Establish norms & standards
for reproduction management
Dr. Carel Muller
Research Associate, Faculty of Animal Sciences, University of Stellenbosch
A
new milk production period starts at
calving. The next reproduction phase
also begins following the voluntary
waiting period of about 40 days.
Poor fertility in dairy cows, either through
management or genetic merit, result in cows
conceiving late or not at all. This may result
in cows being culled reducing the income
of a dairy herd. Culling cows is a direct loss
because the value of cows is their future milk
yield and not their current salvage value. An
indirect cost of poor fertility is extending the
lactation period when the daily milk yield
of cows is lower than earlier in the lactation
period. Although the milk yield per lactation
increases, the average daily milk yield (and
milk income) is reduced. Modeling has shown
that extending the calving interval (CI) from 12
to 14 months results in a decrease in average
daily milk yield of about 2 ℓ/day, reducing
annual milk income by more than R3300 per
cow.
Overall, over the last 30 years, the fertility of
dairy cows has decreased, i.e. extending CIs
from 386 days in 1986 to 412 days in 2004.
Poor fertility is attributed to a number of
factors, i.e. increased milk yield per lactation,
larger dairy herds, poor reproduction and
housing management and possible changes
in genetic merit. Breeding and selection
programmes in dairy herds generally put little
emphasis towards improving the genetic merit
for fertility in dairy cows. Fertility is a complex
trait affected by a number of factors, resulting
in a low heritability. Therefore, to improve
fertility genetically, change would be slow.
At farm level, cows not becoming pregnant,
are culled because of infertility. However,
very few cows are inherently infertile. Poor
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management result in cows not becoming
pregnant, i.e. cows may come on heat but
because of poor heat detection, some cows
are not inseminated. Poor insemination
techniques also result in fewer conceptions.
Overall, this results in management induced
infertility.
To improve fertility in a dairy herd, the level
of reproduction management should be
established to avoid culling cows incorrectly.
The aim of this article is to provide ways
indicating the level of reproduction
management for a dairy herd.
Norms and standard for reproduction
management
In South Africa norms and standards for
reproduction management of dairy cows have
not been established. This is because of a lack
of a national database of service dates and
derived fertility traits. Traditionally, calving
interval (CI) and services per conception (SPC)
are used as indicators of dairy cow fertility.
Although important, both traits are not useful
indicators of the standard of reproduction
management. Cows not calving down again
are not included in the estimation of herd CI.
Inseminator skill affect mean SPC and is not
an indication of dairy cow fertility. Fertility
is defined as follows: the ability of cows to
come on heat soon after calving, conceive
from a minimum number of services while
maintaining pregnancy to the next calving.
An Australian survey suggested norms and
standards using top performing and problem
herds having to seek advice. This system
uses four traits, i.e. 100-day-in-calf rate (the
percentage of cows becoming pregnant within
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