Agriculture Reference
In-Depth Information
INTRODUCTION
Goats have the ability to use browse as well as the herba-
ceous components of the forage resource, and can provide
animal products from rangeland or semiarid environments
that would not suit sheep and cattle. Goats thus assume
major economic importance in less-favored environments,
often in the world's less developed economies.
The interaction of foraging goats with the plant biomass
involves components relating to the animals themselves,
the plant resource available to them, and the extent to
which the system of livestock management permits the
processes of diet selection and intake to proceed. Ingestive
(eating) behavior, diet selection, forage intake, and animal
production are components of a continuum of mechanisms
linking plant resource and animal product.
Table 9.1
Indicative summary of some of the
factors shown to infl uence ingestive behavior
and diet selection in goats.
Factor
1. Species composition of the biomass/ season of year
2. Clover content of and clover position in the “ sward ”
3. “ Presentation ” of the biomass — zero grazing versus
grazing; species in rows cf. mixed sward; species
offered separately or together
4. Sward height, biomass; stocking rate
5. Condensed tannin content of species on offer
6. Dry matter content of the forage
7. Odor/fl avor of the forage
8. Previous experience and adaptation of grazing
animals; species of animal that grazed biomass
previously
9. Differences in possible instantaneous intake rate
between biomass components
10. Breed, gender, age, and physiological state of goats
11. Buccal architecture and integrity of teeth
12. Goats grazing separately or co - grazing with other
species
13. Grazing height, bipedal versus quadripedal foraging
EATING BEHAVIOR AND DIET SELECTION
Free-ranging livestock, including the goat, usually select a
diet that differs in botanical composition and in quality
from the average of the available feed. However, the dem-
onstration that the diet composition differs from the plant
biomass does nothing to elucidate why this is so or why
certain plants were selected or rejected. The fact that goats
often select a diet higher in browse species than would be
selected by sheep or especially cattle tells us little about
why more herbaceous components of the plant biomass
were not selected. Therefore, caution is required in inter-
preting diet selection data.
Some of the factors infl uencing feeding behavior and
diet selection in grazing ruminants are listed in Table 9.1,
and in part have also been discussed elsewhere (AFRC,
1998 ; NRC, 2007 ; Animut and Goetsch, 2008 ). Examination
of the information in Table 9.1 leads to two closely related
conclusions. First, the process of diet selection is exceed-
ingly “multifactorial.” Second, a number of the listed
factors are closely related (for example, season and the
species composition of the plant biomass, or age of goat
and the state of their dentition). A degree of confounding
between the factors is thus not only possible but highly
likely. Unfortunately, studies of diet selection in goats
have not always paid suffi cient attention to this.
should allow selective browsing, and are regarded as
“ intermediate feeders ” (see NRC, 2007 ; Animut and
Goetsch, 2008). The evidence from many published studies
indicates conclusively that when faced with a mixture of
browse, forbs, and grasses, goats will select a diet contain-
ing much more browse than would be selected by sheep
or especially cattle. In a Mediterranean shrubland,
Papachristou (1994) reported that goats took 40-60% of
their bites from browse species. However, when the avail-
ability of the herbaceous component was high, it could
make up >50% of the diet (Papachristou, 1994). By con-
trast, in an oak forest environment, cattle co-grazing with
goats took more than 97% of their bites from the herba-
ceous component of the biomass. In a more recent com-
parison in the Sahelian region of Africa, Sanon et al.
(2007) reported that cattle spent 4.5-6.6% of their time
browsing, depending on season. By contrast, goats browsed
for 43-52% of their time; sheep were intermediate at 4.8-
28% of their time. A feature of many published studies is
that diet selection is measured indirectly in terms of inges-
tive behaviors or features of the plant biomass. It can be
diffi cult to convert plant biomass data, or data about per-
centages of times spent grazing different plant compo-
nents, to actual intakes of those components (Dove and
General Observations on Diet Selection by Goats
Frequently, ruminant livestock have been classifi ed as
being grazers (grass/forb consumers), as concentrate selec-
tors/browsers, or as intermediate or mixed feeders. Sheep
and especially cattle are regarded as grazers, with rela-
tively broad muzzles and a cornifi ed tongue tip designed
for grass consumption at low biomass. Goats, on the other
hand, have a narrow mouth and mobile lips and tongue that
