Bovine embryo transfer manual

Recipients synchronized with PGF must be treated 12 to 24 hours before donor cows because PGF-induced estrus will occur in recipients in 60 to 72 hours [ Kastelic et al.

Although pregnancy rates do not seem to differ in recipients with natural or PGF-induced estrus, pregnancy rates were higher in PGF-synchronized recipients in at least one study [ Hasler et al. It must be remembered that exogenous steroid hormones may induce estrus and even ovulation in post-partum cows and prepubertal heifers that are not cyclic [ Mapletoft et al.

Therefore, postpartum interval, nutrition and body condition in cows, and age, weight and body condition in heifers must be closely monitored. A prospective recipient can be culled prior to embryo transfer because of one or more of these factors. The success of estrus synchronization programs is dependent on an understanding of three general areas: 1 estrous cycle physiology described earlier , 2 pharmacological agents and their effects on the estrous cycle, and 3 herd management factors that reduce anestrus and increase conception rates.

The normal bovine estrous cycle was described earlier; the use of pharmacological agents for the synchronization of estrus follows. PGF has become the most commonly used treatment for estrus synchronization in cattle [ Folman et al. PGF is not effective in inducing luteolysis in the first 5 or 6 days following estrus and when luteolysis is effectively induced by PGF, the ensuing estrus is distributed over a 6-day period [ Kastelic et al.

This is due to follicular status at the time of treatment. In a two-dose PGF synchronization scheme, an interval of 10 or 11 days between treatments has been used because it represents the mid-point of the estrous cycle and theoretically, all animals should have a PGF-responsive CL at the time of the second treatment.

However, a higher conception rate has been reported with a day interval [ Foman et al. Stage of the cycle during which PGF treatment is given affects fertility; pregnancy rates are usually higher when cattle are treated with PGF after mid-cycle e. Various progestins progesterone and progesterone-like compounds have been utilized for estrus synchronization [ Mapletoft et al. These effects are transitory, and fertility in the following cycle is normal.

Progesterone alters ovarian function in cattle by suppressing estrus and preventing ovulation. It also suppresses LH pulse frequency, which in turn causes suppression of the growth of LH-dependent follicles i. Thus, follicular waves continue to emerge in the presence of a functional CL. Progestins given for longer than the CL life-span i. Ovulation of an aged oocyte results in poor fertility. However, it has been reported that the CL resulting from the ovulation of a persistent follicle is capable of supporting a pregnancy after embryo transfer [ Wehrman et al.

More recently, Mantovani et al. Label directions for artificial insemination state that the device should be in the vagina for 7 days; PGF is given 24 hours before device removal and estrus detection begins 48 hours later.

Because of the short treatment period 7 days , persistent follicles do not form. There are several other progesterone-releasing vaginal devices available in other countries such as New Zealand, Australia, Argentina and Brazil, and it is only a matter of time before they become available in North America. Progesterone releasing vaginal devices are well suited to various approaches used to synchronize follicular development and ovulation [ Mapletoft et al.

Figure 4. This is a progesterone releasing device that can be inserted into the vagina and used to mimic luteal function during estrus synchronization or ovarian superstimulation protocols. The removal of the CIDR-B device and injection of prostaglandin results in progesterone withdrawal intended to mimic natural luteolysis and initiate mechanisms responsible for the maturation and ovulation of the growing dominant follicle s.

Figure 5. Various progestin-releasing devices used to control the estrous cycle in cattle available around the world. Behavioral estrus lasts approximately 12 to 16 hours; ovulation normally occurs 24 to 36 hours after the onset of estrus [ Kastelic, ].

Estrous behavior waxes and wanes, but nearly all cattle will be detected in estrus if observation is continuous. Therefore, the incidence of true silent estrus is negligible. Causes of anestrus lack of observed estrus include pregnancy, cystic ovaries, ovarian atrophy, pyometra, embryonic death, free-martinism and white-heifer disease. Most anestrous dairy cows that are non-pregnant are cycling and have a normal genital tract. Dairy heifers and postpartum suckled beef cattle often have a prolonged interval of anestrus due to ovarian inactivity.

The primary sign of estrus is a cow standing firmly when being mounted. Secondary signs of estrus include mounting other cows, mucus discharge, swollen vulva, hyperactivity, and bellowing.

Figure 6. The primary and most definitive sign of estrus in the cow is standing firm when mounted. The two principal problems with estrus-detection are missed estrus and estrus detection errors.

