How Sperm Travels Inside the Bitch: What Breeders Should Know About Fertilisation

How Sperm Reaches the Eggs in Dogs

A simple guide for breeders on how sperm travels inside the bitch and how fertilisation actually happens.

Learn what happens after semen enters the bitch; how sperm moves, survives, reaches the eggs and finally, fertilizes them. This guide walks you through the actual journey sperm takes inside the reproductive tract, how long it survives and what affects its chances of reaching the eggs.

The Journey Begins: Deposition of Semen

During a natural tie or an insemination procedure, semen is usually deposited near the cervix. This placement gives sperm the best chance of survival because it bypasses much of the vaginal environment, which can be acidic and harsh.

Fresh semen has the highest mobility. Chilled or frozen-thawed semen needs a little extra support because it has a shorter life span and is usually inseminated either surgically or through transcervical insemination (TCI). Fresh semen can be collected from the dog and then manually inserted into the bitch using our Semen Collection & Insemination equipment.

The Cervix: The First Major Challenge

The cervix acts as a gatekeeper. It remains mostly closed except during heat and shortly after mating. When a tie occurs, muscular contractions help draw semen through the cervix and into the uterus.

Causes of Impeded Semen Passage 

• Poor semen quality: The sperm may be unable to effectively pass through the cervix if they are unhealthy or have poor motility.
• Improper timing: Mating at the wrong time in the female's oestrous cycle can lead to the sperm not being deposited when the cervix is most receptive, hindering their transport.
• Infections: Infections in the female's reproductive tract, such as an infection in the uterus, can lead to the production of inflammatory cells that are hostile to sperm, preventing them from reaching the eggs.
• Abnormal cervical mucus: In some cases, the quality of the cervical mucus may be abnormal, which can impede the passage of sperm into the uterine lumen.
• Anatomical issues: While less common, anatomical abnormalities in the cervix or uterus could potentially hinder sperm transport.
• Improper insemination: In cases of artificial insemination, if the semen is not deposited correctly (e.g., directly into the uterus rather than the vagina), it could lead to issues with sperm transport as the cervix still acts as a barrier. 

Sperm that can’t get through this barrier simply won’t make it any further. 

Travelling Through the Uterus

Once sperm enter the uterus, their journey becomes easier. The uterine lining is supportive and full of nutrients. The bitch’s body actually helps the best-quality sperm move forward by creating small muscular contractions that guide them toward the oviducts.

This is also the stage where many weaker sperm die off. Healthy, structurally sound sperm continue the race.

Finding the Oviducts: Where Fertilisation Happens

The oviducts are where the sperm meet the eggs.

Ovulation in dogs is unusual because the eggs are released immature and must mature for about 48 hours before they can be fertilised. This is why progesterone testing is useful particularly for frozen and chilled semen, as it identifies ovulation and timing for breeding

Key points breeders should know:

• Sperm can survive inside the bitch for up to 7 days if fresh
  
• Chilled semen survives around 2–3 days
  
• Frozen semen survives only 12–24 hours
  
• Eggs are fertile for roughly 48 hours after maturation

This means a well-timed mating can succeed even if ovulation has just occurred or is a few days away.

Successful Fertilisation

When sperm reach the egg, only one sperm will penetrate. Once this happens, the egg instantly blocks other sperm from entering. Fertilisation usually occurs in the oviduct, and the new embryo soon begins dividing before travelling back into the uterine horns to develop.

By day 18-21 after ovulation, the embryos implant into the uterine horns, marking the true start of pregnancy. Pregnancy can be confirmed via ultrasound at around 28 days, when the embryos start to take shape and foetal heartbeats can be seen. Once pregnancy is confirmed it is a good idea to start ensuring you prepare Whelping Supplies for both mum and pups.

Final Thoughts

Understanding how sperm travels inside the bitch gives you a clearer picture of what affects conception. When you know how timing, semen quality and the reproductive tract all work together, it becomes much easier to plan successful mating's and avoid disappointment. Whether you breed naturally or use artificial insemination (AI), keeping the dam healthy, watching hormone levels and using reliable equipment all help support the best outcome for both pregnancy and future puppies.