Artificial insemination (AI) in dogs is a valuable reproductive tool that allows for the transport of semen nationally and internationally, expanding breeding possibilities. However, achieving successful pregnancy through AI depends on a multitude of factors, including the type and quality of semen used, the fertility of both the stud dog and the bitch, the method of semen deposition, and precise timing of insemination. This guide delves into these critical aspects to help maximize pregnancy rates.
Understanding Semen Types for Canine Artificial Insemination
There are three primary types of canine semen used for artificial insemination, each with distinct viability and handling requirements:
Fresh Semen
Fresh ejaculated semen offers the longest viability. When collected from young, fertile stud dogs, it can remain viable in the bitch’s reproductive tract for up to 5-7 days.
Fresh-Chilled Semen
To extend the viability of fresh semen for shipping, it is diluted with special canine extenders containing egg yolk and buffers. These extenders protect the sperm during a slow cooling process to 4°C. At this temperature, fresh-chilled semen can remain viable for 3-4 days, and in some cases, up to 10 days. This method is particularly useful for transporting semen over long distances, offering a more cost-effective and practical alternative to shipping the dogs themselves.
Frozen Semen
Frozen semen is stored at extremely low temperatures (-196°C) in liquid nitrogen. While this method allows for long-term preservation and international shipping, the freeze-thawing process inevitably causes some degree of sperm damage. Consequently, the viability of frozen semen is significantly reduced, lasting only 12-24 hours in the bitch’s reproductive tract. This makes precise timing of insemination crucial when using frozen semen.
The Critical Role of Timing: Monitoring the Bitch’s Estrous Cycle
Accurate timing is paramount for successful artificial insemination, especially when using frozen semen. Monitoring the bitch’s heat cycle, or estrous cycle, is essential to determine the optimal window for insemination. This monitoring typically involves one or a combination of the following procedures:
- Blood Tests: Measuring progesterone levels in the blood can help pinpoint the stage of the estrous cycle and predict ovulation.
- Vaginal Smears: Cytologic evaluation of vaginal smears aids in determining the best time for insemination and can also identify infectious or inflammatory conditions.
- Vaginoscopy: Visual assessment of the vaginal vault using a vaginscope provides valuable correlation to the stage of the estrous cycle and can help rule out anatomical abnormalities that might impede breeding.
The frequency of testing varies between individual bitches. It is generally recommended to begin testing approximately five days after the onset of heat and continue every second or third day until the ovulatory hormone, luteinizing hormone (LH), surge is detected. The day of the LH surge is designated as “LH Day 0,” and it typically coincides with a progesterone level around 2 ng/ml.
The specific days recommended for artificial insemination depend on the type of semen being used. For instance, with frozen-thawed semen, insemination is often performed on “Day 5” post-LH surge if only one insemination is planned, or on Days 4 and 6, or Days 5 and 6, if two inseminations are to be carried out.
Artificial Insemination Techniques: Site of Semen Deposition
The method by which semen is deposited significantly impacts pregnancy success. The two main techniques are transcervical insemination and vaginal insemination, with surgical intrauterine insemination being less recommended.
Transcervical Insemination (TCI)
Transcervical insemination involves depositing semen directly into the uterus, maximizing the chances of pregnancy, particularly when using frozen-thawed semen or fresh/chilled semen with compromised quality or quantity. This technique, developed in New Zealand, is non-surgical, sedation-free, and relatively stress-free for the bitch. It also allows for multiple inseminations during a single heat cycle. Recent advancements have led to the development of longer and slimmer endoscopes specifically designed for TCI in dogs, facilitating the procedure in larger breeds and maiden bitches. However, TCI may not be suitable for all bitches, especially due to behavioral reasons.
Vaginal Insemination
For fresh or chilled semen with adequate sperm numbers and quality, semen deposition at the far end of the vagina can result in pregnancy rates and litter sizes comparable to natural mating. In this method, a special catheter is inserted, and a bulb at its tip is inflated to mimic the swelling of the bulbus glandis during natural mating. This not only prevents semen backflow but also stimulates uterine contractions. Fresh semen is then slowly injected, followed by a warm canine semen extender to help propel the semen into the uterus. Vaginal insemination is non-invasive, requires less skill and equipment than TCI, and is often used for maiden bitches or when natural mating fails. However, it is generally not the preferred method for frozen-thawed semen due to the reduced lifespan of the sperm and lower sperm counts in typical AI doses, leading to fewer sperm reaching the uterus and oviducts for fertilization.
Surgical Intrauterine Insemination
Surgical intrauterine insemination, which involves a surgical incision into the abdomen to deposit semen directly into the uterine horns, is not recommended and not performed at CSU. This technique requires general anesthesia and carries surgical risks. It can only be performed once during the bitch’s heat cycle and does not offer improved conception rates or litter sizes compared to other methods.
The Importance of Semen Handling and Assessment
Regardless of the type of semen used or the insemination technique employed, proper handling and skillful assessment of the semen are critical for maximizing pregnancy rates. A thorough evaluation of semen quality and quantity by a qualified professional prior to insemination plays a vital role in achieving successful outcomes. Effective management of both the stud dog and the bitch, coupled with careful semen handling and appropriate insemination strategies, are key to successful artificial insemination in dogs.
