Fungal contamination of big-bale grass silage on Irish farms: predominant mould and yeast species and features of bales and silage

The extent of visible fungal growth and the identity of the predominant fungi causing spoilage of baled grass silage were recorded on 180 farms in Ireland. Fungal growth was evident on bales on 174 of the 180 farms visited and on 331 of the 360 bales examined. The mean proportion of surface area of bale, that was affected, was 0·06. Silage-making method, storage characteristics and geographical location were significantly associated with the level of fungal contamination on bales. Fungal contamination was higher (P < 0·001) in bales where the surrounding polythene stretch-film was visibly damaged compared with bales where the film appeared intact. A strong positive relationship was found between polythene film damage and dry-matter content of the silage. The predominant fungus affecting the largest numbers of bales was Penicillium roqueforti. Other fungi frequently isolated included Schizophyllum commune, Pichia fermentans and Penicillium paneum. The distribution of individual fungi on bales was associated with geographical location, weather at harvest, and lactic and butyric acid concentrations of the silage. Penicillium roqueforti and P. paneum were more common on bales harvested in dry weather and with higher concentrations of butyric and propionic acids in the silage. Overall, a high incidence of visible fungal growth was recorded on bales throughout the country and the extent of colonization and fungal species occurring were not random.

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