Farm Animal Metabolism and Nutrition

after fermentation in the ventral sac. This
vertical stratification continues through-
out the nycthemeral period, reaching a
maximum after the meal. Moreover, it has
been shown that particle microbial
colonization increased when particle size
decreased (Gerson et al., 1988). Therefore,
the higher bacterial colonization of the
small particles in the lower parts of the
rumen involves higher microbial enzyme
activity in this part of the rumen (Martin et
al., 1999 ; Fig. 11.1A).
The digestive ruminal capacity shows
spatial variations within the rumen. The
relative locations of nylon bags suspended
within the rumen can also affect digestion
rates. Several methods of suspending the
bags in the rumen are used; currently, the

bags are fastened along a string weighted

with a sinker to ensure that they do not

float on top of the rumen contents. The

anchor weight, from 0.5 to 2 kg for cows

and 75 to 300 g for sheep, does not affect

DM degradability of feeds (Huntington and

Givens, 1997). Some researchers use a

template to allow maximal exchanges

between the feed sample and the incuba-

tion environment, but the results obtained

with this apparatus have not been com-

pared with those obtained by a more

classical process. The length of the string

along which bags are fastened is also an

important factor because it determines the

location of the bags in the rumen. A 25 cm

string would be a sufficient length to allow

free movement of bags in the rumen of

In Sacco Methods 237

Fig. 11.1.Variations of enzyme activities in solid-associated bacteria. (A) Effect of rumen sampling site
(Martin et al., 1999) (μmol reducing sugars g
^1 DM h
^1 ). (B) Effect of sampling time (Martin et al., 1993)
(nmol reducing sugars mg
^1 protein h
^1 ).