Comparison of the content of clostridial spores in wilted grass silage ensiled in either laboratory, pilot-scale or farm silos.

Fifty-two laboratory silages (1.5 1), 108 samples of pilot-scale silos (2-4 tonnes), and 167 sam­ ples of farm silages were analysed for their contents of clostridial spores, proximate composi­ tion and concentrations of fermentation products. Numbers of clostridial spores in the silages ranged from 100 to more than 10 million per gram. Relationships between spore counts as dependant variable and dry matter, butyric acid and ammonia-N contents as independant variables were established for the three types of silages by regression analyses. Similarity ex­ isted in the relationships found for pilot-scale and farm silages, showing a gradual drop of spore counts with higher dry matter levels. Laboratory silages differed in showing either a pronounced clostridial fermentation with high levels of butyric acid, ammonium-N and spores or showing no clostridial fermentation at all. In contrast to the larger-scale silages, no clostridial fermentation was found at dry matter contents above 250 g kg - 1 . In laboratory and in pilot-scale silages about 60 % of the variation in spore count could be explained from either the butyric acid or ammonia content. In farm silages this figure dropped to 20-30 % and it was concluded that the chemical parameters can not be used to predict spore counts in farm silages. The differences between the larger scale silages and laboratory silages are at­ tributed to the heterogeneity of the pilot-scale and farm silages. in silages. Butyric acid and ammonium contents, being products of clostridial activi­ ty,