Microbial and Biochemical Changes during the Moulding of Hay

Abstract

SUMMARY: Experimental batches of hay were baled at different moisture contents, and the microbial and biochemical changes studied by sequential sampling. The type of hay obtained could, in general, be related to the initial moisture content, and to the temperature subsequently attained. Good hays (about 16 % moisture) heated little and contained a small but diverse microflora. Hays baled at about 25 % moisture heated to about 45° and moulded, mainly with Aspergillus glaucus. Wet bales, with initial moisture contents of about 40 %, became very hot (60°-65°) and contained a large flora of thermophilic fungi, particularly Aspergillus fumigatus, Absidia spp., Mucor pusillus, Humicola lanuginosa, and actinomycetes. During the initial heating period, which was correlated with a general rise in numbers of micro-organisms, particularly actinomycetes and bacteria, the acidity and volatile nitrogen increased. Later, when fungi and actinomycetes grew profusely, soluble sugars decreased rapidly and the pH value rose to 7.0 or above. Stacks of wet and dry hays were compared with bales made from the same hays. The wet stack developed a core of brown acid hay, containing many spore-forming bacteria but few fungi, surrounded by a layer of mouldy hay.