aNDF, NDFd, iNDF, ADL and kd: What have we learned?

Recommendations

Info

a reverse-phase column. Ether-linked PCA and FA were calculated as the difference between total and ester-linked phenolic acids. Phenolic acids and respective amounts of their different linkages and lignin types were used in a multiple regression to select those factors explaining most of the variation in kd, 24hr and 96hr NDFD. Since most esterified PCA on lignin are not covalently attached to other cell wall polymers, they should not directly influence cell wall degradability. However some cell wall models show how they can interfere with ferulate-lignin cross linking and in some cases reduce the proportion of lignin bound to cell wall. Figure 2 and 3 show the relationship between 24hr NDFD and PCA content in NDF and ADF residues respectively. Forage groups demonstrated different relationships for digestibility from positive to negative in NDF residues. ADF residues were instead characterized by a consistent negative relationship among all forage groups and similar results were obtained for 96 hr NDFD. Relationship between 24hr and 96hr NDFD with esterified FA content in NDF residues are shown in Figures 4 and 5, respectively. Ester-linked FA had generally a negative relationship except in bmr corn for 24hr and positive for 96hr NDFD. Ferulates primarily form as esters of arabinoxylans and later they cross-link through ether linkages with lignin. So esters of FA should not necessarily limit NDF degradation. This has probably more to do with the degree of arabinoxylans substitution. Ether linkage between FA and lignin has been used a measure of cross-linking between lignin and arabinoxylans and defined as the most important factor limiting energy utilization (Casler, 2001). However in our case we were not able to obtain consistent negative relationship with NDFD. Figure 6 and 7 show the relationship for 24 and 96 hours respectively with divergent relationship for 24 hr and consistent positive ones for 96 hr NDFD. Negative effect of etherified FA on NDFD has been found in elongating internodes in maize but not in internodes that had stopped the elongation process and confirms the hypothesis that secondary cell wall development may mask the negative impact of etherified FA on NDFD. Interestingly also, bmr shows higher content of etherified FA compared to conventional corn in NDF residues, demonstrating that etherified FA is not always a good indicator of cross-linking between lignin and arabinoxylans and this was also shown recently by Marita et al. (2003). However this relationship changes when ADF residues were analyzed for ether linked FA, showing how the solubulization or branching of the lignin structure has in this case more importance than linkages. Acid detergent solution in this case might dissolve those FAs that only etherified (instead of having and ester-ether linkage). A multiple regression with stepwise selection was run within each forage group using the independent variables lignin type (ADL or Klason lignin) and their difference on an NDF basis and phenolic acids with their specific linkages also on an NDF basis. We wanted to determine how much variation in 24hr and 96hr NDFD and kd was explained by the above mentioned variables. The procedure was not able to find any significant variable for the alfalfas (P < 0.10), showing how NDF digestibility cannot be easily explained in legumes by many of these factors. All the other forage groups reached
significance and with R 2 that varied between 0.56 and 0.99. Results confirmed the lack of consistency among the forage types and the properties of the chemical structures and digestibility and rates of digestion. This clearly demonstrates that that factors affecting rates and extents of digestion of NDF vary by forage type and most likely maturity. Table 2: Independent variables selected and their solution for each forage group and dependent variable. Dependent Variable kd ADL: -0.72 EthFA: 0.87 ADL: -0.74 KL: -0.45 R 2 EthFA: -0.68 EstFA: -1.07 EstPCA: 1.04 0.97 0.75 0.79 0.84 24h ivNDFd ADL: -0.84 ADL: -1.12 EthPCA: -0.75 KL: -0.62 R 2 EthFA: -0.52 EstPCA: 0.36 EstPCA: 1.09 0.98 0.97 0.56 0.92 96h ivNDFd ADL: -0.90 KL: 0.16 (KL-ADL): -0.57 R 2 Forage group Grasses Imm. grasses Conv. corn Bmr corn EthFA: -0.40 ADL: -0.59 EthFA: 0.70 EthFA: 0.48 EstPCA: 0.34 0.97 Significance level = 0.10 0.99 0.84 Figure 2: Relationship between 24hr NDFD and ester linked pCA in NDF residues
Page 1 and 2: aNDF, NDFd, iNDF, ADL and kd: What
Page 3 and 4: occurred. As a result the use of ea
Page 5 and 6: The variation associated with using
Page 7 and 8: Lignin is generally accepted as the
Page 9: hydroxycinnamic moiety and the lign
Page 13 and 14: Figure 5: Relationship between 96hr
Page 15 and 16: Take Home Messages � Description
Page 17: Van Milgen, J., M. R. Murphy and L.

aNDF, NDFd, iNDF, ADL and kd: What have we learned?

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?