C. Martin et al., Influence of sampling site on concentrations and carbohydrate-degrading enzyme activities of protozoa and bacteria in the rumen, J ANIM SCI, 77(4), 1999, pp. 979-987
Four ruminally cannulated cows were used to assess the distribution of the
concentrations and carbohydrate-degrading enzyme activities of the liquid-a
ssociated protozoa (LAP) and solid-associated bacteria (SAB) in the rumen.
The cows were fed diets (7 kg of DM/d) of 100% hay (Diet F) or 60% barley p
lus 40% hay (Diet C) in a 2 x 2 crossover experimental design. Samples of r
uminal digesta were collected successively from the dorsal (DS), ventral (V
S), and anterior (AS) sacs Ih before and 3 h after the morning feeding on t
wo sampling days with a 2-d interval. Irrespective of diet and sampling tim
e, the greatest proportion of entodiniomorphs, representing the main popula
tion of protozoa, was found in the DS (40% mean; P < .05). Low pH values ob
served in the DS (P < .05) indicated higher fermentative activity in this s
ite than in the other parts of the rumen. Protozoa may contribute more than
previously thought to the high digestive potential present at the top of t
he rumen that has classically been attributed to bacteria. The specific act
ivity of plant cell wall polysaccharide-degrading enzymes in the LAP was co
rrespondingly greater (P < .05) for DS than for VS or AS. For the two diets
and sampling times, specific activity of fibrolytic enzymes in the SAB ten
ded to be less in the upper than in the lower parts of the rumen, and less
in the VS than in the AS. This tendency became significant (P < .05) for to
tal fibrolytic enzyme activity. Differences in bacterial colonization of pa
rticles among the three sampling sites may explain such differences in fibr
olytic activity of the SAB. Data suggest a spatio-temporal complementary ac
tion of the bacteria and protozoa in ruminal plant cell wall degradation, a
t least with the barley diet, for which the number of protozoa was highest.