Historical Background and Significance of Embryo Transfer Technology in Cattle with its Relevant Applications

Ghulam Jelani1, Qudratullah Kalwar1*, Asmatullah Kaka2, Abdullah Channo2, Ayyaz Ahmed1, Majid Hussain Soomro1, Hidayatullah Soomro1,

Deepesh Kumar Bhuptani1 and Yar Muhammad Jalbani1

1Shaheed Benazir Bhutto University of Veterinary and Animal Sciences, Sakrand 67210, Pakistan.

2Department of Animal Reproduction, Faculty of Animal Husbandry and Veterinary Sciences, Sindh Agriculture University, Tandojam, 70060

Ghulam Jelani and Qudratullah Kalwar contributed equally to this work.

ABSTRACT

In recent decades, many significant improvements have taken place accompanying different assisted reproductive biotechnologies like estrous synchronization, artificial insemination, superovulation, cloning, embryo recovery and its transfer, in vitro fertilization, cryopreservation and transgenesis. Among these technologies, embryo transfer has achieved a great importance having produced numerous offspring from a genetically superior female. After the first successful transfer of mammalian embryos in 1890, it was approximately 60 years before significant progress became quite noticeable in the basic technology of embryo transfer in cattle. In embryo transfer process, embryo is collected from superior quality donor cattle and transferred to other recipient female cattle for complete development unless the gestation accomplishes. This technology involves the selection of donor and recipient animals, management for better breeding evaluation, embryo production, collection and transfer of embryo within a narrow window of suitable estrous time. In cattle, embryo transfer technology is widely used to amplify the reproductive rates of genetically improved superior females, planed mating, twinning, disease control, better pregnancy rate in repeat breeder cattle and increment of production of farm and reproductive rates. However, embryo transfer is widely used owing to its potential benefits. Hormonal protocol and synchronization improvements increase the embryo production rates via superovulation. This review details the embryo production technique, transfer of embryo from donor to recipient and the factor that are necessary for transfer of embryo from donor to recipient for production of offspring. Previously limited information existing regarding embryo transfer and its significance in farm animals therefore, in future this review might be helpful in improving the reproductive potential of farm animals.

Article Information

Received 03 April 2022

Revised 08 May 2022

Accepted 01 June 2022

Available online 03 August 2022

(early access)

Published 19 January 2023

Authors’ Contribution

Conceptualization, GJ, AA. Original draft preparation, GJ and QK. Guidelines and support, MHS and HS. Writing review and editing, AC and DKB. Helps in revision AK and YMJ. All authors have read and agreed to the published version of the manuscript.

Key words

Cryopreservation, Donor selection, Embryo production, Estrous synchronization, Pregnancy rates, Recipient selection, Superovulation

DOI: https://dx.doi.org/10.17582/journal.pjz/20220403060427

* Corresponding author: qudratullahkalwar@gmail.com

0030-9923/2023/0002-959 $ 9.00/0

Copyright 2023 by the authors. Licensee Zoological Society of Pakistan.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

INTRODUCTION

Selective breeding program and assisted reproductive technologies have been the key factors regarding dairying profitability having enhanced genetic potential (Loi et al., 2016). The genetically increased milk and meat yield attracts the demand for transplant animals; hence the breeding for productive animals escalates (Loi et al., 2016). In 20th century breeds improved assisted reproductive technologies like artificial insemination, multiple ovulation and ET (MOET) and multiple newer technologies that include in vitro embryo production, cloning, and transgenesis (Choudhary et al., 2016; Moore and Hsler, 2017). A well-developed reproductive technology embryo transfer (ET) is proved a beneficial to enhance production and replication of genetic superior animals with exploitation of genetic superior female cattle (Batista et al., 2016; Roper et al., 2018; Rico et al., 2012). Another study reported that annually more than one million embryos are produced globally. ET included different procedure like selection of donor cattle, its superovulation, artificial insemination of donor by sexed semen, recovery of embryo, cryopreservation of embryo, preparation of recipient cattle and transfer of good quality embryo in low genetic potential cattle (Hasler, 2014).

Among the assisted reproductive technologies, the beneficial techniques to increase animal production are the multiple ovulation and ET (Faizah et al., 2011; Oguejiofor, 2019).

For more betterment in cattle herds, ET is helpful to generate more embryos of predetermined sex and known genotype (Moore and Hasler, 2017). Superior females are preferred to mate through assisted reproductive technologies (in vitro fertilization, ET, and superovulation) to potentiate genetic improvement (Gaddis et al., 2017). After in-vivo or in-vitro fertilization, the commercial animal embryo production has become an international business (Kidie, 2006). Amidst the genomic era, interest of breeding techniques of developed artificial insemination by hygienic measures and ET technology plays the vital role for production in livestock enterprises (Humblot et al., 2010; Wray-Cahen et al., 2022). In 1940s and 1950s, superovulation and ET technique were pioneered (Hasler, 2014; Moore and Hasler, 2017). ET technology is the third most important and commonly used reproductive technology after artificial insemination (AI), and oestrous synchronization in large animals (Cowan, 2010; Mebratu et al., 2020). It is an important approach for the fortification of genetically superior offspring of animals and enhancing livestock production (Frade et al., 2014; Dochi, 2019; Alkan et al., 2020).

The ET protocol is the collection of embryo from donor (superior genetic) animal and transferring in the recipient (having lesser genetic quality) at proper timing (Block et al., 2010; Stroud, 2012).

Major hurdles for ET are high cost, low laboratory efficiency, low survivability of embryo by cryopreservation and calf produced by ET; cost-effective reproductive technology has restricted usage on farms but has proved to be beneficial (Campanile et al., 2010; Bonilla et al., 2014). In cattle, the number of follicles initiation per follicular wave is more than buffalo (Palanisammi et al., 2020). Hence, the ET technique is mostly practiced in cattle. While, in buffalos embryo production and transfer technology is important as like as in vitro ET (Neglia et al., 2011; Baruselli et al., 2013). Success rate around 90% of developed artificial insemination technique is achieved and this technique is used to control offspring gender by using sex semen for embryo production (Borchersen et al., 2009; Viana et al., 2017). In ET method, different steps followed from donor superovulation for more embryo production and recipient preparation for ET is costly and effective (Viana et al., 2017). In last two decades, embryo production in donor cattle and its transfer into recipient is increased (Baruselli et al., 2010; Watanabe et al., 2018).

This review details the embryo production technique, its transsfer from donor to recipient and the factor that interlinked for embryo production in donor and its transfer to recipient for offspring production. Different factors that effect on this, which are considered for the improvement of effectiveness of ET technology in buffalo and cattle. Perhaps, this review provides historically pioneer attempts at ET along with the swift changes within up to date. Having discussed ET at its peak, also it covers the futuristic steps for ET.

BENEFITS OF ET TECHNOLOGY

Timed ET, ovum pickup, and superovulation are playing an important role to reduce generation interval, and increase genetic improvement in cattle. Previous studies showed that synchronization is a good process for ovulation to assist reproductive technologies (Stewart et al., 2011; Das et al., 2022). In last decade, the insemination and the transfer technique of frozen-thawed semen or embryo were increased due to good fertility rate achievement (Cowan, 2010). In different studies, it is shown that ET is a safe technique and it does not transmit infectious diseases. Therefore, it has been indicated that use of ET is a salvage genetic material in case of disease outbreak and it is a valuable choice in demonstration of disease-free-herds (Wrathall et al., 2004; Mebratu et al., 2020). For high production of beef and dairy cattle, ET brings great number of calves/year/female (Wrathall et al., 2004). Many discriminations are observed in different phases of development on foreign and domestic studies of ET and their viability in cattle (Danchuk et al., 2020; Bollman et al., 2020; Roman et al., 2020; Grymak et al., 2020). The usage of ET technology is increasing in cattle by more offspring production in short lifespan. Normally, cows are monotococus, their ovaries have potential to ovulate routinely one ova and two ova rarely, and only single offspring can be obtained from cow per annum (Crowe et al., 2021). An effective technique of assisted reproductive technology called superovulation followed by timed AI is efficient to create large numbers of embryos in donor cattle (Mapletoft et al., 2009; Stroud and IETS, 2011).

In Vitro Embryo Production

For the genetic improvement in animal, in-vitro embryo production (IVP) shows an important enhancement for dairy and livestock production. In vitro embryo

 

Table I. Historical background of embryo transfer (ET).

