|Fact Sheet||Peer reviewed|
Cite as: Jacela JY, DeRouchey JM, Tokach MD, et al. Feed additives for swine: Fact sheets – flavors and mold inhibitors, mycotoxin binders, and antioxidants.J Swine Health Prod. 2010;18(1):27–32.
Also available as a PDF.
In providing a high quality diet to pigs, it is important to ensure that it contains the correct amount and balance of nutrients for optimal productivity and is highly palatable, safe to the animals, and free of substances that may negatively affect their performance. Thus, the addition of feed additives to prolong shelf-life, prevent mold development, or bind mycotoxins present in the feed may be required in certain situations.
What are mycotoxins?
Mycotoxins are chemical compounds produced by actively growing molds (fungi) as secondary metabolites that can negatively affect pig performance. While not all molds produce toxins, over 300 types of mycotoxins are known to be produced by molds, with aflatoxin, vomitoxin, zearalenone, fumonisin, and ochratoxin generally regarded to be the most significant mycotoxins affecting livestock production (Table 1).1 Young and breeding animals are generally more susceptible to mycotoxins.
Table 1: Regulatory limits for the five major mycotoxins in feedstuffs used in swine diets*
* Source: Food and Drug Administration Center for Veterinary
The molds that produce the common mycotoxins found in livestock diets belong to the genera Aspergillus, Claviceps, Fusarium, and Penicillium.2 Feedstuffs may be contaminated before harvest of the main plant source, during post-harvest handling and storage, and during processing into animal-feed products. Grains such as corn, wheat, and barley may be easily contaminated with molds. Molds are categorized into field and storage fungi. Field fungi are those that grow in grains before they are harvested. These commonly include Fusarium species, which produce vomitoxin, zearalenone, and fumonisin.2 Storage fungi, which include molds of the genera Aspergillus and Penicillium, are significant producers of mycotoxins that commonly affect pigs, such as aflatoxin and ochratoxin.2 These fungi can grow even at very low moisture levels, unlike the field fungi. Aspergillus flavus produces high concentrations of aflatoxin in grains even before harvest. It is important to distinguish between field and storage fungi, since this affects the distribution of mycotoxins. When conditions are favorable for field fungi to produce mycotoxins, grain from a geographic location is expected to be widely affected. Thus, large quantities of grain may be contaminated. In contrast, storage fungi should have a more localized distribution due to specific conditions during storage. In fact, not all grain may be affected evenly within a storage bin. Thus, storage mycotoxins may be difficult to detect without extensive sampling.
With the increase in the availability of distillers grains due to increasing ethanol production, the use of distillers grains in swine diets has also increased. Corn is the major grain product used to produce ethanol. Because most of the starch in the corn is consumed during fermentation, the resulting distillers grains co-product is more concentrated in other proximate components, such as fiber, protein, and fat, than is the source corn. However, if the corn grain used for fermentation has been contaminated with mycotoxins, the resulting distillers grains product may contain as much as three times the concentration of mycotoxins as the source corn.3
Mycotoxicosis refers to poisoning due to the ingestion of mycotoxins. This condition can cause lower resistance to diseases, increased sensitivity to stress, and damage to vital organs, such as the liver and kidney. Ultimately, this may lead to mortalities and poor production performance.
What are mold inhibitors?
Mold inhibitors are feed additives used to minimize mold contamination and prevent mold growth, thereby minimizing the risk of having mycotoxin-producing molds proliferate in grain or feed. Feed additives commonly used for this purpose include propionic acids and other organic acids. However, even if mold growth has been prevented, mycotoxins may still be present, because mold inhibitors have no effect on mycotoxins already present in contaminated feed.
What are mycotoxin binders?
