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Preservatives Can Help With Late-Season Haying

Cooler evenings and shorter fall days reduce drying time for late-season hay, which could result in damaged hay if it is baled while it is too wet.

Hay harvested at 18 per cent or higher moisture content will heat, mould, and lose feed value and palatability, warns North Dakota State University Extension Service dairy specialist J. W. Schroeder. The correct moisture level for baling hay is 13 per cent to 17 per cent.

Preserving forage by ensiling it under anaerobic conditions may be an alternative. But if it’s not, producers can preserve forage by spraying it with organic acids as it is harvested. Preservatives inhibit or reduce the growth of aerobic microbes in moist hay, which eliminates heating and the subsequent loss of digestibility. Severe heating can reduce protein digestibility to almost zero.


Preservatives also allow hay to be baled at a higher moisture content, which reduces the length of time the hay lies in the field and lowers the risk of rain damage. Baling at a higher moisture content reduces the dry-matter and nutrient losses during baling caused by leaf shatter.

“Most hay preservatives do not improve the nutritional quality of the forage but merely prevent the decline in quality caused by heat buildup from excessive aerobic microbial action,” Schroeder says.

Hay preservatives can be grouped into three categories: organic acids and their salts, ammonia-based and microbial additives.

Propionic acid has been the most effective and most tested preservative available, Schroeder says. It is a liquid, so producers must add tanks and a spray application system to their baler. Spray nozzles must be spaced so the chemical is distributed over all the forage as it enters the baling chamber.


The amount of active ingredient that must be applied depends upon the hay’s moisture content. Small bales with 20 per cent to 25 per cent moisture should be treated with about 0.5 per cent propionic acid. Increase the application rate to one per cent for hay with 25 per cent to 30 per cent moisture. Researchers have not found a consistent response to any preservative used on hay containing more than 30 per cent moisture.

Schroeder recommends that for adequate coverage, producers should use a 50 per cent solution and apply twice as much of the diluted acid.

The main disadvantages of propionic acid are its corrosiveness, which can damage machines and injure workers, and the cost of the equipment to apply it to hay. Buffered acids and salts of acids have been developed to overcome some of the corrosion problems.

These products have not been tested as extensively as propionic acid. However, results from one study indicate buffered acid applied at about one per cent (on an as-baled basis) was as effective as one per cent propionic acid when applied to alfalfa hay baled with 30 per cent moisture.

Generally, a mixture primarily or entirely of propionic acid is not harmful to animals, Schroeder says. Buffered propionic acid is safe for all livestock.


Salts, which include sodium diacetate and sodium metabisulphite, are granular and need less expensive application equipment, but they have proven to be less effective than propionic acid. The usual application rates for salts are 0.1 per cent to 0.2 per cent (on an as-baled basis).

Ammonia is toxic to many microbes and can be a very effective preservative for moist hay (up to 30 per cent moisture) when applied at one per cent (dry-matter basis). Higherquality forages such as alfalfa, immature grasses and cereal grain hay should be treated with ammonia only at the rate needed for preservation (one per cent of dry matter) because of the toxicity risk.

The major disadvantages of anhydrous ammonia are that it is a hazardous chemical and difficult to apply. Devices have been made to inject anhydrous ammonia into large round bales, but these are not yet sold commercially. The recommended means of treating moist hay with anhydrous ammonia is to cover the bales with plastic and then inject the appropriate amount of ammonia. The ammonia may not become distributed uniformly; therefore, portions of the stack may spoil.


Bacteria normally found on the hay can convert urea to ammonia, and urea is much simpler to apply than anhydrous ammonia gas. Researchers have found that relatively large amounts of pelleted urea (five per cent to seven per cent, on an as-baled weight basis) applied during baling can be an effective preservative for hay containing up to 30 per cent moisture. However, urea is effective only if the hay is stored shortly after baling and covered tightly with plastic sheeting.

Applying the proper amount of ammonia is extremely important. Application rates below about .8 per cent (dry-matter basis) are much less effective than the one per cent rate. However, high-quality hay must not be treated with more than one per cent ammonia (dry-matter basis) because larger amounts can result in the formation of an unknown toxic compound. Animals consuming ammoniated high-quality forage often exhibit hyperexcitability followed by death. The toxin is transferred into milk, so nursing calves and lambs also are susceptible to the toxin.

Many types of microbial products have been promoted recently for use as hay preservatives, but researchers have found very little positive value in them.

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