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Dairy Pipeline: March 2006
Bennet Cassell
Extension Dairy Scientist,
Genetics & Management
(540) 231-4762 email: bcassell@vt.edu
Genetic evaluations are published four times a year - and have been regularly updated by the USDA for many years. New proofs are routine. It is easy for producers to become complacent about sire selection, but standards for selection need to be adjusted from time to time. Genetic progress takes place. New bulls with better proofs replace older bulls in the active AI lineup. The simple table below shows some useful guidelines for evaluating a proof for Net Merit. The very best 5% of Holstein bulls exceed the $464 Net Merit rating for the 95th percentile. For Jerseys, that mark is $433. The top 20% of bulls exceed $373 and $355 for Holsteins and Jerseys, respectively. The top 20% of active AI bulls includes about 120 Holsteins and 15 Jerseys, so there are plenty of opportunities for selection for other traits among the top group in both breeds.
| Net Merit required for different rankings in Holsteins and Jerseys | ||||
|---|---|---|---|---|
| Breed | 95th percentile | 90th percentile | 80th percentile | 70th percentile |
| Holstein | 464 | 425 | 373 | 331 |
| Jersey | 433 | 409 | 355 | 323 |
USDA made changes to the evaluation system for daughter pregnancy rate (DPR) for the February 2006 proofs. Pregnancy ratings are calculated on individual cows once they are 130 days into first lactation, which is later than for milk records. Some young bulls can have milk proofs based on short daughter records, but no DPR based on daughter information. Formerly, pedigree data was used for the DPR rating for these bulls, but now, USDA predicts DPR using production and somatic cell score (both negatively related to DPR) and productive life (positively related to DPR) as well as pedigree. Effects on "domestic" bull proofs were small, but the change did reduce DPR ratings, on average by 0.4, for the top 100 international bulls. The procedure used makes DPR more useful as reliability is increased, but the method used is temporary, as more accurate predictions are under development for the future.