Events	Year	Citation
ET in rabbit doe	1890, 2003, 2020	(Heape, 1891; Betteridge, 2003; Mebratu, 2020).
4 pregnancies in cattle by ET in Texas	1949	(Umbaugh, 1949).
First calf born by surgical ET	1951	(Willett et al., 1951; Mapletoft, 2013).
In Cambridge (England) Rowson and his college work on ET and get success in cattle and pig	1950-70	(Foote, 1970).
In-vitro fertilization and cloning technique increases after ET technology	Since 1970s	(Kennady et al., 2018).
ET technology developed in North America	1970	(Hasler, 2014; Moore, 2017) .
First calf birth through ET by E.L. Willet et al.,	1973	(Betteridge, 2000).
Establishment of International ET Society (IETS)	1974	(Theiber, 1992).
In 1980 non-surgical ET technique was first time developed on farm	1980	(Gordon, 2003; Wright 1981; John, 2008).
In cattle breeder ET technology used	1980	(SEIDEL, 1981).
Non-surgical (trans cervical catheterization in uterine horn) ET method developed in commercial level	1980	(Gordon, 2003; Wright, 1981; John, 2008; Mapletoft, 2018).
First young one produced through frozen-thawed embryo in mouse, cattle, rabbit, sheep, goat, horse, cat	1971, 1973, 1974, 1974, 1976, 1982, 1988	(Gordon, 2003; Kidie, 2019).
Multiple ovulation and ET (MOET) was first time introduced at University of Guelph in 1987. This concept showed that this technique is helpful for reduction of generation intervals, increased selection intensity and improved genetics	1987	(Smith, 1988).
World Veterinary Congress proposed symposium International Embryo Movement Symposium (IETS) in Montreal	1987	(Smith, 1988).
Pioneer award to Heapes by IETS	1990	(Biggers, 1991).
First calf birth at University of Winconsin by E.L. Willer et al through ET in cattle	2000	(Betteridge, 2000).
In South America invitro embryo production and developed	Since 2000s	(Hasler, 2014; Blondin, 2017)
538,312 embryo produced, out of which 52% were transfered by the freezing technique on farm and 15% produced by in vitro technique.	2002	(Theiber, 2003).
790,000 ET red (240,000 in vivo produced and 550,000 in-vitro produced embryo)	2004	(Theibier, 2005).
614,464 invitro bovine embryo produced and 464,582 ETred in globe	2014	(Perry, 2015).
More than 992,289 in vitro bovine embryo produced in the whole world	2017	(Viana, 2018).

 

production (IVEP) from oocytes recoup by ovum pickup is being increased, improved, and reported in last 20 years (Raghu et al., 2002; Souza-Fabjan et al., 2021). In vitro embryo production and transfer to recipient animal is costly but owing to better results, use of this technique is increasing (Sirard, 2018). For maturation of oocyte, fertilization, and embryo culture alter technique occur after first in vitro calf production (Ferre et al., 2020; Hansen, 2020)

Various studies have basis on improving the efficiency of in-vitro ET technique and different factors like follicular size, oocyte diameter for in vitro embryo production (Viana, 2018). The phase of the follicular wave genetic group and the animal category are influencing the ET technique (Ferreira et al., 2011; Viana, 2018). Since the last decade, Brazil has become highly developed in ET technology, and produced 57% in vitro embryo (IVP) of total world (Adifa et al., 2010).

Twinning in cattle

Embryo production is the best alternative source for the production of twin fetuses in monotococus animals such as cattle (Roman et al., 2020). Naturally, a single cow in her life can produce 8-10 calves with one calf per annum ratio. However, using improved ET technology, approximately 32 embryos can be obtained by single genetically superior cattle annually. The microsurgical ET technique is beneficial in pure breed herds of cattle for the production of identical twins (Muchemi, 2011; Turner, 2019). Indeed, the twinning method is expensive nonetheless; it escalates herd animals by 60%. Cloning is necessary for producing identical twins before transferring the embryo to recipient cattle (Lopez et al., 2017). While genetic selection through twining becomes unreliable. An alternative source of ET happens fruitful in the case of twining to produce more offspring in a short period (Kidie, 2019). Since the last three decades, the twinning rate (due to the production of multiple ova in a single estrous) in dairy cattle is increasing with the milk production (Garcia-Ispeirto, 2019). Sometimes, twining in cattle causes the death of twin fetuses after delivery, reproductive disorder, freemartin condition, and stillbirth (Andre et al., 2012; Philips and Jahinke, 2016; Fufa et al., 2016).

Applications of ET

Selection of donor

Donor selection has an immense role in the ET procedure. For donor selection, three basic attributes are mostly used to select donor cattle, such as reproductive ability, genetic superiority, the high value of progeny market (Mikkola, 2007; Besenfelder et al., 2020). Nutritional status, body condition score, genetic qualities, parity of animal, housing environment of donor, good reproductive age and performance, parity, the timing of superovulation, and the previous fertility record have key role in donor selection (Valenza et al., 2012; Burnett et al., 2018). Good health of donor cattle is necessary for better superovulation, enhancing fertility levels (Burnett et al., 2018). Good nutrition is necessary in donor cattle to maintain hormonal balance for fertilization in salpinx tube and embryo development from zygote at ampulla-isthmus junction before entering in the uterus by the proper hormonal balance that is maintain by good nutrition (Nicholas and Smith, 1983; Burnett et al., 2018). In donors, anovulation, fertilization failure, or early embryonic mortality have a great effect on the vitality of the embryo. In lactating donor dairy cattle, about 3.4-6.7% chances of anovulation occur during estrous (Peixoto et al., 2006). To mimic fertilization, in vitro embryo production, suitable culture media, and provision of a good environment is necessary as in oviduct (Bo and Mapletoft, 2020).

Two selection strategies for donors are proposed by scientists; one of these two is juvenile scheme (donors are heifer and they are selected according to pedigree) selection of male and female during puberty on the interpretation of female ancestor. While the second is “adult scheme” (donors are a high milk-producing animal) that depends on the selection of male on the interpretation of female ancestor (Peixoto et al., 2006; Bo and Mapletoft, 2020), and these strategies are very helpful for the selection of donor.

 

Table II. First young born after transfer of frozen thawed embryos (Gordon 2003, Kidie 2019).

Species	Researchers	Years
Mouse	Whittingham et al.	1971
Cow	Wilmut and Rowson	1973
Rabbit	Bank and Maure	1974
Sheep	Willadsen	1974
Rat	Whittingham	1975
Horse	Bilton and Moore	1976
Goat	Yamamoto et al	1982
Human	Zeilmaker et al	1984
Hmaster	Ridha and Dukelow	1985
Cat	Dresser et al	1988
Pig	Hayashi et al	1989
Rhesus monkey	Wolf et al.	1989

 

Superovulation in donor animal

Since late 1940s, ET was introduce by the best protocol of superovulation for dramatic embryo production and ET to recipient animals (Moore and Hasler, 2017). To achieve high blastocyst yield and pregnancy rate, several researchers are trying to amend super-ovulatory protocol (Mapletoft et al., 2002; Khan et al., 2022). The superovulation technique proved to be efficient for the generation of bulk embryos in donor cattle (Jaton et al., 2016). In the Canadian Holstein population, significant heritability of the great number of viable embryos produced from superovulation has been reported (Watanabe et al., 2017). Bos taurus cattle breed produced less number of follicles as compared to Bos indicus cattle in single ovulation while superovulation is helpful to produce enormous ova (Wolfenson and Roth, 2019). Gonadotropin-releasing hormone (GnRH) stimulates releasing of FSH and LH to regulate the ovarian functions (follicular growth, ovulation, corpus luteum development) (Batista et al., 2014). Anti-Mullerian hormone concentration in cattle breeds and the number of antral follicles in the ovarian cortex display vital role in embryo production via superovulation (Baldrighi et al., 2014; Souza et al., 2014). The high level of circulating anti-Mullerian hormone (AMH) and a huge number of antral follicles in the ovary result in much fruitful superovulation (Batista et al., 2014). Variations in the success of ET program are possible due to the variability of super ovulatory response (Forde et al., 2012).

Hormonal Therapy for Super Ovulation in Donor Cattle

Use of external hormone for superovulation can cause alteration in endometrium lining, salpinx tube, and follicular fluid (Forde et al., 2012; Santos et al., 2018; Fontes et al., 2019). FSH supports the super stimulation process and proves to be essential for follicular growth and maturation (Oliveira et al., 2014; Sanderson and Martinaz, 2020). Normally, saline diluents are used with FSH for superovulation. The use of slow-releasing diluent of FSH has increased the efficiency of superovulation without increasing embryo production levels. Despite high saline diluents with FSH is comparable with the use of hyaluronic acid as diluents in FSH for superovulation (Dias et al., 2013a).

Various reports clearly show that the progesterone and estrogen releasing devices are very helpful for effective follicular growth and superovulation (Dias et al., 2013a; Crosier et al., 2017; Fontes et al., 2019). FSH and eCG protocol are used for superovulation that escalate the estradiol concentration in blood plasma and salpinx tube (Santos et al., 2018; Oliveira et al., 2014; Barajas et al., 2019). In different studies, a beneficial effect of FSH with eCG for superovulation has been observed (Mattos et al., 2011; Barajas et al., 2019). eCG mimics FSH that provides support to growing follicles, owing to better results, eCG replaces the FSH protocols (Stroud and Hasler, 2006). Different studies reported that the progesterone and estrogen releasing devices are very helpful for effective superovulation (Dias et al., 2013a).