Mycotoxin binders or adsorbents are substances that bind to mycotoxins and prevent them from being absorbed through the gut and into the blood circulation. When other preventive measures against molds and mycotoxins have failed, the use of mycotoxin binders can be valuable. There also may be instances when feeds and feedstuffs cannot be checked for mycotoxins on a regular basis. Mycotoxin binders are routinely added in such cases as safety measures and as some form of assurance to customers. A variety of substances have the ability to bind mycotoxins. The most commonly used and most researched mycotoxin-binding agents are the aluminosilicates – clays and zeolites. These are natural adsorbents that include hydrated sodium calcium aluminosilicates (HSCAS), bentonite, and zeolite (Table 2).4,5 Most of these products are efficient binders of aflatoxins. However, they have limited or no activity against other types of mycotoxins. Other substances with toxin-binding capability include cell-wall components of yeasts. Some studies have shown that the cell-wall fraction β-glucan of yeasts such as Saccharomyces cereviceae can be effective in binding a wide range of mycotoxins.6 Unlike clays, they can be added at low levels and are biodegradable. However, research in pigs documenting their efficacy in mitigating the effects of mycotoxins is limited and has shown inconsistent results.7-10
Table 2: Performance of weanling pigs fed aflatoxin-contaminated diets with either bentonite or HSCAS*
* Adapted from Schell et al, 1993.5 Data are means
from three pens of three pigs per pen.
Choosing the appropriate product
In general, the following must be considered when choosing either mold-inhibitor or adsorbent products: efficacy in adsorbing the mycotoxin or inhibiting the mold of interest, and safety to the animal, the handler, and to pork consumers; high stability and ablility to withstand varying conditions during feed mixing; and cost effectiveness. Caution also must be exercised when using clay, because its high adsorptive capacity can limit the bioavailability of minerals. This is most important when diets contain marginal levels of trace minerals. The risk of dioxin contamination associated with the use of natural clays needs to be considered.6 It is important to know the source of clay products that will be used in swine diets. Dioxins are mainly by-products of industrial processes. Contamination of clay sources can be due to improper disposal or accidental leakage of these by-products into the environment.
What is an antioxidant?
An antioxidant is a product added to animal feeds to prevent oxidation of fat or vitamins.11 Antioxidants found in commercial products include ethoxyquin, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and propyl gallate. Combinations of these antioxidants are normally found in commercially available products to take advantage of the different properties of each antioxidant. For instance, an antioxidant-product combination may contain propyl gallate to provide a high level of initial protection and BHA for longer effect. These antioxidants also have an inhibitory effect on mold growth in grains under laboratory settings12,13 and may have some use as mold inhibitors in pig diets in the future.
When is it advisable to use mold inhibitors, mycotoxin binders, and antioxidants?
The use of mold inhibitors and mycotoxin binders in swine diets may be advisable in geographic areas that are highly conducive to mold growth in grains and where mycotoxin contamination is more likely. Mycotoxin binders should be used when it is suspected that feed ingredients are contaminated with mycotoxins at levels deemed unsafe for pigs (Table 1). The use of these products becomes more important in situations when the moisture content of grains to be used for pig diets is greater than 14% and when storage conditions have a relative humidity that is higher than 85% and a temperature greater than 55°F.14 Thus, the use of mold inhibitors or mycotoxin binders may also be needed when diets have to be stored for a relatively longer period of time.
Antioxidants are highly applicable in areas where the climate is warm and when high levels of fat are added to the diet. Antioxidants are widely used in areas where by-products high in unsaturated fat (eg, fish meal) are commonly used. Oxidation of unsaturated fatty acids can produce substances that can cause off-flavors and toxic substances that can cause rancidity. These substances can also destroy nutrients like the fat-soluble vitamins.14 Adding an antioxidant minimizes fat oxidation, keeps the diet highly palatable, and helps prolong the shelf life of the feeds. It should be noted that antioxidants delay, but cannot prevent, fatty-acid oxidation.15
Some species of molds have the ability to produce mycotoxins. Mycotoxin contamination of diets can result in production and financial losses. Mold inhibitors and mycotoxin binders can be effective tools in controlling mold and mycotoxin problems. Antioxidants, on the other hand, can help preserve palatability of feed ingredients or complete diets.
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