Plants allowed to continue their growth cycle beyond their reproductive stage have lower nutritive value as a feed. Haying aims to reduce the quality losses due to maturity while maintaining the nutrient content the plants had at harvest time.
Once in the swath the harvested forage dries at variable rates, depending on factors such as its initial moisture content, swath thickness, solar radiation, ambient moisture and air circulation. Although moderate heating (70°F to 110°F) is practically unavoidable, when excessive, it can result in heat damage and potentially become a fire hazard. Three conditions —combustible material, heat production and oxygen infiltration— are necessary for this to happen.
Moisture content critical
Stored forages with high sugar content usually have higher nutritive values. At the same time, they could be at a greater risk of rising temperatures once exposed to air with poor harvesting and storage practices. As long as there is water activity, plant cells in the swath continue to breathe and perform chemical reactions. Energy for these reactions is obtained by oxidizing sugars which leads to heat buildup.
Higher hay temperatures and air availability favor the growth of bacteria and molds that further escalate temperatures. If air repeatedly penetrates the mass, oxidation by microorganisms may continue until spontaneous combustion occurs.
Plant and microbial respiration of sugars to carbon dioxide produce water and heat. In higher moisture bales, the water generated during plant respiration can raise the moisture content of the hay. For this reason, bales stored with excessive moisture are more susceptible to heating as they are an ideal habitat for microorganisms.
Continue reading this article published in Hoard’s Dairyman.
