Using Mold Inhibitors
Types of Mold Inhibitors
The use of chemical mold inhibitors is a well-established
practice in
the feed industry. However,
mold inhibitors are only one of several tools useful in the
complex
process of controlling the
growth of molds, and they should not be relied upon
exclusively.
The main types of mold inhibitors are (1) individual or
combinations
of organic acids (for
example, propionic, sorbic, benzoic, and acetic acids), (2) salts
of
organic acids (for example,
calcium propionate and potassium sorbate), and (3) copper
sulfate.
Solid or liquid forms work
equally well if the inhibitor is evenly dispersed through the
feed.
Generally, the acid form of a
mold inhibitor is more active than its corresponding salt.
Dispersion
Many factors influence the effectiveness of mold inhibitors, and
proper attention to these factors
can enhance the benefits they provide. Mold inhibitors cannot be
effective unless they are
completely and thoroughly distributed throughout the feed.
Ideally,
this means that the entire
surface of each feed particle should come in contact with the
inhibitor and that the inhibitor
should
also penetrate feed particles so that interior molds will be
inhibited.
The particle size of the carriers for mold-inhibiting chemicals
should
be small so that as many
particles of feed as possible are contacted. In general, the
smaller
the inhibitor particles the greater
the effectiveness. Some propionic acid inhibitors rely on the
liberation of the chemical in the form
of a gas or vapor from fairly large particle carriers.
Presumably, the
inhibitor then penetrates the
air spaces between particles of feed to achieve even
dispersion.
Effect of Feed Ingredients
Certain feed ingredients may also affect mold inhibitor
performance.
Protein or mineral
supplements (for example, soybean meal, fish meal, poultry
by-product
meal, and limestone) tend
to reduce the effectiveness of propionic acid. These materials
can
neutralize free acids and convert
them to their corresponding salts, which are less active as
inhibitors. Dietary fat tends to enhance
the activity of organic acids, probably by increasing their
penetration into feed particles. Certain
unknown factors in corn also alter the effectiveness of organic
acid
inhibitors.
Time Dependence
When mold inhibitors are used at the concentrations typically
recommended, they in essence
produce a period of freedom from mold activity. If a longer
mold-free
period is desired, a higher
concentration of inhibitor should be used. The concentration of
the
inhibitor begins to decrease
almost immediately after it is applied as a result of chemical
binding, mold activity, or both. When
the concentration of the inhibitor is reduced until it is
incapable of
inhibiting mold growth, the
mold begins to use the inhibitor as a food source and grows. In
addition, feeds that are heavily
contaminated with molds will require additional amounts of
inhibitor
to achieve the desired level
of protection.
Influence of Pelleting
The widespread use of pelleted feeds in the feed industry is
beneficial to the use of mold
inhibitors. The heat that the feed undergoes during pelleting
enhances
the effectiveness of organic
acids. Generally, the higher the pelleting temperature, the more
effective the inhibitor. Once mold
activity commences in pellets, however, it proceeds at a faster
rate
than in nonpelleted feed
because the pelleting process that makes feed more readily
digestible
by animals also makes it
more easily digested by molds.
Copper Sulfate
The practice of recommending copper sulfate as a treatment for
fungal
diseases in animals goes
back many decades. The effectiveness of copper as a mold
inhibitor is
difficult to document.
Although copper sulfate in the diet has been shown to improve
body
weight and feed conversion
efficiency in broilers, excessive levels of copper may be toxic
to
young animals and will
accumulate in the environment. In addition, recent research has
indicated that feeding copper
sulfate to poultry causes the formation of mouth lesions similar
to
those formed by some
mycotoxins. Similar mouth lesions might be formed in other animal
species.
The use of brand names in this publication does not imply
endorsement of the products or
services named or criticism of similar ones not mentioned.
Prepared by
Mary Beth Genter, Extension Toxicology Specialist
Winston M. Hagler, Director of NCSU Mycotoxin Laboratory
Jeff A. Hansen, Extension Animal Science Specialist
Bob A. Mowrey, Extension Animal Science Specialist
Frank T. Jones, Editor, Extension Poultry Science
Specialist
Matt H. Poore, Extension Animal Science Specialist
Lon W. Whitlow, Extension Animal Science Specialist
http://www.ces.ncsu.edu/gaston/
