Ingestive Behavior, Diet Selection, and Feed Intake - Goat Science and Production - page 184

saliva of rodents, marsupials, or hares and rabbits. The
PRP detected in sheep and cattle saliva also had a much
lower affi nity for tannins. These studies thus provide no
evidence of there being functional PRP in the saliva of
sheep and cattle.
More recent studies reviewed by Mueller-Harvey (2006)
and by Shimada (2006) indicate that sheep and goat saliva
contained (unidentifi ed) TBSP with a reasonable affi nity
for condensed tannin. However, these TBSPs do not appear
to be the PRPs usually associated with tannin-binding
ability. Lamy et al. (2008) recently reported a comprehen-
sive electrophoretic comparison and characterization of the
salivary protein profi les of both sheep and goats eating a
low-tannin diet. They also specifi cally tested for the pres-
ence of salivary PRP in both animal species and could not
detect them. They suggested there was a need to repeat
such measurements in animals fed high levels of tannin,
but other evidence indicates that TBSP cannot be induced
in the saliva of ruminant livestock by feeding high-tannin
diets.
In summary, the search for TBSP in the saliva of rumi-
nant livestock in general and goats in particular suggests
that some TBSP may be present in saliva. Equally, it indi-
cates that they are not the PRPs associated with tannin
binding in true browsers. Whether the unidentifi ed TBSP
would be of physiological importance as a defense against
high-tannin diets in goats is not yet established (Shimada,
2006 ).
Goats can nevertheless consume high-tannin diets
without ill effect and because they excrete only a small
proportion of dietary condensed tannin in feces, some
other defense mechanism against condensed tannins must
be operating. Two other possible mechanisms could allow
the goat to tolerate high-tannin diets:

one such compound. It should also follow that provi-
sion of a mixed diet of tannin-containing feeds would
allow a greater total intake than could be achieved by
eating any one feed. There is evidence to support this
suggestion in goats. Rogosic et al. (2006b) found that
feeding a mixture of three tannin-rich shrubs ( Quercus
ilex, Arbutus unedo and Pistacia lentiscus ) to goats
resulted in more than twice the intake achieved when
the shrubs were fed separately.

The quantitative signifi cance of these two mechanisms
and the interactions between them have yet to be deter-
mined. This would be a fruitful area for future research.
Although goats can clearly tolerate high dietary intakes
of condensed tannins, diet selection and intake can none-
theless be altered by supplementing foraging goats with
polyethylene glycol (PEG), a polymer that binds to dietary
condensed tannins. For example, Landau et al. (2002)
supplemented Damascus goats with PEG (MW 4,000) in
a rangeland dominated by lentisk ( Pistacia lentiscus ).
Supplementation had no effect on the time spent foraging
(Table 9.2) and in goats, which were not also offered
alfalfa hay, resulted in a large increase in the proportion
of their foraging time spent eating the tannin-rich lentisk.
The time spent eating dry grasses decreased. When the
goats were also offered alfalfa hay while on the range, the
PEG supplement had no effect on the amount of time spent

Table 9.2 Effect of polyethylene glycol (PEG,
MW 4000) on the feeding behavior of Damascus
goats in a rangeland dominated by tannin-rich
lentisk ( Pistacia lentiscus ).

Behavior Control ( − PEG) +PEG

% of time spent foraging 44 39

1. Quantitative studies of the fate of condensed tannins
during gut transit have shown substantial losses between
intake and feces (e.g., Perez-Maldonado and Norton,
1996), suggesting the possibility of microbial metabo-
lism of tannins in the gut.
2. One might expect that a herbivore's intake of a feed-
stuff containing a secondary compound would be
limited by its ability to detoxify the compound. The
predicted consequence of this is that herbivores would
choose a mixed diet to minimize the effects of the
consumption of any particular secondary compound
(see Foley et al., 1999). According to this hypothesis,
the goat would consume its typically mixed diet not
because of its overall capacity to detoxify secondary
compounds, but in order to avoid a high intake of any

Without hay supplement

% of foraging time eating:

Lentisk 41 73 *

Dry grasses 28 12 *

With hay supplement

% of foraging time eating:

Hay 30 26

Lentisk 46 62 *

Dry grasses 13 10

Source: Adapted from Table 2 of Landau et al., 2002 .
Lentisk condensed tannin content = 22% DM.
*Control and +PEG values differ signifi cantly
( P < 0.05).