Ruminal degradation of dry matter and organic matter of hybrid napier grass (Pennisetum purpureum Schumach) fractions

The ruminal degradation characteristics of whole hybrid napiergrass (WNG) and its botanical fractions upper third portion (UTP), middle third portion (MTP) and lower third portion (LTP) were investigated in sacco in three ruminally fistulated sheep. The animals were fed with napier grass (ad libitum) with daily supplementation of concentrate mixture and mineralized salt. Nylon bags with 3 g samples were incubated in the rumen for 0, 6, 12, 24, 48 and 72 h. Residual dry matter were adjusted to an exponential model: D(t)=a+b (1-e raised to negative ct), where D(t) is the percentage dry matter (DM) or organic matter (OM) disappearance in the bags for time t, of the rapidly (a) and slowly (b) degradable components and c is the constant rate of degradation for the second component exressed in percent h. Effective degradation (ED, percent) of DM and OM were calculated according to the formula: ED=a+b/(c+k), where k=0.02/h. Significant differences on some nutrient composition across plant samples were observed. The ash values were 10.23 to 19.07 percent; lowest (0.05) and highest (P0.05) values were observe in LTP and MTP, respectively. The crude protein (CP) content was highest (P0.05) in UTP and lowest (P0.05) in LTP. There were no differences on NDF and ADF across forage samples. ADL and cellulose were higher (P0.05) in LTP. MTP was higher (P0.05) in hemicellulose. Significant differences were also observed in rumimant degradation of various samples across time of incubation including their degradation kinetics. Almost the same pattern was observed on degradation kinetics of DM and OM of various samples. Readily soluble fraction (a) was highest (P0.05) in LTP. Slowly degradable fraction (b) was highest (P0.05) in UTP; consequently, potential degradation fraction (a+b) was highest in these samples. Rate of degradation for both DM (0.052 percent/h) and OM (0.0744 percent/h) was highest (P0.05) in MTP. The ED of DM and OM was 39.44 to 49.19 percent and 51.98 to 60.30 percent, respectively. This study shows variation on the degradation kinetics of napier grass fractions