INTERBULL Routine Genetic Evaluation for Udder Health Traits

November 2002

Introduction
International genetic evaluations for milk somatic cell and clinical mastitis of bulls from Canada, Denmark, Estonia, Finland, France, Germany, the Netherlands, Norway, Sweden, Switzerland, The United Kingdom, The United States of America, Israel, Italy, Australia and Hungary were computed in this evaluation. Ayrshire, Brown Swiss, Guernsey, Holstein and Jersey breed data were included.

Changes in national data

• Australia corrected an error, which involved inclusion of some tests with a wrong Somatic cell score instead of them being coded as missing in the genetic evaluation.
• The Netherlands and Hungary submitted data with corrected EDC's.
• United Kingdom and Australia submitted data with a revised specification of publication status, which more accurately reflects the official publication policy in these countries.

Changes in Interbull procedures

• The requirement for inclusion of second country proofs in the evaluations was changed. Proofs that are based only on 2nd crop daughters (type=21) are included if they are:
  a) identified as meeting the standard national rules for official publication in the country sending the information (official  publication of proof=Y)
  OR
  b) based on minimum 150/30/80 daughters in 50/10/20 herds (Holstein/Guernsey/other breeds).
  
  Number of second country proofs included in the evaluation increased for most populations, although it decreased in some populations similar to production traits.
• A weighted bending procedure (Jorjani et al., 2002, Interbull Bull. 29:1) was implemented to obtain positive definite correlation matrices (number of common bulls was used as weighting factor and a minimum weight of one was required).
• Improved data verification procedures following the ideas of Klei et al., 2002, Interbull Bull. 29:178) was introduced.

Data and method of analysis

Data were national genetic evaluations of AI sampled bulls with daughters in at least 10 herds. For clinical mastitis information to be included, an additional requirement was that bulls had to have at least 50 daughters. Table 1 presents the amount of data included in this Interbull evaluation. Table 2 and table 3 gives heritabilities and some additional information on national evaluations as provided by the participating countries.

Estimated genetic parameters are shown in APPENDIX I.

National proofs were first de-regressed within country and then analysed jointly with a linear model including the effects of evaluation country, genetic group of bull and bull merit. Heritability estimates used in both the de-regression and international evaluation were as in each country's national evaluation (Table 2 and table 3).

Ancestor-bulls without own proofs were traced back two generations from the oldest bulls with proofs in order to increase across country connections and account for the effect of selection.

Genetic groups were defined according to unidentified parents by national origin, breed and birth year of the bull and path of selection (sire, maternal grand-sire, maternal grand-dam). Birth year grouping was by 1-5 year periods. Smaller groups (consisting of less than 30 bulls) were combined.

International genetic evaluations were computed using effective daughter contributions (EDC) as weighting factors.

For each breed, two separate international genetic evaluations were computed. The first included milk somatic cell de-regressed proofs from individual countries. The second included de-regressed proofs for clinical mastitis as a direct trait from countries that made this information available and milk somatic cell de-regressed proofs from all other countries. Note that the second evaluation was not carried out for BSW and GUE since none of the participating countries provided clinical mastitis information.

Genetic correlation estimation procedure

Genetic correlations among countries were estimated using a similar approach as for production traits:

Step 1:

Several subsets of countries were analysed and the highest estimate for a country pair was kept, as per Sigurdsson et al (1996) showing that genetic correlations are not likely to be over-estimated by the method used.

Step 2:

In some cases sufficient genetic links between countries may be missing, resulting in unreasonable genetic correlation estimates. If no reasonable correlations could be estimated one of the the following procedures was followed:
a) Estimates from another breed for the country pair were used, but bended towards the actual estimate
b) Estimates from the low end of the correlation distribution were assigned; for milk somatic cell information in different countries these would normally be around .80, for clinical mastitis information in different countries around .40, and between milk somatic cell information and clinical mastitis information in different countries around .35 (estimates between milk somatic cell and clinical mastitis above .80 were considered unrealistic and bended downward).

Step 3:

Since genetic correlation estimates were not derived simultaneously, the full covariance matrix needed to be bended in order to ensure it was positive definite.
 

Publication of INTERBULL evaluations

Results were distributed by the Interbull Centre to designated representatives in each country. The international evaluation file comprised international proofs expressed on the base of each country included in the analysis. Such records readily provide more information on bull performance in various countries, thereby minimising the need to resort to conversions.

At the same time, all recipients of Interbull results are expected to honour the agreed code of practice, decided by the Interbull Steering Committee, and only publish international evaluations on their own country scale. Evaluations expressed on another country scale are confidential and may only be used internally for research and review purposes.

Next routine international evaluation

The next routine international evaluation for dairy production, udder health and conformation traits is scheduled for February 2003. New data for that run should reach the Interbull Centre not later than January 28, 2003, 17:00 Central European Time (CET); in any case, the most recently received data will be considered. The target time for distribution of results for internal review to designated representatives who have signed a confidentiality agreement with the Centre is February 6, 2003. Official release date of the results is targeted to be February 10, 2003.
 

Next test international evaluation

The next test international evaluation for dairy production traits, conformation traits, and udder health traits is scheduled for March 2003. Countries wishing to enter the system for the first time or planning to submit new information (modified national evaluation procedure, new breeds etc) for following routine evaluations must have their data tested in this test-run.

Deadline for sending data to the Interbull Centre for the next test-run is March 1, 2003.

Means of result distribution from the Interbull Centre

Electronic exchange of data is probably more efficient than anything else. Currently most countries in the service have established internet connections and receive international evaluation results on the day of their release. Subscribers to the service that do not already has this option are encouraged to consider it and establish an internet connection and ftp account. When such accounts are available, please provide their specifications to the Interbull Centre. Until then, data will be delivered on CD-ROM's.

For more information about the international genetic evaluation service please contact the Interbull Centre: address: SLU Box 7023, 750 07 Uppsala, Sweden; fax: +46-18-672648;