by: Stephen B. Blezinger
Ph.D., PAS

Production of quality hay has been a concern to cattle producers for decades. The value of quality hay, whether it be grass or legume, has always been important as it provides for a significant portion of the animal's nutrient needs, especially protein and energy. The current economy, with higher input costs in virtually every stage of hay production (fuel, fertilizer, equipment, labor), emphasizes that the quality of hay produced needs to be as high as possible, first to get the most nutrient value out of the dollars invested and secondly to minimize the need for expensive supplements.

Production of hay requires significant planning at all stages. While most hay is produced in late spring, summer and early fall, winter is the perfect time to plan. This provides the opportunity to create a planning calendar outlining when actions need to occur, purchases need to be made, etc. Initially, hay producers have to consider:

1) Soil Fertility – It is always useful to soil test well in advance of the growing season. This helps in determining fertilization needs and timing and planning for when these purchases need to be made.

2) Weed Control – reduction of weed species via herbicide application in many cases acts like an application of fertilizer since weeds drain nutrients that desirable plants require. Depending on location, plant and predominant weed type, economics, etc. decisions regarding herbicide type (pre- or post- emerge), chemical composition, make, price, timing need to be made at this time.

3) Harvesting - this is dictated by whether the producer has hay equipment of his own or has his crop custom harvested. Equipment owners need to use this time to determine if tractors, cutters, rakes, balers, etc. are all in proper condition or if repairs need to be made in advance of the season. While a bit late at this point, it is also time to determine if any equipment needs to be replaced. Producers that have their hay custom harvested can use this time to contact custom balers in the area to determine what their rates will be for the coming year. This is also a good point to discuss timing. One of the problems with using custom balers is timing. In some cases, due to their work load and demand by other producers, having them at your farm or ranch at the proper time can be a problem. It is important that you talk with your “hay guy” concerning this issue since timing is a large factor affecting hay quality and nutrient levels. Some if not all forages, after a certain age/stage of maturity can rapidly lose protein and other nutrients. Additionally, fiber levels can increase rapidly at this time resulting in decreased digestibility and reduced energy values. Proper timing of harvest can be your most critical management factor.

4) Storage – How hay is stored, especially in higher rainfall areas can have a significant effect on nutrient and hay volume losses. If at all possible hay needs to be stored off the ground (if nothing else on a rock or gravel base) and covered either in a barn or with a tarp to reduce weather effects.

Use of Preservatives

An additional opportunity for the production of quality hay is in the well-planned use of preservatives. Hay preservatives, applied at harvest, have actually been around for some time. And while their use does incur some extra expense and special equipment, in certain situations, application of an appropriate hay preservative can make a significant difference in the final quality of the hay at feeding, especially if harvest is during a period where normal drying is a problem.

Dr Bill Weiss with The Ohio State University explains that preservatives work by inhibiting or reducing the growth of aerobic (oxygen requiring) microbes in moist hay. If microbial growth is eliminated, heating and the subsequent depression in digestibility does not occur. Most hay preservatives do not improve nutritional quality of the forage, but merely prevent the decline in quality caused by heat buildup from excessive aerobic microbial action facilitated by higher than desirable moisture conditions.

One of the technologies used for preserving hay harvested above optimum moisture levels is to apply organic acids to the hay at harvest time. 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, product handling and corrosiveness, and increased use of large bale packages.

When hay is baled and put into storage at moderate moisture levels (18 – 30 percent), a favorable environment exists for the growth of undesirable bacteria, fungi, and yeast. 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 typically a one percent loss of dry matter for each percent moisture loss during storage to reach a stable equilibrium. These losses are from the non-fiber components of the plants. 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. Even if the hay does not heat to the point of combustion, the heat production can and does damage the nutrients in the plant material. The heat buildup causes a reaction to occur between proteins and carbohydrates which render both fractions less digestible. Protein digestibility can be reduced to almost zero with severe heating. The amount of heat necessary to produce the reaction depends on several factors. Generally bale temperatures less than 100 degrees F cause no problems, but bale temperatures above 150 degrees F almost always severely reduce protein and carbohydrate digestibility. When bale temperatures remain between 100 and 150 deg. F, the length of elevated temperature determines the amount of nutrient loss. Damage occurs more rapidly at higher temperatures.

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 (Rankin, University of Wisconsin Extension).

