Agriculture Reference
In-Depth Information
70
60
50
Figure 9.4
Comparison of the
proportion of their foraging
time spent by goats and sheep
in four defi ned strata, during
three seasons of the year (mid-
dry season, late-dry season,
wet season) in the Brazilian
caatinga (recalculated from the
data of Pfi ster et al., 1988).
Mid-dry, Goats
Mid-dry, Sheep
Late dry, Goats
Late dry, Sheep
Wet, Goats
Wet, Sheep
40
30
20
10
0
Ground level
(0-5 cm)
Animal height
(6-75 cm)
Quadripedal browsing
(76-115 cm)
Bipedal browsing
(116-160 cm)
about 8% of foraging time in the wet season. In the other
two seasons, it accounted for much less.
In the data reported to date, goats have spent 10% or
less of their foraging time in bipedal mode. Depending on
the relative availabilities of forage in the different strata,
goats may on occasions be forced to spend more of their
foraging time in the bipedal stance. They are also known
to climb into trees to obtain forage. To confi rm the quan-
titative importance of these behaviors, we need more mea-
surements of ingestive behavior under fi eld conditions.
grasses tend to make up a larger proportion of the diet of
pregnant or lactating goats, compared with nonpregnant,
nonlactating goats, which consumed more browse in their
diet. Hence, there are effects of breed, gender, age, and
physiological state on ingestive behavior and diet compo-
sition. Given the magnitude of the effects, future studies
need to pay much more attention to controlling or at least
reporting these factors.
B
UCCAL
A
RCHITECTURE
, D
ENTITION
The oral and dental features of goats are often mentioned
when discussing their ingestive behavior, but the actual
quantitative contribution of these mouth features has not
been well defi ned. Mellado et al. (2007) recently used
multivariate statistical procedures to relate diet choice by
crossbred goats in Mexico to a range of oral measure-
ments. Overall, there was a good relationship between the
measured oral characteristics and the main plant species
ingested (canonical correlation = 0.81). Muzzle width,
incisor breadth, and jaw length were the main oral mea-
surements associated with the extent of ingestion of spiny
shrubs. Incisor length and the distance between the fi rst
molars had the dominant effect on the ingestion of grasses
and coarse shrubs. The importance of incisor length is
consistent with the known importance of incisors in the
prehension and ingestion of grass.
A related effect is the state of the incisor teeth them-
selves (for example, missing, loose, or broken incisors),
as infl uenced by such things as age. In ewe/lamb systems,
it has been amply demonstrated that, independently of
the effect of age, bad incisor dentition can reduce feed
intake and animal performance. This is especially impor-
tant in lactating ewes. In goats, Mellado et al. (2005)
B
REED
, G
ENDER
, A
GE
,
AND
P
HYSIOLOGICAL
S
TAT E
OF
G
OATS
All of these factors can infl uence ingestive behavior and
diet selection. There is evidence that Saanen goats browse
for more of their total foraging time than Angoras, which
graze for a much greater proportion of their foraging time.
A practical consequence of this difference in feeding
behavior is that helminth burdens may be more of a
problem in Angoras, presumably because they forage in
the layer occupied by nematode larvae. The interaction
between feeding behavior, nutritional status, and helminth
infestation is an area that would be worthy of detailed
study in goats.
In general, juvenile goats spend 20-90% more of their
day foraging than do adult goats. Differences in diet com-
position have also been reported for bucks versus nonpreg-
nant, nonlactating does. Bucks consume a higher proportion
of browse and tend to avoid grasses more than does. It has
been suggested that sex dimorphism in buccal architecture
may have contributed to differences in diet composition.
Superimposed on the above effects can be an effect of
physiological state. Depending on availability, forbs and