Factors affecting the superovulation

Different factors effect on the superovulation in cattle. The best time for AI in super ovulated cattle is 12-24 after showing first sign of estrous, single insemination is widely accepted but twice insemination is quite preferable for superovulation (Peter, 2019). The date of a donor’s last estrus with the appropriate heat dates is an important tool for the ability of superovulation (Dias et al., 2013a). Age, breed, parity and reproductive ability of donor whereas climate, nutrition of animal and FSH preparation are also dependent for superovulation in cattle (Besenfelder et al., 2020). In hot season, owing to heat stress embryonic reduction occurs via superovulation (Gadisa et al., 2019). Embryonic chromosomal anomaly is observed by using MOET as compared to in vitro embryo production (Hansen, 2020).

Selection of recipient

Selection of diseased free (mainly reproductive disease) recipient cattle is necessary to receive embryo and perform great number of pregnancy (Selk, 2010). Recipient selection has an essential role in the success of ET. Cattle having sound health, reproductive ability, milking yield, and good mothering ability is preferable as the recipient (Wu and Zan, 2012). In recipeint cattle, presence of well deveopled corpus luteum (Cl) after estrous have great role in intrauterine embryo development in good progesterone serum concentration (Mattos et al., 2011; Hansen, 2020).

Reproductive performance, nutritional status, parity, and body condition score checkup is necessary for selecting recipient cattle of a mixed breed, Bos tauras, Bos indicus (Gadisa et al., 2019; Selk, 2010). In some researches, a heifer seems fit as a recipient for ET, while some researchers prefer selected cows for ET. In Danish, selected 65% of recipients for the ET technique were milk-producing dairy cows (Wu and Zan, 2012).

 

Table III. Conception rate in repeat breeder cows after AI or ET (Arkadiusz, 2021).

Work	Conception rate of AI	Conception rate of ET	References
Surgically transferred of fresh embryo in cattle	-	70%	(Tanabe et al., 1985)
Frozen-thawed embryos used with timed ET after using control internal drug releasing device	heat 7.7% vs TAI 18.5%	53.8%	(Son et al., 2007)
Frozen-thawed invitro fertilized embryos used with the following AI	20.4%	41.5%	(Dochi et al., 2008)
Frozen-thawed embryos (92%) and fresh embryos (8%) following AI after natural heat	30%	52.6	(Canu et al., 2010)
Frozen-thawed in vitro fertilized embryos following AI	-	46.9%	(Yaginuma et al., 2019)

 

A proper estrous period is necessary for recipient cattle, whereas less pregnancy rate is observable in recipient cattle with an improper estrous period (Santos et al., 2018). For the recipient, a good progesterone level >16.9ng/ml and functional corpus luteum are necessary to maintain pregnancy in recipient cattle following ET (Abdelatty et al., 2018). Progesterone concentration in blood decreases below 1ng/ml reduces conception rate (Mattos et al., 2011). Fluctuation of pregnancy rate is observable in the recipient by using frozen and fresh embryos (Rodrigues et al., 2018).

Hormonal protocol in recipient animal for estrous synchronization

Synchronization by spontaneous and induced prostaglandin treatment of the recipient is necessary for ET. Uterine environment and optimal interaction of embryo in recipient cattle are necessary for embryo development (Baldrighi et al., 2014). Estrous period and estradiol blood concentration are influential for the change of uterine environment and viability of pregnancy by the growth of embryo (Rodrigues et al., 2018). In preliminarily cycling recipient cattle use of synchronizing products (estradiol, ECG, prostaglandin) helps to prepare the suitable uterine environment for embryo development and pregnancy viability (Genzebu, 2015; Macmillan et al., 2020). In the reproductive tract of recipient cattle estrogen, progesterone receptors and another growth factor such as insulin-like growth factor (IGF1) are necessary to prepare the uterine environment for embryo reception and for further pregnancy establishment (Bridges et al., 2013). To achieve high pregnancy rates, external progesterone supplementation through daily injection, insertion of controlled internal drug releasing (CIDR), or progesterone-releasing intravaginal device (PRID) have been reported (Núñez-Olivera et al., 2020; Siqueira et al., 2009).

Factors affecting the recipient for ET

In the recipient heifers and cows, many factors affect pregnancy by transfer of in vivo and in vitro produced embryos in cattle, and different studies have elucidated these factors (Gomez-Seco et al., 2017). Optimal management of recipient cattle is necessary for the success of ET program (Mebratu et al., 2020). In recipient cattle, corpus luteum is the transient gland present on the ovary results to maintain better pregnancy (Pugliesi, et al., 2013; O’Hara et al., 2014). The endocrine system has a great effect to prepare a suitable uterine environment and progesterone hormone level for embryo development in recipient uterus animals (Núñez-Olivera et al., 2020). Many researchers have used the NSAID protocol with flunixin meglumine as inhibitor, for PGf2α-synthesis to regress corpus luteum in the pregnant uterus in recipient (Wallace et al., 2011). Embryo survival rate and uterine tone can have dramatic reduction by protein accumulation due to the placing of large fluid in recipient uterine body (Wahjuningsih and Djati, 2013).

Cryopreservation of Embryo

Today embryo is transferred in recipient after freezing and thawing method (Hasler, 2014). An important technique of cryopreservation is fruitful to preserve embryos for future ET and transport to other states (Moore and Hasler, 2017). In cryopreservation, suitable cryopreserved are used for survival and viability of in vitro produced embryos (Kasimanickam et al., 2019). The slow freezing and controlled-rate freezing method are put in practice for cryopreservation of bovine embryos. In this method, an embryo is loaded in straw after dilution in suitable diluents and gradually cooled at 0.3-0.5 oC and the temperature gradually decreases up to -30 to -65oC, and then the straw plunged in liquid nitrogen -196 oC temperature (Martins et al., 2018b). Wahjuningsih and Djati (2013) have used sucrose with dimethyl sulphoxide solution having saline as diluent to cryopreserve embryo. Embryos can be stored at room temperature for one day for direct transfer from the donor to the recipients. For periods of 24 to 72 hours, the embryos must be stored at 4°C in PBS, medium 199, or medium L15, each supplemented with 50% FBS and these are adequate for maintaining the viability of the embryo between donor and recipient (Abdelatty et al., 2018). In North America during 2002, more than half of total embryo were freeze in ethylene glycol for future use direct transfer in animals (Abdelatty et al., 2018).

Result of Embryo After Cryopreservation

In embryo of Bos taurus cattle is less sensitive in comparison with Bos indicus in cryopreserved (Marinho et al., 2015). A previous study reported that the high pregnancy rate appears while using fresh embryos as compared to the frozen/thawed embryo (Ferraz et al., 2017). The negative effect on fertility and embryo quality can be decreased by the cryopreservation technique (Huang et al., 2019). The success of ET not only depends on the cryopreservation technique of the donor embryo but also depends on recipient animals (Ferraz et al., 2016). By cryopreservation, poor survivability of blastocyst of a produced embryo is observed (Estrada-Cortes et al., 2019). Minute changes of embryonic morphology are considerable having used cryopreservation and the pregnancy success is somehow altered (Febretrisiana and Pamungkas, 2017; Mori et al., 2015). Thawing is necessary for stored frozen embryo and improper thawing can decrease the viability of embryo cells and can cause low pregnancy success (Mori et al., 2015). After storage in cryoprotectant and transporting to long distances, approximately, 65% frozen-thawed embryos survive (Estrada-Cortes et al., 2019).

Pregnancy Rates and Factor Affecting after Frozen ET

Different factors affect the pregnancy rates in cattle by the widespread use of ET technology on commercial scale (Vieira et al., 2014). In these factors quality of embryo, season, fresh or thawed embryo used, parity of donor and recipient mother, nutritional status, technicality, site, and time of embryo deposition in uterine horn have gigantic influence (Moore and Hasler, 2017). The technique of using frozen embryos is common, but 10-15% less pregnancy rate occur by using frozen embryos beside the fresh embryos (Luo et al., 2021). The highest pregnancy rate is achievable having used the highest quality embryo (Gadisa et al., 2019).

Experienced professionals have reported that 60% and 70% pregnancy rates occur having processed thawed embryo and fresh embryo, respectively (Block et al., 2010). Better pregnancy rate in recipient cattle are achieved by human chorionic gonadotropin (Hcg) gonadotrpin releasing hormone treatmment in first week of estrous cycle (Pereira et al., 2016). And also effectiveness of luteotropic hormone is seen in increasing pregnancy rate after ET in recipient cattle (Vieira et al., 2014).

In 2017, it was reported that 50% of global embryos were produced in 2014 and pregnancy rates of in vivo derived embryo were higher than in vitro derived embryo (55.9% compared with 19.8%) (Block et al., 2010; Gadisa, 2019). In the recipient dairy heifers, mostly embryo losses have been seen between 32-60 days of pregnancy (Pereira et al., 2016). While 0-34% of pregnancy losses seen in recipient cows having in-vitro fertilized ET (Ealy et al., 2019). Great pregnancy loss occurs during early pregnancy diagnosis after ET in recipient cattle (Souza et al., 2014). Pregnancy loss can occur due to less match of endometrial cell and conceptus rate (Viana et al., 2017). The post-estrous uterine development asynchrony of donor and recipient mother affects pregnancy rate (Ferraz et al., 2016).

