Misleading relationships between in situ rumen dry matter disappearance, chemical analyses and in vitro gas production and digestibility, of sugarcane bagasse treated with varying levels of electron irradiation and ammonia

Twelve samples of sugarcane bagasse, representing untreated material or bagasse irradiated with doses of 200, 400, 600, 800 and 1000 KGy in an electron accelerator and afterwards with or without 20 g/kg dry matter (DM) of NH3. These were analysed for changes in neutral detergent fibre (NDF), phenolic compound and reducing sugars content. DM disappearance was evaluated using both 48 h in situ and in vitro incubations, 0 h DM disappearance (washing losses) and in vitro volatile fatty acid (VFA) production. In situ disappearance was highly correlated with NDF (negatively), phenolic compound (positively) and reducing sugar (positively) content. However, washing losses were similarly correlated to NDF, phenolic compounds and reducing sugars, and little variation in either in vitro gas or VFA production was recorded. It is therefore concluded that the variations in situ disappearance observed were an artefact of washing losses and did not accurately reflect differences in rumen fermentability. These results may help to explain why the performance of animals, reported in the literature, offered treated bagasse is not as good as that anticipated from in situ analyses.