cent - 70 per cent), indicating that cows responded well
to the synchronisation protocol, and inseminations were
conducted at a suitable time.
For sexed semen, however, much greater herd to herd
variation in conception rates was noted (range 32 per cent
to 67 per cent). In 8 of the 24 herds, conception rates with
sexed semen were equal to conventional semen (60 per
cent for both). On the other hand, 6 herds had excellent
performance with conventional semen (66 per cent),
but poor performance with sexed semen (42 per cent).
The cows in these 6 herds responded appropriately to
synchronisation and were highly fertile when inseminated
with conventional semen, so the question is `why did sexed
semen not work in these 6 herds'?
A problem with the sexed semen product as the primary
cause can be ruled out, as the remaining 18 herds, on
average, had good conception rates with sexed semen
(54 per cent), indicating that the sexed semen was also
fertile. While the viability of sexed semen sperm is not in
durability of the selected male sperm as they have come
through a fairly rigorous, if not quite `brutal' segregation
process. In other words, they may not have the energy
to `hang around' while waiting to impregnate an egg.
Timing of insemination therefore, is critical to achieving
comparable conception rates to conventional semen.
Hence the research and e ort being put into securing
more information on optimum insemination timings for
sexed semen. If the 6 herds with the poorest conception
rates with sexed semen are excluded, the conception
rates were 59.9 per cent, 52.6 per cent and 54.7 per cent
for CONTROL, SEXED-16 and SEXED-22, respectively.
Hence, in these 18 herds, SEXED-16 and SEXED-22 were
88 per cent and 91 per cent as good as CONTROL-16,
respectively. Conducting inseminations with sexed semen
at 16 and 22 hours after the final GnRH injection resulted
in similar conception rates and supports the concept of
delaying the timing of AI to at least 16 hours after heat
onset. Inseminating cows too early after heat onset is
a likely cause of poor results when using sexed semen.
Farmers need to be aware that sexed semen is a fragile
product, and that it's use needs to be carefully managed.
Dr Butler concluded that the levels of fertility
performance obtained in this study, makes sexed
semen a viable strategy for generating replacement
heifers on commercial farms, but more work is
needed to identify the reasons for poor performance
with sexed semen in a subset of herds that can achieve
excellent performance with conventional semen.
With the value of dairy bull calves very low, the need for
a reliable sexed semen product has never been greater.
Ultimately, the hope must be that sexed semen will deliver
comparable fertility results to conventional semen with
minimal chemical intervention or none. That will be the
ultimate test of the technology.
It is understandable that the Teagasc research used fixed
time AI protocols delivered by synchronisation in order to
achieve exact and comparable ovulation and insemination
timings in the trial herds.
While the benefits of synchronisation are obvious,
these interventions may or may not be accepted herd
management practice in the future.