Ovum Pick Up (OPU) is a non invasive technique for recovering oocytes or egg cells from the follicles of live cows. OPU is done by needle guided, trans-vaginal ultrasound that recovers the oocytes using vacuum suction. The oocytes are washed, sorted, and graded. The oocytes are then In-Vitro fertilized, cultured, and finally frozen in individual straws. The frozen straws are returned to the dairy to be transferred into the uteri of recipient cattle.

The OPU process was originally developed to assist with human infertility.¹  It was performed in cattle for the first time in 1988 by Dutch researchers at Utrecht University.²  The oocytes recovered using OPU are turned into embryos using a process called In-Vitro Fertilization (IVF). IVF of cattle was first performed in 1981³.  In other words, OPU and IVF are mature technologies that are several decades old.

If OPU and IVF are so great, why has it taken so long for them to catch on? In my opinion, interest in OPU/IVF has increased in recent years because of the arrival of two other technologies: Genomics and sex-sorted semen. Clarifide is a genomic test marketed by Zoetis that provides Genomic Predicted Transmitting Abilities (GPTA’s) that are significantly more reliable than traditional parent average/pedigree index values. Thanks to the arrival of a low-cost, reliable genomic test, OPU/IVF has the ability to accelerate genetic progress in cattle at an unprecedented rate. The ability to use sex-sorted semen doubles the amount of female offspring that can be produced by IVF.

The advantages of OPU/IVF:

• decreased generation interval
• acceleration of genetic progress by leveraging female as well as male genetics
• generates more pregnancies from a single dose of semen
• generates more pregnancies per donor

Ability to rapidly multiply valuable or rare genes Genetic progress per year can be expressed with the following formula:

Genetic Variation measures how variable the trait is in the population and is the one factor in this equation that breeders do not control.

Accuracy is the correlation between the real genetic value and the estimated genetic value. Historically, progeny or pedigree records were used to calculate Predicted Transmitting Abilities (PTA’s). PTA’s or more recently GPTA’s are often used as the estimate of the genetic value.

Intensity measures the difference between the parents and the population average. If the parents are close to the average, the Intensity is small. If there is a big difference between the parents and the average, the Intensity is large. In other words, the selection Intensity reflects whether the parents are from the top 25%, 5%, 1%, etc. of the population (i.e. percentile rank).

Generation Interval (GI) is the amount of time between birth of an individual and birth of its replacement. Because GI is the lone term in the denominator of the genetic change equation, it has the largest impact on Genetic Progress per year.

Historically, Accuracy and GI are tied together. To increase Accuracy we needed older bulls with more progeny records and older cows with more production records, thus GI increased⁴.  Thanks to genomic data we can use GPTA’s to identify the best bulls in the breed and the best heifers in the herd within months after birth. Genomics help alleviate this negative relationship between Accuracy and Genetic Interval.

Moreover, in intensive breeding programs younger animals often have superior genetic merit compared to older animals, thus using young animals increases the selection Intensity. Genomics allow us to increase Accuracy and Intensity while simultaneously decreasing Genetic Interval. Artificial Insemination (AI) studs have been using this Genomic technology since it was introduced.

Everyone that uses commercially available semen from AI studs has benefitted from this increase in Genetic Progress per year on the bull side of the genetic equation. However, Genomics can also give the same benefits on the cow side of the genetic equation if dairies utilize it in their heifers.

OPU can also be used to decrease Generation Interval even further. OPU can be performed on heifers as young as 6 months of age. We routinely start heifers as young as 7 or 8 months in our lab in Idaho. If the Generation Interval in heifers is 22 months, by using OPU we can decrease the GI by 6 months. That is a 28% decrease in GI. This decrease in GI and the advantage of increased Intensity and Accuracy by using genomics to select breeding stock in heifers has the potential to accelerate Genetic Progress per year tremendously in your herd in particular and the Holstein breed in general.

When OPU is done on a heifer, her oocytes are washed, graded, and are placed in a micro-centrifuge tube full of maturation media (MAT tube). After the oocytes have been placed in the MAT tubes they are placed in an incubator at 37.5C and transported to the IVF lab.

The IVF process has an average production rate of 30%, thus meaning that 30% of all oocytes fertilized will develop into viable embryos. Historically, the oocytes from each heifer are fertilized separately. Fertilization is one of the most expensive parts of the process as it includes the cost of the semen and the cost of the actual IVF procedure. The cost per embryo is lower for donors who produce large amounts of oocytes compared to donors who produce less. This custom of fertilizing each donor’s oocytes in a different fertilization group puts the price per embryo very high and makes it less attractive to commercial dairies. However, by pooling donors into fertilization groups, we can maximize the amount of oocytes that are fertilized in one fertilization group and lower costs significantly.

The average number of oocytes collected is about 15 per donor per OPU session. There is a large range of variability in the amount of oocytes collected between donors. Some donors give 30 oocytes, some only give 5. However, donors are usually very consistent in the amount of oocytes they produce. For example, a heifer that gives a large amount of oocytes can usually be depended upon to always give a large amount of oocytes. The opposite is also true, heifers that start out giving only a few oocytes can always be depended on to disappoint.

