🔁 What Is the Estrous Cycle?

The canine estrous cycle—commonly referred to as "being in heat"—is a complex hormonal process that governs a female dog’s ability to reproduce. It includes four stages: proestrus, estrus, diestrus, and anestrus. Understanding these phases can help with breeding timing, spaying decisions, and spotting abnormal cycles. 🧬

📅 The Four Phases of Heat

1. Proestrus

• 🩸 Swollen vulva and bloody vaginal discharge
• 🐕 Male dogs are attracted, but the female won’t allow mating
• 📈 Estrogen rises as ovaries prepare for ovulation
• ⏳ Lasts ~10–14 days (but can range from a few days to several weeks)

2. Estrus

• 🟡 Vaginal discharge becomes straw-colored
• ❤️ Female is receptive to males
• 🔄 LH surge triggers ovulation
• ⏳ Lasts ~7 days (part of the “heat” period)
• 📉 Estrogen falls, progesterone rises

3. Diestrus

• 🧬 High progesterone, whether or not she is pregnant
• 🍼 Mammary development, appetite changes, and even milk production may occur
• 🤱 Can result in a false pregnancy in unbred dogs
• ⏳ Lasts ~60 days if pregnant, up to 75 days if not

4. Anestrus

• 😴 Resting phase between cycles
• 🩺 Low estrogen and progesterone
• 🛠️ Uterus recovers and preps for next cycle
• ⏳ Lasts 4 months on average (range: 2–10 months)

🗓️ When Does the First Heat Happen?

• 📏 At 2/3 adult size (usually 6–18 months of age)
• ⏳ Sighthounds (e.g., greyhounds, Afghan hounds) may start at >2 years old
• 🔁 Heat cycles repeat ~every 6 months (some breeds, like Basenjis, may cycle only once a year)

❌ No More Heat: Spaying

Spaying removes the ovaries (and usually the uterus), stopping all heat cycles permanently. Benefits include:

• 🚫 No pregnancy risk
• 🛡️ Prevention of pyometra (life-threatening uterine infection)
• 📉 Reduced risk of mammary cancer (especially if spayed before first or second heat)

Spaying can be performed via:

• OVH (ovariohysterectomy): Removes ovaries + uterus
• OVE (ovariectomy): Removes only the ovaries
• Hysterectomy: Removes only the uterus (not recommended if heat suppression is the goal)

👩‍⚕️ Breeding Considerations

If you intend to breed your dog:

• 📅 Track heat phases to optimize timing
• 📈 Ovulation typically occurs ~48 hours after the LH surge
• 🧪 Progesterone tests may help pinpoint ovulation
• 🐶 Ensure pre-breeding health tests are completed

🧠 Breed clubs can offer valuable guidance about best practices and health screening.

📋 Quick Estrous Cycle Summary Table

🔧 Ask A Vet Can Help

Need help tracking your dog’s cycle or deciding the best age to spay? Use the Ask A Vet app for expert guidance on heat behavior, breeding timing, and reproductive planning. 🐕📱

🐾 Final Thoughts from Dr Duncan Houston

The heat cycle is completely natural—but it can also be confusing and sometimes frustrating. Whether your goal is to breed or prevent pregnancy, knowing the stages of the estrous cycle will help you make informed, health-focused decisions. 💙