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. However, acetic acid 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 (i.e. propionic acid). Some products contain as little as 15 percent actual propionate. Typically, the most cost-effective products are those with the highest concentration of 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 developed buffered propionic acid products. Buffered propionic acid products are made 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.

As mentioned, buffered acids as well as salts of acids have been developed to overcome the corrosion problem. These products have not been tested as extensively as propionic acid. Buffered acid applied at about one percent (as baled basis) was as effective as one percent propionic when applied to alfalfa hay baled with 30 percent moisture (results from one study only). If buffered acids continue to prove to be as effective as propionic acid, then producers will have to balance the added cost of buffered acids with the reduced wear they cause on equipment. Salts are granular and need less expensive application equipment. Salts include sodium diacetate and sodium metabisulfite. These compounds have proven less effective than propionic acid. Application rates of 0.1 to 0.2 percent (as baled basis) are usually used. Results from a limited number of studies indicate that this type of preservative is effective on hay containing no more than approximately 25 percent moisture.

Other options include the many types of microbial products that have been promoted recently for use as hay preservatives. The downside is that very little positive value has been demonstrated with these products. Nebraska researchers found that inoculating either large round bales or small square bales of alfalfa with 200,000 colony forming units of lactic acid producing bacteria per gram of dry forage had little effect on hay quality and preservation over a wide range of moisture concentrations. Other types of bacterial inoculants (non lactic acid producers) have been tested with little beneficial results. Certain types of nonlactic acid bacteria have increased the visual quality of moist hay (up to 25 percent water), but quantitative data on improved feed value are lacking. In general, the microbial products used as hay preservatives do no harm but have shown few benefits. In general these products are probably better suited for use in haylage/baleage products that contain higher levels of moisture. This would also necessitate wrapping the bales in some manner to reduce exposure to oxygen.

Application Rates

One primary question asked when considering a preservative is the addition rate. 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 percent moisture requires about 15 pounds of acid per ton of dry matter (25 percent moisture - 10 = 15 lbs acid required per ton).

Recommended application rates assume a hay product that is uniform in moisture. If some bales or parts of bales are significantly higher in moisture than the field average, application rates will need to be adjusted higher to insure effective preservation of the entire hay lot.

To be effective, preservative must be uniformly distributed on the hay crop as it enters the baling chamber. This often means that multiple application nozzles are needed on the baler. Many hay producers dilute the propionic acid (or ammonium propionate) product with water and then increase flow rates through the application equipment to improve coverage on the crop.

Other considerations include bale type and density. For small square bales, an organic acid preservative is recommended once moisture levels reach about 20 percent. Applying preservative to small square bales over 30 percent moisture is not recommended.

Large and medium square bales typically are more dense than small square bales allowing for less natural airflow through the stack. For this reason, an organic acid preservative should be used when baling large square bales or densely packaged round bales that are 17 percent moisture or above. Baling these larger bales at moisture levels over 25 percent 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.

To summarize, let's examine the pro's and cons of using hay preservatives

Advantages of Using Hay Preservatives

•      Preservatives allow hay to be baled at a higher moisture content which reduces the length of time hay lays in the field and lowers the risk of rain damage.

•      Baling at a higher moisture content reduces dry matter and nutrient losses during baling caused by leaf shatter.

•      Preservatives lengthen the potential baling period. Hay can be baled during early morning and late evening hours if dew does not raise moisture level above 25-30 percent.

•      Preservatives can maintain nutrient levels where they might otherwise be lost in less than optimal harvest conditions.

Disadvantages of Using Hay Preservatives

•      Use of preservatives adds cost to the hay product. This includes the added equipment cost and the preservative itself

•      Organic acids can be corrosive, can damage machines and injure workers. Significant added care must be taken.

•      Effectiveness of many hay preservatives available currently has not been tested thoroughly and may not work under many conditions.

Finally, it is essential that the moisture content of the hay be known. Adding a preservative to hays with appropriate moisture levels may not be advantageous. Hay containing more than 30 percent moisture should not be baled even with a preservative. Application rates of other preservatives should be modified according to moisture content of the hay.


Production of quality hay is not a simple process. It requires planning and use of appropriate technologies. Preservatives are one such technology that can be considered as an option and can effectively maintain quality when conditions might otherwise rob the hay of nutrient levels. It is important, however to weigh evaluate the situation and use products of this nature when appropriate.

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be reached by phone at (903) 352-3475 or by email at


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