novel approaches to expression and detection of oestrus in dairy cows

al., 2006). However, aged sperm have been reported to incur damage to
their DNA if they are in the reproductive tract too long. This is reported to
affect the oocyte’s development after fertilisation which could result in
early pregnancy loss due to impaired embryo development (Ahmadi and
Ng, 1999). AI after ovulation can also compromise fertility rates because
the oocyte becomes aged, impacting upon fertility and development
(Roelofs et al., 2006). Instability in the nuclear and cytoplasmic organelles,
disruption of cortical granules and the zona block can increase the chances
of polyspermy in an aged oocyte, increased further by late insemination as
there are a larger number of active sperm (Hunter and Greve, 1997). A
further problem of late insemination is that the reproductive tract
conditions alter post ovulation, therefore the environment becomes hostile
to sperm compromising the chance of conception (Hunter and Greve,
1997).
There are conflicts in reports concerning the optimal time to inseminate
post-standing to be mounted (see Figure 1.2). Early studies established the
a.m.-p.m. guideline; cows in oestrus during the a.m. should be submitted
for AI during the next p.m., and cows in oestrus during the p.m. should be
submitted for AI during the next a.m. (Pursley et al., 1998). It has been
reported that the pregnancy rates of cows inseminated at the earliest; 0
hours and latest times; 32 hours, post-standing oestrus had significantly
lower pregnancy rates per AI. Considerably higher pregnancy rates were
achieved in cows bred at 16 hours (middle time period) after the onset of
standing oestrus (Pursley et al., 1998). Dransfield et al., 1998, reported
similarly, that conception rates were increased 4-12 hours after the onset
of standing activity. Therefore, oestrous detection is imperative for the
correct timing of AI and getting cows in calf for the efficiency of dairy
production.
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