Dairy Pipeline: December 2005/January 2006
Extension Dairy Scientist,
Genetics and Management
(540) 231-4762 email: firstname.lastname@example.org
There are two kinds of statistical evaluations of fertility available to dairy farmers. One of these, daughter pregnancy rate or DPR is a genetic evaluation. It measures the expected genetic difference between daughters of bulls in the likelihood of a pregnancy to any given insemination. A bull with a DPR of +2 is expected to produce average daughters with a 2-point higher pregnancy rate than the average daughter of a bull with a DPR of 0. DPR is a selection tool that should be used to improve the genetic merit of future generations for fertility.
The second statistical measure of fertility, Estimated Relative Conception Rate or ERCR, measures the likelihood (relative to other bulls) of a cow not returning to heat within 70 days following insemination with semen from the bull for which the ERCR was calculated. Thus, a bull with an ERCR of +2 has a 2 percentage point higher expectation of producing a pregnancy than a bull with an ERCR of 0. ERCR's are published by DRMS Raleigh in May and November of each year.
The latest ERCR's are available on the DRMS web site (http://www.drms.org/) or on the sire summaries available on VT Dairy (http://www.vtdairy.dasc.vt.edu/) as well as on other sire lists. The table below will help interpret ERCR's in Holsteins and Jerseys.
Distribution of November 2005 ERCR's on Holstein and Jersey bulls.
|Number of active AI bulls|
|3 or higher||33||9|
|1 or 2||114||14|
|-1 or -2||76||8|
|-3 or lower||17||7|
Bulls with ERCR ratings of plus or minus 3 are outliers. There aren't very many of them. Bulls in the +1 or +2 category are more widely available. I classify ERCR ratings of +1 as "fertile" and +2 or more as "highly fertile". There are lots of opportunities to use bulls with lower ERCR ratings in well run breeding programs, though "informed use" is an important concept.
ERCR's should be one consideration when buying semen, along with price, genetic merit, and other factors. Remember that cows and heifers must be healthy, in heat, and bred with properly handled semen correctly placed in the reproductive tract at the right time for conception to occur.