Use of Sexed Semen for ET

For optimal breeding, the conventional use of sexed semen for embryo production is increasing day by day (Garcia-Guerra et al., 2016). For embryo production, the use of sexed semen is more beneficial and has a clear advantage for the end-user. Embryo by sexed semen helps produce animal according to need like milk or meat producing animal (Stewart et al., 2011; Tribulo et al., 2012). For increasing efficiency of animal production, great potential and increasing ratio in cattle is observable via utilizing sex-sorted semen for embryo production (Ulbrich et al., 2010; Heikkila and Peippo, 2012). In dairy cattle, pregnancy cost decreases by the use of embryos produced through sexed semen for in-vitro embryo production (Maxwell et al., 2004, Dire, 2020).

Effect of heat stress on embryo

Gametes (sperm and egg) are thermolabile because they form and remain active at an optimum temperature in uterine environment that is below normal body temperature; heat stress degrades and blood flow regulates it (Schenk et al., 2006; Smith et al., 2018). Heat stress have great effect on the pregnancy rate. In heat stress conditions, hormonal levels disrupt as the ovarian function changes, resultantly, embryo rejection occurs. Lately, it’s been reported that lactating cows inseminated through AI under a thermal stress environment have 18% chances of infertility (Baruselli et al., 2020). According to AI, ET has a great chance of viability and survival in the hot climate. ET at blastocyst stage have thermal stress resistance, meanwhile, ET in heat stress condition has high fertility rate (Whitfield, 2016; Cotter, 2017). High environmental ambient temperature and relative humidity affect on the homeo thermic status of animal that indirectly effect on the uterine environment that can caused detrimental effects on the embryo production and its mortality (Nabenishi et al., 2017). In heat stress, body temperatures increases that caused releasing of the prostaglandin hormone and negative impact occurs on corpus luteum that can cause the embryonic loss and reduces the pregnancy loss (Kim et al., 2014; Sakatani, 2017; Besbaci et al., 2021).

Embryo transfer in repeat breeder

Repeat breeders are the animals that are not conceiving by three or more artificial insemination and natural breeding (Dochi et al., 2008; Tiwari et al., 2019). Many authors reported that better pregnancy rate is achieving by ET in repeat breeder cattle. In repeat breeder cattle, uterine environment effects on the oocyte and embryo development. While, ET in repeat breeder has deleterious effect on pregnancy (Ahmed et al., 2016). In the repeat breeder cattle, great pregnancy success achieved through ET following AI (Mori et al., 2015).

CONCLUSIONS

The constantly increasing human population influences the food chain thus demand for excessive production escalates, since then, ET is one of the major drivers to balance the animal productivity in order to balance the supply-and-demand chain. This advanced technology has enhanced the parity, improvised conception rate, and reduced pregnancy failures/complications. This review details the embryo production technique, transfer of embryo from donor to recipient and the factor that are necessary for transfer of embryo from donor embryo production to offspring. Perhaps, this review provides historically pioneer attempts at ET along with the swift changes within up-to-date. Having discussed ET at its peak, also it covers the futuristic steps for ET.

Statement of conflicts of interest

The authors have declared no conflict of interest.

References

Abdelatty, A.M., Iwaniuk, M.E., Potts, S.B., and Gad, A., 2018. Influence of maternal nutrition and heat stress on bovine oocyte and embryo development. Int. J. Vet. Sci. Med., 6(Suppl.): S1-S5. https://doi.org/10.1016/j.ijvsm.2018.01.005

Adifa, N.S., Astuti, P., and Widayati, D.T., 2010. The effect of chorionic gonadotrophin addition into maturation medium on the ability of oocytes maturation, fertilization, and embryo development in vitro on the Ettawa crossbreed. Livest. Bull., 34: 8-15. https://doi.org/10.21059/buletinpeternak.v34i1.101

Ahmed, N., Kathiresan, D., Ahmed, F.A., Lalrintluanga, K., Mayengbam, P., and Gali, J.M., 2016. Initiating Ovsynch on day 6 post estrus onset ± post AI early luteal phase GnRH treatment to improve ovarian and fertility response in repeat breeding crossbred cattle. Indian J. Anim. Reprod., pp. 5–7.

Alkan, H., Karasahin, T., Dursun, S., Satilmis, F., Erdem, H., and Guler, M., 2020. Evaluation of the factors that affect the pregnancy rates during ET in beef heifers. Reprod. Domest. Anim., 55: 421-428. https://doi.org/10.1111/rda.13623

Andre, W., Vaz quez, C., Garcia-Ispeirto, I., Ganau, S., Fricke, P.M., Lopes G.F., 2012. Effect of twinning on the subsequent reproductive performance and productive live span of high producing dairy cows. Theriogenology, 78: 2061-2070. https://doi.org/10.1016/j.theriogenology.2012.07.027

Arkadiusz, N., 2021. ET as an option to improve fertility in repeat breeder dairy cows. J. Vet. Res., 65. https://doi.org/10.2478/jvetres-2021-0018

Baldrighi, J.M., Sá Filho, M.F., Batista, E.O.S., Lopes, R.N.V.R., Visintin, J.A., Baruselli, P.S., and Assumpção, M.E.O.A., 2014. Anti-Mullerian hormone concentration and antral ovarian follicle population in murrah heifers compared to Holstein and Gyr kept under the same management. Reprod. Domest. Anim., 49: 1015-1020. https://doi.org/10.1111/rda.12430

Barajas, J.L., Cedeño, A., Andrada, S., Ortega, J., Oviedo, J.M., Tribulo, A., Tribulo, R., Tribulo, H., and Bó, G.A., 2019. Embryo production using follicle stimulating hormone (FSH) or FSH + equine chorionic gonadotropin in beef donors. Reprod. Fertil. Dev., 31: 223. https://doi.org/10.1071/RDv31n1Ab196

Baruselli, P.S., Ferreira, R.M., Vieira, L.M., Souza, A.H., Bó, G.A., and Rodrigues, C.A., 2020. Use of ET to alleviate infertility caused by heat stress. Theriogenology, 155: 1-11. https://doi.org/10.1016/j.theriogenology.2020.04.028

Baruselli, P.S., Ferreira, R.M., Sá Filho, M.F., Nasser, L.F.T., Rodrigues, and Bó G.A.C., 2010. Bovine ET recipient synchronisation and management in tropical environments. Reprod. Fertil. Dev., 22: 67-74. https://doi.org/10.1071/RD09214

Baruselli, P.S., Soares, J.G., Gimenes, L.U., Monteiro, B.M., Olazarri, M.J., and Carvalho, N.A.T., 2013. Control of buffalo follicular dynamics for artificial insemination, superovulation and in vitro embryo production. Buffalo Bull., 32: 160

Batista, E.O.S., Macedo, G.G., Sala, R.V., Ortolan, M.D.D.V., Sa Filho, M.F., Del Valle, T.A., Jesus, E.F., Lopes, R.N.V.R., Renno, F.P., and Baruselli, P.S., 2014. Plasma antimullerian hormone as a predictor of ovarian antral follicular population in Bos indicus (Nelore) and Bos taurus (Holstein) heifers. Reprod. Dom. Anim., 49: 448-452. https://doi.org/10.1111/rda.12304

Batista, E.O.S., Guerreiro, B.M., Freitas, B.G., Silva, J.C.B., Vieira, L.M., Ferreira, R.M., Rezende, R.G., Basso, A.C., Lopes, R.N.V.R., and Rennó, F.P., 2016. Plasma anti-Müllerian hormone as a predictive endocrine marker to select Bos taurus (Holstein) and Bos indicus (Nelore) calves for in vitro embryo production. Domest. Anim. Endocrinol., 54: 1-9. https://doi.org/10.1016/j.domaniend.2015.08.001

Besbaci, M., Abdelli, A., Belabdi, I., and Raboisson, D., 2021. Non-steroidal anti-inflammatory drugs at ET on pregnancy rates in cows: A meta-analysis. Theriogenology, 171: 64-71. https://doi.org/10.1016/j.theriogenology.2021.04.010

Besenfelder, U., Brem, G., and Havlicek, V., 2020. Environmental impact on early embryonic development in the bovine species. Animal, 14(S1): s103–s112. https://doi.org/10.1017/S175173111900315X

Betteridge, K.J., 2000. Reflections on the golden anniversary of thefirst ET to produce a calf. Theriogenology, 53: 3–10. https://doi.org/10.1016/S0093-691X(99)00235-6

Betteridge, K.J., 2003. A history of farm animal ET and some associated techniques. Anim. Reprod. Sci., 79: 203-244. https://doi.org/10.1016/S0378-4320(03)00166-0

Block, J., Bonilla, L., and Hansen, P.J., 2010. Efficacy of in vitro ET in lactating dairy cows using fresh or vitrified embryos produced in a novel embryo culture medium. J. Dairy Sci., 93: 5234–5242. https://doi.org/10.3168/jds.2010-3443

Blondin, P., 2017. Logistics of large scale commercial IVP embryo production. Reprod. Fert. Dev., 29: 32-36. https://doi.org/10.1071/RD16317

Bo, G.A., and Mapletoft, R.J., 2020. Super stimulation of ovarian follicles in cattle: gonadotropin treatment protocols and FSH profiles. Theriogenology, 150: 353–359. https://doi.org/10.1016/j.theriogenology.2020.02.001

Bollman, M., Greenhawk, A., Shipley, A., Gibbons, P., 2020. Ovarian profile and pregnancy rates following ovulation synchronization and timed-artificial insemination in dairy cows. College of Veterinary Medicine. Lincoln M.U. pp. 1291-1300.

