Determination of Oxalic Acid by HPLC and Silica Contents by Conventional Method in Different Varieties of Napier Grass (Pennisetum purpureum)

Napier grass (Pennisetum purpureum) is used as a common feed source for livestock especially ruminant. Although it is used as a fodder due to its moderate nutritive values, it contains the anti-nutrients. Oxalic acid and silica contents are examples of anti-nutritive factors that present in Napier grass. The soluble form of oxalate salts is the anti-nutrients as it can be combined with blood calcium or magnesium to form an insoluble oxalate crystal that excreted in the faeces. On the other hand, silica is the hairy part on the leaves that will reduce palatability and caused some physical damages. Therefore, the aim of this study was to determine the contents of oxalic acid and silica in the Napier grass. Seven varieties of Napier grass including Taiwan, Zanzibar, Australian Dwarf, Pakchong, Purple, Kobe and Indian were planted under standard level (300 kg NPK/ha/year) of fertiliser application. Plants were harvested at 2 months of plant maturity. Total oxalate and soluble oxalate contents in samples were determined by high-performance liquid chromatography (HPLC), while silica content was measured by conventional method using ashing method. Results showed that Dwarf Napier contained the highest total oxalate content (3.23%) followed by Kobe (2.61%), Zanzibar (2.60%), Purple (2.44%), Taiwan (2.43%), Indian (2.15%) and Pakchong (1.95%) varieties. Similarly, Dwarf Napier contained the highest soluble oxalate content (3.00%), while Pakchong showed the lowest soluble oxalate content (1.80%). No significant (p>0.05) differences were
observed on insoluble oxalate content among Napier grass varieties. There were no significant (p>0.05) differences on silica content among Napier grass varieties. Dwarf Napier, however, showed numerically the highest silica content (4.19%), while Pakchong showed the lowest silica content (3.14%). In conclusion, Pakchong variety is safer than
Dwarf variety for ruminant feeding. However, careful attention should be needed for grazing animals since leaf contains more soluble oxalate than stem parts. Further feeding experiments using Napier grass varieties are needed on oxalate toxicity in ruminants.