aids on farm consultants in confirming their diagnosis.
• Interpretation of the results and a final diagnosis is often a combination of the above.
• Laboratories may differ in reported results. Interpretation of results based on experience remains imperative.
• The incorporation of blood tests, however good, often has a long delay between sampling and reporting.

Prevention of mycotoxicosis

• On the field. This is very difficult to implement. Changes in farming practices of which ‘no till’ ploughing has resulted in an increase of the mycotoxin contamination levels of many animal feed products. Global warming and severe changes in weather patterns also contribute.
• Are there differences in the contamination of white and yellow cultivars? It may be that certain yellow cultivars are more robust or resistant to contamination.
• Harvesting and storage methods are important, especially the storage of grains that are high in moisture.
• Intelligent use of mycotoxin binders.
• The formulation of diets.

 

Return on investment!
Like many things in intensive farming practices the use of additives remains an emotional decision. Advocating the use of a good effective binder remains important.

Let us take a grower feed that has been contaminated with mycotoxins as an example:

The pigs consume about 200 kg of feed from 10 weeks of age to 22 weeks of age. In this period, they can grow from 30 kg to 110 kg of live mass.

A FCR of 2.5 and an ADG of 952 grams is common on good farms.

Mycotoxicosis has been diagnosed. The pigs have a reduced intake resulting in a lower market mass at 22 weeks of age of 104 kg as well as a reduced feed intake of 192 kg. The parameters now read FCR = 2.59 and ADG = 925 grams.

A mycotoxin binder is included at 1kg per ton and a cost of R100/ton.
 
Scenario 1
Cost of feed R6.10/kg 
200 kg of feed = R1220   Income 110 kg live x 0.765 = 84.15 kg @ R34/kg = R2861.10
Margin = R1641.10

Scenario 2 
192 kg of feed x R6.10 = R1171.20   Income 104kg x 0.76 = R79.04 @ R34/kg = R2687.36
Margin = R1516.16
Reduced profit of R124.94 per pig

Scenario 3
Cost to restore performance to scenario 1 costs R100/ton. The feed now costs R6.20/kg. From experience we know that performance is never restored to the 100% we had without contamination.
196 kg of feed intake and 108 kg live mass is the new performance parameter.
196 kg x R6.20 = R1215.20     Mass 108kg live x 0.76 = 82 kg = R2790.72
Margin = 1575.52 

The margin is better than scenario 2 but not as good as scenario 1 where there was no contamination.
For an investment of R20 an improved but still reduced performance, a ‘profit’ of R59.36 is realized. 
This exercise accentuates the importance of carcass mass.
At R34/kg the ratio of carcass mass to feed price is 5.57.
Three kilograms of carcass mass = R102 increased income.
Three kilograms of extra feed = R18.30 

 

Summary
Regular testing and assessment of mycotoxin contamination remain important on farm decisions. 
Records and the interpretation of records are equally important.
New products are regularly introduced to the market and the continual assessment of binders, and their capabilities, are very important for economic reasons.