APPLIED SCIENCE
By Lynsay Beavers and
Brian Van Doormaal
[HEIGHT MATTERS
Taking a closer look at stature in Holsteins and how it affects cow health, breed goals and traits
T
here’s no doubt in anyone’s mind,
Holsteins are getting bigger. Problems related to larger animals can
include higher maintenance, more injury,
issues fitting in existing stalls, increased
calving difficulties and more. Let’s take a
look at stature trends, breed goals and trait
correlations to gain a better understanding
of the impact of taller cows.
average, over half a centimetre in height
per year from 1991 to 2005. Since 2005,
when the implementation of the MultiBreeds Classification Program and the associated changes were made, this trend has
slowed down significantly, averaging 0.18
cm per year. This slower increase in average
stature is likely a reflection of the revised
objectives of the conformation assessment
program and is also influenced by artificial
insemination use of certain bloodlines and
more consistent heifer rearing over time.
HOW IS STATURE
MEASURED?
HOW ARE PROOFS
CALCULATED?
For many decades, Holstein Canada has
been using a type classification system that
includes stature. Since 1993, this trait has
been measured objectively. Stature is defined as the height of the cow at her hips.
In the classification report left on farm,
measured stature is converted and expressed on a nine-point linear scale used
for descriptive type traits. These values
are adjusted for the cow’s age at calving,
as well as lactation stage. Cows receiving
a linear score of six, seven or eight receive
the highest credit in terms of contributing to the overall score for dairy strength,
while a score of nine contributes less. The
same linear scale ratings from one to nine
are used as input into the genetic evaluation system for calculating bull proofs and
cow indexes for each trait.
As is the case with all type traits, sires
of daughters with average stature have
a genetic evaluation of 0 for the trait.
Bulls expected to sire taller than average
daughters have a proof greater than zero,
while bulls that sire daughters expected to
be shorter than average have a proof less
than zero. Given the genetic relationship
between stature and other type traits, it is
relatively rare to see a high-ranking sire for
either national index, LPI or Pro$ that has
a negative proof for stature.
EVOLUTION OF BREED
GOALS
Over time, breed goals change once landmarks are achieved, new traits are added or the needs of the industry evolve.
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APRIL
2016
| MILKPRODUCER
MAY 2015
| MILKPRODUCER
STATURE’S RELATIONSHIP
WITH OTHER TRAITS
HOLSTEINS HAVE gained, on
average, over half a centimetre in
height per year from 1991 to 2005,
according to a phenotypic trend.
One clear example of this is selection for
daughter fertility, a trait that only became
relevant in the early 2000s after decades of
heavy selection for production, which took
a negative toll on breed fertility. Over the
years, Holstein Canada’s type classification
system has shifted focus, gradually reducing the emphasis of stature’s contribution
to dairy strength, and as a result, to overall
final score. After various changes over the
years to the conformation assessment program offered by Holstein Canada, stature
currently contributes only 2.4 per cent of
a cow’s final score, noting linear scores of
six to eight are considered ideal.
STATURE TRENDS
Figure 1 shows the genetic and phenotypic
trends in stature for Holstein cows born
since 1991. The genetic trend for stature
has been quite steady at nearly one EBV
point every two years. In terms of interpreting sire proofs for stature, every fivepoint increase in proof translates to almost
a centimetre taller in terms of the average
stature of their daughters. The phenotypic
trend is based only on cows classified at 26
months of age to demonstrate the increase
in average stature over time for a fixed age.
This trend shows Holsteins gained, on
While breed goals have changed over time
and the phenotypic trend for stature has
slowed. A major reason for this is due to
stature’s genetic relationship with other
traits. Stature also has positive correlations
with mammary system and feet and legs,
but genetic correlations with production
yields are only slightly positive and virtually negligible.
Correlation results between stature and
selected traits in the United States aren’t
always consistent with those seen in Canada. In the U.S., stature has a stronger
positive correlation with major type traits,
particularly predicted transmitting ability (PTA) type. Even more importantly,
stature is negatively correlated with productive life and daughter pregnancy rate
meaning taller cows have poorer longevity
and fertility. In Canada and the U.S., stature has an undesirable relationship with
calving ease, with larger calves leading to
significantly more difficult births.
Why are correlations so different between Canada and the U.S.? There are
several contributing factors. First, trait
definitions vary between countries. For