Embryo transfer and OPU KPIs

Definition

Embryo transfer (ET) programs have two halves, each with its own KPIs.

Recipient side: ET conception

ET conception rate (pregnancies per embryo transferred, P/ET) is the share of embryo transfers with a known outcome that result in a confirmed pregnancy in the recipient. It is the ET equivalent of conception rate, with one transfer in place of one insemination.

It depends heavily on the embryo, so it must be split by:

Embryo source: in vivo (flushed from a superovulated donor) vs in vitro produced (IVP/IVF) (oocytes collected by OPU, matured, fertilized and cultured in a lab).
Fresh vs frozen: transferred the day it is produced or flushed, or frozen (slow-frozen or vitrified) and thawed at transfer. Frozen embryos usually give a lower P/ET, especially IVF embryos.
Embryo stage and grade (e.g. IETS stage 4–7, grade 1–3).
Recipient type: heifer vs lactating cow, and how well her estrous stage matches the embryo’s age (synchrony, usually within ±1 day).

Pregnancy loss after a positive check is higher with ET (especially IVF) than with AI, so report P/ET at the first check and again at a later check.

Donor / lab side: OPU-IVF yield

Ovum pick-up (OPU) is transvaginal ultrasound-guided aspiration of follicles from a donor’s ovaries. Each OPU session produces oocytes (cumulus-oocyte complexes, COCs). The lab grades them, matures and fertilizes the viable ones, and cultures them to the blastocyst stage (day 7). The yield KPIs are:

Oocytes per OPU: total COCs recovered per session (sometimes also viable or cultured oocytes per OPU, after grading).
Embryos per OPU: transferable blastocysts (or embryos frozen) per session.
Embryos per oocyte (blastocyst rate): transferable embryos ÷ oocytes cultured. It measures lab and oocyte quality.
Recovery rate: oocytes recovered ÷ follicles aspirated, if follicle counts are recorded.

Embryos per OPU = oocytes per OPU × embryos per oocyte, so a low embryo yield can be a donor problem (few oocytes) or a lab problem (low blastocyst rate).

Formula

Plain text:

P/ET (%) = pregnant recipients / (pregnant + open recipients) × 100        (transfers with a known outcome)

Oocytes per OPU    = total oocytes recovered / OPU sessions
Embryos per OPU    = transferable embryos produced / OPU sessions
Embryos per oocyte = transferable embryos produced / oocytes cultured × 100
Recovery rate      = oocytes recovered / follicles aspirated × 100

Embryos per OPU = oocytes per OPU × (embryos per oocyte / 100)    when "oocytes" means the same thing in both

LaTeX:

\mathrm{P/ET} = \frac{N_{\text{preg}}}{N_{\text{preg}} + N_{\text{open}}} \times 100
\qquad
\frac{\text{embryos}}{\text{OPU}} = \frac{\text{oocytes}}{\text{OPU}} \times \frac{\text{embryos}}{\text{oocyte}}

Use the same oocyte count (all recovered, or only cultured) in “oocytes per OPU” and “embryos per oocyte”, or the identity above does not hold. Pool across sessions (total embryos ÷ total sessions); don’t average the per-session ratios.

How to pull it in DC305

Recipient P/ET. In DC305, an embryo transfer is usually recorded as a BRED event on the recipient with a breeding-type code (often separate codes for fresh and frozen embryos) and the embryo’s sire or donor in the sire field. Pregnancy checks then give the outcome, so BREDSUM by breeding code reports P/ET on the row for each ET code.

BREDSUM\YO                   heifer recipients, by breeding code (ET codes get their own rows)
BREDSUM\O FOR LACT>0         cow recipients, by breeding code
BREDSUM\XOT FOR LACT>0       cross table: breeding code × technician
BREDSUM\YS                   heifer services by service sire (embryo sire or donor code)

Keep ET transfers out of AI conception and sire conception reports, or they distort both.

OPU and IVF yield. These are usually not in DC305. They come from the IVF lab’s or ET company’s records per donor and session: date, oocytes recovered, oocytes cultured, embryos produced, embryos transferred fresh or frozen. Join those to DC305 recipient outcomes by embryo ID or recipient ID and transfer date.

Typical range

Herd context: US Holsteins; recipients are mostly nulliparous heifers in freestall, dry-lot or heifer-grower housing; embryos from commercial in vivo or OPU-IVF programs; first check at about 28–40 days of gestation.

Measure	Typical
P/ET, in vivo, fresh	55–65%
P/ET, in vivo, frozen	45–60%
P/ET, IVF, fresh	40–50%
P/ET, IVF, frozen / vitrified	30–45%
Oocytes per OPU (Holstein)	8–20
Embryos per oocyte (blastocyst rate)	20–35%
Embryos per OPU (Holstein)	2–5

Lactating-cow recipients usually have a lower P/ET than heifers.
Heat stress: ET is sometimes used in summer because the embryo bypasses the early stages most damaged by heat. Recipients still need to be cooled.

Donor variation: oocytes per OPU vary several-fold between donors and are fairly repeatable within a donor, so report by donor.

Common mistakes

Pooling fresh and frozen, or in vivo and IVF into one P/ET. They differ by 10–20 points.
Counting ET as AI. If ET transfers sit in the same BRED stream without filtering, they distort CR and sire reports.
Only reporting the first check. ET pregnancies, especially IVF, have more late embryonic and early fetal loss. Report P/ET at a later check too.
Mixing “oocytes recovered” and “oocytes cultured” between the per-OPU and per-oocyte KPIs.
Averaging per-session ratios instead of pooling totals.
Ignoring recipient synchrony. A low P/ET can be a recipient problem (poor synchrony or a small corpus luteum), not an embryo problem. Track it by technician and by recipient group.
Small samples. A donor with 2 OPU sessions or a lab batch with 20 transfers has a wide confidence interval; see the table on sire conception rate.