Nordic ringtest on INDF content and NDF degradation characteristics in three feeds

NDF and indigestible NDF (INDF) content in barley, rapeseed meal and grass silage was measured in fi ve research laboratories. NDF content (%DM) was similar for grass silage (50-52%), but varied from 21 to 25% in barley and from 19 to 31% in rapeseed meal. The variation in INDF content was also high, mainly due to differences in NDF analysis of the residue. Differences in effective rumen NDF degradability were also high for grass silage (52-64%), barley (50-70%) and rapeseed meal (38-56%), respectively. This ringtest underlines the need for standardization of the NDF analysis and of in situ procedures.


INTRODUCTION
Rumen fermentation of the fi bre fraction is one of the most important submodels in the new dynamic feed evaluation systems.These sub-models are usually both generated and evaluated based on experimental data compiled from multiple research institutes, and it is therefore crucial that the variation between laboratories in the quantitative and qualitative characteristics of the fi bre fraction is minimized.The aim was therefore to compare the results from fi ve research laboratories on fi bre content and rumen degradation of three commonly used feeds.

MATERIAL AND METHODS
Barley, rapeseed meal (RSM) and freeze-dried grass silage, were ground to pass a 1.5 mm screen and sent to 5 research laboratories (Lab1-Lab5).NDF analysis was, in all laboratories, based on Van Soest et al. (1991), but with individual modifi cations.Lab1 used the Ankom method with addition of Na 2 SO 3 and amylase.Lab2 used amylase only for barley and used an alternative oven method (Chai and Udén, 1998) and subsequently corrected for ash.Lab3 used the Ankom technique with addition of both amylase and Na 2 SO 3 , and correction for content of ash.Lab4 used the Fibertec system with the addition of Na 2 SO 3 and amylase (barley only) and a subsequent correction for ash.Lab5 used addition of Na 2 SO 3 and amylase and subsequent correction for ash and used the Ankom method for nylon bag residue and Fibertec for NDF in original feeds.
NDF in situ degradation was done using local procedures.Rumen effective degradability (ED, %) was calculated based on correction for particulate loss during washing (Hvelplund and Weisbjerg, 2000) and using a fractional passage rate of 2 %h -1 and a model including a lag time.Laboratories determined INDF (indigestible NDF) using their own nylon bag method regarding incubation time, in situ nylon bag pore size, sample weight, etc.In the fi ve laboratories an incubation time and nylon bag pore size of 114 h/37 µm, 96 h/28 µm, 240 h/37 µm, 288 h/17 µm and 504 h/37 µm, respectively, were used.Potential NDF digestibility (PD, %) was calculated as 100 × (NDF-INDF)/NDF.
To evaluate the effect of variation due to bags vs variation due to cows/NDF analysis, four laboratories (Lab1, Lab2, Lab4, Lab5) weighed each feed in eight of their own bags, and send two bags to each of the four laboratories for a six days (144 h) incubation.In total 32 observations on INDF content in each feed could subsequently be analysed based on effects of origin of bags and of place for incubation.Statistical analysis was done using NLIN and GLM in SAS 8.e.

RESULTS
Only minor differences were found in NDF content in barley (CV=9.4) and especially grass silage (CV=0.78),whereas for RSM, the variation in NDF content was high (CV=19), and NDF varied from 19.4 to 30.8% in the DM.INDF content varied in % of DM from 4.7 to 8.1% in grass silage, from 3.3 to 5.5% in barley and from 6.4 to 12.9% in RSM.There was no relationship between a high NDF content and a high INDF content between laboratories, and therefore large variations were also found in PD.PD varied from 84.1 to 90.8% for grass silage, from 75.8 to 86.6% for barley and from 42.8 to 68.0% for RSM.For all three feeds, the highest INDF content and the lowest PD was found in Lab1 (144 h incubation), whereas for Lab5 (504 h incubation), PD was generally high.There was only minor differences in the form of the degradation curve for grass silage between laboratories, whereas much larger variations were seen for barley and RSM (data not shown), resulting in large variations in ED (Table 1).The statistical analysis on INDF residue (g per kg DM) showed large interactions between feeds, origin of bags and place of incubation, which is illustrated in Figure 1.Across feeds, there was no signifi cant effect of origin of bags (P=0.94),whereas there was a signifi cant effect of place for incubation/ analysis (P<0.001).For grass silage, both origin of bags (P=0.002) and place for incubation/analysis (P<0.001) had a signifi cant effect.Lab1 residues were highest (90 g) and residues from Lab4 were lowest (50 g).Similar effects of origin of bags (P<0.001) and place for incubation (P=0.004) was found for barley.The most pronounced effect of place of incubation was found for RSM.No signifi cant effect (P=0.17) was found for origin of bags, whereas place for incubation was signifi cant (P<0.001) as illustrated in Figure 1.Residue varied from on average 73 g for bags incubated in Lab2 to 130 g for Lab1.

DISCUSSION
Although laboratories based their NDF analysis on the same principles, major differences were found in problematic feeds like barley containing starch and RSM containing fat.Differences in potential digestibility was not only due to differences in incubation time or bag pore size.There were also problems with the reproducibility in the determination of residual NDF when bag type was balanced and incubation time was fi xed.This could have been due to differences between cows, but more likely due to laboratory differences in losses during washing of bags and in NDF analysis of bag residues.CONCLUSIONS NDF content and potential digestibility of NDF are important parameters in new feed evaluation systems.Although partitioning of fi bre into indigestible and potentially digestible fi bre was different between laboratories, there also seemed to be problems with the reproducibility of the NDF analysis on some feeds.The variation in INDF content was primarily due to used cows, washing procedures and/or method for residual NDF analysis, and to a minor extent due to bag type.