Dr Carel Muller, Research Associate,
Faculty of Animal Sciences, University of Stellenbosch
W
hen starting a new dairy farm,
some management actions must
be undertaken correctly from
the start. Although cows are fed
and milked (which is harvesting of milk) daily,
some management decisions could affect the
production performance of cows positively
or negatively for a long time afterwards.
Reducing the amount of concentrates or
feeding poor quality roughage would affect
the milk yield of cows within a few days,
actions such which as sires are selected,
the way heifers are reared and when cows
become pregnant, has a long term effect on
the milk yield of cows. It is therefore important
that the correct decisions are taken from
day one. For example: the daughters of sires
selected today only come into milk three
years later, while, only after another year,
is it possible to determine the production
potential of these daughters. To see the
lifetime performance of the daughters of
sires another 3-4 years are required. In many
dairy herds the culling rate among cows is
high, i.e. only about 10% of first lactation cows
eventually cows reach a 5 th or 6 th lactation. The
way heifers are reared, affects their age at first
calving and milk yield potential. Heifers being
reared poorly often calve down late (after 24
months of age). Poor heifer survival will also
have a negative effect on replacement rate
and herd growth. Some of these aspects are
discussed in this paper.
Get cows pregnant
Dairy farming is a continuous process of cows
calving down and getting them pregnant again
while being in milk. The next calving down
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date should be less than 13 months from the
present calving date. Extending the calving
interval, i.e. the number of days between
subsequent calving down dates, reduces the
milk yield of the herd while also slowing down
the herd’s genetic progress.
Natural service (using a bull) or artificial
insemination (AI) can be used to get cows
pregnant. For small herds it is costly to keep a
bull while management problems may occur.
Using a bull of poor genetic merit limits the
herd’s genetic progress. Inseminating cows is
a relatively simple technique although proper
training is required beforehand. In commercial
dairy herds AI is a standard practice. When
doing AI genetic progress can be quicker
because a world-wide range of bulls are
available. The cost of buying semen is often
less than keeping a bull.
However, in AI, the fertility of dairy cows
depends on the ability of people to detect
cows in heat and to deposit semen at the right
time and place for conception to take place.
After calving, the cow’s uterus recovers and
shrinks back to its normal size. The time of
recovery can range from 25-50 days. Calving
difficulties may cause uterine infections
extending the recovery period of the uterus.
Normal heat cycling returns after the recovery
of the uterus. Thereafter cows come on
heat every 19-21 days. Heat cycling involves
the development of a follicle in the ovaries
towards discharging an ovum for fertilization.
When no fertilization occurs, the process
repeats itself.
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