When Do Dogs Get Their First Period?

Dogs experience a reproductive cycle that includes bleeding, but the process and purpose differ from human menstruation.

What “First Period” Means

The term “first period” in dogs usually refers to the first estrous cycle, commonly called “heat” or “in heat,” and it is not equivalent to human menstrual bleeding.^[1]

Canine bleeding is generally associated with the proestrus stage of the cycle, which commonly lasts about 7–10 days before the female becomes receptive to males during estrus.^[1]

Key terminology used throughout: “proestrus” (the pre-receptive bleeding phase), “estrus” (the receptive phase when ovulation occurs), “diestrus” (the period after estrus when progesterone is high), and “anestrus” (the non-reproductive interval). These terms are based on canine reproductive physiology described in veterinary references.^[1]

Typical Age Range and Breed/Size Factors

Small and toy breeds commonly have their first heat earlier, often around 6–9 months of age, whereas many large and giant breeds typically have their first heat later, frequently between 12–24 months of age.^[2]

Medium breeds often fall between those ranges, with many showing first estrus around 6–12 months of age depending on genetics and nutrition.^[2]

Genetics drive much of the variance: breeds selected for small size usually mature faster, while giant-breed skeletal and reproductive maturity can lag by a year or more compared with toy breeds.^[2]

Typical age of first heat by general breed size

Breed size	Common age at first heat	Example breeds	Notes
Toy	6–9 months	Chihuahua, Maltese	Often earlier maturity
Small	6–9 months	Beagle, Cocker Spaniel	Varies with weight
Medium	6–12 months	Bulldog, Border Collie	Commonly within first year
Large/Giant	12–24 months	German Shepherd, Great Dane	Delayed skeletal maturity

Signs and Stages of the Heat Cycle

Proestrus generally lasts about 7–10 days and is marked by bloody vaginal discharge, swelling of the vulva, increased urination, and attention from males without acceptance of mounting.^[1]

Estrus commonly lasts about 5–9 days and is the time when the female will stand to be mated; discharge may become lighter and more straw-colored during this stage.^[1]

Diestrus follows estrus and typically lasts about 60–90 days whether or not the dog becomes pregnant; progesterone is high during this period, and false pregnancy (pseudopregnancy) signs can occur.^[1]

• Vaginal bleeding or spotting, most noticeable in proestrus
• Swelling of the vulva and increased licking
• Behavioral changes such as clinginess, restlessness, or changes in appetite

Many owners track heat by marking the first day of noticeable bleeding as “day 1” and using a calendar or heat-tracking app to anticipate receptivity windows and future cycles; this practical approach helps estimate likely estrus and diestrus periods for planning veterinary care or preventing pregnancy.^[2]

Duration and Frequency of Cycles

A single heat episode (from the start of proestrus through the end of estrus) commonly lasts about 2–3 weeks in total for most dogs.^[1]

On average, many domestic dogs cycle about twice per year, or every 4–8 months, though some small breeds cycle every 4–6 months and some large breeds cycle once every 12 months or longer.^[2]

Seasonal patterns are less strict in many companion dogs than in wild canids; however, irregular cycles and variability in intervals can occur because of health, nutrition, or genetic factors.^[2]

First Heat vs Later Heats

The first heat is often less predictable: the behavioral signs can be inconsistent and the duration of proestrus and estrus may deviate from later patterns before stabilizing after a few cycles.^[1]

Owners may notice that subsequent heats become more regular after the dog completes two or three cycles and that bleeding and behavioral signs often become easier to interpret over time.^[1]

Some health implications are more relevant at first heat, such as higher owner concern about accidental mating and the need for early veterinary guidance if abnormalities appear; veterinary assessment is prudent when unusual bleeding patterns or prolonged discharge occur.^[2]

Health Risks, Abnormal Bleeding & When to See a Vet

Continuous or very heavy bleeding, foul-smelling discharge, fever, lethargy, or severe loss of appetite during or after a heat cycle are reasons to seek veterinary attention as these signs can indicate infection or other problems.^[2]

Pyometra, an infection of the uterus that can be life-threatening, most commonly develops during diestrus and may present with vaginal discharge, abdominal pain, and systemic illness; it typically requires urgent veterinary care and often surgical intervention.^[4]

Persistent post-estrual bleeding lasting more than 2 weeks or recurrence of bleeding outside of expected interestrus intervals warrants a veterinary exam including a physical exam and possibly bloodwork and imaging to rule out underlying disease.^[2]

Practical Care During Heat

Hygiene measures can include using washable dog diapers or pads to protect furniture and flooring; diapers do not prevent mating and should not be relied on as a sole contraceptive barrier.^[5]

Limit unsupervised outdoor time and avoid dog parks during receptivity to reduce the chance of unwanted mating; secure fencing and attentive supervision are important because males can jump or dig to reach a receptive female.

Shorter, controlled walks on leash and avoiding high-traffic dog areas can reduce stress—most dogs tolerate reduced off-leash time for the 2–3 weeks of a heat episode without harm to fitness when exercise is kept consistent and safe.^[5]

Preventing Pregnancy and Breeding Considerations

To prevent pregnancy, the most reliable methods are strict supervision, physical barriers such as securely fenced yards and closed doors, and preventing contact with intact males during the fertile window generally centered on estrus.^[2]

Owner-level measures like diapers or indoor separation reduce accidental mating risk but do not guarantee prevention because males can sometimes mate through garments or while contact is brief.

If breeding is intended, breeding on a female’s first heat is often discouraged by many breeders and veterinarians because reproductive maturity, pelvic development, and overall health may not be optimal; genetic and health screening is recommended prior to breeding and timing should be guided by veterinary reproductive advice.^[3]

Managing Male Dogs and Household Dynamics

When an intact male lives in the same household, separation into different rooms with closed doors and supervised, staggered access to common areas reduces mating opportunities and helps prevent stress-related behaviors; scent can trigger males, so laundering bedding and isolating the female’s area is useful.

Training and temporary management plans—including short-term confinement in a secure crate or room during the most fertile days—are commonly used strategies to prevent accidental mating and reduce tension among dogs in the home.^[5]

If using boarding, dog-walking, or daycare services while a female is in heat, disclose her status in advance and confirm the facility’s policies; many reputable kennels will refuse or separate females in heat to protect them and other dogs.

Spay/Neuter: Timing, Benefits, and Risks

Spaying before the first heat can substantially reduce the lifetime risk of mammary tumors compared with spaying after one or more heats, according to veterinary surgical and oncology guidance; many recommendations emphasize discussing timing with your veterinarian because risks and benefits can vary by breed and individual health factors.^[3]

For giant and some large-breed dogs, many clinicians recommend delaying elective gonadectomy until growth plates have closed—often after 12–18 months of age—to reduce certain orthopedic risks associated with early removal of sex hormones.^[4]

Surgical risks are generally low for healthy young dogs, but specific perioperative recommendations, anesthetic protocols, and post-operative care should be reviewed with a veterinarian; see-and-discuss timing relative to first heat, breed, and planned activities or breeding goals is standard practice.^[4]

Sources

• merckvetmanual.com — authoritative veterinary manual on canine reproduction.
• vcahospitals.com — veterinary clinic resources on heat cycles, ages, and signs.
• aaha.org — American Animal Hospital Association guidance on spay/neuter timing and benefits.
• avma.org — American Veterinary Medical Association resources on surgical timing, risks, and conditions like pyometra.
• wsava.org — World Small Animal Veterinary Association guidance on practical care and kennel policies.