The commercial application of artificial insemination (AI) and conventional embryo transfer (ET) in bovine reproductive systems has allowed for rapid genetic improvements in years past. However, few significant advancements have been made in these technologies, leading cattle producers to explore the possibility of adding in vitro fertilization (IVF) to their arsenal of reproductive tools. As the cost and technical limitations associated with IVF once hindered its practical use on a large scale, IVF had previously found its niche as the last resort to recover valuable genetic material from a donor struggling with infertility. Today, many of these technical constraints have been overcome, allowing IVF to become an economically viable and powerful tool to add to the progressive cattleman’s reproductive toolbox.
Understanding the IVF Process
The general premise of IVF is not unlike conventional ET – generate numerous viable embryos from genetically superior donor cows for transfer into recipient cows – but it is how the embryos are produced that makes IVF a unique and powerful tool. With IVF, unfertilized oocytes are collected from the donor and are matured and fertilized in a controlled laboratory setting prior to being transferred into recipients or frozen.
To collect oocytes, the technician administers epidural anesthesia to the donor so that the ovary can be stabilized by rectal palpation. An aspiration handle, comprised of an ultrasound transducer and a needle guide, is then inserted vaginally and manipulated to visualize the ovary. The ultrasound allows the technician to visualize the fluid-filled follicles on the ovary so that the needle (located in the needle guide) can be inserted into each follicle. The contents of each follicle, including the oocytes, are aspirated out through the needle and collected in a vial. The vial contents are then screened through a filter allowing the oocytes to be isolated and rinsed into a dish. Using a microscope, the oocytes are retrieved from the dish, counted and graded based on quality.
For the next eight days, the oocytes are housed in the laboratory in conditions specifically designed to mimic the bovine reproductive environment. During the first 22-24 hours, the oocytes are matured in an incubator to prepare the oocytes for fertilization. Semen is then added to the oocytes, allowing fertilization to take place. The fertilized oocytes are cultured in an incubator for seven days to facilitate their development into embryos. At this point, the embryos are evaluated for quality and are prepared either for fresh transfer into recipient cows or for freezing. Additionally, IVF embryos may be biopsied or shipped overnight when fresh transfer at a distant location is desired.
Advantages of IVF
Overcome reproductive anomalies
Historically, the most common application of IVF has been for donors who were unsuccessful in a conventional ET program. Whether the donor was nonproductive due to a physical abnormality of her reproductive tract (i.e.: scarring, impassable cervix, etc.), was prone to overstimulation or produced a number of unfertilized oocytes, many of these anomalies can be overcome with the use of IVF.
No hormones, less labor
In vitro fertilization offers a viable alternative to standard superovulatory protocols as donor cows can be aspirated with acceptable results without use of superovulatory drugs such as follicle-stimulating hormone (FSH). This not only limits the expense and amount of hormones needed but also eliminates the labor needed to administer drugs, detect heat and breed a donor cow for traditional flushing. A donor can be aspirated with virtually no preparatory work.
Cows continue to generate follicles even while pregnant, but the pool of genetic material housed within those follicles is inaccessible by conventional flushing technologies. Because oocyte aspiration for IVF does not require hormone use nor does it invade the cervix or uterus, the oocytes can be harvested without disrupting an existing pregnancy. Generally speaking, a donor cow can be safely aspirated from seven to 100 days of gestation. Aspiration can extend further into gestation as long as the ovaries are accessible to the technician.
Similarly to pregnant cows, anestrus cows and heifers generate cohorts of follicles despite their failure to exhibit estrus. These follicles can be aspirated to create embryos from cows soon after calving and from heifers prior to reaching puberty. Oocytes can also be recovered from valuable cows prior to or just after death.
Maximize semen use
In AI or conventional ET, sperm must navigate the length of the cow’s reproductive tract in order to fertilize the oocyte(s). With IVF, the sperm are placed directly into a small dish containing the oocytes. Thus, less semen is typically required for IVF and a single semen straw can fertilize oocytes from several donors. This is particularly beneficial when rare, expensive or sex-sorted semen is being used. The small quantity of sperm cells needed for IVF also provides a unique application for those producers desiring sex-specific embryos. Some (but not all) conventionally-frozen semen can be reverse-sorted for Gender Select™ (i.e.: a single straw of frozen semen is thawed and then sex-sorted) to obtain the desired sex. This can be advantageous when sex-sorted semen is not commercially available.
Because oocyte fertilization happens in a controlled environment, multiple matings can be generated from one donor collection (assuming a sufficient number [≥ 24] of quality oocytes are retrieved). Oocytes from a single donor would simply be separated into individual wells, allowing semen from multiple sires to be utilized. By keeping the oocytes separated for fertilization, parentage of the resulting offspring can be easily identified without the need for genetic testing.
Short interval between procedures
Donors can typically be aspirated for IVF every two weeks. Depending on the productivity of the individual donor, more embryos may be produced via IVF than by conventional ET. In vitro fertilization can also complement a conventional ET program, allowing donors to be aspirated between flushes. To view a comparison timeline of IVF and conventional ET, please click here.
Important Considerations for IVF
Individual IVF results are variable and are dependent upon a number of factors including (but not limited to): cow age, breed, health status and nutritional plane as well as semen quality. Generally speaking, oocyte recovery averages around 18-22 ova per aspiration in beef cattle. Of those oocytes, approximately 30-35% will develop into transferable/freezable embryos.
Although we utilize advanced technologies to mimic the cow’s reproductive tract in the laboratory, the best environment to create and mature a bovine embryo is still in the actual reproductive tract of a cow. As a result, embryos produced from IVF are not quite as robust as conventionally-produced embryos and reduced pregnancy rates are to be expected. Fresh transfer pregnancy rates of 55% up to 70% in well-managed recipient herds are typical. Pregnancy rates for frozen IVF embryos are generally 10-15% lower than conventionally-frozen embryos.
Because of the semi-invasive nature of oocyte recovery, producers may be concerned about damage or scarring to the ovary. Rest assured that the ovary is a surprisingly regenerative organ and little to no scarring results when oocyte recovery is performed by our skilled technicians.
Large Offspring Syndrome (LOS)
This defect occasionally presents itself in calves produced from IVF due to manipulation of the embryo early in its development. We take great care to minimize these disruptive effects. For example, LOS has partially been attributed to the use of serum in the media. To alleviate this problem, all of our media is serum-free.
Interested in adding IVF to your reproductive toolbox? We are here to help you develop a plan. We understand that IVF is not for every cow or every situation, so we will work with you to identify which donors are the best candidates for IVF to maximize your reproductive efficiency. Give us a call and let us put our unbeatable customer service to work for you today!