Several factors can contribute to missed estrus. Often the observer does not spend adequate time observing cattle for estrus or tries to combine estrus detection with other farm activities e. If many cattle are in estrus at the same time, they will congregate and form a "sexually active group", which facilitates estrus detection.

However, if only a single animal is in estrus, mounting activity will be much less frequent. Slippery or hard surfaces will also reduce mounting activity. Factors contributing to estrus detection errors include misinterpretation of signs of estrus, misinterpretation or misuse of estrus detection aids, and standing estrus in pregnant cows.

Means by which estrus detection can be improved include allocating adequate time for observation, using estrus detection aids, predicting the next estrus and inducing estrus pharmacologically [ Kastelic, ]. Figure 7. Estrus detection is the most important factor affecting widespread use of AI and an impediment to the successful use of embryo transfer. These methods should be utilized in addition to, and not as a substitute for, visual observation of estous behavior.

Marker animals are typically given several treatments with testosterone to initiate mounting activity, followed by periodic treatments to maintain activity. It has been reported that freemartin heifers implanted with Synovex-H four implants in each ear were effective marker animals. The duration of effectiveness of the implants was approximately 3 months. This is an extra-label use of these implants and the appropriate withdrawal period prior to slaughter is unknown.

Figure 8. Kamar Heatmount Detectors are valuable heat detection aids that assist in identifying cattle that are in estrus. The detector is a pressure sensitive device with a built-in timing mechanism designed to be activated by pressure.

Glued onto the sacrum tail head , pressure from the brisket of a mounting animal requires approximately 3 seconds to turn the detector from white to red. This timing mechanism helps distinguish between true standing estrus versus false mounting activity. Figure 9. The Kamar Heatmount Detector is glued onto the sacrum tail head of the cow. Cows must be observed twice daily to determine when the detector turns from white to red. Figure Heat detection using tail-chalk.

Freshly applied chalk is positioned on the tail head. When cows are mounted, the chalk is removed rubbed off , with more and longer mounts resulting in the removal of more chalk. Courtesy of Dr. Glen Selk. In recipients it is possible to eliminate the need for estrus detection by taking advantage of protocols that have been developed for fixed-time AI in cattle [ Mapletoft et al.

The use of progestin devices and the synchronization of follicular wave emergence were described earlier. Gonadotropin releasing hormone GnRH became available in the 's as a treatment for follicular cysts [ Drost and Thatcher, ].

However, treatment of a cow with a growing dominant follicle with GnRH will also induce ovulation [ Macmillan and Thatcher, , Thatcher et al. The Ovsynch protocol has been more efficacious in lactating dairy cows than in heifers [ Wiltbank, ]. GnRH-based protocols have also been used to synchronize ovulation in recipients that received in vivo - [ Baruselli et al.

In these studies, more recipients received embryos because the GnRH-based protocol was not dependent on estrus detection; although conception rates were often lower than in controls, pregnancy rates were higher.

If the first GnRH does not synchronize follicular wave emergence, ovulation following the second GnRH may be poorly synchronized [ Martinez et al. Prevention of the early ovulations by addition of a progestin-releasing device to a 7-day GnRH-based protocol has improved pregnancy rates in heifers after fixed-time AI [ Martinez et al. The same investigators treated recipients with GnRH plus a progestin-releasing vaginal device without estrus detection with an overall pregnancy rate of In summary, results indicate that acceptable pregnancy rates can be achieved when embryos are transferred to recipients that have been treated with a GnRH and progestin device protocol to synchronize ovulation, without the necessity of estrus detection.

Recent studies have shown that reducing the period of follicle dominance by removing the progestin device 5 days after insertion and increasing the time from progestin device removal to the second GnRH treatment and FTAI may improve pregnancy per AI in beef and dairy cattle treated GnRH-based protocols [ Bridges et al. When Bridges et al. Santos et al. The hypothesis proposed was that the 5-day protocol provided for a longer proestrus with increasing estradiol concentrations due to continuous gonadotropin support for the dominant follicle.

The ovulatory follicle of cows in the 5-day program benefited from this extra time and additional gonadotropin support. However, due to a shorter interval between the first GnRH and induction of luteolysis in the 5-day protocol, two injections of PGF 6 to 8 hours apart were necessary to induce complete regression of the GnRH-induced CL. More recently, Colazo et al. In that study, the use of the first GnRH in the 5-day Cosynch protocol also did not seem to be necessary as pregnancy rates did not differ when it was not used.

