The 4 Stages of a Dog's Heat Cycle: What Breeders Need to Know

The canine estrous (heat) cycle has four distinct stages — proestrus, estrus, diestrus, and anestrus — each with different hormonal profiles, behavioral signs, and implications for breeding.

Overview

The entire cycle averages 6-7 months: Small breeds often cycle every 4-5 months; large and giant breeds every 8-12 months.

1. Proestrus — 7-10 days (range: 3-17 days)
2. Estrus — 5-9 days (range: 3-21 days)
3. Diestrus — 60-90 days
4. Anestrus — 4-5 months

Stage 1: Proestrus

Hormonally: Estrogen rises. Ovarian follicles developing. Preparing for ovulation.

Physical signs: Swelling of vulva, bloody vaginal discharge, increased urination. Males attracted to the female.

Behavioral signs: Females attract males but will NOT allow mating — they sit, snap, or move away.

Duration: 7-10 days average.

For breeding: Do NOT breed during proestrus. The bloody discharge frequently causes confusion — many people think the female is ready when they first see blood, but the fertile window comes days later.

Stage 2: Estrus — The Fertile Window

Hormonally: Estrogen drops as the LH surge occurs. Ovulation follows 2 days after the LH surge. After ovulation, eggs take 2-3 more days to mature. The fertile window spans approximately days 2-6 after the LH surge.

Physical signs: Discharge lightens from red to straw-colored or clear. Vulva remains swollen.

Behavioral signs: Female ACCEPTS the male — stands still, deflects tail (flagging), actively solicits the male.

Duration: 5-9 days average, but the fertile window within estrus is 4-6 days.

Progesterone testing approach:

• LH surge: progesterone approximately 1-2 ng/mL
• Ovulation: progesterone approximately 5 ng/mL
• Optimal breeding: progesterone 10-25 ng/mL

Stage 3: Diestrus

Hormonally: Progesterone remains elevated 60-90 days. This is identical whether pregnant or not.

Physical signs: Discharge stops, vulva swelling resolves, female no longer accepts males.

Some females undergo false pregnancy (pseudopregnancy) during diestrus — nesting, mammary development — even without true pregnancy.

For pregnant females: Whelping occurs at the end of diestrus, approximately 63 days after ovulation.

Stage 4: Anestrus — The Resting Phase

Duration: 4-5 months average. Low estrogen, low progesterone. The reproductive system is resting.

Why Day-Counting Fails

A common mistake is timing by day from first bleeding. The problem: Proestrus length varies enormously — 3 to 17+ days. Breeding on day 11-13 works by accident in average females and fails consistently with short or long proestrus.

Progesterone testing eliminates this variability. Test progesterone to find the fertile window, not the calendar.

The Silent Heat

Some females cycle with minimal visible signs — little or no bloody discharge, minimal vulvar swelling. A progesterone test or relaxin pregnancy test confirms what happened.

Summary

Proestrus (bloody discharge, 7-10 days) is not the fertile window. Estrus (stands for mating, 5-9 days) is the fertile window — use progesterone testing, not day-counting. Diestrus (60-90 days) follows whether pregnant or not. Anestrus (4-5 months) is the resting phase. Understanding these stages — especially proestrus length variability — is the foundation of breeding at the right time.