HAY BALED with excessive moisture may lose nutritional value to spontaneous heating, according to University of Arkansas Division of Agriculture research.

“We monitored moisture content and heat in bales of Bermuda and tall fescue bales,” said Wayne Coblentz, animal scientist at the Arkansas Agricultural Experiment Station. “Sugar content in the grass acts as a fuel that is oxidized by enzyme systems that are still active in the plants. Naturally-occurring bacteria and other microbes also feed on these sugars.”

“Moisture enhances the growth of these microbes in grass,” said animal scientist Ken Coffey. “These microbes digest the very best part of the hay, and that causes heating.”

UA researchers evaluated digestion characteristics of hays baled at different moisture contents to determine the relationship between levels of spontaneous heating and livestock utilization of the different nutrients in the hay.

Coffey said digestion of dry matter and fiber declined by more than 10 percent as the level of spontaneous heating increased. “Animals eat less of the more heated hay and are able to digest less of what they eat,” he said. “The crude protein is especially sensitive to heating. It's digestibility is reduced by more than 25 percent.

“Based on this, producers feeding heated hay should reduce the protein values from their hay analysis by 25 percent before calculating the protein needs of their cows to provide them with adequate digestible protein,” he said.

The loss of these nutrients causes fiber content to become concentrated, which contributes to the decrease in digestibility, Coblentz said.