novel approaches to expression and detection of oestrus in dairy cows

investigating conception rate based on insemination at the time of low
progesterone concentration report low pregnancy rates (Eddy and Clark,
1987), but online monitoring of progesterone is an effective method for
detecting silent oestrus (Ranasinghe et al., 2010). It can also confirm
errors in detection when combined with other methods which can positively
affect detection rates (Nebel, 1988).
To overcome the need for detection of oestrus the use of oestrous
synchronisation and timed AI are becoming widespread among production
systems which avoids the practical difficulties associated with detection
(Macmillan, 2010;Pursley and Martins, 2012). The original and most basic
programme is the Ovsynch protocol which uses timed injections of GnRH
and PGF 2α to control follicle development, luteolysis and ovulation, and
finally timed AI to eliminate oestrous detection altogether (Thatcher et al.,
1989;Pursley et al., 1995). However, cows detected in oestrus without
hormone treatment are reported to have higher conception rates than
those undergoing synchronisation and timed AI (Stevenson et al.,
1999a;Macmillan, 2010). The calving to conception interval is decreased by
using synchronisation, although the incidence of anoestrus and early
embryonic death is increased (Macmillan, 2010). Progesterone treatments
(PRIDs, CIDRs etc.) are also used for synchronisation, but still require
oestrous detection, yet at a more precise time, and can result in reduced
fertility depending on length and precise timing of treatment (Yavas and
Walton, 2000). Synchronisation can reduce the incidence of problem cows
not showing oestrus such as anoestrus and cystic cows (Lucy et al., 2004).
However there are many negatives associated with use of hormone
treatments; availability of hormones due to cost, legislation and regulations
and also public perception of hormone use. Using hormone treatments may
improve submission rates, but conception rates are not necessarily higher,
although pregnancy rates may be increased due to increased submission
for AI (Lucy et al., 2004). It is clear that although online progesterone
monitoring can detect oestrus, and manipulation of the oestrous cycle
removes the need for oestrous detection, neither is a simple solution to
improving dairy cow fertility within current management systems for the
modern dairy cow. In order to improve reproductive performance the novel
approaches discussed in this thesis are advantageous over current
methods.
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