novel approaches to expression and detection of oestrus in dairy cows

CHAPTER 2 – Effect of Cow Factors on Oestrous
Expression
2.1 INTRODUCTION
A main contributory factor to poor fertility in the dairy cow (Royal et al.,
2000a;Butler, 2003) is poor oestrous expression; only 50% of cows are
reported to show signs of standing to be mounted, the definite sign that a
cow is in oestrus (Van Eerdenburg et al., 2002). Other measures of oestrus
suggest that duration and intensity of oestrus has also decreased; only 8.5
standing events at oestrus and duration only lasting on average 7 hours in
Holsteins (Dransfield et al., 1998).
Associations have been found between parity (Macmillan et al., 1996)
(Garnsworthy et al., 2008), seasonal variations (Critser et al., 1987) and
milk yield (Royal et al., 2000a) and their effects on fertility. Previous work
has recognised that oestrous expression can be influenced by cow factors,
focussing on duration and intensity, and standing events (Van Eerdenburg
et al., 1996;Peralta et al., 2005), but there have been few investigations
into the effects of cow factors and their associations with activity at
oestrus, measured by activity monitors.
Emphasis should be placed on identifying cows at risk of poor oestrous
expression. It is important to identify factors that affect oestrous
expression in order to implement management systems for improvement of
oestrous detection. This study investigated the effects of parity, time
period of oestrus, oestrous number, days post partum and milk yield for
their effects on activity. Associations between the activity increase on day
of oestrus and probability of conception were also investigated. The aims of
this study were to identify the effects of measurable cow factors on activity
increases at oestrus.
2.2 MATERIALS AND METHODS
2.2.1 Animals
Animals used in this study were 205 Holstein Friesian dairy cows housed at
Nottingham University Dairy Centre. The lactating cows were kept indoors
in groups of approximately 40. Housing consisted of a purpose built shed
with 4 pens, which was well ventilated, with rubber matting, cubicles and
shavings for comfort whilst lying. All cows were fed the same silage based
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