Milk income is reduced
by poor reproduction
Dr Carel Muller, Research Associate,
Faculty of Animal Sciences, University of Stellenbosch
M
ilk production systems in the
Western Cape Province vary from
fully or partially pasture-based to
zero-grazing total mixed ration
(TMR) systems. The rainfall in many parts of
the province is low and erratic. This results
in cultivated pastures having to be irrigated,
especially during summer. Dairy farms with
limited access to water sources for irrigation
use a zero-grazing system based on forage
crops like oats, wheat or barley produced
during winter. The feed cost of dairy cows in
zero-grazing system is generally higher than in
pasture-based systems. The reason for this is
the cost and feeding value of roughages used
in the two systems. The cost of oat hay could
be R2.40 per kg DM while cultivated pasture
could be R1.80 per kg DM. The energy and
protein levels of oat hay are also lower than
that of cultivated pastures. Therefore, the
composition and cost of diets providing similar
protein and energy levels while containing oat
hay or cultivated pastures as roughage sources
would differ considerably. The concentrate
component of a total diet containing oat hay
is 63% in comparison to 27% for the pasture-
based diet. The concentrate portion is also more
expensive, i.e. being 74% vs. 44%, respectively,
of the total diet cost. The higher feed cost
increases the break-even milk yield levels for
TMR-based diets in comparison to pasture-
based diets. This explains the push for high
milk yield levels in TMR-based dairying systems.
However, feeding high levels of concentrates
increases milk yield although at a diminishing
rate per kg of concentrates fed. This could
affect profit margins negatively. Milk prices
AgriKultuur |AgriCulture
and concentrate costs affect the optimum
concentrate feeding levels in optimizing income
over concentrate cost. In South Africa limited
studies have been conducted to determine the
effect of increasing concentrate feeding levels
on the milk yield and profit margins of dairy
cows.
Milk yield vs. fertility
The fertility of dairy cows has decreased in recent
years. Research has shown that while the milk
yield of Holstein cows has increased from 4750
in 1951 to 9000 kg in 1996, the conception rate
of cows decreased from 68% to 40%. In South
Africa the calving interval of Holstein cows also
increased from 386 days in 1986 to 412 days in
2004. This has been associated with the increase
in milk yield although other factors could also
have contributed to this as dairy herds have
become larger with less attention to individual
cows. It is not clear whether the fertility of dairy
cows has deteriorated genetically over time or
whether a ceiling in the management capacity
of people has been reached especially for high
producing dairy cows in large herds in intensive
housing conditions.
Cows at high milk yield levels respond
differently when on heat, i.e. showing fewer
and less intensive heat signs while the period
of standing heat is often shorter. However,
although the general perception is that a high
milk yield affects fertility negatively, this is not
always demonstrated at the herd level. In well-
managed herd fertility can be high even at high
milk yield levels.
The fertility of dairy cows is generally
regarded as complex trait which is affected
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