EndocrinologyHigh evidence 9 min readLast reviewed: 2025-05-14

Progesterone timing for optimal breeding

How serum progesterone maps to the LH surge, ovulation, and the fertile window in the bitch.

Summary

Serial serum progesterone is a practical indirect marker for estimating periovulatory events in the bitch. Its interpretation is central to timing natural mating and insemination, but absolute concentrations must be read in the context of the assay and the individual progesterone curve.

Key evidence

Large prospective data place the mean progesterone concentration near estimated LH0 around 2–3 ng/mL, with individual and assay-related variation.
Ovulation generally follows the LH surge by about 2–3 days; reported periovulatory progesterone concentrations overlap and should not be treated as universal cutoffs.
Canine oocytes require an additional 48–72 hours to complete meiosis and become fertilizable.
Frozen-thawed semen has a shorter functional lifespan than fresh semen, so insemination timing requires a tighter estimate of the post-ovulatory, oocyte-maturation window rather than a universal day or progesterone threshold.

Physiological background

Unlike most mammals, the bitch ovulates primary oocytes that must mature in the oviduct before fertilization is possible. This unique biology is the reason progesterone — secreted by luteinizing follicles even before ovulation — is such a useful surrogate marker for the reproductive events that matter clinically.

Interpreting the curve

Progesterone begins to rise before ovulation. Population studies report concentrations around 2–3 ng/mL near estimated LH0 and higher values over the following periovulatory days, but the exact relationship varies between individuals and assays. As concentrations rise, an isolated absolute value becomes less reliable for assigning the optimal insemination day, so the serial curve and physiological sequence remain essential.

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Practical implications

Timing decisions should be made by a licensed veterinarian based on serial quantitative progesterone, vaginal cytology, and — where appropriate — ultrasonography. Single measurements are rarely sufficient.

References

Concannon PW. Reproductive cycles of the domestic bitch. Anim Reprod Sci. 2011.
Kutzler MA. Estrus induction and synchronization in canids and felids. Theriogenology. 2007.
Root Kustritz MV. Clinical canine and feline reproduction: evidence-based answers. Wiley-Blackwell.
Hollinshead FK, Hanlon DW. Normal progesterone profiles during estrus in the bitch: a prospective analysis of 1420 estrous cycles. Theriogenology. 2019;125:37-42. doi:10.1016/j.theriogenology.2018.10.018.
Joonè CJ. Evidence-based practice in canine artificial insemination. Aust Vet J. 2024;102(8):377-384. doi:10.1111/avj.13336.