Resumen:
Besides the liver, rumen is one of the most important components of
metabolism in ruminants. However, the microbes residing in the rumen are
influenced by several complex factors such as diet, which result in fluctuations
in the rumen pH. Rumen pH affects feed intake and feed digestibility,
subsequently causing microbial shift in the individual members of microbial
community residing in the foregut and hindgut. This in turn causes an
increase in lipopolysaccharide concentration, among other factors, in the gut
fluid and animal blood. Irrespective of diet fed to animals, Firmicutes would
probably be the most dominant in high grain diet while Bacteroidetes are
dominant in hay diet, and both have a relative abundance of about 80% or
more at times. The shift in microbial population is not limited to adult
ruminants alone but also occur in calves. Firmicutes, Bacteroidetes,
Actinobacteria, and Proteobacteria were the most abundant in both hay and
concentrate diet of newly weaned calves. Prolonged, depressed pH, causes
subacute ruminal acidosis. This leads to compromise in the integrity of both
foregut and hindgut of ruminants, eventually causing structural changes in the
gut physiology. Furthermore, diet containing C-12:0 and C-14:0, which are
medium-chain fatty acids, were toxic to rumen protozoa. Phytochemical
content in some plant residues when fed to animals also causes shift in
microbial population. Therefore, foregut and hindgut pH stability is important
for ruminant health and for optimal productivity.