How to Tell if Your Dog Is in Heat: Signs and Next Steps

Vulvar swelling, a bloody discharge, and increased interest from male dogs can indicate that an intact female dog is entering her heat cycle. These signs do not tell you exactly when she ovulates or establish that breeding is appropriate.

Understand the four cycle stages

The Merck Veterinary Manual’s reproduction guide explains that timing varies between dogs. A fixed calendar based only on breed size should not be treated as a reliable prediction.

What should you record?

Record when you first notice swelling or discharge, changes in behavior, and previous cycle dates. Share those observations with your veterinarian. If breeding is planned, contact the clinic early enough to arrange the assessment and testing schedule.

Do visible signs confirm breeding readiness?

No. Merck describes physical examination, hormone testing, and vaginal cytology as tools for assessing timing. For progesterone testing, Merck’s clinical investigation guidance emphasizes trends rather than interpreting one result in isolation. The clinic should interpret findings using its test method and the dog’s history.

If you do not want a pregnancy

Prevent access to intact male dogs and contact your veterinarian about reproductive care. Supervise outings and make a separation plan for dogs in the same household. Do not use a diaper or a change in discharge as proof that pregnancy cannot occur.

When to call a veterinarian

Ask for veterinary advice if the discharge or timing seems unusual, or the dog seems unwell. Marked weakness, collapse, severe pain, or breathing distress requires urgent care. Do not assume every discharge in an intact female is a normal heat cycle.

For breeders planning an appointment

Read our stud-selection checklist and TCI appointment guide. Review breeding supplies after confirming the clinic’s requirements. Products marketed for fertility do not establish the stage of a cycle or replace testing.

Common questions

Does the first day of bleeding tell me the insemination date?

No. Observations help establish a history; a veterinarian should assess the timing.

Does a first heat mean the dog should be bred?

No. Breeding suitability also requires assessment of health, maturity, and the care plan.