ARS | Publication request: The effect of harvest moisture and bale wrapping on temperature and mold counts in grass hay

Submitted to: Extension Publications
Publication Type: Experiment Station
Publication Acceptance Date: June 20, 2011
Publication Date: August 19, 2011
Citation: Martinson, K., Sheaffer, C., Coblentz, W.K. 2011. The effect of harvest moisture and bale wrapping on temperature and mold counts in grass hay. Extension Publications. University of Minnesota Extension, St. Paul, MN.

Technical Abstract: Harvesting hay can be complicated by poor drying conditions and the threat of rainfall. In an effort to avoid rain and other adverse weather conditions, hay is often baled before the hay is dried adequately, resulting in mold development and reduced forage quality. Hays baled at moisture levels <15% are assumed to be relatively stable and typically exhibit little evidence of microbial respiration. It is common knowledge that horses are highly sensitive to several molds, and that ingesting moldy feed can result in both short-term and long-term respiratory problems, specifically heaves, and gastrointestinal problems, such as colic. Maintaining forage quality and reducing mold growth in large-round bales of orchardgrass hay was achieved by baling dry hay (12%) or by wrapping hay in plastic, regardless of initial bale moisture. Results of our research are consistent with the current moisture threshold of 15% for safe storage of dry (unwrapped) hay packaged in large-round bales, and suggest this recommendation also is appropriate specifically for orchardgrass. For dry hay, this recommendation should be carefully followed; orchardgrass bales were prone to significant molding and forage quality losses at moisture concentrations >15%. This abrupt line between high-quality and moldy hay is likely one reason some horse owners assume it is difficult to harvest and feed quality round bales to horses.