Proposal and validation of new indexes to evaluate maize silage fermentative quality in lab-scale ensiling conditions through the use of a receiver operating characteristic analysis

•The Flieg-Zimmer’s Score (FZS) was compared with new indexes to evaluate silage quality.•The FZS did not show a normal distribution among lab-scale maize silages.•Compared to FZS the new indexes include also pH, ethanol, ammonia and mannitol.•The new indexes, unlike FZS, managed to differentiate silages with different DM.•The new indexes are better suited in differentiating the quality of silages than FZS.