Tese
Alternativas de manejo de pastagem natural submetida a pastoreio rotativo
Fecha
2012-02-15Registro en:
GARAGORRY, Fabio Cervo. Management alternatives in natural grassland submitted to rotational grazing. 2012. 210 f. Tese (Doutorado em Zootecnia) - Universidade Federal de Santa Maria, Santa Maria, 2012.
Autor
Garagorry, Fabio Cervo
Institución
Resumen
This study aimed to evaluate different alternatives for management of natural pasture.
Vegetation dynamics was evaluated for a period of six years in a natural pasture, submitted
along 16 years to fire and grazing treatments. Furthermore, we evaluated the production and
behavior of beef heifers from 12 to 18 months of age, maintained on natural pasture under two
grazing frequencies. In the first experiment, the treatments consisted of a combination of
burning factors (presence or absence) and grazing (presence or absence), in concave and
convex slope positions, in a completely randomized design with factorial arrangement of four
treatments and two topographic positions. Rotational grazing was used, with intervals
calculated by the thermal time (760 degree days) necessary for the emergence of four leaves
of Paspalum notatum and Andropogon lateralis. Burning was performed at the end of winter
in a bimodal fashion. The treatments excluded from disturbances had a behavior atypical due
to a burning caused by a lightning leading vegetation to a succession process. The grazed
treatments had a stable prevalence of Paspalum notatum, on concave slope and its association
with Andropogon lateralis, in convex slope. Natural grassland proved to be resilient to
burning and grazing. However, the use of burning and grazing on concave slope areas can
cause a reduction in vegetation diversity. In the second experiment, we evaluated the effect of
two defoliation intervals, 375 and 750 degree days (DD), on the productive performance of
beef heifers maintained on natural pasture under rotational grazing in the growing season of
2010 and 2011. The experimental design was completely randomized with two treatments and
three replications. We evaluated the forage mass, height, green material and dead material in
pasture. The performance measurements in animals were evaluated stocking rate, average
daily gain and gain/ha. The greatest height, mass of green material, dead material and forage
mass were observed in 750 DD treatment. Treatment with 375 DD presented a higher
percentage of green material in relation to herbage mass. The highest average daily gain and
gain per area were observed in the treatment 375 DD. The shortest interval between grazing
permits satisfactory performance in rearing of beef heifers, since the natural pasture is
managed with green material above 1500 kg DM/ha and grazing periods lower than three
days. In the third experiment were related parameters and performance of grazing animal and
its ingestive behavior. Ingestive behavior of heifers was measured as times of grazing,
ruminating and resting, bite rate, bites per feeding station, feeding stations per minute,
displacement rates by stations and time. The multiple regression equations had coefficients of
determination of 48, 68 and 89% for grazing time, average daily gain and gain/ha. The
average temperature, day of occupation, number of bites/min and bits per season were the best
predictors of ingestive behavior of beef heifers grazing on natural grassland.