Fertilization groups can contain 40–60 oocytes. For example, if we take 4 donors who produce 15 oocytes a piece and pool them into one fertilization group of 60 oocytes we will reduce our fertilization expenses by 75%, when compared to fertilizing each of the four donors separately. Also, fertilizing 60 oocytes with one dose of semen is a very efficient use of semen.

Although there is great variability in oocyte production, it is possible for a heifer to produce over 50 calves per year.⁵  This is remarkable when you consider that without OPU, the typical cow produces only one calf per year. If sex-sorted semen is used, it almost doubles the amount of females that are produced when compared to conventional semen. Using sex-sorted semen in OPU avoids spending valuable resources to produce bulls that will not contribute to the herd. This ability to rapidly multiply genes can be particularly useful when the desired traits are valuable or rare. Examples are animals with genes for: polled, A2 beta-casein, Net Merit $, disease resistance.

OPU has the advantage that it can be performed without giving donors any hormones prior to the OPU session. However, many veterinarians recommend a series of Follicle Stimulating Hormone (FSH) to increase follicle size. FSH does not increase the number of follicles only their size. In an internal study run by Trans Ova Genetics, FSH was found to increase the number and quality of viable embryos per OPU. Additionally, FSH in dairy animals adds about 2.4 embryos or about 51% more viable embryos per OPU.⁶  While a series of FSH injections is expensive, the increase in viable embryos actually decreases the cost per embryo. FSH also increases the ratio of Grade 1 to Grade 2 embryos. This increase in embryo quality results in higher transfer rates when transferred into recipients.

The OPU process is performed by a veterinarian and an embryologist. The Veterinarian uses an ultrasound with a micro-convex probe encased in a probe holder. The probe holder encases a needle guide. The author prefers the short needle system developed by the Brazilians. The needle is connected to a vacuum pump that provides suction to aspirate the oocytes. Oocytes are collected in 50ml conical vial. Warmers for the collection vials are essential in order to keep the oocytes at the correct temperature. Once oocytes are collected the embryologist takes over and washes, sorts, and grades them. The embryologist then places them in maturation media and puts the oocytes in a battery powered incubator suitable for transport. Oocytes are overnighted to the IVF lab. The Lab fertilizes, cultures them for 7 days, and then freezes the embryos. Embryos are returned in liquid nitrogen to the dairy where they are stored until they are transferred into recipients using a specialized technique similar to AI.

Veterinarians interested in adding OPU to the list of services they offer should undergo training in the procedure. I received my training from Trans Ova Genetics. They were kind enough to train me how to perform the OPU procedure. I also went and observed other veterinarians who offered OPU services. Trans Ova Genetics also trained my embryologist as well. The cost of training for both me and my embryologist was about £2,500 and didn’t include travel expenses. I spent several months practicing on cows before our first OPU session. At first, everything went very slow. We did about 10 heifers every session and that took all day. As we developed competency, we were able to speed up and OPU more heifers. Currently we OPU between 20–40 heifers per OPU session. We average about 6 donors an hour.

The equipment needed will be:

• Micro convex ultrasound console with good resolution
• Vacuum pump with a tube warmer, boost button, and pedal
• Probe holder • Battery operated warmer for 50ml conical tube
• Battery powered incubator
• Cryo-tank to hold frozen embryos
• Tokai Hit Glass Heated Stage Warmer
• Olympus SZ61 Stereo-Microscope with LED base
• Slide Warmer
• Water Bath
• Pelican travel cases for transport of equipment

When I purchased the equipment in 2017, the cost was approximately £30,000. WTA and Trans Ova Genetics have proven to be valuable resources for advice on purchasing equipment.

In conclusion, OPU is a mature technology that when combined with IVF, genomics, and sex-sorted semen can accelerate genetic progress. Once out of reach of commercial dairies, strategies like pooling donors are putting OPU within their grasp.

References

1. Gleichert N, Friberg J, Fullan N, Giglia RV, Mayden, K. et al. (1983) Egg retrieval for in vitro fertilization by sonographically controlled vaginal culdocentesis. Lancet 508–509.

2. Pieterse MC, Vos PLAM, Kruip TAM, Wurth YA, van Beneden TH, et al. (1991) Transvaginal ultrasound guided follicular aspiration of bovine oocytes. Theriogenology 35: 857–862.

3. Brackett BG, Bousquet D, Boice ML, Donawick WJ, Evans JF, et al. (1982) Normal development following in vitro fertilization in the cow. Biol Reprod 27: 147–158.

4. Decker JE. (2014) Decreasing Generation Interval to Increase Genetic Progress University of Missouri Extension.

5. Qi M, Yao Y, Ma H, Wang J, Zhao X, et al. (2013) Transvaginal Ultrasound guided Ovum Pick-up (OPU) in Cattle. J Biomim Biomater Tissue Eng 18:118. doi:10.4172/1662- 100X.1000118

6. Demetrio D, Looney C, Rees H, Werhman M. (2020) Annual Report of the AETA Statistical Information Committee