Lima et al. Similarly, Sala et al. In a series of studies, estradiol treatment was found to suppress antral follicle growth and suppression was found to be more profound when it was given with a progestin.

The mechanism responsible for estrogen-induced suppression of follicular growth appears to involve suppression of FSH through a systemic pathway. Once the estradiol is metabolized, FSH surges and a new follicular wave emerges. In estrus synchronization programs, a second, lower dose of estradiol is given 24 hours after PGF treatment and progestin device removal to induce LH release, which occurs approximately 16 to 18 hours later, synchronizing ovulation for fixed-time AI approximately 24 hours after the estradiol treatment [ Mapletoft et al.

Pregnancy rates to fixed-time AI have been high with this protocol. Estradiol treatments are the most commonly used treatment to synchronize follicle wave emergence and ovulation in beef and dairy recipients in South America [ Baruselli et al. The protocol consists of insertion of a progestin-releasing device and the administration of 2 mg estradiol benzoate on Day 0 to synchronize follicular wave emergence , and PGF either 5 days later, or at the time of insertion and removal of the progestin device to ensure luteolysis.

The progestin device is usually removed on Day 8 and ovulation is induced by the administration of 0. As estrus detection is usually not preformed, Day 9 is considered to be the day of estrus. In a commercial embryo transfer program in Argentina, In a commercial embryo transfer program in Brazil, Nasser et al. In another study involving recipients of in vitro -produced, frozen-thawed embryos in China [ Remillard et al.

In a study in Mexico with Brahman-influenced recipients, treatment with eCG increased the number of recipients receiving an embryo, with similar conception rates, resulting in higher pregnancy rates [ Looney et al. Considering that feeding recipients until they become pregnant is one of the most costly items in an embryo transfer program [ Hinshaw, ], a protocol that increases the number of pregnant recipients per synchronization treatment seems cost-effective, especially considering that this treatment also avoids the necessity of estrus detection [ Looney et al.

As estradiol is not available in many countries, GnRH has been used to synchronize follicle wave emergence and ovulation in fixed-time protocols.

In addition, pregnancy rates did not differ whether cows did or did not receive a progestin device or eCG. On the other hand, eCG significantly increased pregnancy rates in a Colombian study [ Mayor et al. Bos indicus cross heifers were randomly allocated in one of three treatment groups. Progestin devices were removed on Day 8 and 1 mg of EB was administered on Day 9.

In summary, the addition of eCG to estradiol- or GnRH-based protocols which included the use of progestin devices resulted in increased pregnancy rates depending on the type and body condition of the recipients.

However, treatment with eCG may not improve pregnancy rates in Bos taurus beef recipients managed under more optimal conditions. There have been several studies investigating the relationship between circulating progesterone concentrations and pregnancy rates in recipients [ reviewed in Baruselli et al. However, the use of supplementary progesterone has resulted in inconsistent effects on pregnancy rates.

An alternative strategy to increase circulating progesterone concentrations in recipients is to create an accessory CL by induction of ovulation of the first wave dominant follicle around the time of embryo transfer [ reviewed in Thatcher et al. Again, results have not been entirely clear. In Bos indicus recipients, treatment with human chorionic gonadotropin hCG on Day 7 day of embryo transfer increased progesterone concentrations [ Marques et al.

However, pregnancy rate in non-treated control recipients was lower than normally expected in these studies. This result was confirmed in another experiment [ Rodrigues et al.

Small et al. In a very recent study [ Wallace et al. Serum progesterone concentrations in pregnant cows with lower body condition score i. The authors concluded that giving hCG at embryo transfer increased the incidence of accessory CL and serum progesterone resulting in increased pregnancy rates in recipients with lower body condition scores. Finally, lower embryonic losses in recipients that received GnRH two days prior to the transfer of in vitro -produced embryos were reported more recently [ Garcia Guerra et al.

With the exception of the last report, the beneficial effects of increasing circulating concentrations of progesterone seem to be evident when pregnancy rates in control not treated recipients were lower than expected. In one approach, animals receive a new or used progestin device at the time of embryo transfer, or on Days 12 or 13 after estrus.

Recipients not detected in estrus were presumed pregnant, whereas those in estrus were examined by ultrasonography 7 days later and if found not to be pregnant were reused for embryo transfer. In any case, embryo transfer programs can be designed, utilizing these approaches, or variations on these approaches, to minimize the interval between a diagnosis of non-pregnancy and transfer of another embryo. Normally, a recipient is removed from an embryo transfer program after being given two and sometimes three opportunities to become pregnant.

