Great Lakes Dairy Sheep Symposium - the Department of Animal ...

first of these quantities have been described in detail by Molle et al. (2004) and the second by
Avondo and Lutri (2004). They can be summarised as follows:
Methods to assess biomass availability
The available biomass, expressed in tons of dry matter per hectare (t DM/ha), consists of
all the dry and green matter present on each surface unit. It can be estimated by measuring the
height of the sward, thanks to the strong correlation between these two parameters. The
definition may be "undisturbed" sward height, which is measured either empirically or with more
precision with a sward-stick (Barthram, 1985), or a system which uses a herbometer to take into
consideration the density as well as the height of the sward (Holmes, 1984). These two
measurements are closely correlated as shown in Table 13.
Table 13 - Linear regression analyses (y = a + bx) between the pasture height (cm) measured
with the herbometer (EH = x) and with the sward-stick (SSH = y) (from Molle et al., 2004).
Grazing
Height Range (cm)
Species method Season SSH EH a b R 2
Italian
ryegrass
Continuous Spring 1.2-17.2 0.3-14.5 1.21 1.05 0.89
Italian
ryegrass
Not grazed Spring 3.6-41.4 1.5-25.5 0.54 1.42 0.91
Annual
ryegrass
Rotational Winter-Spring 9.3-30.6 4.2-20.2 3.59 1.29 0.97
Meadow a Rotational Winter 0.9-49.9 1.6-41.1 1.33 1.23 0.95
a
Annual ryegrass or pure Sulla
After measuring sward height with a herbometer, the available biomass is calculated
using the relationships shown in Table 14 (Molle et al., 2004).
Table 14 - Linear regression analyses (y = a + bx) between biomass availability (y, t DM/ha) and
the height (x, mm) measured using the herbometer (Molle et al., 2004).
Range,
Species Grazing method Season mm a b R 2
Annual ryegrass Rotational Winter-Spring 56 – 417 0.116 0.013 0.84
Italian ryegrass Rotational Winter-Spring 37 – 290 0.016 0.01 0.75
Italian ryegrass Continuous Winter-Spring 30 – 90 0.32 0.04 0.61
Italian ryegrass Continuous Late Spring 30 – 90 0.22 0.07 0.85
Sulla Rotational Winter-Spring 58 –678 0.793 0.01 0.75
Burr medic Rotational Winter-Spring 12 – 330 -0.026 0.016 0.57
Two simple equations that estimate the biomass availability of Mediterranean pasture (P,
in kg/ha of DM) as a function of its height (h, in cm) have been developed by Filigheddu and
Pulina (1986).
[12] winter period P = 180 + 40 h (r = 0.425)
[13] spring period P = -44 + 80 h (r = 0.69)
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