Optimum preservation of hay depends primarily on handling and harvest management. Drying rate, mechanical handling of the crop and moisture content at baling all impact on the quality and quantity of hay. The primary objective of producing hay is to reduce the moisture content of the forage as quickly as possible to a level that will inhibit biological and chemical reactions, while retaining the maximum amount of leaf material which contains a large proportion of the feed value of the hay.

Two of the most critical processes to be controlled or prohibited during hay storage are mold growth and browning reactions. When hay is baled and stored between 18-30% moisture content, the predominant microorganisms that grow are molds, which consume crop nutrients causing a loss of dry matter, digestible nutrients and energy. Mold growth also causes heating and may lead to hay fires. In addition to reducing hay quality, molds also produce toxins and spores that are detrimental to both the animal and the producer. If mold growth goes unchecked the hay may reach 100°F or higher, leading to severe browning reactions. This causes amino acids and sugars to bind, resulting in increased levels of acid detergent insoluble protein (ADIP). This can lead to additional heating, greatly reducing the quality of the plant protein available to the animal.