Bonilla, L., Block, J., Denicol, A.C., and Hansen, P.J., 2014. Consequences of transfer of an in vitro produced embryo for the demand resultant calf. J. Dairy Sci., 97: 229–239. https://doi.org/10.3168/jds.2013-6943

Borchersen, S., Peacock, M., and Danish, A.I., 2009. field data with sexed semen. Theriogenology, 71: 59–63. https://doi.org/10.1016/j.theriogenology.2008.09.026

Bridges, G.A., Day, M.L., Geary, T.W., and Cruppe, L.H., 2013. Deficiencies in the uterine environment and failure to support embryonic development. J. Anim. Sci., 91: 3002-3013. https://doi.org/10.2527/jas.2013-5882

Burnett, T.A., Polsky, L., Kaur, M., and Cerri, R.L.A., 2018. Effect of estrous expression on timing and failure of ovulation of Holstein dairy cows using automated activity monitors. J. Dairy Sci., 101: 11310–11320. https://doi.org/10.3168/jds.2018-15151

Campanile, G., Baruselli, P.S., Neglia, G., Vecchio, D., Gasparrini, B., Gimenes LU., Lindsay, U. Gimenes, L.Z. and Michael, J.D., 2010. Ovarian function in the buffalo and implications for embryo development and assisted reproduction. Anim. Reprod. Sci., 121: 1e11. https://doi.org/10.1016/j.anireprosci.2010.03.012

Choudharyn, K., Kavya K., Jerome, A. and Sharma, R., 2016. Advances in reproductive biotechnologies. 9: 388-395. https://doi.org/10.14202/vetworld.2016.388-395

Cotter, P., 2017. Basophilia and basophiliosis in caged hens at 18 and 77 weeks. Int. J. Poult. Sci., 16: 23–30. https://doi.org/10.3923/ijps.2017.23.30

Cowan, T., 2010. Biotechnology in animal agriculture: Status and current issues. Analyst in natural resources and rural development. Congress. Res. Ser., pp. 3.

Crosier, A.E., Comizzoli, P., Koester, D.C., and Wildt, D.E., 2017. Circumventing the natural, frequent oestrogen waves of the female cheetah (Acinonyx jubatus) using oral progestin (Altrenogest). Reprod. Fertil. Dev., 29: 1486-1498. https://doi.org/10.1071/RD16007

Crowe, A.D., Lonergan, P., and Butler, S.T., 2021. Invited review: Use of assisted reproduction techniques to accelerate genetic gain and increase value of beef production in dairy herds. J. Dairy Sci., 104: 12189-12206. https://doi.org/10.3168/jds.2021-20281

Danchuk, O.V., Karposvkii, V.I., Tomchuk, V.A., Zhurenko, O.V., Bobryts’ka, O.M. and Trokoz, V.O., 2020. Temperament in cattle: A method of evaluation and main characteristics. Neurophysiology, 52: 73–79. https://doi.org/10.1007/s11062-020-09853-6

Das, D.N., Paul, D., and Mondal, S., 2022. Role of biotechnology on animal breeding and genetic improvement. In: Emerging issues in climate smart livestock production. Academic Press. pp. 317-337. https://doi.org/10.1016/B978-0-12-822265-2.00015-6

Dias, F.C.F., Dadarwa, L.D., Adams, G.P., Mrigank, H., Mapletoft, R.J., and Singh, J., 2013a. Length of the follicular growing phase and oocyte competence in beef heifers. Theriogenology, 79: 1177-1183. https://doi.org/10.1016/j.theriogenology.2013.02.016

Dire Babura, M., 2020. Comparative study on efficiency of sexed semen and conventional semen on in vivo produced bovine embryo quality and quantity of boran and holstein-boran cross breed in bishoftu, Ethiopia. Doctoral dissertation, Addis Ababa University.

Dochi, O., Takahashi, K., Hirai, T., Hayakawa, H., Tanisawa, M., Yamamoto, Y., and Koyama, H., 2008. The use of ET to produce pregnancies in repeat-breeding dairy cattle. Theriogenology, 69: 124–128. https://doi.org/10.1016/j.theriogenology.2007.09.001

Dochi, S., 2019. Direct transfer of frozen-thawed bovine embryos and application in cattle reproduction management. J. Reprod. Manage., 65: 389-396. https://doi.org/10.1262/jrd.2019-025

Ealy, A.D., Wooldridge, L.K., and McCoski, S.R., 2019. Post-transfer consequences of in vitro-produced embryos in cattle. J. Anim. Sci., 97: 2555–2568. https://doi.org/10.1093/jas/skz116

Estrada-Cortes, E., Ortiz, W.G., Chebel, R.C., Jannaman, E.A., Moss, J.I., de Castro, F.C., Zolini, A.M., Staples, C.R., and Hansen, P.J., 2019. Embryo and cow factors affecting pregnancy per ET for multiple-service, lactating Holstein recipients. Transl. Anim. Sci., 3: 60–65. https://doi.org/10.1093/tas/txz009

Faizah, H.M.S., Richard F., Meena P., Stanley, K.L., Amriana, H., Alhassany, A., Yadav, S.B., Marie, L., Crouch, B., and Saipul, B.A.R., 2011. Multiple ovulation ET (MOET) in dairy cattle in Gatton. Malays. J. Vet. Res., 9: 109-116.

Febretrisiana, A., and Pamungkas, F.A., 2017. Utilization of assisted hatching techniques to enhance embryo implantation. Watazoa, 27: 35-44. https://doi.org/10.14334/wartazoa.v27i1.1412

Ferraz, P.A., Burnley, C., Karanja, J., Viera-Net, A., Santos, J.E.P., Chebel, R.C., and Galvão, K.N., 2017. Factors affects the success of a large ET program in Holstein cattle in a commercial herd in the southeast region of the United States. Natl. Center Biotechnol. Inf., 86: 1834-1841. https://doi.org/10.1016/j.theriogenology.2016.05.032

Ferraz, P.A., Burnley, C., Karanja, J., Viera-Neto, A., Santos, J.E.P., Chebel, R.C., and Galvão, K.N., 2016. Factors affecting the success of a large ET program in Holstein cattle in a commercial herd in the southeast region of the United States. Theriogenology, 86: 1834-1841. https://doi.org/10.1016/j.theriogenology.2016.05.032

Ferre, L.B., Kjelland, M.E., Taiyeb, A.M., Campos-Chillon, F., and Ross, P.J., 2020. Recent progress in bovine in vitro-derived embryo cryotolerance: impact of in vitro culture systems, advances in cryopreservation and future considerations. Reprod. Domest. Anim., 55: 659–676. https://doi.org/10.1111/rda.13667

Ferreira, R.M., Ayres, H., Chiaratti, M.R., Ferraz, M.L., Araújo, A.B., Rodrigues, C.A., Watanabe, Y.F., Vireque, A.A., Joaquim, D.C., Smith, L.C. and Meirelles, F.V. 2011. The low fertility of repeat-breeder cows duringsummer heat stress is related to a low oocyte competence to develop into blastocysts. J. Dairy Sci., 94: 2383–2392. https://doi.org/10.3168/jds.2010-3904

Fontes, P.K., Razza, E.M., Pupulim, A.G.R., Barros, C.M., and de Souza Castilho, A.C., 2019. Equine chorionic gonadotropin increases estradiol levels in the bovine oviduct and drives the transcription of genes related to fertilization in super stimulated cows. Mol. Reprod. Dev., 86: 1582–1591. https://doi.org/10.1002/mrd.23243

Foote, R.H., and Onuma, H., 1970. Superovulation, ovum collection, culture and transfer. A review. J. Dairy Sci., 53: 1681. https://doi.org/10.3168/jds.S0022-0302(70)86463-3

Forde, N., Carter, F., di Francesco, S., Mehta, J.P., Garcia- Herreros, M., Gad, A., Tesfaye, D., Hoelker, M., Schellander, K., and Lonergan, P., 2012. Endometrial response of beef heifers on day 7 following insemination to supraphysiological concentrations of progesterone associated with superovulation. Physiol. Genom., 44:1107–1115. https://doi.org/10.1152/physiolgenomics.00092.2012

Frade, M.C., Frade, C., Cordeiro, M.B., Sá Filho, M.F., Mesquita, F.S., Nogueira Gde, P., Binelli, M., and Membrive C.M., 2014. Manifestation of estrous behavior and subsequent progesterone concentration at timed-ET in cattle are positively associated with pregnancy success of recipients. Anim. Reprod. Sci., 151: 85–90. https://doi.org/10.1016/j.anireprosci.2014.09.005

Fufa, N., Abera, D., and Kabeta, T., 2016. Review on bovine ET. Eur. J. biol. Sci., 8: 79-84.

