June 6, 2013

The moisture content of hay when it is baled influences yield, quality, and storability of the hay. Preservatives can help us get it right.

When hay is baled too dry, leaves fall off, reducing quality and yield. Unfortunately, hay baled too wet can get moldy, overheat, or even catch fire. So we have a narrow moisture range that results in good hay that keeps well.

One way to extend your options is to apply a preservative like propionic acid when baling hay that's still a bit wetter than usual. To get good results from preservatives, though, it helps to know how it works and what it can and can not do.

Baled hay naturally contains millions of bacteria and mold fungi. As they consume hay nutrients, these microbes produce heat. The duration and intensity of this heat determines the amount of damage the hay receives. This heat also forces moisture out of the bale, something we often call “going through a sweat.” Usually, hay gets dry enough that the microbes soon die or go dormant. But when too much moisture is present, heating becomes excessive and/or mold develops.

Preservatives kill many of the microbes so less heat is produced. This gives hay time to dry out naturally, without the “sweat.” As the hay dries, the preservative vaporizes and disappears. If we stack bales tightly into storage soon after baling or fail to allow drying to occur in other ways, the remaining microbes eventually will produce the mold and heat we wanted to avoid.

Problems also can develop if rain, high humidity, or other sources moisten the hay later. Since the preservative lasts only a short time, the added moisture can favor the redevelopment of microbial activity.

Preservatives can help make good hay at higher moisture levels, but correct management is needed to keep that hay in good condition.

Bruce Anderson
Extension Forage Specialist