The two management factors that determine the success or failure of an estrus synchronization program are nutrition and post-partum interval. If cows lose weight during pregnancy, the onset of estrous cycles after calving will be delayed. In a field study, recipients were body condition scored at the time of embryo transfer on a scale of 1 thin to 5 obese. Pregnancy rates were significantly higher in recipients scoring 3 and 4 than in those scoring 1, 2 or 5 [reviewed in Mapletoft, ].

Therefore, the nutritional status of recipients must be evaluated before setting up an embryo transfer program. Other nutrients important to reproductive efficiency are phosphorus and trace minerals. Although effects of mineral deficiencies can be profound in affecting reproductive function, a much more common and dramatic effect on reproduction occurs with energy deficiencies. In the early days of commercial bovine embryo transfer, embryos were collected surgically around Day 4 after estrus [ Betteridge, ; ].

Three methods of non-surgical embryo recovery were described in [ Drost et al. Non-surgical techniques are preferred as they are not damaging to the reproductive tract, are repeatable and can be performed on the farm [ Mapletoft, ; ]. Briefly, the donor cow is placed in a squeeze chute and the rectum is evacuated of feces and air. The perineal region and vulvar labia are washed thoroughly and dried, and the tail is tied out of the way.

Embryo recovery is not attempted until a satisfactory epidural anesthetic is completed. It is also important to avoid ballooning of the rectum with air as sensitivity of palpation and manipulation is compromised; collection efficiency will be poor if air is not expelled. Non-surgical techniques involve the passage of a cuffed catheter through the cervix and into one of the uterine horns on Days 6 to 8 after estrus [ Mapletoft, ; ]. Once the catheter is in place, the cuff is inflated with saline or flushing medium.

Care must be taken not to over-distend the cuff as the endometrium may split causing loss of collection medium and embryos into the broad ligament. There are two basic types of catheters used for non-surgical embryo collection. Original reports were on the use of two-way and three-way Foley catheters [ Rowe et al.

Many groups still use the Foley catheter as it is inexpensive and readily available. However, the rubber is soft and the catheter is short and difficult to thread into the uterine horn. Furthermore, the distance from the cuff to the catheter tip is short. The two-way Rusch catheter has been preferred by many [ Schneider, ]. It is 67 cm long, or gauge O. The tip in front of the cuff measures 5. The catheter is stiffened for passage through the cervix by a stainless steel stilette, which locks into the Luer-Lok fittings.

It is long enough for large cows and is stiff enough that it can be easily threaded down the uterine lumen. Many other catheters are now available from embryo transfer suppliers, but they are really modifications of the above two types.

The more important consideration today is whether the catheter can be autoclaved or it must be considered disposable. Silicon catheters are most commonly used nowadays. Basically, there are two methods of embryo collection [ Mapletoft, ]: the continuous or interrupted flow, closed-circuit system and the interrupted-syringe technique.

However, any combination of these two techniques is possible. It must be recognized that each system has advantages and disadvantages relative to the other. With the closed system, it is easier to maintain sterility and there is less chance of losing medium and consequently, embryos.

However, it is cumbersome and the extra tubing provides extra potential for contamination by either microbes or chemicals. Again, embryo transfer suppliers now provide disposable equipment for closed-circuit systems. With the interrupted syringe method, it is possible to use fully-disposable equipment, with the exception of catheters, and to search for embryos while the collection is in progress.

The embryo recovery medium is prepared before preparation of the cow. Dulbecco's phosphate-buffered saline PBS or other basic salt solutions can be prepared in to ml bottles and kept refrigerated ready for use. Holding medium is normally passed through a disposable 0. Nowadays, ready-made embryo collection and holding media are available commercially; they are ready for use and have been filtered previously.

However, if they contain animal products, e. Very recently, collection and holding media that do not contain animal products contain polyvinyl alcohol or pluronate as a surfactant have become available making refrigeration unnecessary [ Hasler, ]. Temperature does not seem to be critical to embryo survival, provided extremes are avoided. Room temperature seems satisfactory. Similarly, sterility is not possible, but every attempt should be made to be as clean as possible.

Sterilization with chemicals is more likely to kill embryos than microbial contaminants. Thorough washing of in vivo -derived embryos with sterile medium has been shown to remove all infectious agents [ Singh, ]. As a routine, embryos should be passed through 10 washes of fresh, sterile medium prior to transfer or freezing.

