[en] The relationship between grazing pressure and differences in the defoliation rate of grass species is not well understood for tropical savannas even though it is likely to have a substantial influence on the persistence of preferred species, pasture condition and sustainability of the grazing system. The objective of this study was to examine the relationship between grass species characteristics and their defoliation rate in a paddock under increasing levels of utilization. Nine steers grazed a Eucalyptus savanna woodland for 14 days. Total pasture utilization reached 70% on day 13. The results confirm that with increasing pasture utilization, the defoliation rate of grasses varied among species. Bothriochloa pertusa (Bp) was the preferred
species, with the highest levels of utilization after 5, 7 and 13 days. This species had the highest leaf/stem ratio and basal area (P<0.05), and intermediate stem tensile resistance, stem density, bulk density and plant height. These characteristics probably allowed the steers to achieve high
nutrient intake rates. The steers avoided B. ewartiana possibly due to its tough stems and low leaf/stem ratio. In this tropical pasture the steers heavily grazed the preferred species at low to intermediate levels of overall pasture utilization (10 to 38%). In order to increase the utilization of less preferred species it was necessary to achieve high levels of pasture utilization (60 to 70%).
Disciplines :
Animal production & animal husbandry Environmental sciences & ecology
Author, co-author :
Benvenutti, Marcelo; INTA EEA Cerro Azul, Argentina