Sire Conception Rate Replaces ERCR

By Steve Schnell
Dairy Genetic Consultant

Starting with the August 2008 sire summary, USDA AIPL¹ has released Sire Conception Rate (SCR) as a replacement for Estimated Relative Conception Rate (ERCR) which had been available to the industry since 1988. Initially, ERCR was calculated by Dairy Records Management Systems (DRMS). For the past two years, AIPL has calculated ERCR while conducting research to improve the evaluations.

There are several differences and improvements to SCR versus ERCR. SCR results are based on confirmed pregnancies, while ERCR was based on a 70-day non-return rate. In addition, the new system includes many more services in the same time frame. This is due to SCR using the first seven qualifying services for a cow during each lactation. ERCR used only the first service. Another improvement is that data now comes from herds representing the majority of the United States.

When developing SCR evaluations, AIPL found there are other important factors that need to be adjusted for that are not related to the bull's fertility but to the cow's. The biggest factors being herd differences, number of times the cow has calved and how often she was serviced during the lactation. Other factors accounted for include location, season and standardized milk yield.

Factors related to the bull that are found in the model include the inbreeding level of the bull and of the potential embryo, mating age of the bull, stud year and the main factor, the bull itself.

SCR will be expressed as a percentage difference from an average of zero. Therefore from a bull with a 1.2 percent SCR, you would expect a 1.2 percent higher conception rate than a bull that is 0.0 percent. A bull with a -2.4 percent SCR would have an estimated 2.4 percent lower conception rate than a bull that is 0.0 percent.

To have an evaluation published, a Holstein bull needs to have a minimum of 300 services with at least 100 in the last year and also services in at least 10 herds. For breeds with fewer total services the requirements for publication are adjusted appropriately.

For more information, go to www.aipl.arsusda.gov.