Hay production

The low moisture of hay (8-15%) stops degradation and preserves forage. Longer drying time is associated with higher nutrient losses due to plant respiration. Two hay storage problems are mold growth and heating. Hay additives include drying agents, mold inhibitors (such as, propionic acid, ammonia, and urea), and microbial inoculants.

Hay is defined as forage that has been dried to 8-15% moisture. By reducing the moisture of forage, we stop degradation and preserve it. With good management, there are minimal nutrient losses during storage.

Field Drying of Hay:

Hay drying is sped up in a number of ways. First, it is typical to use a mower-conditioner which forces the forage through rollers to crimp plant stems and increase the surface area of the plant. It is also common to spread out the forage when it is mowed for faster drying and then to come back with a rake and turn the forage swath over to expose the wet bottom layer and speed the drying process.

The speed at which hay dries in the field is also dependent on the type of crop. Grasses will dry more quickly than legumes and alfalfa will dry quicker than red clover. More mature forage will dry faster. Of course, higher volumes of forage in a windrow will dry slower.

Nutrient Losses:

Most of the nutrient losses occur during the drying down process. Normally, it is recommended that forage be raked at 50% moisture and then baled at 18-20% moisture. The longer it takes to dry forage, the more nutrients are lost. Nutrients are lost due to respiration. This is a natural process in which the plant’s sugars are broken down into carbon dioxide and water. It has been estimated that 10-15% of the plant’s nutrients are lost from respiration. If hay is rained on before it is dry, more nutrients will be leached out of the forage and respiration losses will be increased. Nutrients are also lost because of degradation by bacteria during the dry-down period. Handling losses can be significant. Leaves shake off when the forage is turned and handled, especially when the hay is very dry. The leaf is the most digestible and valuable part of the plant. Too much sunlight on hay will cause bleaching and a loss of beta-carotene and Vitamin A activity.

Problems Encountered in Hay Storage:

1. Mold Growth: Especially above 20% moisture in hay, molds will grow. Molds grow on digestible nutrients in the hay, reducing the amount of digestible nutrients for the cow. Molds also produce toxins, called mycotoxins, which are unhealthy for the cow to eat (especially causing reproductive problems), reduce the amount of dry matter that the cow will eat, and reduce milk production.

2. Heating: Excessive mold growth, will cause the hay to heat. A limited amount of heating will slightly reduce rumen degradation of forage proteins and increase the efficiency with which it is used by the cow. Heating above 100oF will lead to a non-enzymatic browning reaction (Maillard reaction). This reaction reduces the digestibility of forage carbohydrates and proteins by binding them together. It makes the forage turn brown in color. In a forage laboratory analysis, the Maillard reaction will show up as an increase in ADIN (Acid Detergent Insoluble Nitrogen or Bound Protein) levels and a reduction in available crude protein. A lot of heating will result in spontaneous combustion and a barn fire.

Hay Additives:

Drying agents can be applied to make the forage dry down quicker prior to baling at the normal moisture content (18-20%). Solutions containing potassium carbonate and/or sodium carbonate can be applied at mowing in order to decompose the waxy cuticle on the outside of the plant so that it is more susceptible to the drying action of the environment. Drying agents should be used only on legumes and they are most effective on cuttings other than first-cutting. On average, drying agents make it possible to bale late on the second day after mowing rather than waiting until the third day.

Inhibitors can be used to restrict the growth of aerobic (oxygen-loving) organisms, such as molds. Inhibitors make it possible to store hay at higher moisture levels, thus reducing leaf loss and rain damage.

Propionic acid, preferably buffered propionic acid with a pH of 5.5 to 6.0, will restrict the growth of aerobic molds at hay moisture levels greater than 20%. Its effectiveness is primarily determined by its level of addition to the forage. 20 lb./ton of hay (1%) is recommended. Marketed products vary in their propionic acid concentrations and therefore, their application rate. Generally, the more concentrated the better because it means you to add less water onto the hay.

Ammonia or urea can also be used to prevent mold growth and heating. As moisture content increases, more ammonia is needed. Also, since ammonia evaporates, its effectiveness is increased if the bales are wrapped or covered.

Microbial Inoculants are also used on hay. Lactic acid bacteria cannot grow at moisture contents less than 35% and under the aerobic conditions of hay storage. For this reason, silage inoculants are not recommended for use on hay. Bacilli are spore-forming organisms which can grow on hay and may be advantageous to apply for reduction of mold growth. More research is needed to determine the effectiveness of hay inoculants.

Hay Storage:

Hay should be covered for storage. When round bales are stored outside, at least 4-6 inches of hay on the outside of the bale is damaged. The first 6 inches is 1/3 of the bale! So that means you will lose 20-30% of the bale’s nutritive value when you store it outside.


Kung, Jr., L. 1991. Hay preservatives: Propionic acid and microbials. Advanced Nutrition Seminar for Feed Professionals, Arlington, WI.

Pitt, R.E. 1990. Silage and hay preservation. Northeast Regional Agricultural Engineering Service. Ithaca, New York.

Van Soest, P.J. 1982. Nutritional ecology of the ruminant. O&B Books, Inc., Corvallis, OR.

Related Links:

Hay Preservatives: Propionic Acid and Microbials
Limin Kung, Jr., Ph.D., University of Delaware

Hay Dessicants and Preservatives
Dan Undersander, Ph.D., University of Wisconsin

Feeding Systems In: Feeding the Dairy Herd North Central Regional Extension Publication
J.G. Linn et al.


Mary Beth de Ondarza

Mary Beth de Ondarza
45 articles

Nutritional consultant for the dairy feed industry at Paradox Nutrition, LLC.

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Dr. de Ondarza received her Ph. D. from Michigan State University and her Masters Degree from Cornell University, both in the field of Dairy Nutrition.

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Paradox Nutrition

Paradox Nutrition

Paradox Nutrition, LLC is a nutritional consultation business for the dairy feed industry. Mary Beth de Ondarza, Ph.D. is the sole proprietor.

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