Dear Colleagues,
Below is a desciption of how the Interbull UK IAM evaluations were incorporated into the UK TDM May evaluations. The same methododolgy will be implemented in this August run.
A description of the procedure used to convert Interbull IAM results to the TDM scale for subsequent publication in the UK
Background
The UK test day model (TDM) evaluations were submitted to Interbull in February and passed all the required tests. Work on preparing data for the first live run in May then continued. However, with only 4 hours to go, it was discovered that pedigrees sent to Interbull had not been formatted according to their specification. Interbull results were withdrawn leaving us with no option but to use the February Interbull proofs calculated using the individual animal model (IAM). This required the merging of Interbull IAM results incorporating UK data up to December 2005 with UK TDM results incorporating UK data up to March 2005.
Method
Initially, an analysis involving 7960 bulls with at least 20 daughters in at least 20 herds in both the February IAM run and March TDM run were used to estimate a prediction equation to express IAM PTAs on a TDM scale. The correlations between TDM and IAM PTAs for these bulls were 0.97 for milk and fat (kg) and 0.98 for protein (kg). The prediction equation was then used to compute the proof (Z) published for foreign bulls as follows:
Z = a + s(W)
Where W is the Interbull PTA and the estimates for a and s for the Holstein breed were:
Milk Fat Protein
s = 1.103 1.231 1.181
a = -371.609 -10.634 -11.800
The inclusion of the value for a takes account of the fact that there has been a base change between the February IAM and the May TDM. The scaling factor s is the ratio of the standard deviations of TDM PTA to IAM PTA for each trait and is needed to account for the fact there is additional information in the TDM and differences in heritability between the evaluation systems.
For bulls that have UK daughters incorporated into their Interbull evaluations, the
difference in reliability between UK IAM PTA and the Interbull reliability was used
to estimate the foreign contribution measured by effective daughters. A similar approach
has previously been utilized by (Harris, 1998) in New Zealand to estimate overseas daughters in Interbull evaluations.
Using the effective daughters, Interbull evaluations were partitioned into UK contribution and foreign contribution. The foreign contribution was then scaled to the TDM equivalent using the prediction equation derived earlier. The scaled foreign contribution was then incorporated into the UK TDM PTA again using effective daughters to derive the appropriate weights.
Results
As expected, for bulls with daughters in the UK, the influence of the foreign contribution upon incorporation into the UK TDM is not very large except for bulls with few UK daughters.
For Example:
MILK PTAs (kg)
UK FOR UK FOR UK + FOR ADDED
NE NE PTA PTA PTA
PICSTON SHOTTLE 136 8 668 603 664
MARS SILVER BOY 72 5 298 355 302
DESLACS STRIKER ET 95 8 -272 -480 -288
A HILLTOP-HANOVER 112 30 246 161 228
A MR PACHA ET 37 32 25 -217 -86
SOLID-GOLD LIFEBOAT- ET 35 24 146 332 222
WAUREGAN VIPER ET 38 32 -202 -82 -147
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FOR= Foreign, NE = effective daughters.
Conversion equations
Conversion equations for converting evaluations from foreign countries to the UK were based on the on the UK IAM February run. These were similarly converted to the UK TDM scale by weighting by the prediction equations indicated earlier.
Conclusion
The method described above to incorporate IAM proofs into TDM proofs is sound and robust and allows for the use of all available information on a bull.
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