Fibre digestibility and its relationships with chemical and morphological traits in thirty-two sugarcane varieties

The objectives of this study were to determine the range of neutral detergent fibre (NDF) digestibility across sugarcane varieties and predict dry-matter (DM) and NDF digestibility based on morphological and chemical composition. Whole plants of thirty-two commercial varieties were collected after 12 months regrowth (second cut) and evaluated for morphological traits, chemical composition, in situ digestibility of NDF (NDFD) and of DM (DMD), in vitro NDFD (IVNDFD) and gas production dynamics from isolated NDF. The content of NDF ranged from 404 to 547 g kg(-1) DM, DMD was between 593 and 739 g kg(-1) and NDFD varied from 270 to 363 g kg(-1). Cluster and discriminant analyses for NDFD agglomerated sugarcane genotypes into three groups (high, medium and low NDFD). The contents of NDF and lignin were the best univariate predictors of sugarcane DMD and NDFD respectively. Therefore, associating NDF and lignin improved the accuracy of DMD prediction. Associating lignin concentration with the number of dry leaves and stalk length significantly improved the goodness of fit of NDFD prediction. Contrary to expectations, silicon concentration was not related to NDFD. The principal component analysis patterned the content of neutral detergent solubles, NDFD and variables related to DM yield in different components. Hence, these characteristics would coexist in the same variety. Based on Lucas test and kinetics of gas production from NDF, sugarcane potentially digestible NDF (pdNDF) can be considered almost uniform (pdNDF digestibility = 677 g kg(-1)). In conclusion, associating chemical composition and morphological traits can successfully improve the screening of sugarcane genotypes for animal nutrition.