novel approaches to expression and detection of oestrus in dairy cows

indication for the optimal time to AI, approximately 12 hours post onset of
standing heat (Dransfield et al., 1998). Identifying the primary sign of
oestrus is extremely accurate, resulting in only 2% error in wrongly
identifying oestrus (Kiddy, 1977). Secondary signs can also be used to
identify cows in heat, but are not as reliable an indicator of true oestrus as
standing to be mounted, however, these behaviours are useful to identify a
recent heat or cows coming into heat, therefore should be more closely
observed for the next 48 hours or 17-20 days later (Diskin, 2008).
Traditionally the only method of oestrous detection was to perform visual
observations and although accurate this method is time consuming and
requires attentive observation so that specific oestrous behaviour is not
missed (Firk et al., 2002). Current issues are that too little time is spent
observing the herd, observation occurs at the wrong time and in the wrong
place; during feeding time or at milking and is infrequent (Diskin, 2008).
With intensification, the modern dairy herd is much larger therefore
efficiency of detection is compromised. Observations 2 or 3 times a day for
30 minutes, which is typical of commercial farms, yielded 70% efficiency
(Van Vliet and Van Eerdenburg, 1996) but in another study only 53% of
standing oestruses were observed using the same observation method
(Lyimo et al., 2000). Another problem with visual observation is continuity;
mounting activity is displayed more frequently early morning and late
evening (Hackett and Mcallister, 1984) and 65% of all oestrus activity has
been reported to occur between 1800 and 0600 hours (Hurnik et al., 1975)
when the herdsman is not present. Therefore, efficiency of visual detection
is compromised by modern practice.
A major problem hindering visual detection is poor expression of oestrus in
the modern dairy cow. Standing behaviour is not observed in over 50% of
cows in oestrus (Van Eerdenburg et al., 2002), and the number of silent
heats has increased (Harrison et al., 1990). Reduced intensity and duration
(Dransfield et al., 1998) also exacerbate the problem of observation at set
times. Standing to be mounted is reported in less than 37% of oestruses
when observed for 30 minutes 12 times per day are used. This is reduced
to 12% when only 3 observations of 30 minutes (Van Eerdenburg et al.,
1996) which is a more practical time frame. Therefore a continuous method
of oestrous detection is required to improve the efficiency of visual
detection.
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