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novel approaches to expression and detection of oestrus in dairy cows

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CHAPTER 1 – Introduction & Literature Review<br />

1.1 INTRODUCTION<br />

Dairy cow fertility has been decl<strong>in</strong><strong>in</strong>g rapidly for the past 2 decades <strong>and</strong><br />

despite be<strong>in</strong>g widely reported <strong>and</strong> <strong>in</strong>ternationally recognised (Royal et al.,<br />

2000a;Lucy, 2001;Pryce et al., 2004) is a still a major problem that<br />

persists <strong>to</strong> the present. Fertility is reported <strong>to</strong> be decl<strong>in</strong><strong>in</strong>g at a rate <strong>of</strong> 1%<br />

per annum <strong>in</strong> the UK (Royal et al., 2000a), with similar patterns <strong>in</strong> the US,<br />

decl<strong>in</strong><strong>in</strong>g at 0.45% per annum (Butler <strong>and</strong> Smith, 1989). The decl<strong>in</strong>e <strong>in</strong><br />

fertility has been associated with a rapid <strong>in</strong>crease <strong>in</strong> milk yield per cow<br />

(Pryce et al., 2004), whilst genetic selection has focussed on higher milk<br />

yields, selection for fertility has been ignored, facilitat<strong>in</strong>g the current<br />

problem. This negative correlation between yield <strong>and</strong> fertility <strong>and</strong> health<br />

has also been reported across Europe (Veerkamp et al., 2003;Barbat et al.,<br />

2010). In Sc<strong>and</strong><strong>in</strong>avian countries fertility <strong>and</strong> health traits have s<strong>in</strong>ce been<br />

<strong>in</strong>corporat<strong>in</strong>g <strong>in</strong><strong>to</strong> breed<strong>in</strong>g programs <strong>to</strong> provide a <strong>to</strong>tal merit <strong>in</strong>dex (TMI)<br />

for each bull <strong>in</strong>clusive <strong>of</strong> yield (Philipsson <strong>and</strong> L<strong>in</strong>dhé, 2003). However the<br />

negative trend for <strong>dairy</strong> cow fertility is still been reported (Rodriguez-<br />

Mart<strong>in</strong>ez et al., 2008).<br />

This challenge will not be aided by current trends <strong>in</strong> the UK <strong>dairy</strong> <strong>in</strong>dustry<br />

over the past decade (which are documented <strong>in</strong> Table 1.1) where the <strong>to</strong>tal<br />

number <strong>of</strong> <strong>dairy</strong> farms <strong>and</strong> the <strong>to</strong>tal number <strong>of</strong> <strong>dairy</strong> <strong>cows</strong> <strong>in</strong> the UK has<br />

decl<strong>in</strong>ed but milk yield rema<strong>in</strong>s high as the <strong>to</strong>tal milk yield per cow has<br />

<strong>in</strong>creased. The average herd size is also larger (DairyCo, 2012b). Therefore<br />

there are fewer <strong>cows</strong> produc<strong>in</strong>g more milk <strong>and</strong> more <strong>cows</strong> on farm coupled<br />

with fewer staff. In conclusion <strong>in</strong>fertility <strong>in</strong> the <strong>dairy</strong> herd still persists <strong>and</strong><br />

is l<strong>in</strong>ked <strong>to</strong> the current trends.<br />

Table 1.1 Trends <strong>in</strong> the UK <strong>dairy</strong> <strong>in</strong>dustry<br />

2001 2010 2011<br />

Number <strong>of</strong> <strong>dairy</strong><br />

26556 15300 14793<br />

farms<br />

Dairy cow numbers 2251 1857 1814<br />

(thous<strong>and</strong> head)<br />

Average herd size 83 121 123<br />

Milk yield (litres per 6346 7273 7533<br />

cow per annum)<br />

Source: Dairy Statistics - An <strong>in</strong>sider’s guide 2012 (DairyCo, 2012b)<br />

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