Certain infectious agents such as the Bovine Herpes virus, have been shown to "stick" to the zona pellucida. If these agents are of concern, two trypsin treatments after wash number 5 is recommended to dissociate the agent from the zona pellucida.

Although embryos are usually transferred as soon as possible after collection, it is possible to maintain embryos in holding medium for several hours at room temperature. It is also possible to cool bovine embryos in holding medium and to maintain them in the refrigerator for as long as 2 or 3 days. As a final alternative, embryos may be frozen for use at a later date. Embryos are normally held in the same or a similar medium to that in which they were collected.

Media must be buffered to maintain a pH of 7. More complex media with a carbonate buffer generally yield superior results for long term culture of bovine embryos in a laboratory setting. As indicated earlier, embryo collection, holding and freezing media that are free of animal products have become available recently, avoiding the need for refrigeration and at the same time, increasing biosecurity. Evaluation of bovine embryos must be done at 50 to X magnification, with the embryo in a small culture dish.

The International Embryo Transfer Society IETS has a numerical system for classification of embryo developmental stage, ranging from 1 single cell zygote to 8 hatched blastocyst and quality from 1 good and excellent to 4 dead. It is important to be able to recognize the various stages of development and to compare these with the developmental stage that the embryo should be based on the days from estrus.

Often a decision as to whether an embryo is worthy of transfer will depend on the availability of recipients. Fair quality embryos should be transferred fresh, if recipients are available, while good and excellent quality embryos have a high probability of surviving cryopreservation. Evaluation of bovine embryos must be done at 50 to X magnification, with embryos in a small culture dish.

The overall diameter of the bovine embryo is to um, including a zona pellucida thickness of 12 to 15 mm. The overall diameter of the embryo remains virtually unchanged from the one-cell stage to blastocyst stage. The best predictor of an embryo's viability is its stage of development relative to what it should be on a given day after ovulation. An ideal embryo is compact and spherical. The blastomeres should be of similar size with a homogenous color and texture.

The cytoplasm should not be granular or vesiculated. The perivitelline space should be clear and contain no cellular debris.

The zona pellucida should be uniform, neither cracked nor misshapen and should not contain debris on its surface. Embryos of good and excellent quality quality code 1 and at the developmental stages of late morula to blastocyst yield the highest pregnancy rates. It is advisable to select the stage of embryo development to correspond to the stage of the cycle in the recipient synchrony.

A bovine embryo with about 16 cells, as it would appear in the uterus of a cow about 4 to 5 days after ovulation. The diameter of this embryo about 0. Courtesy of Harold Hafs. A bovine morula with a mass of at least 32 cells. Individual blastomeres are difficult to discern from one another. The cellular mass of the embryo occupies most of the perivitelline space. Expanded, hatching and hatched blastocysts produced by in vitro fertilization with frozen-thawed semen following in vitro maturation.

One blastocyst has hatched from the zona pellucida and a second has begun to hatch; note that the zona pellucida is very thin. Courtesy of Sanjay Khanna and John Parks. A bovine blastocyst hatching through a crack in the zona pelucida. Note that the inner cell mass and some of the trophoblast are outside the zona pellucida. John K.

The IETS recommended codes for embryo quality range from "1" to "4" as follows:. The Manual of the International Embryo Transfer Society states, "It should be recognized that visual evaluation of embryos is a subjective evaluation of a biological system and is not an exact science. Furthermore, there are other factors such as environmental conditions, recipient quality and technician capability that play important roles in obtaining pregnancies from transferred embryos.

It is also recognized that many different systems are used for "grading" embryos and that some are more sophisticated than others. The criteria for assigning a "quality code" in the standardized forms were simplified to be "user friendly".

Generally, unless otherwise specified, only Code 1 embryos should be utilized in international commerce". In the superovulated cow, there is likely to be a considerable range of embryo stages on any given day during development. On Day 7 after estrus, there may be morulae and blastocysts or even hatching blastocysts within the same collection. At the same time, there may be embryos of excellent quality and unfertilized and degenerate embryos. Generally, wide variations in embryo quality and stages of development are signals that normal-appearing embryos maybe stressed or compromised and that pregnancy rates may be disappointing.

Embryos of excellent and good quality quality code 1 , at the developmental stages of compact morula stage code 4 to blastocyst stage codes 5 or 6 yield the highest pregnancy rates, especially after cryopreservation. Fair and poor quality embryos yield poor pregnancy rates after cryopreservation and should be transferred fresh. It is advisable to select the stage of embryo development for the synchrony of the recipient.

