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

Abstract

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 (Daisy(II) 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 technique 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.

Effects of various inulin levels on in vitro digestibility of corn silage, perennial ryegrass (<i>Lolium perenne</i> L.) and common vetch (<i>Vicia sativa</i> L.)/oat (<i>Avena sativa</i> L.) hay

“…The IVTD NDF is an important parameter for determining forage quality and feed intake and consequently the productivity of ruminants. The IVTD NDF reported by Spanghero et al (2010) for CS at the end of the 48-hour incubation period was similar to the control group of the present study. Furthermore, Oba & Allen (2016) determined that the in vitro true neutral detergent fibre digestibility values of CS ranged from 35.1 to 48.1% at 24 hours.…”

Use of principal component analysis to classify forages and predict their calculated energy content

“…The 48 h in situ assay is the time suggested by NRC (2001) as an alternative to calculate the tdNDF value and, being less affected by both lag time and rate of degradation than earlier incubation times (Mertens, 1992;Spanghero et al, 2010), it could be used to compare different forages. However, some authors evaluated the opportunity to reduce the length of the rumen incubation to 30, 24 h or even shorter (Ferreira and Mertens, 2005;Spanghero et al, 2010;Tagliapietra et al, 2011).…”

“…However, some authors evaluated the opportunity to reduce the length of the rumen incubation to 30, 24 h or even shorter (Ferreira and Mertens, 2005;Spanghero et al, 2010;Tagliapietra et al, 2011). Despite an increased data variability (Spanghero et al, 2010), a reduced rumen incubation time could better describe the real NDF degradation dynamic in the rumen of high-producing dairy cows at high levels of intake (Goeser and Combs, 2009;Tagliapietra et al, 2011).…”

“…In situ digestible and indigestible NDF (iNDF) determinations The digestibility of NDF (dNDF) was measured in situ by incubating nylon bags in the rumen of two cannulated dry cows for 12, 24, 48 and 288 h (Spanghero et al, 2010). Animal care was in accordance with the EC Council Directive guidelines for animals used for experimental and other scientific purposes (EC, 1986).…”

“…In contrast, in the summative approach, a unique equation is used to estimate the NE L of different feeds, but a large number of parameters are needed. A major disadvantage of complex models is the large number of laboratory parameters, with some being poorly repeatable, timeconsuming and expensive (Cherney, 2000;Spanghero et al, 2010). In addition to chemical parameters, biological parameters such as in situ rumen NDF degradation characteristics have been proposed to properly evaluate forages used in dairy cow diets (Van Amburgh et al, 2003;Robinson et al, 2004;Krä mer et al, 2012).…”