Variations in chemical composition associated with tissue aging in palatable and unpalatable grasses native to central Argentina

Tissue aging in unpalatable grasses appears to be associated with a rapid decay in nutritional value because grazers usually start to avoid them at early stages of maturity. The objective of the present study was to determine and compare seasonal variations in fiber, lignin, crude protein and minerals (P, Ca, Mg, K and Na) in a palatable (Stipa clarazii) and in an unpalatable (Stipa eriostachya; syn: S. gynerioides) grass species, following a summer burning in central Argentina. Fiber and lignin contents were higher in the unpalatable grass than in the palatable grass, whereas crude protein and mineral contents were lower in the former than in the latter species. In both species, fiber and lignin increased over time, whereas crude protein and mineral contents declined with time. However, temporal changes were more pronounced and faster in the unpalatable grass than in the palatable grass. Our results suggest that the relatively high nutritive value of the unpalatable species at early plant growth stages following burning may create a window of time, in which it may be more readily grazed by livestock.