Holstein Journal - February 2010

PROOF RUN BASE CHANGE - AN EXPLANATION
Genetic Trends 2009 - Female Type - Composite Traits
1.5
Type Merit
1.0
Mammary
Legs&Feet
0.5
0.0
Have Type proofs
PTA Score -0.5 changed for foreign sires?
As with production, sires with semen imported into the UK have
-1.0
their proofs expressed on the UK base and receive no advantage or
disadvantage as a result – this is also true of UK sires exported to
-1.5
foreign countries through Interbull evaluation.
-2.0
Type Merit is calculated for ALL sires (both UK and Foreign with no UK
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Year of Birth proof) using a formula which consists of the following:
- Mammary Composite 40%
Data Source: The Centre for Dairy Information
- Leg and Foot Composite 30%
- Combination of Linears
degree of stability in the proofs. to predict ‘Lifespan’ 30% (these include the Body Conformation and Dairy
Also, the wider base reﬂ ects the Strength linears of: Stature, Angularity, Body Depth,
different breeding policies for Chest Width, Rump Angle and Rump Width)
the Friesians compared to the
This method avoids any problems created by varying degrees of emphasis being placed
Holsteins.
on different traits within the exporting countries’ evaluations. The formulae aims to
Whilst the production proofs of
maximise lifespan and the weightings of these traits and composites are determined by
each animal are equally affected
what the fi eld offi cers are doing here in the UK and the relative importance of traits
by a base change, (i.e. milk, fat
such as Legs and Feet and Mammary here in the UK. Therefore it is not possible to
and protein kg alters by a fi xed
compare an overall Type score for a bull between the UK and different countries.
amount across the board), this is
not the case however with Type.
Expression of Type Proofs
As Type traits are published as
Type proofs are expressed as ‘standard deviations’ that usually fall between +/- 3. The
‘standardised’ proofs (divided
distribution of proofs for any Type trait for the breeding age group of males follows a
by the standard deviation of
‘bell-shaped’ or normal distribution curve. This means that fewer animals have proofs
the breeding values of the base
at the extremes with most bulls scoring around average. A Type proof thus describes
population), the amount of change
a sire’s position within the present breeding population, whether his daughters, on
within a particular trait is not
average, will be above or below the mean of the current breeding population and by
the same for each animal. It is
how much.
important to note though, that When reading a type proof, it is particularly
the base change will not affect the
important to remember the following;
ranking of bulls.
• Appreciate that the fi gures are only predictions of how extreme the daughters
As well as different levels of
are likely to be within the population as a whole for a specifi c trait NOT what
change within traits, there are also
they will look like.
different levels of change between
• Attach greater importance to individual linear trait scores rather than
traits. Some traits such as Rump
composite type traits to correct a specifi c problem, for example with Rump
Angle, do not vary much over time
Angle – where high pins are a problem, you may need to use a sire with an
so the base remains much the
extreme score for lowering the pins:
same, but other traits, especially
those associated with increased
Rump angle High pins

Low pins 2.8
milk production, will have altered
considerably over recent years.
What is to be remembered is that
Other traits that this situation may relate to could include Rear Leg Set &
the standardised range describes
Locomotion. Care must be taken with this strategy however to ensure the
the bull’s position within the
bull is not a ‘one trick pony’ and doesn’t have weaknesses in other key traits.
breeding population for all traits.
• Appreciate that to improve a particular trait, a score above +1.0 is likely to be
needed, with the exception of the mid-score optimum traits – Rear Leg Side
Is the same true for
and Rump Angle, where values close to zero are desirable – except if you have
composite traits?
a very specifi c problem such as high pins or sickled/posty legs.
Yes. Composite trait proofs for
• Remember that the Standard Deviations (+3 to -3) refer to the average of the
bulls with a UK proof are produced
bull’s daughters for any particular trait or composite compared to the average
using the classifi cation scores of the
of all bulls’ daughters.
bull’s daughters. Again, the base
 Animals with a +3 or -3 lie within the top or bottom 1% of the
change will not affect the ranking
population
of bulls for composite traits.
THE JOURNAL FEBRUARY 2010 83
Proof Run Base Change - Jan 2010.indd 3 28/01/2010 15:28:07
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