Agriculture Reference
In-Depth Information
especially if goats are grazing sown pasture. When supple-
ments are offered to animals in the fi eld, true supplementa-
tion (i.e., the supplement is offered and there is no reduction
in forage intake) is actually a rare event. The most common
outcome is for the consumption of the supplement to result
in a reduction of the forage intake. The extent of the reduc-
tion, per kg supplement fed, is referred to as the “substitu-
tion rate.” If supplementary feeding is managed properly,
substitution rate will usually be
has not previously experienced, a useful management tool
is to include within the herd a few “experienced” (usually
older) animals that have had some experience of the sup-
plement. This has been shown to increase the supplement
intake of the inexperienced animals.
In low-cost, more extensive production systems, often
characterized by a generally lower-quality forage base, it
may be appropriate to supplement animals using feed
blocks, constituted to provide nutrients in poor supply in
the diet (for example, minerals, rumen-degradable N). In
general, the evidence that the provision of feed blocks
results in an increase in forage intake by goats is inconclu-
sive. However, where the forage contains plant species
with condensed tannins, feed blocks may be a cost-
effective way of supplementing with PEG, to overcome
the negative effects of condensed tannins and to increase
intake.
1 so that total intake will
in fact be increased, as intended. Moreover, since the
quality of the supplement (for example, digestibility) is
often better than the average of the forage on offer, the
digestible DM intake may be increased by an even greater
proportion.
A range of factors infl uences the degree of substitution
between supplement and forage. Generally speaking, sub-
stitution will be higher under the following circumstances:
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1. Substitution rate increases when more forage is avail-
able or when forage is of higher quality, or if higher
quality supplements are fed, because of associative
effects between the digestion of supplement and the
digestion of the fi ber of the forage.
2. It is usually greater (though not always) if more supple-
ment is fed or if the supplement is fed infrequently.
3. For a given quantity and quality of forage on offer, the
degree of substitution can be altered by the animals'
physiological state. For a given forage base and supple-
ment, animals with a higher nutrient demand (such as
lactation) will usually exhibit a lower substitution rate.
Drought Feeding of Goats
Drought feeding differs from other forms of supplemen-
tary feeding in that the emphasis is on survival of the herd
and not on high levels of animal production. This alters
what can and ought to be done. For a detailed and very
practical treatment of the issues involved in drought
feeding of the goat herd, the reader is referred to McGregor
(2005). In drought feeding, the issues of prior experience
of the feed, or of a training or introductory period for feeds
such as whole grain, are equally relevant. Substitution may
be less of an issue, because by defi nition, drought will
involve a shortage of forage. However, for exactly the
same reason, animals in drought will often be hungry, so
careful management of feeding is very important to avoid
the dominance effects described above. If the drought feed
is offered as a feed trail, it may be necessary to offer a
space of somewhat more than 0.5 m/animal.
Drought conditions may also imply hot conditions, and
under these circumstances, dominant goats will not only
fi ght for space at the feed trough, but also for access to
water and shade (McGregor, 2005). They may even
exclude submissive animals from these areas. This means
that the location of drought feeding areas and the fre-
quency of feeding must be very carefully considered in
relation to the location and nature of shade areas and
watering points.
Under fi eld conditions, supplements may be offered by
trailing them along the ground in a thin stream. This can
ensure that all animals, including the so-called “shy
feeders,” will get a share, but there is also an interaction
with feeding frequency. If supplements are trailed out
infrequently, then dominant animals can overeat on the day
of feeding, with resultant digestive disturbances if, for
example, whole grain is being fed. If supplements are fed
in troughs, then the above comments about allowing suf-
fi cient trough space apply equally in the fi eld, if not more
so. For example, allowing too much trough space can also
result in aggressive behavior by dominant goats, by allow-
ing them the space to claim and defend a “territory”
(Solaiman, 2006 ).
The economics of supplementary feeding are much
more favorable if animals take only a short period to begin
eating the supplement. As discussed above, this is in part
a function of their previous experience. Goats will more
readily eat a supplement if they have experienced it before,
even pre-weaning. For supplementary feeds that the herd
SUMMARY
The capacity of the goat to select and consume substantial
quantities of browse places it in a unique position, com-
pared with other domesticated ruminants, to contribute to
