Grasslands of the World.pdf - Disasters and Conflicts - UNEP

ELBIO BERRETTA
The South American Campos ecosystem 189
Plate 5.4
Grazing management : forage deferred for winter grazing .
lambing and improved grasslands 40 to 30 days before lambing. These values
are modified by weather conditions, which affect the growth rate, and also by
the amount of forage present at the start of the accumulation period.
Most ewe hoggets are mated at 2.5 years (four teeth) since many of them
(40–60 percent) do not reach the minimum liveweight for mating at 1.5 years).
This has adverse productive and economic consequences for the industry, as
it reduces the number of lambs produced by each ewe in her lifetime, reduces
genetic progress of the flock and constrains the overall efficiency of the system.
To increase lamb production it is very important to increase the reproduction
rate of hoggets.
Several management strategies have been defined to improve the liveweight
gain of hoggets on natural grassland on basalt soils (San Julián et al., 1998). The
use of improved grassland and sown pastures allows winter liveweight gains of
60 to 90 g/head/day. Such rates of gain allow a high proportion of hoggets (80–
90 percent) to attain mating weight at two-tooth, implying weights exceeding
32 and 35 kg for Merino and Corriedale hoggets, respectively. To attain these
gains in winter it is necessary to provide 1 500 kg DM/ha of deferred forage,
with a height of 5 to 6 cm, on natural grasslands or 1 000 kg DM/ha, with a
height of 4 to 5 cm, on improved grasslands (San Julián et al., 1998).
In a study in the basalt zone (Ferreira, 1997), three groups of farmers could
be distinguished according to production systems and technical demands. The
first group , 56 percent of farmers studied, had low-potential natural resources
and used a defensive strategy in their decision-making, which resulted in very
low levels of technology adoption, and the technology available for shallow