Analysis of Bull Proofs for Intermediate Optimum Traits - CGIL

Introduction
Analysis of Bull Proofs for
Intermediate Optimum Traits
G. Kistemaker, G. Huapaya, B. Van Doormaal
Since February 1997, Canada has used the classification data for two intermediate optimum
traits, namely Rump Angle and Rear Legs Side View, to produce two sets of genetic
evaluations. Bull proofs for Rump Angle and Rear Legs Side View include an unsigned
numerical rating plus a letter code, which is referred to as the tendency scale. Proofs for Pin
Setting and Set of Rear Legs reflect the likelihood of producing a daughter that has the ideal
rating of 5, which are expressed on a desirability scale ranging from about -15 to +15 similar to
most other type traits (see table).
Interpretation of Bull Proofs for Pin Setting and Set of Rear Legs (Desirability Scale)
Proof (Signed) -15 -12 -9 -6 -3 0 +3 +6 +9 +12 +15
Proof Interpretation
Interpretation of Bull Proofs for Rump Angle and Rear Legs Side View (Tendency Scale)
Numerical Rating (no sign) 15 12 9 6 3 0 3 6 9 12 15
Rump Angle - Letter H H H H H L L L L L
Rear Legs Side View - Letter S S S S S C C C C C
Proof Interpretation
The need for this approach arose from the fact that there were several bulls that have an
average daughter score near the ideal of 5 but the distribution of daughters shows relatively few
desirable daughters and a similar proportion of daughters at each extreme. The objective of this
analysis was to determine if this situation still existed for bulls in the current Holstein population
and if not, then the use of the genetic evaluations on the desirability scale could be dropped.
Material and Methods
Least likely
to sire ideal
daughters
Tendency towards "High" pins or
"Straight" rear legs
Severe
tendency
Moderate
tendency
Breed average for siring
ideal daughters
No clear
tendency
Most likely to
sire ideal
daughters
Tendency towards "Low" pins or
"Curved" rear legs
Moderate
tendency
Severe
tendency
Holstein data files and official bull proof files from the November 2005 genetic evaluation run
were used. For each bull the standard deviation of daughter records and the percentage of
daughters with a score of 5 were calculated using data on the 1 to 9 scale. From these data
sets bulls that had proofs near breed average (-2 to +2) on the tendency scale were selected
and results were plotted. In this way, the relationship between average daughter score and the

sire’s proof on the desirability scale could be examined. The underlying hypothesis of this
approach is that the publication of proofs on the tendency scale alone would suffice if bulls with
proofs near the breed average showed a consistently desirable pattern for producing desirable
daughters.
Results & Discussion
Bull proofs aim to reflect the expected average performance of future daughters assuming a
continuous linear scale. For type traits with an intermediate optimum that are recorded on a 9point
linear scale, previous research found various bulls to have desirable daughter averages
near the optimum score of 5 based mainly on daughters at each extreme of the linear scale
rather than a majority at the ideal mid-score value. Computing genetic evaluations using these
data yield bull proofs near the ideal of zero (meaning no clear tendency towards either extreme)
and therefore suggest these bulls are breed improvers. For these reason, in 1997, it was
decided to use the same classification data, but on a folded scale of 1 to 5, to produce genetic
evaluations on a desirability scale, published as Set of Rear Legs and Pin Setting.
Figures 1 and 2 show a clear relationship between the percentage of daughters that have an
ideal score of 5 and the sire’s proof for Set of Rear Legs and Pin Setting, respectively, based on
bulls that have a proof on the tendency scale that is near breed average. Daughters of bulls
that are close to average for Rear Leg Side View and have a Set of Rear Legs proof of less than
-10 have about a 20% probability of having an ideal score of ‘5’ for Rear Leg Side View. In
contrast, daughters of bulls with an average proof for Rear Leg Side View and are at least +10
for Set of Rear Legs have more than 40% chance of having a score of 5. Similar results were
observed for Rump Angle/Pin Setting in Figure 2 with the spread in likelihood of having an ideal
daughter being from 30% at -10 to 50% at +10 for Pin Setting.
The standard deviation of daughter scores for bulls at opposite ends in their proof for Set of
Rear Legs (and Pin Setting) also has a clear trend based on bulls that have a proof near breed
average for the proof on the tendency scale. Basically, a higher standard deviation of daughter
scores for negative proofs on the desirability scale reflect that these bulls have a large variation
in how their daughters are scoring. Less variability in daughter scores for highly rated bulls on
the desirability scale indicate that the system is appropriately identifying bulls that are producing
daughters that consistently have the ideal phenotype.
Conclusion and Recommendation
The results of this analysis, as presented in Figures 1 and 2, clearly show that there are bulls
evaluated as ideal (i.e.: near zero) on the tendency scale that are inappropriately considered as
siring daughters near the ideal rating of 5. Therefore, the proof information on both the
tendency and desirability scales are required for a proper interpretation of bull proofs for these
intermediate optimum type traits. While this analysis was done only for the Holstein breed there
is no reason to assume that a similar result would not also occur for other breeds. It is
recommended that the current procedure for calculating proofs on both the tendency and
desirability scales be continued.

Standard Deviation of the
Score
Standard Deviation of the Score
Figure 1: Relationship between phenotypic score for Rear Leg Side View and
the proof for Set of Rear Legs for bulls with a Rear Leg Side View proof ranging
from -2 to +2
1.8
70%
1.6
1.4
1.2
1
0.8
0.6
0.4
1.8
1.6
1.4
1.2
-13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15
Set of Rear Legs proof
1
0.8
0.6
0.4
Standard Deviation Percent with a score of 5
Figure 2: Relationship between phenotypic score for Rump Angle and the proof
for Pin Setting for bulls with a Rump Angle proof ranging from -2 to +2
-15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15
Pin Setting proof
Standard Deviation Percent with a score of 5
60%
50%
40%
30%
20%
10%
0%
% of records with a
score of 5
70%
60%
50%
40%
30%
20%
10%
0%
% of records with a score of 5