novel approaches to expression and detection of oestrus in dairy cows

CHAPTER 6 – Overall Discussion & Conclusions
6.1 OVERALL DISCUSSION
Declining fertility in dairy cows has become an international problem
strongly associated with genetic selection for high milk yield with little
selection for other traits (Royal et al., 2000a;Butler, 2003;Pryce et al.,
2004). A major part of the decline in fertility can be attributed to poor
detection of oestrus (Van Eerdenburg et al., 2002). It is crucially important
for cows to express oestrus and for oestrus to be detected in order for AI
to occur at an appropriate time relative to ovulation (Evans and Walsh,
2011). Therefore detection of oestrus is a key determinant of profitability in
dairy herds (Pecsok et al., 1994). Poor detection of oestrus can be
attributed to the decline in oestrous expression. The number of cows
standing to be mounted has declined from 80 to 50% (Dobson et al., 2008)
and oestrus is less intense and of shorter duration, averaging only 7 hours
in Holsteins (Dransfield et al., 1998). The decline in oestrous detection has
been associated with larger herd sizes with the average herd size in the UK
increasing from 75 cows in 1996 to 123 cows by 2011 (DairyCo, 2012c).
This does vary worldwide with some herds in China and America having
15000 cows. Less labour per cow and a general lack of time dedicated to
oestrous expression may also contribute to poor oestrous detection rates.
Currently the national average for oestrous detection rate is only 50%
where there is potential to be much higher and achieve a realistic target of
over 70% (DairyCo, 2009).
Traditionally oestrous detection was performed by visual observation and
although this method is accurate at detecting oestrus events which occur
during observation periods (Van Vliet and Van Eerdenburg, 1996), due to
time constraints and impracticality it is largely inefficient (Lehrer et al.,
1992). Continuous visual observation of synchronised cows (Chapter 5)
detected all cows in oestrus, but continuous observation is not a viable
method for commercial use. Many oestrous detection aids are available,
with different detection efficiencies and accuracies (Roelofs et al., 2010).
Automated methods of detection are becoming increasingly popular, but
there is still scope for improvement of detection rates.
Activity increases at oestrus (Farris, 1954;Kiddy, 1977) and activity
monitoring is a convenient way of detecting oestrus. Detection rates for
activity monitoring are often 80 to 90% (Firk et al., 2002), some even
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