Technical note: Precision and accuracy of in vitro digestion of neutral detergent fiber and predicted net energy of lactation content of fibrous feeds

摘要

The objective of this study was to test the precision and agreement with in situ data (accuracy) of neutral detergent fiber degradability (NDFD) obtained with the rotating jar in vitro system (Daisy11 incubator, Ankom Technology, Fairport, NY). Moreover, the precision of the chemical assays requested by the National Research Council (2001) for feed energy calculations and the estimated net energy of lactation contents were evaluated. Precision was measured as standard deviation (SD) of reproducibility (S_R) and repeatability (S_r) (between- and within-laboratory variability, respectively), which were expressed as coefficients of variation (SD/mean × 100, S_R and S_r, respectively). Ten fibrous feed samples (alfalfa dehydrated, alfalfa hay, corn cob, corn silage, distillers grains, meadow hay, ryegrass hay, soy hulls, wheat bran, and wheat straw) were analyzed by 5 laboratories. Analyses of dry matter (DM), ash, crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) had satisfactory S_r, from 0.4 to 2.9%, and S_R, from 0.7 to 6.2%, with the exception of ether extract (EE) and CP bound to NDF or ADF. Extending the fermentation time from 30 to 48 h increased the NDFD values (from 42 to 54% on average across all tested feeds) and improved the NDFD precision, in terms of both S_r (12 and 7% for 30 and 48 h, respectively) and S_R (17 and 10% for 30 and 48 h, respectively). The net energy for lactation (NE_L) predicted from 48-h incubation NDFD data approximated well the tabulated National Research Council (2001) values for several feeds, and the improvement in NDFD precision given by longer incubations (48 vs. 30 h) also improved precision of the NE_L estimates from 11 to 8%. Data obtained from the rotating jar in vitro tech-rnnique compared well with in situ data. In conclusion, the adoption of a 48-h period of incubation improves repeatability and reproducibility of NDFD and accuracy and reproducibility of the associated calculated NE_L. Because the in vitro rotating jar technique is a simple apparatus, further improvement would probably be obtained by reducing the laboratory differences in rumen collection procedures and type of animal donors, which, however, reflect practical conditions.