Fair and poor quality embryos are most likely to survive transfer if they are placed in the most synchronous recipients. Transfer of embryos in cattle will result in a high pregnancy rate providing the preceding estrus in the donor and recipient occurred within 24 hours of each other [ Hasler et al. Alternately, recipients must be synchronous with the stage of development of embryos that had been previously cryopreserved. Recipients can be made available by maintaining a large herd to obtain natural synchrony or by estrus synchronization, which is much more economical.

Today most recipients are synchronized regardless of whether or not embryos are transferred "on farm". Initially, embryo transfers in the cow were done surgically, whereas most are done today using non-surgical methods [ Betteridge, ; ]. Surgical transfers were first done by way of a midline incision, which necessitated the use of general anesthesia and rather elaborate surgical facilities. During the mid to late 's, this gave way to a standing flank approach, an approach that could be done more quickly and because of lesser requirements in facilities made "on farm" embryo transfer possible.

Most recently, the use of non-surgical embryo transfers has increased the utilization of embryo transfer on farm [ Rowe et al. Non-surgical embryo transfer techniques involve the use of specialized embryo transfer pipettes. After confirming the synchrony of estrus, the recipient is restrained and the rectum is evacuated of feces. At the same time, the presence and side of a functional CL is confirmed. Care is taken to prevent ballooning of the rectum with air.

An epidural anesthetic is administered and the vulva is washed with water no soap and dried with a paper towel. The embryo is loaded in 0. Care is taken to ensure that the straw engages the sheath tightly so as to avoid leakage. The sheath is coated with sterile, non-toxic obstetrical lubricant and the sheathed pipette is passed through the vulvar labia while avoiding contamination.

The embryo is placed in the uterine horn adjacent to the ovary bearing the CL by passing the pipette through the cervix, very similar to artificial insemination. However, an attempt is usually made to pass the transfer pipette at least half-way down the uterine horn. The uterine lumen should be lined-up prior to passage so as to prevent trauma to the endometrium. Alternatively, embryos can be refrigerated in transfer medium for up to 24 hr with no appreciable loss of viability.

Splitting embryos into identical halves by microsurgery is practiced by a few commercial embryo transfer teams. The number of embryos to be transferred can be doubled with only a minor reduction in pregnancy rates. However, techniques to freeze manipulated embryos require improvement. Since , the current preferred and most common method to transfer cattle embryos into synchronized recipients is via nonsurgical techniques.

The embryo is loaded into a small plastic straw 0. The gun is passed through the cervix, aided by palpation per rectum, and advanced into the uterine horn ipsilateral to the corpus luteum.

The contents of the straw are then deposited as cranial as possible into the uterine horn with care to avoid prolonged and unnecessary manipulation. Although increased pregnancy rates may be obtained with transfer of multiple embryos, the risk of dystocia and retention of fetal membranes associated with twin pregnancies and the increased probability of producing freemartin calves preclude widespread use of this approach.

The use of sexed semen in embryo transfer programs is considered economically viable, especially if attention is given to inseminate donor cows with sperm numbers comparable to those used in artificial inseminations with conventional nonsorted semen. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world.

The Merck Veterinary Manual was first published in as a service to the community. This site complies with the HONcode standard for trustworthy health information: verify here. Common Veterinary Topics. Videos Figures Images Quizzes. Embryo Transfer in Farm Animals. Test your knowledge. Large animal neonates are born immunocompetent but lack antibodies. Classification of embryos is far from an exact science. For example one practitioner will diagnose an embryo as a 1 while a second practitioner will call it a 2.

Recently in a published paper there were no differences in pregnancy rates between embryos designated as 1's or 2's by two different practitioners. A number of years ago we were discussing how to grade embryos following freezing and thawing.

Embryos prior to thawing classified as a 1 often show some damage so I grade them as a 2 or even a 3. However, some claim that freezing damage should be ignored leaving the original grade. This opinion obviously defeats the purpose of grading, which is an attempt to predict the coming pregnancy chances which will be lower due to freezing damage.

Remember the next time you transfer some embryos, pregnancy rates depend on the quality of the embryos before freezing, the ability of the person freezing the embryos, the storage practices, the quality and preparation of the recipients, and the skill of the person performing the transfers. So if you experience unacceptable pregnancy rates don't forget it may not be the fault of the practitioner transferring the embryos who usually receives the blame.