Hay preservatives have pros and cons.

Whether to inoculate may be one of the forage grower’s top questions this spring.

A late spring not only complicates planting; it could overlay first-cut haying. Then, depending on the weather, continued wet conditions could complicate haying further. As a result, I anticipate more interest in the use of preservatives this year.

Most commonly, preservatives are used with alfalfa, which usually is wilted, with 15 percent or less moisture, prior to baling for hay. However, harvesting at low moistures increases the loss of leaves (protein) during baling and reduces nutritive value. In addition, long wilting times increase the risk for damage from rain. To retain more nutrients and prevent rain damage, hay can be baled at higher moistures, but the risk of spoilage from undesirable microbial metabolism during storage increases dramatically.

Although much is known about the microbiology of silage, less is known about microbial metabolism in moist hay. Although bacilli can be associated with spoilage of wet hay (greater than 20 percent moisture), most research suggests fungi are the microbes that cause spoilage problems in moist hay.

Moist hay undergoes several distinct heating cycles when stored in stacks. The significance of the heating peaks and associations with plant or microbial metabolism are poorly understood. However, if the moist hay does not undergo some heating, the bales never appear to "dry down" during storage. But excessive heating of the hay bale can lead to an increase in heat-damaged protein (acid detergent insoluble nitrogen). Heat-damaged protein lowers the protein value of the hay.

Various hay preservatives inhibit mold and may be useful in reducing drying time and field losses by allowing baling at higher moisture levels. If properly done, baling at higher moisture levels can reduce dry-matter loss (from leaf shattering) and potential damage from rain.

The two most commonly used preservatives for high-moisture hay are bacterial inoculants and propionic acid-based solutions.

For propionic acid to be effective, correct levels must be used. At least 1 percent propionic acid is needed to preserve hay with 32 percent moisture. Propionic acid solutions will vary from 10 to 100 percent propionic acid. I don’t recommend using very diluted products because larger volumes of water are applied to the crop. Why add more water to your already wet hay?

Depending on the product and application rate, treating with propionic acid-based products will cost $5 to $20 per ton of hay. Seldom does the increase in leaf retention pay for the use of the additive. However, acid preservation may be most beneficial when the producer is faced with potential loss from rain damage. Uniform distribution of propionic acid is important because "pocketing" of molds (only parts of the bale being moldy) has been observed. And, as you might surmise, acid products are corrosive to metal machinery.

Microbial inoculants can improve silage fermentation and animal performance. This success has created much interest in using microbial inoculants to reduce spoilage in moist hay. Advantages of an efficacious additive include lower cost, a lower liquid application rate and the use of a biologically safe (noncorrosive) product.