Gaddis, KL., Parker, S.E., Dikmen, D.J., Null, J.B., Cole, B. and Hansen, P.J., 2017. Evaluation of genetic components in traits related to superovulation, in vitro fertilization, and ET in Holstein cattle. J. Dairy Sci., pp. 2877-2891. https://doi.org/10.3168/jds.2016-11907

Gadisa, M., Walkite, F., and Misgana, D., 2019. Review on ET and it’s application in animal production. Asian J. Med. Sci. Res. Rev., 1: 04-12.

Garcia-Guerra, A., Sala, R.V., Baez, G.M., Fosado, M., Melo, L.F., Motta, J.C.L., Leffers, L., Walleser, E.A., Ochoa, J.C., Moreno, J.F., and Wiltbank, M.C., 2016. Treatment with GnRH on day 5 reduces pregnancy loss in heifers receiving in vitro-produced expanded blastocysts. Reprod. Fertil. Dev., 28: 185. https://doi.org/10.1071/RDv28n2Ab110

Garcia-Ispeirto, I., and Lopez Gatiuz, F., 2019. Abortion in dairy cattle with advanced twin pregnancies incidence and timing. Reprod. Domest., 54(Suppl-4): 50-53. https://doi.org/10.1111/rda.13510

Genzebu, D., 2015. A review of ET technology in cattle. Glob. J. Anim. Sci. Res., 3: 562-575.

Gomez-Seco, C., Alegre, B., Martinez-Pastor, F., Prieto, J.G., González-Montaña, J.R., Alonso, M.E. and Domínguez, J.C., 2017. Evolution of the corpus luteum volume determined ultrasonographically and its relation to the plasma progesterone concentration after artificial insemination in pregnant and nonpregnant dairy cows. Vet. Res. Commun., 41: 183–188. https://doi.org/10.1007/s11259-017-9685-x

Gordon, I., 2003. Laboratory production of cattle embryos second edition. Ireland Biotechnol. Agric., 27: 13-17. https://doi.org/10.1079/9780851996660.0000

Grymak, Y., Skoromna, O., Stadnytska, O., Sobolev, O., Gutyj, B., Shalovylo, S., Hachak, Y., Grabovska, O., Bushueva, I., Denys, G., Hudyma, V., Pakholkiv, N., Jarochovich, I., Nahirniak, T., Pavliv, O., Farionik, Т., and Bratyuk, V., 2020. Influence of Thireomagnile and Thyrioton preparations on the antioxidant status of pregnant cows. Ukrain. J. Ecol., 10: 122-126. https://doi.org/10.15421/2020_19

Hansen, P.J., 2020. Mplications of assisted reproductive technologies for pregnancy outcomes in mammals. Annu. Rev. Anim. Biosci., 8: 395–413. https://doi.org/10.1146/annurev-animal-021419-084010

Hasler, J.F., 2014. Forty years of ET in cattle: A review focusing on the journal Theriogenology, the growth of the industry in North America, and personal reminisces. Theriogenology, 81: 152–169. https://doi.org/10.1016/j.theriogenology.2013.09.010

Heikkila, A., Peippo, J., 2012. Optimal utilization of modern reproductive technologies to maximize the gross margin of milk production. Anim. Reprod. Sci., 132: 129–138. https://doi.org/10.1016/j.anireprosci.2012.05.004

Huang, Z., Gao, L., Hou, Y., Zhu, S., and Fu, X., 2019. Cryopreservation of farm animal gametes and embryos: recent updates and progress. Front. agric. Sci. Eng., 6: 42-53. https://doi.org/10.15302/J-FASE-2018231

Humblot, P., Le Bourhis, D., Fritz, S., Colleau, J.J., Gonzalez, C., GuyaderJoly, C., Malafosse, A., Heyman, Y., Amigues, Y., Tissier, M. and Ponsart, C., 2010. Reproductive technologies and genomic selection in cattle. Vet. Med. Int., 2010: 192787. https://doi.org/10.4061/2010/192787

Jaton, C., Koeck, A., Miglior, F., Price, C.A., Sargolzaei, M., and Schenkel, F.S., 2016. Genetic analysis of super ovulatory response of Holstein cows in Canada. J. Dairy Sci., 99: 3612–3623. https://doi.org/10.3168/jds.2015-10349

John, F.G., 2008. Utilization of ET in beef cattle agriculture and natural resources, 17: 8. http://ohioline.osu.edu

Kader, A.K., Choi, A., Orief, Y., and Agarwal, A., 2009. Factors affecting the outcome of human blastocyst vitrification. Reprod. Biol. Endocrinol., 7: 1-11. https://doi.org/10.1186/1477-7827-7-99

Kasimanickam, R., Kasimanickam, V., Gold, J., Moore, D., Kastelic, J.P., Pyrdek, D., Ratzburg, K., 2019. Injectable or transdermal flunixin meglumine improves pregnancy rates in ET recipient beef cows without altering returns to estrus. Theriogenology, 140: 8-17. https://doi.org/10.1016/j.theriogenology.2019.08.011

Kennady, V.J., Manimegalai, Ranjeet, V., and Vikas, C., 2018. ET technology in animals: An overview. J. Ent. Zool. Stud., 6: 2215-2218.

Khan, S.U., Jamal, M.A., Su, Y., Wei, H.J., Qing, Y., and Cheng, W., 2022. Towards improving the outcomes of multiple ovulation and ET in sheep, with particular focus on donor superovulation. Vet. Sci., 9: 117. https://doi.org/10.3390/vetsci9030117

Kidie, H.A., 2019. Review on growth and development of multiple ovulation and ET technology in cattle. World Sci. News, pp. 191-211.

Kim, S.S., Bang, J.I., Fakruzzaman, M., Lee, K.L., Ko, D.H., Ghanem, N., Zhongde, W. and Kong, I-K., 2014. Effects of flunixin meglumine and prostaglandin F2a treatments on the development and quality of bovine embryos in vitro. Reprod. Domest. Anim., 49: 957e63. https://doi.org/10.1111/rda.12413

Loi, P., Toschi, P.F., Zacchini, G., Ptak, P.A., Scapolo, E., Capra, A., Stella., Marsan, P.A. and Williams, J.L., 2016. Synergies between assisted reproduction technologies and functional genomics. Genet. Sel. Evol., 48: 53. https://doi.org/10.1186/s12711-016-0231-z

Lopez, Gatiius, F., Andreu, V.C., Mur Novales, R., Cabrera, V.E., Hunter, R.H.F., 2017. The dilemma of twin pregnancy in dairy cattle a review of practical aspects. Livest. Sci., 197: 12-16. https://doi.org/10.1016/j.livsci.2017.01.001

Luo, Y., Liu, S., Su, H., Hua, L., Ren, H., Liu, M., and Li, Y., 2021. Low serum LH levels during ovarian stimulation with GnRH antagonist protocol decrease the live birth rate after fresh ET but have no impact in freeze-All cycles. Front. Endocrinol., 12: 405. https://doi.org/10.3389/fendo.2021.640047

Macmillan, K., Gobikrushanth, M., Sanz, A., Bignell, D., Boender, G., Macrae, L., Mapletoft, R.J., Colazo, M.G., 2020. Comparison of the effects of two shortened timed-AI protocols on pregnancy per AI in beef cattle. Theriogenology, 142: 85-91. https://doi.org/10.1016/j.theriogenology.2019.09.038

Mapletoft, R.J., Bo, G.A., and Baruselli, P.S., 2009. Control of ovarian function for assisted reproductive technologies in cattle. Anim. Reprod., 6: 114e24.

Mapletoft, R., 2013. History and perspectives on bovine ET. Anim. Reprod., 10: 168-173.

Mapletoft, R.J., 2018. History and perspectives on bovine ET. Anim. Reprod., 10: 168-173.

