Quality of grass silage infected with spores of Clostridium tyrobutyricum

The influence of adding clostridial spores to silage was studied in 2 successive years. Direct‐cut, precision‐chopped herbages were infected with spores of Clostridium tyrobutyricum in doses varying from 0 to 10 6 g −l fresh material (FM), and ensiled in experimental silos. The material was treated with or without 4 ml formic acid (85%) kg −1 FM. Silo contents were studied after 4.20 (or 50) and 100 days of ensiling. Contents of dry matter, water‐soluble carbohydrate, nitrate as well as buffering capacity of FM varied between the 2 years at harvest, whereas the numbers of clostridial spores were about the same (< 10 2 g −1 ). Infecting the crop with clostridial spores negatively affected the quality of silage in the first year. After 50 days spore numbers in the silages had increased by 40 × 10 3 to 150 × 10 3 times in the infected silage, compared with 5 × 10 3 in the uninfected silage. No effect was seen in the second year. Silage with high spore counts showed no residual nitrate content. Formic acid improved silage quality from a chemical point of view but had no anti‐clostridial effect. Ensilability of a crop seems to be more important than the initial count of Clostridia for a successful ensiling process.