In Vitro Fertilization in Dogs

Although in vitro fertilization (IVF) has been practiced for many years in humans and other animals, until recently it has not been practiced in dogs due to the difficulty of the process in canines. In vitro fertilization is the process of combining an egg and a sperm outside of the reproductive system, creating an embryo that can then be implanted into the reproductive system of a host animal and carried to term. The process is complicated in dogs who only come into heat, releasing eggs, once or twice a year, which limits the time window to accomplish egg harvesting from the donor female. In addition, when a dog ovulates the egg is not ready to be fertilized right away, it must remain in the fallopian tubes and mature. This makes coordination of the process very time-sensitive. Also, canine sperm is prevented from developing adequately when exposed to magnesium in its early stages. Magnesium is usually present in the IVF substrate that sperm is stored in. However, removing magnesium from the substrate does not entirely resolve the issue, as at a later stage, prior to penetration of the egg, magnesium increases sperm activity. Omitting magnesium exposure from sperm used for IVF in early stages of the process and allowing exposure later in the process allows donor sperm to be viable enough to penetrate the egg in an artificial environment. Fertilized canine eggs produce embryos that can then be frozen for later insertion in a donor females uterus. This process when used in combination with genetic screening and editing has potential to reduce genetically mediated diseases. As some breeds are strongly susceptible to certain inherited disorders, IVF may be used in the future to mitigate these disorders and produce disease-free embryos. The technology and process to accomplish IVF in dogs is still in its early stages, and IVF for dogs is not widely available. In addition, the complexity of the process in dogs makes it resource prohibitive in many cases. 

Female dogs only ovulate once or twice a year, and after the ovum are released, require 48 to 72 hours in the oviduct to mature. At this point, they can be harvested for use in producing embryos outside of the donor dog’s reproductive system.

Ovulation is determined by collecting blood or observing signs of heat such as discharge from the female dog’s vulva. Day five to six from release, the egg, or oocyte, is mature and ready for fertilization. Ovum may be harvested by performing a spay on the female donor dog at this point and dissecting the oviduct to obtain mature oocytes. Oocytes are stored in a medium with mineral oil in preparation for fertilization with donor sperm. 

Sperm collected from donor male dogs is kept in a medium where magnesium levels are appropriately maintained at different stages so as to promote development of sperm, making them viable for fertilization of eggs. Sperm is tested to ensure viability before using for IVF.

Sperm is introduced to the oocytes and storage media with a pipette, and left for approximately 14 hours to allow for fertilization of the oocytes. At this point the zygotes are washed with fresh medium to remove excess sperm and cells and the zygotes returned to the culture. Embryos are then observed 48 hours post-fertilization and may then be frozen for future use or continued in fresh medium and observed for development before use.

Cryopreserved, frozen, embryos are then thawed and placed in an appropriate medium for preservation prior to use. Host females are observed for estrus and when naturally occurring estrus is present, embryos are transferred on the appropriate synchronized day. For example, an 8 or 10 day old fertilized egg, embryo, would be implanted 8 to 10 days after estrus in the host female dog’s uterine horn. To affect transfer, laparotomy is performed to expose the uterine horn or oviducts and an incision is made into the cranial area of the uterine horn or oviduct where embryos can be transferred with a pipette.

IVF attempts in dogs were unsuccessful until recently due to complexity in the fertilization process in dogs and the inability to replicate natural process in an artificial environment. With the understanding that canine oocytes require maturation after release in the oviduct prior to fertilization, and canine sperm development requires exposure to magnesium at specific stages prior to use for fertilization, success was eventually achieved. Although an understanding of these reproductive requirements has been successful in achieving IVF in dogs, and live births, the process is complex and resource consuming. Developed IVF procedures in dogs yields live births rates in the 30 to 40% range. Success is limited and the process is still being investigated and developed. The potential to mitigate genetic disorders, and allow for offspring from endangered canine breeds and species may be realized by IVF in the future.

Recovery for IVF in dogs is largely due to surgical procedures to harvest oocytes and transfer embryos in host dogs. Surgical procedures will require post-surgical observation for complications such as hemorrhage, infection, or incision rupture. An e-collar to prevent interference with surgical wounds will be required.

As this procedure is relatively new in dogs and is a complicated procedure only available through a few facilities, cost of IVF in dogs has not been well established. Most procedures are still being performed as part of a research process and may not be commercially available. 

Because dogs only cycle once or twice a year, the opportunity to harvest from donor females and transfer to recipient females is limited. Success rates are still somewhat limited and the process is not widely available for commercial purposes currently.

IVF, combined with gene editing, may be a useful technology for the prevention of inheritable genetic disorders in dogs in the future.