Agriculture Reference
In-Depth Information
Table 10.3
Recommended grazing heights and rest periods.
Forage Type
Begin Grazing Height, cm
End Grazing Height, cm *
Rest Time Days
Tall fescue, orchard grass, and legume,
annual ryegrass, or small grains
20 (8 ″ )
10 (4 ″ )
14 - 45
Bermudagrass crabgrass
13 - 20 (5 - 8 ″ )
7.6 (3 ″ )
14 - 45
Alfalfa
30 - 38 (12 - 15
″
)
7.6 (3
″
)
24 - 32
Sudan grass, pearl millet
30 - 46 (12 - 18
″
)
20 (8
″
)
14 - 30
Native warm season grasses
30 - 46 (12 - 18
″
)
20 (8
″
)
30 - 50
*Due to parasites and desired intake it is recommended that goats not graze below a height of 13 cm (5
″
). Rotation
timing should be based on minimum forage height, not days grazing (adjusted for goats by Ann Peischel).
Source: Brann, 2005 .
Stocking rate usually is determined by the availability
of forage and number of paddocks. Overstocking and
understocking rules apply in this system, too, so the
optimum stocking rate must be predetermined for a spe-
cifi c type of forage and environmental conditions that alter
forage availability.
Strip grazing has gained popularity in goat production
systems. In this system, goats are allowed to graze a strip
of pasture a few hours each day to partially meet their daily
needs. This system requires less land, but it requires more
intensive management and labor. Perimeter fences are
required to hold animals in pastures and to protect them
from predators. Rotational and controlled grazing and strip
grazing require temporary or interior fencing to subdivide
the pasture into paddocks for rotation. For proper fencing
and watering on pasture, the reader is referred to more
specialized fencing manuals and Chapter 17, Housing
Requirements.
include tannins that limit the nutritive value of plants by
forming complexes with proteins and carbohydrates,
phenolic acids and terpenes that disturb rumen fermen-
tation, and pyrrolizidine alkaloids that are hepatotoxins.
One possible collateral benefi t of consuming browse is that
these materials contain secondary compounds that may
reduce internal parasite infestations. Goats select tree
foliage, shrubs, forbs, fl owering parts, seeds, and nuts
when they are available. Available browse can serve as a
supplement in pasture-based feeding systems when forage
declines in quality, and this can help sustain grazing animal
performance. Conversely, pastures that are predominantly
browse can be improved by supplementing animals with
conventional feeds (e.g., corn, barley) to dilute secondary
compounds and provide limiting nutrients.
Goats are resistant to many plant toxins and antinutritive
factors. Thereby, goats can readily defoliate most plant
species, many of which cattle will not use. Although the
proportion will vary with availability, goats typically
consume a diet that is predominantly browse (65-70%)
with smaller amounts of grasses (20-25%) and forbs (5%).
Goats prefer woody plants like blackberry and raspberry
bushes and use their upper mobile lips to select the tender,
more digestible young leaves and leave the less digestible
branches and thorns. Browsing by goats with proper man-
agement can prune and stunt bushes, and this helps to
encourage grass growth. However, many browse plants
contain antinutritional factors like high lignin content,
silica, and terpene-based organic compounds, tannins, and
other alkaloids. High levels of tannin compounds reduce
the availability of protein; however, when a diet is supple-
mented with polyethylene glycol (PEG), it reduces the
antinutritional effects of tannins by improving protein
availability (Decandia et al., 2000) that in turn will increase
ovulation rate (Lassoued et al., 2006) in goats. Animal
B
ROWSE
Browse materials, shoots, leaves, and very high quality
parts of shrubs, forbs, and trees, often are the goat's staple
food. Goats prefer foliage from trees and shrubs. These
novel dietary ingredients are rich in nutrients even though
they often contain high levels of plant toxins and antinutri-
tive factors. The chemical composition of browse differs
from that of grasses. Grasses are rich in a relatively unlig-
nifi ed cell wall (NDF = 50-70%) that is readily available
for cellulolytic fermentation in the rumen, whereas browse
materials have a relatively lower cell wall (NDF = 30-
50%) that is highly lignifi ed but is rich in readily fermented
cell contents. Browse materials also contain secondary
plant metabolites (SPM) that are absent in most grasses.
These biologically active compounds help protect plants
from herbivore and insect damage. Some SPMs of interest
