Effect of spatial and temporal variation in concentration of condensed tannins in different sainfoin (Onobrychis viciifolia) accessions on in situ ruminal degradation kinetics of dry matter and crude protein
B.N. Azuhnwi1, 2*, B. Thomann2, Y. Arrigo1, B. Boller3, H.D. Hess1, M. Kreuzer2 and F. Dohme1
1 Agroscope Liebefeld-Posieux Research Station ALP, Posieux, Switzerland
2 ETH Zurich, Institute of Plant, Animal and Agroecosystem Sciences, Switzerland
3 Agroscope Reckenholz -Tanikon Research Station ART, Zurich, Switzerland
*Corresponding author: nche.azuhnwi@alp.admin.ch
Condensed tannins (CT), when ingested at optimal doses, are thought to play a part in the rumen escape protein mechanism in which ruminal microbial digestion of dietary protein is slowed, thus increasing the protein outflow from the rumen (Waghorn et al., 1987). Sainfoin is a perennial temperate legume with moderate to high CT concentration which was found to reduce ruminal ammonia turnover in growing lambs (Scharenberg et al., 2007). Also, CT in sainfoin have been shown to vary amongst accessions and also across sites and cuts (Azuhnwi et al., 2009). The significance of this variation on ruminal degradability of feed is not yet known. The in situ technique is widely used around the world to evaluate the rate and extent of degradation in the rumen because of its relative quick and inexpensive nature (Wilkerson et al., 1995). The aim of the present study was to investigate the variation in ruminal degradation kinetics of dry matter (DM) and crude protein (CP) in five sainfoin accessions cultivated at three different sites in Switzerland and harvested at two different time points using this technique.
Methods
Field plots of five sainfoin accessions comprising of three landraces (Moiry, Premier, and Sarzens, all of single cut / communis type) and two commercial cultivars (Perly and Visnovsky, both of multiple cut / bifera type) were established in spring of 2007 at Thun (TH, altitude 565 m above sea level (a.s.l.)), Ellighausen (EL, 520 m a. s. l.) and Reckenholz (RE, 440 m a. s. l). The plant material was harvested for first and second cut of 2008 at about 5 cm from ground level and frozen. Samples were lyophilised in March 2009 and ground to pass a 3-mm screen. The chemical composition was determined using standard protocols while the butanol/HCl method (Terrill et al., 1992) was employed to measure the concentration of CT with a standard obtained from the Visnovsky accession. The in situ technique as described by Shannak et al. (2000) was used to determine ruminal degradation kinetics of DM and CP using three ruminally cannulated cows and by incubating the forage samples in nylon bags for 2, 4, 8,
16, 24 and 48 h (n=3). Ruminal degradation kinetics of DM and CP were evaluated by the equation p=
a + b(1 – e-c(t—L)), where p is ruminal disappearance at time t, a the rapidly soluble fraction, b the insoluble but degradable fraction, c the rate constant of degradation of b (%/h) and L the lag time. The degradation of DM and CP determined at the different time points was corrected for small particles.
The potentially degradable fraction d was calculated as the sum of the fractions a + b. The effective degradability of DM and CP (EDDM and EDCP) were calculated at an assumed ruminal fractional passage rate of 8 %/h, representative for a high feeding level. Effects of accession, site and cut were evaluated by analysis of variance based on a three-factorial experimental design. The relationship between CT content and degradability of DM andCP were examined by Pearson correlations.
Results and Discussion
Averaged across accessions, sites and cuts, CT concentrations ranged from 55.3 to 70.5 g/kg DM, with the landraces having higher (P < 0.001) CT concentrations compared to cultivars. The concentration of CT was higher (P < 0.001) at EL than at RE and TH while first cut CT concentrations were lower (P < 0.001) than those of the second cut. These results are in agreement with those reported in Azuhnwi et al. (2009). Crude protein ranged from 141 to 175 g/kg DM, with cultivars having lower (P < 0.001) CP values compared to landraces and first cuts having lower (P < 0.001) CP values than those of the second cut.
There were effects (P < 0.001) of accession, site and cut on DM fraction a, with the values ranging from 23.9 % to 34.2 %. Similarly, accession, site and cut effects (P < 0.001) were observed for the b fraction of DM. An effect (P < 0.05) of accession was observed for the constant c of DM while no site or cut effects (P > 0.05) were evident. Significant effects (P < 0.001) of accession, site and cut were also evident on the fraction d. Lag time (L) which describes the interval between incubation and start of degradation was not affected (P > 0.05) by any of the three effects. The EDDM was influenced (P < 0.001) by accession, site and cut. Accession × site × cut interactions (P < 0.001) were observed for all fractions describing ruminal DM degradation kinetics except for c and L.
There was no effect (P > 0.05) of accession on fraction a of CP; conversely, site (P < 0.01) and cut (P < 0.001) had an effect on this fraction. For fraction b of CP, effects (P < 0.001) of site, accession and cut were observed. Accession and cut had an effect (P < 0.05) on c while there was no effect (P > 0.05) of site. Fraction d of CP was influenced (P < 0.001) both by site and accession but not by cut (P > 0.05). As reported for DM above, no effects (P > 0.05) of the three factors were found on L.
Effects (P < 0.001) of all three factors were observed for EDCP. Accession × site × cut interactions (P < 0.001) were observed for all fractions describing ruminal degradation kinetics of CP except for constant c.
A negative correlation (-0.43, P < 0.01) was calculated between CT and EDCP, while CT and EDDM were not correlated (-0.31, P = 0.09). There was no correlation (+0.07, P = 0.68) between CP and EDCP.
Conclusion
Generally, ruminal degradability was higher in sainfoin low in CT compared to sainfoin higher in CT and this was true across accessions, sites and cuts. Condensed tannins seem to have affected CP degradation more than DM degradation and this suggests a specificity of CT on protein degradation.
The interactions observed indicate differential ranking of accessions when considered across sites and cuts.
References
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This study was supported by the Arbeitsgemeinschaft zur Förderung des Futterbaues (AGFF).
