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AgridianDairy KB

Services per conception

Definition

Section titled “Definition”

Services per conception (SPC) is the average number of inseminations it takes to produce one pregnancy. It is the inverse of conception rate: a 40% CR means 2.5 services per conception.

Like CR, it is a per-service measure and uses only services with a known outcome (resolved services). A service is resolved when it is:

  • pregnant: the next result is a confirmed pregnancy (PREG);
  • open: the next result is an OPEN check, or the cow was bred again before any pregnancy check (the re-breeding implies she was open).

Services still waiting for a check are pending and left out. So are “other” outcomes: the cow left the herd before a check, or a pregnancy loss was recorded with no confirmed pregnancy.

A re-breeding (result code R, rebred) is not a conception. It marks the previous service as open. See bred result codes.

Services per pregnant cow

Section titled “Services per pregnant cow”

A different number sometimes reported under the same name is services per pregnant cow: total services to cows that became pregnant ÷ those cows. It ignores every service to cows that never got pregnant (culled open), so it is always lower and flatters the herd. Prefer SPC from resolved services.

Formula

Section titled “Formula”

Plain text:

SPC = (pregnant services + open services) / pregnant services
    = 100 / CR (%)

LaTeX:

\mathrm{SPC} = \frac{N_{\text{preg}} + N_{\text{open}}}{N_{\text{preg}}} = \frac{100}{\mathrm{CR}\,(\%)}

Pending and “other” services are in neither count.

How to pull it in DC305

Section titled “How to pull it in DC305”

BREDSUM shows SPC beside %CONC on each row and on the total line:

BREDSUM FOR LACT>0        cows
BREDSUM\Y                 heifers (youngstock switch)
BREDSUM\B FOR LACT>0      by service number (times bred)
BREDSUM\YB                heifers, by service number

To rebuild it from exported BRED events, give each service an outcome from the next relevant event for the same cow and lactation:

  1. next event is PREG for this service → pregnant;
  2. next event is OPEN, or the next event is another BRED → open;
  3. neither yet, cow still in the herd → pending (exclude);
  4. cow left the herd, or the outcome can’t be known → other (exclude).

Typical range

Section titled “Typical range”

Herd context: US Holsteins, freestall or dry-lot housing, mix of timed AI and detected heats, first pregnancy check at about 28–40 days after breeding.

Group Typical SPC Corresponding CR
Lactating cows, all services 2.5–3.3 30–40%
Lactating cows, good herds < 2.5 > 40%
Nulliparous heifers 1.7–2.0 50–60%
  • Heat stress pushes summer SPC for lactating cows to about 4–6 or more in Southwest herds without strong cooling.

Common mistakes

Section titled “Common mistakes”
  • Counting R (rebred) as a conception. A re-breeding means the earlier service failed.
  • Counting pending services as open, which inflates SPC for recent months.
  • Reporting services per pregnant cow as if it were SPC. It leaves out cows culled open.
  • Averaging SPC across rows instead of pooling: total resolved services ÷ total pregnancies.
  • Mixing heifers and cows.
  • Small samples. SPC is a ratio of counts; a sire or technician row with 15 services has a very wide interval. Compare CR with a confidence interval (e.g. a Wilson score interval), and suppress or flag rows with fewer than about 10 resolved services.
  • Using SPC as the reproduction KPI. It says nothing about how quickly eligible cows get bred; use pregnancy rate.
Section titled “Related”