Mapletoft, R.J., Bó, G.A., Baruselli, P.S., Menchaca, A., and Sartori, R., 2018. Evolution of knowledge on ovarian physiology and its contribution to the widespread application of reproductive biotechnologies in South American cattle. Anim. Reprod., 15(Suppl. 1): 1003-1014. https://doi.org/10.21451/1984-3143-AR2018-0007

Mapletoft, R.J., Bennett S.K., and Adams, G.P., 2002. Recent advances in the superovulation in cattle. Reprod. Nutr. Dev., 42: 601e11. https://doi.org/10.1051/rnd:2002046

Marinho, L.S., Sanches, B.V., Rosa, C.O., Tannura, J.H., Rigo, A.G., Basso, A.C., Pontes, J.H., and Seneda, M.M., 2015. Pregnancy rates to fixed ET of vitrified IVP Bos indicus, Bos taurus or Bos indicus × Bos taurus embryos. Reprod. Domest. Anim., 50: 807–811. https://doi.org/10.1111/rda.12591

Martins, T., Pugliesi, G., Sponchiado, M., Gonella-Diaza, A.M., Ojeda-Rojas, O.A., Rodriguez, F.D., Ramos, R.S., Basso, A.C., and Binelli, M., 2018b. Perturbations in the uterine luminal fluid composition are detrimental to pregnancy establishment in cattle. J. Anim. Sci. Biotechnol., 9: 70. https://doi.org/10.1186/s40104-018-0285-6

Mattos, M.C., Bastos, M.R., Guardieiro, M.M., Carvalho, J.O., Franco, M.M., Mourão, G.B., and Barros, C.M., 2011. Improvement of embryo production by the replacement of the last two doses of porcine follicle-stimulating hormone with equine chorionic gonadotropin in Sindhi donors. Anim. Reprod. Sci., 125: 119-123. https://doi.org/10.1016/j.anireprosci.2011.02.028

Maxwell, W.M.C., Evans, G., Hollinshead, F.K., Bathgate, R., De Graff, S.P., Eriksson, B.M., Gillian, L., Morton, K.M., and O’Brien, J.K., 2004. Integration of sperm sexing technology into the ART toolbox. Anim. Reprod. Sci., 82-83: 79-95. https://doi.org/10.1016/j.anireprosci.2004.04.013

Mebratu, B., Fesseha, H., and Goa, E., 2020. ET in cattle production and its principle and applications. Int. J. Pharm. Biomed. Res., 7: 40-54. https://doi.org/10.18782/2394-3726.1083

Mikkola, M., 2007. Superovulation and ET in dairy cattle effect of management factors with emphasis on sex-sorted semen. Academic dissertation, pp. 79.

Moore, S.G., and Hasler, J.F.A., 2017. A 100-year review: Reproductive technologies in dairy science. J. Dairy Sci., 100: 10314–10331. https://doi.org/10.3168/jds.2017-13138

Mori, M., Hayashi, T., Isozaki, Y., Takenouchi, N., and Sakatani, M., 2015. Heat shock decreases the embryonic quality of frozen-thawed bovine blastocysts produced in vitro. J. Reprod. Dev., 61: 423-429. https://doi.org/10.1262/jrd.2015-003

Muchemi, J., 2011. New ET technology to boost dairy farmers fortune, Sunday Nation, Kenya, pp. 26-27.

Nabenishi, H., Kitahara, G., Takagi, S., Yamazaki, A., and Osawa, T., 2017. Relationship between plasma anti-Müllerian hormone concentrations during the rearing period and subsequent embryo productivity in Japanese black cattle. Domest. Anim. Endocrinol., 60: 19–24. https://doi.org/10.1016/j.domaniend.2017.01.002

Neglia, G., Gasparrini, B., Vecchio, D., Boccia, L., Varricchio, E., Di Palo, R., Zicarelli, L. and Campanile, G., 2011. Long term effect of ovum pick up in buffalo species. Anim. Reprod. Sci., 123: 180. https://doi.org/10.1016/j.anireprosci.2011.01.011

Nicholas, F.W., and Smith, C., 1983. Increased rates of genetic change in dairy cattle by ET and splitting. Anim. Prod., 36: 341-353. https://doi.org/10.1017/S0003356100010382

Núñez-Olivera, R., Cuadro, F., Bosolasco, D., de Brun, V., de la Mata, J., Brochado, C., Meikle, A., Bó, G.A., and Menchaca, A., 2020. Effect of equine chorionic gonadotropin (eCG) administration and proestrus length on ovarian response, uterine functionality and pregnancy rate in beef heifers inseminated at a fixed-time. Theriogenology, 151: 16-27. https://doi.org/10.1016/j.theriogenology.2020.03.031

O’Hara, L., Forde, N., Kelly, A.K., and Lonergan, P., 2014. Effect of bovine blastocyst size at ET on day 7 on conceptus length on day 14: Can supplementary progesterone rescue small embryos? Theriogenology, 81: 1123-1128. https://doi.org/10.1016/j.theriogenology.2014.01.041

Oguejiofor, C.F., 2019. Prospects in the utilization of assisted reproductive technologies (ART) towards improved cattle production in Nigeria. Niger. J. Anim. Prod., 46: 73-80. https://doi.org/10.51791/njap.v46i5.278

Oliveira, A.C.S., Mattos, M.C.C., Bastos, M.R., Trinca, L.A., Razza, E.M., Satrapa, R.A., Sartori, R., and Barros, C.M., 2014. Efficiency of super stimulatory protocol P-36 associated with the administration of eCH and LH in Nelore cows. Theriogenology, 82: 715-719. https://doi.org/10.1016/j.theriogenology.2014.06.006

Palanisammi, A., Satheshkumar, S. and Rangasamy, S., 2020. Superovulatory response and embryo yield in buffaloes (Bubalus bubalis). J. Entomol. Zool. Stud., 8: 1468-1470.

Peixoto, M.G.C.D., Bergmann, J.A.G., Fonseca, C.G., Penna, V.M., and Pereira, C.S., 2006. Effects of environmental factors on multiple ovulation of zebu donors. Arquivo Brasil. Med. Vet. Zoot., 58: 567-574. https://doi.org/10.1590/S0102-09352006000400019

Pereira, M.H.C., Wiltbank, M.C., and Vasconcelos, J.L.M., 2016. Expression of estrus improves fertility and decreases pregnancy losses in lactating dairy cows that receive artificial insemination or ET. J. Dairy Sci., 99: 2237-2247. https://doi.org/10.3168/jds.2015-9903

Perry, G., 2015. Statistics of embryo collection and transfer in domestic animals. Embryo Transfer Newsl., 33: 9.

Peter, J.H., 2019. Embryo and cow factors affecting pregnancy per ET for multiple-service, lactating Holstein recipients. Transl. Anim. Sci., 3: 60–65. https://doi.org/10.1093/tas/txz009

Philips, P., and Jahinke, M., 2016. Embryo transfer (Technique, donors, and recipients). Articles in veterinary clinics of North America Food animal practice. pp. 366-384.

Pugliesi, G., Oliveria, M.L., Scolari, S.C., Lopes, E., Pinaffi, F.V., Miagawa, B.T., Paiva, Y.N., Maio, J.R., Noqueira, G.P., and Binelli, M., 2013. Corpus luteum development and function after supplementation of long-acting progesterone during the early luteal phase in beef cattle. Reprod. Dom. Anim., 49: 85-91. https://doi.org/10.1111/rda.12231

Raghu, H.M., Nandi, S., and Reddy, S.M., 2002. Follicle size and oocyte diameter inrelation to developmental competence of buffalo oocytes in vitro. Reprod. Fertil. Dev., 14: 55–61. https://doi.org/10.1071/RD01060

Rico, C., Drouilhet, L., Salvetti, P., Dalbi`es-Tran, R., Jarrier, P., Touz´e, J.L., Pillet, E., Ponsart, C., Fabre, S., and Monniaux, D., 2012. Determination of anti-Müllerian hormone concentrations in blood as a tool to select Holstein donor cows for embryo production from the laboratory to the farm. Reprod. Fertil. Dev., 24: 932–944. https://doi.org/10.1071/RD11290

Rodrigues, M.C.C., Bonotto, A.L.M., Acosta, D.A.V., Boligon, A.A., Correa, M.N., and Brauner, C.C., 2018. Effect of oestrous synchrony between embryo donors and recipients, embryo quality and state on the pregnancy rate in beef cattle. Reprod. Domest. Anim., 53: 152–156. https://doi.org/10.1111/rda.13084

Roman, L., Sidashova, S., Danchuk, O., Popova, I., Levchenko, A., Chornyi, V., Bobritska, O., and Gutyj, B., 2020. Functional asymmetry in cattle ovaries and donor-recipients embryo. Ukrain. J. Ecol., 10: 139-146.

Roper, D.A., Schrick, F.N., Edwards, J.L., Hopkins, F.M., Prado, T.M., Wilkerson, J.B., Saxton, A.M., Young, C.D., and Smith, W.B., 2018. Factors in cattle affecting ET pregnancies in recipient animals. Anim. Reprod. Sci., 199: 79–83. https://doi.org/10.1016/j.anireprosci.2018.11.001

Sakatani, M., 2017. Effects of heat stress on bovine preimplantation embryos produced in vitro. J. Reprod. Dev., 63: 347e52. https://doi.org/10.1262/jrd.2017-045

Sanderson, N., and Martinez, M., 2020. A single administration of a long-acting recombinant ovine FSH (roFSH) for cattle superovulation. Theriogenology, 154: 66–72. https://doi.org/10.1016/j.theriogenology.2020.04.037

Santos, P.H., Satrapa, R.A., Fontes, P.K., Franchi, F.F., Razza, E.M., Mani, F., Nogueira, M.F.G., Barros, C.M., and Castilho, A.C.S., 2018. Effect of super stimulation on the expression of microRNAs and genes involved in steroidogenesis and ovulation in Nelore cows. Theriogenology, 110: 192–200. https://doi.org/10.1016/j.theriogenology.2017.12.045

Schenk, J.L., Suh, T.K., and SeidelJr, G.E., 2006. Embryo production from super ovulated cattle following insemination of sexed sperm. Theriogenology, 65: 299-307. https://doi.org/10.1016/j.theriogenology.2005.04.026

Selk, G., 2010. ET in cattle. Division of Agriculture and Natural Resource, Smith, A. (2015). Principles of ET. Proceeding of the Australian Reproduction Veterinarian (ARV). pp. 1-4.

