by Terry Lidral in collaboration with Chace Sherrill of Champion Genetics
BST talked with Chace Sherrill of Champion Genetics about breaking down the layers of embryo transfer. Sherrill is the lead on Champion Genetics’ IVF program to which he brings 4 years of IVF experience with over 10,000 donors aspirated. He has an undergraduate degree in Animal Science from Tarleton State University and a Master’s Degree in Reproductive Physiology from McNeese State University. He has worked with Flying Cow Genetics and ABS in their IVF programs.
BST: What is embryo transfer?
Sherrill: This question is very common but has many answers. The most rational answer to what is embryo transfer is: the act of implanting an embryo into the uterus of a recipient in hopes of that recipient becoming pregnant.
Embryo transfer in cattle was first developed in the 1970’s and 1980s to propagate the genetics of specific cows (donors) and bulls (herd sires). In a natural situation a cow can only produce one live calf per year because of the length of gestation. The average bull breeding by live cover will sire 15 to 50 calves per year depending on the length of the breeding season. With the use of artificial insemination, the number of calves a bull can sire has been greatly increased. Until embryo transfer was developed, the reproductive potential of the female had yet to be exploited. Once the techniques were developed to collect embryos and successfully transplant them into recipients to obtain pregnancies, the number of calves a cow can produce has also been increased.
BST: How are embryos collected?
Sherrill: The most common way (In vivo) that embryos are collected is through a nonsurgical recovery usually referred to as “flushing”. A rubber catheter is inserted through the cervix into the uterus of the donor cow. Then a specific type of fluid is passed in and out of the uterus to harvest embryos seven days after estrus. The fluid is passed through a filter that collects the embryos which are later retrieved and evaluated using a microscope.
IVF (in vitro) is another collection method used to produce embryos for embryo transfer. This method collects oocytes, unfertilized embryos, using an ultrasound guided needle and aspiration pump called Ovum Pick-Up. These oocytes are then fertilized and cultivated into seven-day old embryos in a lab using media and incubators to simulate the natural conditions inside the uterus.
BST: What conditions are essential to the success of embryo collection and transfer?
Sherrill: To have good success while collecting and transferring embryos, there are standards that the working facility needs to meet. Cattle should be moved relatively stress free though the pens/alley ways; you also need to be able to restrain the animal with a squeeze chute; and a palpation cage needs to be attached to the chute. The squeeze chute should be covered to protect the embryos and technician from weather. It is also recommended that you have an enclosed room that is temperature controlled and has electricity. This room should also be in close proximity of the squeeze chute to serve as the “laboratory” for the embryologist to search, grade and freeze the embryos. Some embryologists have mobile labs, usually a trailer that is climate controlled, in case you cannot provide this.
BST: Are all embryos good?
Sherrill: When the embryos are found under the microscope, they are then evaluated and put into several different categories or grades. This grading system is typically 1-4, Grade One being an excellent embryo, Grade Two being a fair or acceptable embryo, Grade Three being an embryo that is poor in quality, and finally, Grade Four which is an embryo that is dead or degenerating. The evaluation of embryos is standardized by the International Embryo Transfer Society and are based on the stage of development and quality of each embryo.
BST: How are embryos stored? What conditions are needed to protect the embryos?
Sherrill: Once the embryos are frozen, they need to be stored in a cryogenic tank. A cryogenic tank is a vacuum tank that is specifically designed to hold liquid nitrogen for extended periods of time. Keeping embryos under negative 150 degrees Celsius will ensure that they will not be damaged and can be stored indefinitely.
You can find Champion Genetics’ website here: https://championgenetics.com/
Freezing embryos has become a very popular option in embryo transfer. The direct transfer method of freezing and unfreezing embryos has made the process relatively simple. This also allows you to preserve genetics/embryos for an extended period of time as well as maximize the use of recipients.
BST: What is Superovulation? Is there a maximum number of embryos that can be had from one cow?
Sherrill: Each female cow has a finite number of oocytes inside her ovaries which she is born with. This number can be anywhere between 20,000 to 250,000 so it is very rare that a donor will be collected enough to deplete her of potential embryos.
Superovulation is a very important step in the process of embryo transfer. Normally the female will ovulate one follicle per reproductive cycle. Inside that follicle is an oocyte, if that oocyte is fertilized it becomes an embryo. With the help of superovulation, multiple follicles can be ovulated at the same time, increasing the number of potential embryos produced in one reproductive cycle. This stimulation of follicular development is controlled by a hormone called FSH, follicle stimulating hormone, which is administered intramuscularly. This hormone combined with the use of progesterone (CIDR) is the most effective way to produce multiple embryos utilizing the reproductive potential of the female.
BST: What conditions can affect a cow’s production of embryos besides hormonal treatment?
Sherrill: There are other factors that can affect the production and viability of embryos. The donor needs to be on a good plane of nutrition and be free of any diseases, viruses, or parasites. If you have any questions or concerns about herd health, it is recommended that you speak to your local veterinarian. Stress is also a big factor in the production of embryos as it can raise cortisol levels and lead to infertility or poor-quality embryos. To make it simple, healthy cows produce healthy embryos.
BST: Which cows are good recipients?
Sherrill: The selection of recipient cows is a dynamic factor to the success of embryo transfer. These cows should be reproductively sound, with a good history of calving ease, milking and mothering. They should also be in excellent body condition – not being fat or malnourished and in overall good health. These are all critical to a successful embryo transfer and should be taken seriously. The recipients that are selected should not be cows that are late in calving or have shown to have trouble breeding.
The synchronization of recipients should also be a factor in selection. To maximize the survival rate of the embryo after transfer, the uterine conditions of the receipts should be the same as the donors’ at time of collection. Typically, this is seven days after estrus. This means that your recipients should be seven days post estrus at time of embryo transfer.
BST: What are the percentages of success?
Sherrill: With good herd management, embryo transfer can be a very efficient way to rapidly increase the genetic potential of your herd. Success rates with embryo transfer are normally very consistent with pregnancy rates exceeding 50%. The major factors that influence pregnancy rate are embryo quality and recipient’s suitability, assuming that the process is properly conducted.
Check out BST’s interview with Champion Genetic’s Craig Barton on what you need to know about semen collection here: https://buckingstocktalk.com/bucking-bull-semen-collection-champion-genetics-provides-the-facts/
Author: Terry Lidral
Terry Lidral is a western writer/journalist who lives in Idaho. She is the publisher and editor of the online magazine Bucking Stock Talk and the online magazine Western Living Journal. Her publishing credits include Storyteller for Real American Cowboy Magazine, writing feature articles for Humps N Horns Magazine as well as a wide variety of national and international web sites, historical magazines and news publications. She is known for her "up close and personal" profiles of celebrities and industry moguls such as NPR's Tom Bodett; PBR's Wiley Petersen and D.H. Page, PRCA's Sammy Andrews, Cindy Rosser and Julio Moreno to name a few. She has been applauded for her way of making a personal connection between her readers and her subjects. She indulges in her love of rodeo by serving as an associate board member for the Caldwell Night Rodeo. She is also an accomplished trainer and handler in dog agility. Her shelties Amelie and Milo are titled in NADAC, USDAA and AKC.
