Preservatives can help growers make good hay at higher moisture levels, but correct management is needed to keep that hay in good shape, says Bruce Anderson, University of Nebraska-Lincoln extension forage specialist. To get good results from preservatives, he says it helps to know how they work and what they can and can’t do.

Baled hay naturally contains millions of bacteria and mold fungi that produce heat as they consume hay nutrients. The duration and intensity of this heat determines the amount of damage to the hay. The heat also forces moisture out of the bale, something called “going through a sweat,” Anderson states. Usually, hay gets dry enough that the microbes die or go dormant, but when too much moisture is present, heating becomes excessive, mold develops, or both. Preservatives work to kill many of the microbes, resulting in less heat. This gives hay time to dry out naturally, without the sweat.

However, the preservative also vaporizes and disappears as it dries. If bales are not allowed to dry properly or are stacked tightly and stored soon after baling, the remaining microbes eventually will produce the heat and mold that the preservative was working to combat. Also, Anderson points out, if rain, high humidity or other sources moisten the hay later, microbial activity can redevelop since the protection from preservatives lasts only a short time.