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AIPL RESEARCH REPORT
SCR1 (7-08) |
Sire conception rate: New national AI
bull fertility evaluation H.D. Norman, J.L. Hutchison, and
J.R. Wright Animal Improvement Programs Laboratory, ARS-USDA,
Beltsville, MD 20705-2350 301-504-8334 (voice) ~ 301-504-8092 (fax) ~
inquiry@aipl.arsusda.gov ~
http://aipl.arsusda.gov |
Starting in August 2008, sire conception rate (SCR), a new and
more accurate evaluation of the fertility of artificial-insemination
(AI) service-sire fertility will be available to dairy
producers from USDA. From 1986 to November 2005, bull fertility evaluations
termed estimated relative conception rate (ERCR) were provided to the
dairy industry by Dairy Records Management
Systems (DRMS; Raleigh, NC). In May 2006, USDA's Animal Improvement
Programs Laboratory assumed responsibility for phenotypic evaluation of U.S.
bull fertility. As an initial step, ERCR evaluations were implemented without
change in calculating methods.
Over the next 4 years, an intense research effort primarily by Dr.
Melvin Kuhn was made to develop methods that would improve the accuracy of bull
fertility evaluations as well as broaden the scope of the data used for those
evaluations. Those studies can be roughly categorized into two approaches.
First, factors were identified that were related to the bull that provided the
unit of semen and that helped to improve the prediction of whether that unit of
semen resulted in a pregnancy. Second, factors were identified that were
related to the cow receiving the unit of semen and that distorted the fertility
measure for the bull providing the semen (nuisance variables); those nuisance
variables were removed to allow obtaining the best measure of the bull's
success in impregnating the cow.
Which factors associated with service sire
contribute to SCR? |
Which nuisance variables are removed to improve
SCR? |
- Inbreeding of the bull
- Inbreeding of the embryo from the mating
- Age of the bull
- AI organization combined with year of the mating
- Effect of the bull itself
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- Group effect of cow herd, year of mating, cow lactation
number, and cow registry status
- Month and year of mating combined with State in which mating
occurred
- Lactation number of the cow
- Service number
- Effect of having a short interval between matings
- Age of the cow
- Standardized milk yield of the cow
- Effect of the cow (both permanent environmental and genetic)
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Comparison of ERCR and
SCR
Category |
ERCR |
SCR |
Trait evaluated |
First service 70-day nonreturn rate |
Conception rate |
Breeds evaluated |
Holstein, Jersey |
Ayrshire, Brown Swiss, Guernsey, Holstein, Jersey,
Milking Shorthorn |
Lactation numbers included |
All lactation numbers with 6th and above set to
6th |
1st through 5th |
Service numbers included |
1st |
1st through 7th |
Bulls included |
AI, <12 years old |
AI (not inactive,) <13 years old |
Minimum number of matings |
≥300 first services |
≥300 services in the last 4 years and ≥100 in
the last year for Holsteins; somewhat fewer services for other breeds |
Minimum number of herds |
None |
10 for Holsteins and Jerseys, somewhat fewer for
other breeds |
Fertility expression |
Deviation from mean (nearest 1%) |
Deviation from mean (nearest 0.1%) |
Base assigned |
Published bulls sum to 0 |
Published bulls sum to 0 |
Dairy records processing centers participating |
AgSource
Cooperative Services, DRMS,
Minnesota Dairy Herd Improvement
Association |
AgriTech
Analytics, AgSource Cooperative
Services, DRMS |
Interpretation of
SCR
How SCR evaluations should be used remains largely unchanged from how
ERCR evaluations were used. Technically, 70-day nonreturn rate and conception
rate differ in that conception rate is based on confirmed pregnancy. However,
the two traits are highly related when derived from the same cows. A bull with
an SCR of 2.0% is expected to produce a conception rate of 32% in a herd that
normally averages 30% and historically has used average CR bulls. The term
“expected“ indicates what the results would be if based on
extremely large numbers of matings. Obviously, a herd with only two
inseminations to that bull could realize only a conception rate of 0, 50, or
100% for his matings.
Improved
accuracy
The addition of more inseminations for calculation of SCR is one of
the main reasons for the higher accuracy compared with ERCR. Not only are more
services (2nd through 7th) being used from the same herds, which approximately
tripled the data, but new large herds are now included, specifically from
AgriTech Analytics (Visalia, CA). In
addition to incorporating many desirable features of ERCR, SCR also includes a
number of new benefits that have been shown to improve accuracy of predicting
conception rate for an independent data set.
Additional resources
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