Volume 22 • Issue 01 • 2018
more alkalotic (higher pH) rumen environment
negatively affects NDF degradation, DMI from
pasture and the absorption of essential nutrients
like magnesium, which is necessary for energy
and calcium metabolism.
Excess NFC leads to a fall in rumen pH, which
is a less favorable environment for cellulolytic
bacteria to function in. This may happen
when cattle consume abundant amounts of
carbohydrate-rich supplements or, for example,
soon after being turned out onto maize stover
lands where they pick up many cobs. This will
lower NDF degradation, passage rate and DMI.
If less DM is consumed per day, less beef will be
grown – leading to a lower income.
Rumen bacteria need soluble and degradable
protein to meet their N requirements. The
degradable protein requirement is for
supporting optimal utilization of NFC and FC to
meet respective microbial growth requirements.
The rate of microbial growth of each category is
directly proportional to the rate of carbohydrate
digestion, so long as a suitable nitrogen source
is available. The extent of digestion in the
rumen depends on digestion of FC and NFC feed
fractions and how rapidly the feed passes out
of the rumen. In the early grass growth season
it may be faster than during the late winter – as
is evident from faecal consistency being loose
or firmer, respectively. The extent of digestion
thus depends on factors such as level of intake,
particle size, rate of hydration, lignification, and
characteristics of each carbohydrate and protein
fraction.
Veld and supplement management
during the dormant season (autumn,
winter) and their effect on rumen health
Estimation of the available pasture DM left in
the “pantry” at the end of the grass growing
season (onset of the dormant season) gives an
indication of DM available during the dormant
season – until new grass yield becomes available
in the next growing season. This must be
matched with the number of animal units (1 AU
= 450kg) to be “over-wintered” – each requiring
about 10kg DM daily. Timely destocking at the
start of the dormant season is a critical action to
prevent running out of pasture DM – which will
lead to a loss in condition during late gestation.
This results in an increased ketone body
concentration in serum which is mirrored in the
follicular fluid and will affect oocyte quality.
Nitrogen, more specifically RDP, is the most
limiting nutrient to the rumen microbes in
winter – especially on sourveld. Apart from
RDP, rumen bacteria need an adequate source
of fermentable carbohydrate to incorporate
NPN into microbial protein. Microbial protein
is essential for the dry, mid-pregnant cow to
efficiently regain body fat reserves that were
lost during the previous lactation. This gain
in body fat reserves should take place well in
advance of the last 2 months before calving.
The biological value (BV; amino acid balance for
gain of body fat reserves) of microbial protein
is almost ideal for the pregnant cow, which at
this stage of her production cycle (4-7months
pregnant) has a relatively low nutrient
requirement.
Winter supplement intake must always be
closely monitored. Knowing the average N
concentration of winter pasture and the DMI
thereof, one can calculate the percentage total
crude protein (TCP) as well as RDP intake
from the total diet DM. Rumen bacteria will be
compromised in their function should the TCP
of the final diet DM be below 70g/ kg (7%). If
winter supplement intake is excessive, it may be
as a result of i nsufficient pasture DM availability
– i.e. the cattle are hungry. This may lead to
rumen alkalosis should RDP intake be too
high. Fecal consistency is a handy indicator of
rumen function and fiber degradation with dry,
hard feces being an indicator of poor microbial
degradation of fiber – leading to a slow passage
rate of ingesta.
Veld and supplement management
during the growth season and its effect
on rumen health
The primary objective is to supply Phosphorous
(P) for both rumen microbes AND the lactating
cow – which must re-conceive in this period.
P is required for efficient energy metabolism
– which is essential to prevent an excessive
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