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But precisely the point at which the compromises become
unacceptable is diffi cult to quantify and open to debate. Established
research has estimated that for every percentage increase in
inbreeding, around 15kg milk will be lost per lactation and 0.4 days
will be added to calving interval. This has led to a (somewhat arbitrary)
threshold of 6.25 percent inbreeding being regularly quoted as the
point not to cross.
Here in the UK, our more favourable position stems in part from our
base of British Friesian bloodlines (kept pure for many years when
imports were restricted) and, perhaps paradoxically, the subsequent
opening of our markets to a wide assortment of Holstein bloodlines
from almost every country in the developed dairying world, from the
late 1980s onwards.
Today, the UK’s national black and white milking herd as a whole (all
ages) stands close to three percent – a level which gives us little cause
for concern.
But there is categorically no room for complacency, as around this
average there are many individual animals whose inbreeding levels are
far too high; (most herds have at least one cow which exceeds the 6.25
percent threshold); and the trend as a whole is most defi nitely in an
of computers, the table below may be of some
upward direction.
In fact, if current
help in determining the suitability of a proposed
trends continue,
mating.
Inbreeding levels
the UK’s average
Clearly the table suggests that aspiring to zero
Mating Inbreeding %
inbreeding level
inbreeding is unrealistic, and it’s worth pointing
will increase by
out that it’s probably also undesirable as it is
Sire/daughter 25
about one percent
widely felt that slight losses from low levels of
Full brother/full sister 25 every six years, at
inbreeding are more than offset by the genetic
which rate it will
gain which can potentially be made by using
Half brother/half sister 12.5
only be 16 years
good bloodlines.
Grandsire/granddaughter 12.5
before we reach
This has been brought into sharp focus in recent
the threshold of
months, since sons of O-Man – as well as the
Grandson/grandam 12.5
6.25 percent.
bull himself – have begun to feature so strongly
Uncle/niece 6.25
So what practical
amongst the top PLI sires. I’ve been asked on
action can be
numerous occasions since the last proof run,
Son/granddaughter 6.25
taken to ensure
whether the use of this bull and his sons will lead
Daughter/grandson 6.25
we don’t reach this
to unacceptable levels of inbreeding. And my
position?
answer remains that if the principles discussed in
Full cousins 6.25
Perhaps most
this article are adhered to, there is no reason why
Grandson/granddaughter 3.13
fundamental it should.
of all is to keep O-Man has reached the position he has through
Half cousins 3.13 impeccable his tendency to transmit high volumes of milk,
breeding records. without compromising essential fi tness traits
Members of - and it is precisely these qualities which the
Holstein UK have a head start in this respect as the very act of profi t-driven milk producer needs. And since
registering their herd ensures their bloodlines are recorded for neither the bull himself, nor his sire (Manfred)
posterity. nor maternal grandsire (Elton) were widely used
But then they need to go further. They not only need to trawl the
in the UK, there remains plenty of scope for
sire proofs for those with the genetic qualities they desire (such as
O-Man bloodlines to be used without inbreeding
high Profi table Lifetime Index; high type; high production or good
concerns. In fact, with almost every British AI
management and fi tness qualities), but they must then study the
company marketing an O-Man son - which
pedigrees to ensure the bloodlines they choose won’t unacceptably
descend from a wide variety of maternal lines -
raise inbreeding in their herd.
I’d argue that the UK’s position to use these
This can be a fairly complicated process, so I would urge every
bloodlines should be grasped.
breeder to consider the simple alternative to the time-consuming and
For those who have different breeding
manual approach. This involves using a computer mating program –
objectives, there remain many excellent bulls
such as that offered by Holstein UK’s Webmate - which specifi es a level
within the top 100 PLI list, which represent
of inbreeding for every suggested mating. Avoid any which raise the
offspring of 50 different sires. So whatever your
level beyond 6.25 percent, and for cows which have already reached
breeding priorities, there’s really no need to
this point, choose an outcross bloodline which will bring this level back
concentrate on only a few related bloodlines,
down.
and if you can choose an outcross pedigree (and
For those who are keen to review their whole herd’s position, there
there will be plenty of these without resorting to
is also the availability of the DairyCo breeding+ Herd Genetic Report.
crossbreeding), so much the better for your herd.
This is free to all milk recording producers and states the level of
inbreeding for every animal as well as the level for the whole herd.
To register for a free Herd Genetic Report,
And for those who prefer to approach the issue without the use
please call DairyCo on 02476 692051 or visit www.
dairyco.org.uk.
THE JOURNAL OCTOBER 2009 93
e5-09 Management - Inbreeding.indd 3 23/09/2009 12:41:46
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