Ovulation in a queen arrives roughly 25 to 27 hours after an hCG injection, which gives a single insemination dose a window of about one day. Miss it and the cycle is gone. The numbers are unforgiving: with fresh semen deposited in the vagina, 20 million sperm produced a 6.6% conception rate in one controlled study, 40 million produced 33.3%, and 80 million produced 77.8%. Dose and timing are not details here; they are the whole procedure.
Why a queen needs a chemical trigger at all
Cats are induced ovulators. A queen in heat does not release eggs on a schedule the way a dog does — the vagina and cervix have to be stimulated, normally by three or four intromissions spread over 24 to 48 hours, before the pituitary releases enough luteinising hormone to rupture the follicles. Natural mating therefore involves repeated matings, not one. Artificial insemination has to replace that stimulus, which is why every feline AI protocol begins with an injection rather than with a catheter.
The clock starts at the injection, not at the first signs of heat
Follicles ovulate about 25 to 27 hours after hCG. Two protocols dominate clinical practice. The simpler one gives 100 to 250 IU of hCG intramuscularly on day 2 or 3 of oestrus, judged from behaviour and vaginal cytology rather than from the calendar. The heavier one gives 100 to 150 IU of equine chorionic gonadotropin, then 75 to 100 IU of hCG 80 to 90 hours later; it yields more follicles, but also more superovulation, follicular cysts and premature luteinisation. A 4.7 mg deslorelin implant is a third route: in 13 queens it produced oestrus within 5.0 ± 2.2 days, with 4.8 ± 1.6 follicles each, a response closer to a normal cycle than gonadotropin stimulation.
Where the semen lands changes the dose by a factor of ten
The vagina is a hostile waiting room for sperm; the uterus is not. Published minimum doses for an acceptable conception rate differ by roughly an order of magnitude depending on deposition site, and by roughly fivefold depending on whether the sample was frozen.
| Semen | Site | Minimum dose | Conception rate reported |
|---|---|---|---|
| Fresh | Intravaginal | 80 million | 77.8% |
| Fresh | Intrauterine | 8 million | 80% |
| Frozen-thawed | Intrauterine | 50 million | 57.1% |
| Frozen-thawed | Intravaginal | 39 million motile | 0% |
Transcervical catheterisation can beat those figures when the catheter actually passes the cervix: 10 million fresh or 30 million frozen-thawed motile sperm gave a 100% conception rate in the queens where cannulation succeeded. Endoscopic catheterisation reached the uterus in 12 of 14 queens, so the limiting factor is often the anatomy and the operator, not the sperm count.
Fresh, chilled and frozen run on three different clocks
Fresh semen is the most forgiving. Published protocols inseminate at 15, 20 or 30 hours after hCG with no significant difference in outcome, so a four-hour delay is survivable. Chilled semen is extended, cooled to 4 to 5 °C and shipped; it stays usable overnight and for about 24 hours, with quality declining from there. Frozen-thawed sperm has the shortest life and the least tolerance for error: it is thawed at 35 to 37 °C, kept at body temperature for no more than a few minutes, and deposited 28 to 30 hours after hCG, inside the uterus. The same frozen sample placed in the vagina produced zero pregnancies in two separate studies.
The transport leg is where cooled samples die
A chilled shipment is a 4 to 5 °C problem, not a cold-chain ritual. The sample goes into an insulated box with a temperature logger, never in direct contact with a frozen gel pack, and never into a fridge freezer compartment that cycles below zero. Epididymal sperm stored at 4 °C for 24 hours showed no significant loss of post-thaw motility, but storage for 48 hours reduced it significantly — a useful proxy for how much slack a transported ejaculate really has. A courier delay of one day is recoverable; a sample that partially freezes on the way is not.
Two doses, 24 to 48 hours apart, buy margin
Because ovulation timing in a naturally cycling queen is inferred rather than measured, most clinicians inseminate twice. The usual interval is 24 to 48 hours, and the second dose matters most when cervical patency is short: insemination on day 2 of oestrus, with a repeat two days later, is the recommendation that came out of the Chatdarong work on cervical patency, oestrus behaviour and serum oestradiol. With frozen semen, the second dose is not optional padding — it is the cheapest insurance against a follicle that ruptured late.
Proving the timing worked
Ovulation can be confirmed indirectly with a serum progesterone above 2 to 3 ng/ml measured 5 to 6 days after hCG. Pregnancy then follows the standard feline calendar: ultrasound from day 21, X-ray for a fetal count at day 55, and 63 to 65 days from ovulation to birth. A queen that ovulated but did not conceive will still show a progesterone rise and a false pregnancy, which is exactly why the day-21 scan is the checkpoint that matters rather than the behaviour of the queen.
The failures that are really timing failures
- Inseminating after ovulation. Conception rates were significantly higher when sperm went in before ovulation than after it, in the same study that defined the 8 million intrauterine dose.
- Putting frozen semen in the vagina. Zero pregnancies in 12 queens, twice, in two laboratories.
- Using a dose sized for intrauterine delivery in a vaginal insemination — a tenth of the sperm is a tenth of the result.
- Urine contamination during collection, which is common with electroejaculation and lethal to a small sample.
- Treating a queen with gonadotropins in dioestrus, where no follicle will respond.
What this means if you are the one paying for it
Feline AI is a referral procedure, not a cattery shortcut. It requires an anaesthetic or heavy sedation for the queen, a trained operator for collection, a laboratory that can assess motility within minutes of collection, and a liquid nitrogen chain if frozen semen is involved. When natural mating is possible, it remains the better option — multiple matings provide both the ovulation stimulus and a larger sperm dose than any single AI. AI earns its place when a tom is geographically distant, when a mating injury or behavioural incompatibility blocks natural service, or when a valuable tom dies and epididymal sperm is recovered within hours. Screening both cats first, with genetic and infectious disease tests plus a blood type check, costs less than a wasted cycle.
Disclaimer: This article summarises published veterinary protocols for information only and is not a substitute for veterinary diagnosis or a treatment plan. Doses, drug choices and insemination timing must be set by a licensed veterinarian who has examined the queen and the tom; giving gonadotropins or performing insemination without that supervision risks ovarian cysts, infection and loss of the breeding cycle.
Frequently asked
How many hours after the hCG injection should a cat be inseminated?
Ovulation occurs about 25 to 27 hours after hCG. Fresh semen protocols inseminate at 15, 20 or 30 hours with no significant difference in conception rate, so most clinicians aim for roughly 20 to 30 hours and repeat the dose 24 to 48 hours later. Frozen-thawed semen is tighter still: it is usually deposited 28 to 30 hours after hCG, and only into the uterus.
Can frozen cat semen be inseminated into the vagina?
No. Two independent studies reported zero pregnancies from intravaginal insemination of frozen-thawed cat semen (0 of 12 and 0 of 8 queens), while intrauterine deposition of the same samples produced 41.7% to 75% conception. Frozen sperm survive too briefly outside the uterus, so the deposit has to be transcervical or surgical.
How much does the sperm dose have to change if I use the vagina instead of the uterus?
Roughly tenfold. About 8 million fresh sperm into a uterine horn gives an 80% conception rate, whereas intravaginal insemination needs around 80 million for 77.8%. For frozen-thawed semen the intrauterine minimum is about 50 million, five times the fresh intrauterine dose.