Introduction Weather patterns in the upper Midwest often make it difficult to field-cure hay below 20 percent moisture on a consistent basis. In some cases, growers may desire to harvest hay at higher moisture levels to reduce harvest losses from mechanical leaf shattering and improve forage quality. For these reasons researchers and hay producers are always looking for methods and technologies that will either accelerate drying time in the field or preserve desirable feeding characteristics of hay harvested above the optimum moisture level for safe storage. Falling into the latter category is a group of chemicals collectively referred to as organic acids. The use of organic acids has proven to be an effective strategy for preserving baled hay. Interest in using these products has increased with improvements in application equipment, ease of handling, product corrosiveness, and with a larger percentage hay being baled into large packages. Why
are hay preservatives needed? A favorable environment for the growth of undesirable bacteria, fungi, and yeast exists when hay is baled and put into storage at moderate moisture levels (18 - 30%). Both moisture and temperature drive the population growth of these microorganisms. Fungi such as Aspergillus and Fusarium can produce a wide range of toxic metabolites and greatly reduce hay palatability. Actinomycetes, a special class of heat-tolerant bacteria, provide the causative agent for Farmer's Lung Disease in humans. Moist hay that is put into storage can suffer extensive dry matter loss because of increased plant respiration and microbial activity. There is usually about a 1% loss of dry matter for each percent moisture loss during storage to reach a stable equilibrium. These losses are entirely non-fiber components. As a result, a corresponding increase in the levels of acid detergent fiber (ADF), neutral detergent fiber (NDF), and acid detergent insoluble nitrogen (ADIN) also takes place. Finally, wet hay that is put into storage has an increased risk of heating to the point of spontaneous combustion. Organic acids, when applied at the proper rates, effectively control the development of molds on moist hay by preventing the growth of fungi and actinomycetes. Do
all organic acid products have equal effectiveness? Not all organic acids or commercial organic acid products are created equal in terms of effectiveness, cost per pound of acid, or concentration of active ingredient. The most commonly used organic acid for hay preservation has been propionic acid. Not surprisingly, it is also one of the most effective. Some commercial products also contain a small percentage of acetic acid, which by itself is a less effective hay preservative. When purchasing a propionic acid product, be sure to read the product label for the actual percentage of active ingredient (propionic acid). Some products are as little as 15% actual propionate. Typically, the most cost-effective products are those with the highest percent propionate. Base purchase decisions on cost per pound of active ingredient and not cost per pound of product. For many years, the major disadvantages to using propionic acid were its corrosiveness to machinery, pungent smell, and volatility. To address these problems, manufacturers now offer a buffered propionic acid product. This is done by adding compounds such as ammonium hydroxide to the acid to form ammonium propionate. Several research studies have shown that the buffered product is equal in hay preservation qualities to that of unbuffered propionic acid. The tradeoff is that buffered products are more costly than those not buffered. At what rate should organic acid preservative be applied? Bale moisture is the primary factor determining effective application rates. Inhibition of fungal growth requires a minimum level of acid concentration in the water component of the hay. An easy method to determine effective preservation rate (actual pounds of propionate per dry matter ton) is to take the moisture percentage of the hay and subtract 10. For example, hay baled at 25% moisture requires about 15 pounds of acid per ton of dry matter (25 - 10). Recommended application rates assume a hay product that is uniform in moisture. If some bales or parts of bales are actually higher in moisture than the average determined moisture, rates will need to be determined based on the highest moisture reading to insure effective preservation of the entire hay lot. To be effective, preservative must be uniformly distributed on the hay crop. This often means mounting more than one application nozzle on the baler. Many hay producers dilute the propionic acid (or ammonium propionate) product with water and correspondingly increase flow rates through the application equipment to improve coverage on the crop. Does
bale type and density influence when organic acids should be used? For small square bales, an organic acid preservative is recommended once moisture levels reach about 20%. Applying preservative to small square bales over 30% moisture is not recommended. Large and medium square bales typically are denser than small square bales allowing for less natural airflow through the stack. For this reason, begin using an organic acid preservative when baling large square bales or densely packaged round bales that are 17% moisture or above. Baling these larger packages at moisture levels over 25% is risky (even when a preservative is used). Because of differences in on-farm moisture testers and bale densities, individual hay producers will need to develop their own "learning curve" relative to the use and effectiveness of organic acid preservatives for their specific situation. What
is the duration of preservation effect?
Organic acids have proven to be reliable for inhibiting mold growth and preventing excess heating in hay. Results from several research studies suggest that the preservation effect initially gained from using organic acids is not long-term in nature. Over time, the acid will dissipate from the hay. This can result in mold formation after 4 to 6 months of storage if enough moisture is present to support such growth. Using an organic acid preservative will not necessarily improve storage characteristics such as long-term dry matter loss or hay color. What
are the economics of organic acid use? Primary costs for using organic acid preservatives include the cost of the product and application equipment. Small square balers can usually be equipped with a tank, pump, and nozzle(s) for $250 to $400 depending on the system chosen. For large package balers, equipment costs are in the range of $500 to $800. Product cost for a buffered acid are currently about $1.10 per pound of active ingredient. An unbuffered product can be purchased for $0.20 to $0.30 less per pound. Thus, it costs about $11 per ton to treat hay with the buffered product at a 10 lb. per ton rate of application. This does not include any pro-rated equipment costs. However, these should be minimal on a per ton basis. Organic acid preservatives will be most economical to use when large acreages are baled and the product is used discriminately to avoid rain damage on cut forage when the situation arises. They also have merit for custom hay balers who must please their customers with a quality product while at the same time bale large acreages in relatively short periods of time.
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