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When to spay? The right time in a dog's cycle

Updated: October 2026 · Reference values from the MSD Veterinary Manual, Cornell Riney Canine Health Center and dvm360

Whether a female dog should be spayed is a decision with many sides, and it belongs in a conversation with your vet. When in the cycle to spay, on the other hand, is clear, and this is where many people make an avoidable mistake: they book the operation without knowing which stage the dog is in.

The right time: anestrus

Spaying belongs in anestrus, the hormonal resting phase. That is at the earliest two to three months after the end of the heat and ends a few weeks before the next one. The reasons:

• During the heat the uterus is heavily supplied with blood and enlarged. The risk of bleeding during surgery is higher.
• In diestrus, the roughly two months after the heat, progesterone is high. If you spay now it drops abruptly, prolactin rises, and the dog can slip into a false pregnancy that, without ovaries, no longer ends on its own. Such false pregnancies can last for months.
• During a false pregnancy the same applies: don't operate, wait until it has subsided, if necessary with the help of a prolactin inhibitor.

With an interval of six months between two heats, the good window is therefore roughly in the third to fifth month after the last heat. Lunella calculates this window from the recorded heats and shows it in the calendar.

Before or after the first heat?

There is no single right answer for all dogs, only trade-offs:

In favour of early spaying (before or after the first heat):

• The risk of mammary tumours rises with every heat. In the classic study, dogs spayed before the first heat had only 0.5 percent of the risk of intact females, 8 percent after the first heat, 26 percent after two or more. Spayed after about two and a half years of age, no protective effect could be shown. More recent reviews rate the evidence as weak, but pointing in the same direction.
• Uterine infection (pyometra) and false pregnancy are ruled out.
• No heat with all its restrictions, no unwanted mating.

In favour of waiting:

• Sex hormones control growth. In large breeds spayed before growth is complete, the growth plates close later. This can lead to longer limbs and more joint problems, such as cruciate ligament ruptures and hip dysplasia. For many large breeds it is therefore recommended to wait at least for the first heat, for some also the second.
• Urinary incontinence is more common in spayed females, especially in large breeds and after very early spaying.
• Coat changes, weight gain and, in individual breeds, a higher risk of certain tumours are under discussion.
• Personality matures under the influence of the hormones. An insecure young dog can stay insecure after spaying.

For small breeds the balance often comes out differently than for large ones. Ask your practice what is known for your breed and your dog.

Alternatives and wrong turns

• Hormonal heat suppression with progestogen injections (progesterone-like hormones) clearly raises the risk of pyometra and mammary tumours and is no longer recommended for healthy dogs.
• The hormone implant (GnRH implant) common in males is not licensed for females and often triggers a heat first. Only in exceptional cases and after veterinary advice.
• Removing only the ovaries (ovariectomy) instead of ovaries and uterus (ovariohysterectomy): both prevent heat and pyometra equally, because without ovaries no more progesterone is produced. The smaller operation is now common practice in Europe when the uterus is healthy.

How Lunella helps

Record the heats and Lunella shows you when anestrus begins and how long the favourable window for spaying lasts. The app also warns if signs of a false pregnancy are recorded in this period. You can take the report with all data to the consultation.

This article does not replace veterinary advice. If your dog shows signs of illness, see your vet.