Volume 22 • Issue 01 • 2018
in the water holding capacity. Soil aggregate
is mainly the result of a carbon-rich substance
called Glomalin, which is produced by the
mycorrhizal fungi. These have a close symbiotic
relationship with plant roots. Capillary water in
porous soils is available for uptake by the grass
plant. In compacted soils, the Ethylene-Oxygen
Cycle cannot take place and hence nutrient
availability for plant root uptake becomes
limited – leading to a lower grass yield per Ha.
The healthy rumen
The capacity of the rumen of a normal adult
beef cow is about 150 liters, containing 107
– 1012 bacteria and about 105 protozoa and
many species of fungi per one milliliter of
rumen fluid. These microorganisms thrive in an
anaerobic environment. The rumen is a large
fermentation vessel in which about 600 liters
of gas (mainly methane and carbon dioxide)
is produced daily by the 3 to 6 kg bacteria
it contains. Apart from approximate water
intake of 50-80 liters per day, 100-190 liters of
bicarbonate- and phosphorous containing saliva
contributes to the fluid influx in the rumen. This
is important to buffer the volatile fatty acids
produced from bacterial fermentation.
Rumen bacteria can be classified
according to the type of carbohydrates
they ferment:
• Fiber or structural carbohydrate (FC or SC)
fermenters: They ferment cellulose and
hemicellulose and grow slowly. They use
ammonia as their primary nitrogen (N) source
and utilize 0,15g carbohydrate per gram of
bacteria per hour. The N may be from natural
degradable protein or from non-protein
nitrogen (NPN) sources like urea.
• Non-fiber carbohydrate (NFC) fermenters:
They ferment starch, pectin and sugars
and grow at a faster rate. They use amino
acids (from natural protein feed sources)
and ammonia as their primary N source
and utilize 0,05g carbohydrate per gram of
bacteria per hour.
The microbial population in the rumen
could also be classified according to
the site in the rumen where they occur
predominantly:
1. Bacteria attached to fibre particles: They
have a relatively slow growth rate as well
as a low maintenance requirement. They
are responsible for the breakdown of plant
cell walls. They remain in the rumen for
a relatively long period. The more these
bacteria “colonize” fibre particles, the faster
degradation is – leading to a faster rumen
passage rate and ultimately a higher dry
matter intake (DMI). Their main end-product
is acetic acid, the precursor of milk fat which
makes up for the bulkiness of milk and which
serves as the main energy source for the
suckling calf during its first 2-3 months of life.
2. Bacteria in the rumen fluid: They live off
soluble substrate (starches, sugars (neutral
detergent solubles, NDS) and rumen
degradable protein). They are mainly
amylolytic bacteria. They grow relatively fast
and have a high maintenance requirement.
Their retention time in the rumen is short
because they leave the rumen in the fluid
phase.
3. Protozoa in the rumen fluid: They live off
the rumen bacteria, particularly those (the
starch and sugar fermenters) in the fluid
part. The large protozoa are the first to
disappear during insufficient roughage intake
when rumen pH falls below 5,8 - 6,0. They
release ‘plant root-available’ nitrogen and
phosphorous.
4. A small group of bacteria adhering to the
papillae of the rumen wall: These are in
particular responsible for the hydrolysis of
dietary and salivary urea to ammonia. They
play an indirect role in fibre digestion by
making ammonia available to cellulolytic
bacteria.
Rumen pH
pH is the scale by which we measure the degree
of acidity of alkalinity of a fluid or substance. A
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