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MANAGEMENT
DOES INBREEDING
PRESENT A
RISK TO YOUR HERD?
Inbreeding has been in the news in recent months – fi rst
when the RSPCA pointed the fi nger of blame for many
dairy cow ills at high levels of inbreeding; and later when
this summer’s sire proofs became dominated by just
one bull. Geneticist, Marco Winters, director of DairyCo
breeding+ has looked at the facts behind the concerns
and suggests the action Holstein breeders should take
T
here

are a few incontrovertible facts in the inbreeding debate. suggests they do not – at least, with some
And perhaps the most important is that a high level of inbreeding provisos. The most up-to-date ancestry records
– or breeding between close relatives which leads to a narrowing of reveal that the youngest heifers milking in the
bloodlines – is not a good thing. It’s well known that this can lead to national herd have an average inbreeding level
a decline in the general ‘fi tness’ of a population, otherwise known of 3.5 percent. This is somewhat higher than the
as ‘inbreeding depression’, and can also increase the occurrence of older cows (so the situation is getting worse) but
genetic defects. considerably lower than the average Holstein in
But I already hear the breeders amongst you beginning to protest. North America, where the level of inbreeding is
After all, it’s equally well-known that desirable traits can be ‘fi xed’ by
now over fi ve percent (see graph).
the very same process (often referred to as ‘line breeding’), leading to
At this level, North American breeders should
true-breeding lines and the type of uniformity in a herd to which many
unquestionably be more concerned, as it is widely
breeders aspire.
accepted that when inbreeding reaches high
So the question we must answer is where does the boundary lie?
levels it will unacceptably compromise animal
How much inbreeding is too much; is zero inbreeding either possible
performance and fi tness.
or desirable; how does the UK
fare overall; and how do we avoid
Inbreeding trends in the black and white dairy cattle
reaching the point at which we
damage the national herd?
population in the UK, Canada and the USA
These questions have been much-
debated in the farming press in
recent months – fi rst when raised by
the RSPCA in connection with the
health and fi tness of the Holstein
breed and more recently when
one bull (O-Bee Manfred Justice)
dominated the PLI (Profi table
Lifetime Index) rankings. Here,
he accounted for eight of the top
10 bulls, leading many journalists
to ask whether bloodlines were
becoming too narrow.
Our job at DairyCo breeding+ is
to keep a close eye on the situation
and monitor inbreeding levels
across the national herd - which we
Source: DairyCo breeding+. UK data supplied by Holstein UK and milk records
have been doing for many years -
organisations, CIS, UDF and NMR. Canadian data from Canadian Dairy Network
so that we can gauge whether the
(CDN) 2008 (http://www.cdn.ca); US data from Animal Improvement Programs
concerns have any foundation.
And our most recent evidence
Laboratory (AIPL USDA) 2009 (http://www.aipl.arsusda.gov/).
92 THE JOURNAL OCTOBER 2009
e5-09 Management - Inbreeding.indd 2 23/09/2009 12:41:42
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