Comparison of detergent fiber analysis methods for forages high in pectin

Pectin and ash can interfere with detergent fiber analysis of brassica forages. Non-sequential (NONSEQ) and sequential (SEQ) fiber analysis sequences were compared for amylase neutral (aNDF) and acid (ADF) detergent fiber with and without correction for acid detergent residual ash in individually (Experiment 1) and batch-processed samples (Experiment 2). Hemicellulose concentration was calculated as the difference between aNDF and ADF. Samples included brassica forage, legumes, CT containing legumes and grasses. Fiber analysis sequence and ash correction affected ADF and hemicellulose independently, with fiber analysis sequence having the larger impact. Forage groups differed in response to treatment for most variables. Compared to NONSEQ analysis, SEQ analysis reduced ADF of brassica forages by 41 and 34 g/kg in Experiments 1 and 2, respectively, reduced ADF of legume forages by 22 and 34 g/kg in Experiments 1 and 2 and gave comparable increases in hemicellulose for both forage groups in both experiments. Estimates of ADF and hemicellulose in grasses were unaffected by analysis sequence. Under individual processing, ash correction reduced ADF only for brassicas (205 g/kg versus 191 g/kg for uncorrected and ash-free), but under batch processing, ADF of all forage groups was reduced by ash correction (mean 282 g/kg versus 274 g/kg for uncorrected and ash-free, respectively). The difference between NONSEQ and SEQ ADF increased with pectin concentration (r2 = 0.30, P<0.001). Sequential fiber analysis with correction for residual ash was preferred for high-pectin forage brassicas and non-tannin legumes, but non-sequential methods were acceptable for grasses.