Effects of season, variety and botanical fractions on oxalate content of napiergrass ( Pennisetum purpureum Schumach)

Abstract

Various tropical grasses sometimes contain oxalate in sufficient concentration as to induce calcium deficiency in grazing animals. Napiergrass ( Pennisetum purpureum ), a useful tropical grass for ruminants was examined for oxalate levels with regard to season, variety and botanical fractions. It was observed that oxalate content was significantly ( P  < 0.001) affected by the season with the highest value (3.77%) being associated with early summer samples and the lowest value (1.76%) with late autumn samples. Compared to a normal, non‐dwarf variety, a dwarf variety exhibited a higher oxalate content but the difference was not statistically significant. With regard to the botanical fractions, oxalate content was significantly ( P  < 0.05) higher (2.78%) in leaf tissues compared to stem with leaf sheath (2.05%). In another experiment, a late, dwarf variety was re‐grown four times to evaluate re‐growth period effects on oxalate content during the early summer. Oxalate content increased gradually from the re‐growth period 1 (6 June to 28 June) to re‐growth period 3 (21 June to 12 July), and declined in re‐growth period 4 (28 June to 19 July). Results suggest that when napiergrass is grown in early summer, it could achieve oxalate levels that are toxic to ruminants.