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Beef Cattle Semen Fertility
Artificial Insemination Sires Differ in Semen
Fertility
Is there variation in fertility of semen from artificial insemination (AI)
sires?
Have you ever suspected that semen from some bulls gets cows pregnant more often
than semen from some other bulls?
Do conception rates for a specific AI sire tend to be similar over time?
Sometimes an AI bull gets a reputation as having poor semen fertility. Have you
ever considered if this reputation is deserved? ~
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Why is semen fertility important? Semen fertility is important because
poor fertility semen requires more services to get a cow pregnant and this
results in increased days open and subsequent calving intervals. In addition,
semen with poor fertility requires more units of semen to result in a pregnancy
and a subsequent calf. Both of these impacts are economically important to
producers and, as a consequence, semen from sires with poor fertility is not
nearly as good of an investment as semen from high fertility sires (assuming
other genetic evaluations are similar).
In some countries information on semen fertility is available on most AI sires
that have been used heavily as service sires. In the US, the widely accepted
measure of AI semen fertility is called Expected Relative Conception Rate or
ERCR. Each individual bull has an ERCR and this ERCR is calculated much like we
calculate genetic evaluations for production traits or other traits. These ERCRs
are made available on bulls once they have been used for a significant number of
recorded services and we have information on the outcome of these services.
However, these ERCRs have a slightly different interpretation and use compared
to other routine genetic evaluations.
Breeding companies work diligently to ensure that AI semen is of the highest
quality possible.
Breeding companies continually monitor semen quality from each sire and work to
optimize semen processing for specific sires. In some situations, breeding
companies include higher sperm numbers per straw for some bulls in an attempt to
increase the conception rate to a reasonable level. One of the most important
things that breeding companies do to ensure the best semen quality is to
eliminate bulls from their programs that are not good semen producers or who
produce very poor quality semen. You can be assured that semen from the major
breeding companies around the world is as good as possible given current
technologies. However, breeding companies do not currently have the technology
to make the fertility of semen from all AI bulls equal. As a consequence, it is
true that semen from some AI sires is more fertile than semen from other AI
sires.
Large differences in fertility among AI sires are rare because of the efforts of
the breeding companies, but AI sires can differ by several percent in conception
rate. Some of the poorest bulls for conception may produce semen that has a
conception rate of 5% to 10% lower than some of the best bulls for conception.
For example, you might expect a first service conception rate for an outstanding
bull to be 40% in a specific herd and a first service conception rate of 30% for
very poor bull when used in the same herd. In this example herd, most bulls
would be expected to have conception rates close to 35% but there would be
variability among the other bulls as well.
Research data from several studies in several countries indicates that AI sire
fertility tends to be similar for specific bulls across time. Bulls that have
had poor fertility in the past will very likely have poor fertility in the
future. This means that semen fertility is very repeatable over time and this
allows geneticists to use past data to predict future semen fertility. As a
result, we can have confidence in the measures of semen fertility over time.
What else might these semen fertility measures on AI sires tell us? Does semen
fertility for a sire tell us much about what to expect for fertility of semen
from his sons? Perhaps more important, does semen fertility tell us anything
about the expected fertility of a sire's daughters?
The answer to both questions, unfortunately, is that the semen fertility from an
AI sire is not a very good predictor of his sons' fertility or his daughters'
fertility. There are no studies in dairy cattle that have indicated a close
association between semen fertility for a sire and the fertility of his
daughters. Somewhat contrary to these results in dairy cattle, research results
in beef cattle and swine do indicate that male scrotal measurements are useful
for predicting female offspring reproductive performance.
It is clear that, despite the best efforts of breeding companies, semen from AI
sires do vary somewhat in fertility. This variability is predictable over time
and poor fertility AI sires identified from past data will more likely have poor
fertility in the future.
Fortunately this variability in semen fertility is moderated by the work of the
breeding companies so producers can expect reasonable conception rates from AI
bulls marketed by reputable breeding companies.
However, fertility of semen from AI bulls should be considered when making semen
investment decisions.
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