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

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Figure 5.3
Forage offer (FO ) and
daily liveweight gain s
per animal (DLWG )
and per hectare (LW)
and its effect on solar
radiation conversion
efficiency, on a natural
grassland of Rio
Grande do Sul, Brazil .
LW gain/ha (kg) [G]
150
140
130
120
110
100
90
80
G/ha= - 17.9 + 29.2 OF - 1.3 OF 2
1 006 1 444
Forage remaining - kg DM/ha
Grasslands of the world
70
0.009 0.015 0.017 0.013
0.1
2 4 6 8 10 12 14 16 18
Forage on offer - % LW/day
568
GD= - 0.212 + 0.108 OF - 0.004 OF 2
1 882
dominate, with near disappearance of winter species and little contribution of
legumes, decrease in Andropogon lateralis , Aristida jubata and Eryngium horridum
, and increased bare soil. Regrowth does not reflect its forage production
and daily LWG is low. With an increase of FO to 8.0 percent LW, animals show
better body condition but the grassland is vulnerable, lacking protection for
grazing-sensitive species.
At medium and low grazing pressures (12.0 and 16.0 percent LW) and
higher FO , the grassland showed greater height, with more bunchgrasses of
varying diameter. Winter species were more frequent and increased grassland
quality, such as Stipa neesiana , Piptochaetium montevidense and Coelorachis
selloana , besides native legumes, with an important presence of Desmodium
incanum . Forage production and seed production of native legumes was
only seen after 8–10 years of this grazing treatment. Under lighter stocking
rates , animals graze more selectively and choose higher quality fractions of
available forage, leaving higher, less grazed plants. This contributes to maintaining
higher leaf area and promotes faster regrowth after each defoliation
under continuous grazing . With selective grazing, on lightly stocked swards,
forage production is higher, as is the voluntary intake of the animals, which
produced daily liveweight gain (DLWG ) of 0.500 kg per head (Figure 5.3).
This DLWG would not be possible if one considers the average crude protein
content s of the forage. The increased FO allows the animals to select a
more nutritious diet than average; the animal is harvesting more because it is
harvesting better.
0.6
0.5
0.4
0.3
0.2
Daily LW gain (kg) [GD]