Seneda, M.M., Zangirolamo, A.F., Bergamo, L.Z., and Morotti, F., 2020. Follicular wave synchronization prior to ovum pick-up. Theriogenology, 150: 180-185. https://doi.org/10.1016/j.theriogenology.2020.01.024

Siqueira, L.G.B., Torres, C.A.A., Souza, E.D., MonteiroJr, P.L.J., Arashiroc, E.K.N., Camargoc, L.S., Fernandesd, C.A. and Vianac, J.H.M., 2009. Pregnancy rates and corpus luteum-related factors affecting pregnancy establishment in bovine recipients synchronized for fixed-time ET. Theriogenology, 72: 949–958. https://doi.org/10.1016/j.theriogenology.2009.06.013

Sirard, M.A., 2018. 40 years of bovine IVF in the new genomic selection context. Reproduction, 156: R1–R7. https://doi.org/10.1530/REP-18-0008

Smith, C., 1988. Genetic improvement of livestock using nucleus breeding units. World Anim. Rev., 65: 2-10.

Smith, M.F., Geisert, R.D., and Parrish, J.J., 2018. Reproduction in domestic ruminants during the past 50 yr: discovery to application. J. Anim. Sci., 96: 2952-2970. https://doi.org/10.1093/jas/sky139

Souza, A.H., Carvalho, P.D., Rozner, A.E., Vieira, L.M., Hackbart, K.S., Bender, R.W., Dresch, A.R., Verstegen, J.P., Shaver, R.D., and Wiltbank, M.C., 2014. Relationship between circulating anti-Müllerian hormone (AMH) and super ovulatory response of high producing dairy cows. J. Dairy Sci., 98: 169-178. https://doi.org/10.3168/jds.2014-8182

Souza, A.H., Carvalho, P.D., Rozner, A.E., Vieira, L.M., Hackbart, K.S., Bender, R.W., Dresch, A.R., Verstegen, J.P., Shaver, R.D., and Wiltbank, M.C., 2014. Relationship between circulating anti-Müllerian hormone (AMH) and superovulatory response of high producing dairy cows. J. Dairy Sci., 98: 169-178. https://doi.org/10.3168/jds.2014-8182

Souza-Fabjan, J.M., Batista, R.I., Correia, L.F., Paramio, M.T., Fonseca, J.F., Freitas, V.J., and Mermillod, P., 2021. In vitro production of small ruminant embryos: Latest improvements and further research. Reprod. Fertil. Dev., 33: 31-54. https://doi.org/10.1071/RD20206

Stewart, B.M., Block, J., Morelli, P., Navarette, A.E., Amstalden, M., Bonilla, L., Hansen, P.J., and Bilby, T.R., 2011. Efficacy of ET in lactating dairy cows during summer using fresh or vitrified embryos produced in vitro with sex-sorted semen. J. Dairy Sci., 94: 3437–3445. https://doi.org/10.3168/jds.2010-4008

Stroud, B., 2012. IETS. Statistics and data retrieval committee report. The year 2011 worldwide statistics of ET in domestic farm animals. Embryo Transfer News Lett., 30: 16-26.

Stroud, B., and Hasler, J.F., 2006. Dissecting why superovulation and ET usually work on some farms but not on others. Theriogenology, 65: 65–76. https://doi.org/10.1016/j.theriogenology.2005.10.007

Stroud, B., and IETS, 2011. Statistics and data retrieval committee reported the year 2010 worldwide statistics of ET indomestic farm animals. Embryo Transfer Newsl., 29: 14–23.

Tiwari, I., Shah, R., Kaphle, K., and Gautam, M., 2019. Treatment approach of different hormonal therapy for repeat breeding dairy animals in Nepal. Arch. Vet. Sci. Med., 2: 28-40. https://doi.org/10.26502/avsm.007

Tribulo, A., Rogan, D., Tribulo, H., Tribulo, R., Mapletoft, R.J., and Bo, G.A., 2012. Superovulation of beef cattle with a split-single intramuscular administration of Folltropin-V in two concentrations of hyaluronan. Theriogenology, 77: 1679–1685. https://doi.org/10.1016/j.theriogenology.2011.12.013

Turner, J.W., 2019. Nearly everyone is now aware of ET, the science fiction character, but to cattlemen these initials mean far more than a promotion for movie entertainment; for ET has become a commercial reality in cattle breeding. This technology holds some exciting opportunities for the cattle industry and promises. Beef Cattle Sci. Handb., 20: 21.

Ulbrich, S.E., Zitta, K., Hiendleder, S., and Wolf, E., 2010. In vitro systems for intercepting early embryo-maternal cross-talk in the bovine oviduct. Theriogenology, 73: 802- 816. https://doi.org/10.1016/j.theriogenology.2009.09.036

Valenza, A., Giordano, J.O., Lopes, G., Vincenti, L., Amundson, M.C., and Fricke, P.M., 2012. Assessment of an accelerometer system for detection of estrus and treatment with gonadotropin-releasing hormone at the time of insemination in lactating dairy cows. J. Dairy Sci., 95: 7115– 7127. https://doi.org/10.3168/jds.2012-5639

Viana, J.H.M., Figueiredo, A.C.S. and Siqueira, L.G.B., 2017. Brazilian embryo industry in context: Pitfalls, lessons, and expectations for the future. Anim. Reprod., 14: 476-481. https://doi.org/10.21451/1984-3143-AR989

Viana, J., 2018. Statistics of embryo production and transfer in domestic farm animals. Embryo Technol. Newsl., 36: 8-25.

Vieira, L.M., Rodrigues, C.A., Mendanha, M.F., Sá Filho, M.F., Sales, J.N.S., Souza, A.H., and Baruselli, P.S., 2014. Donor category and seasonal climate associated with embryo production and survival in multiple ovulation and ET programs in Holstein cattle. Theriogenology, 82: 204–212. https://doi.org/10.1016/j.theriogenology.2014.03.018

Wahjuningsih S., and Djati, S., 2013. Ultrastructure of goat’s oocyte after cryopreservation using vitrification method. Animal Reproduction Department, Faculty of Animal Husbandry, University of Brawijaya, Malang. J. Vet. Med., 7: 101-104.

Wallace, L.D., Breiner, C.A., Spell, A.R., Carter, J.A., Lamb, G.C., and Stevenson, J.S., 2011. Administration of human chorionic gonadotropin at ET induced ovulation of a first wave dominant follicle, and increased progesterone and transfer pregnancy rates. Theriogenology, 75: 1506-1515. https://doi.org/10.1016/j.theriogenology.2010.12.012

Watanabe, Y.F., de Souza, A.H., Mingoti, R.D., Ferreira, R.M., Batista, E.O.S., Dayan, A., and Baruselli, P.S., 2018. Number of oocytes retrieved per donor during OPU and its relationship with in vitro embryo production and field fertility following ET. Anim. Reprod. (AR), 14: 635-644. https://doi.org/10.21451/1984-3143-AR1008

Watanabe, Y., Souza, H., Mingoti, R.D., Ferreira, R., Batista, E.O.S., Dayan, A., Watanabe, O., Meirelles, F.V., Nogueira, M.F.G., Ferraz, J.B.S., and Baruselli, P.S., 2017. Number of oocytes retrieved per donor during OPU and its relationship with in vitro embryo production and field fertility following ET. Anim. Reprod., 14: 635-644. https://doi.org/10.21451/1984-3143-AR1008

Whitfield, L.K., 2016. Heat stress and its impact on fertility in dairy cattle. Livestock, 21: 218–221. https://doi.org/10.12968/live.2016.21.4.218

Wolfenson, D., and Roth, Z., 2019. Impact of heat stress on cow reproduction and fertility. Anim. Front., 9: 32-38. https://doi.org/10.1093/af/vfy027

Wrathall, A.E., Simmons, H.A., Bowles, D.J. and Jones, S., 2004. Biosecurity strategies for conserving valuable livestock genetic resources. Reprod. Fertil. Dev., 16: 103-112. https://doi.org/10.1071/RD03083

Wray-Cahen, D., Bodnar, A., Rexroad, C., Siewerdt, F., and Kovich, D., 2022. Advancing genome editing to improve the sustainability and resiliency of animal agriculture. CABI Agric. Biosci., 3: 1-17. https://doi.org/10.1186/s43170-022-00091-w

Wright J.M., 1981. Non-surgical ET in cattle: Embryo-recipient interactions. Theriogenology, 15: 43-56. https://doi.org/10.1016/S0093-691X(81)80017-9

Wu, B., and Zan, L., 2012. Enhance beef cattle improvement by embryo biotechnologies. Reprod. Domest. Anim., 47: 865-871. https://doi.org/10.1111/j.1439-0531.2011.01945.x