Evaluation of autoclave procedures for fibre analysis in forage and concentrate feedstuffs

Autoclave procedures for amylase-treated neutral (aNDF) and acid detergent fibre (ADF) analysis in concentrate and forage feedstuffs were evaluated. Dried and ground samples were weighed in polyester filter-bags, heat sealed, placed into a 500 ml Erlenmeyer flask and treated with neutral or acid detergent solution in an autoclave. Different times and temperatures were tested: 40 min at 110 °C (1); 60 min at 110 °C (2); 40 min at 120 °C (3) or 60 min at 120 °C (4). Results from autoclave treatments were compared to those obtained with the conventional standard method by regression. Conventional method included the use of Berzelius beakers and Gooch-crucibles, as well as refluxing and filtration apparatus. For aNDF analysis, all autoclave methods showed high level of precision as indicated by low standard deviation (S.D.) from regressions (mean of 40.4 g aNDF/kg dry matter). Slope of the regression for autoclave treatment at 110 °C during 60 min, however, differed from 1 (P<0.05). Autoclaving treatment at 110 °C during 40 min had the lowest (24.1 g aNDF/kg dry matter) and at 120 °C during 60 min had the highest (75.6 g aNDF/kg dry matter) bias. For ADF analysis, although the level of precision of regressions for all treatments was relatively high (S.D. mean of 34.5 g ADF/kg dry matter), the slope of regression did not differ from 1 only for 110 °C during 40 min treatment. Moreover, bias using this treatment was near 0 while it varied from 73 to 174 g ADF/kg dry matter using the others autoclave treatments. In conclusion, aNDF and ADF analysis in forage and concentrate feedstuffs may be carried out simultaneously in an autoclave and not biased from Gooch-crucible conventional method, using filter bags and a temperature of 110 °C for 40 min.