enhance beef cattle improvement by embryo biotechnologies

Review Article

Enhance Beef Cattle Improvement by Embryo Biotechnologies

B Wu1 and L Zan2

1Arizona Center for Reproductive Endocrinology and Infertility, Tucson, AZ, USA; 2College of Animal Science and Technology, The National BeefCattle Improvement Center in China, Northwest A&F University, Yangling, Shaanxi Province, China

Contents

Embryo biotechnology has become one of the prominent highbusinesses worldwide. This technology has evolved throughthree major changes, that is, traditional embryo transfer(in vivo embryo production by donor superovulation), in vitroembryo production by ovum pick up with in vitro fertilizationand notably current cloning technique by somatic cell nucleartransfer and transgenic animal production. Embryo biotech-nology has widely been used in dairy and beef cattle industryand commercial bovine embryo transfer has become a largeinternational business. Currently, many developed biotechnol-ogies during the period from early oocyte stage topre-implantation embryos can be used to create new animalbreeds and accelerate genetic progression. Based on recentadvances in embryo biotechnologies and authors currentstudies, this review will focus on a description of theapplication of this technology to beef cattle improvementand discuss how to use this technology to accelerate beef cattlebreeding and production. The main topics of this presentationinclude the following: (i) how to increase calf productionnumbers from gametes including sperm and oocyte; (ii)multiple ovulation and embryo transfer breeding schemes;(iii) in vitro fertilization and intracytoplasm sperm injection inbovine; (iv) pronuclear development and transgenic animals;(v) sex selection from sperm and embryos; (vi) cloning andandrogenesis; (vii) blastocyst development and embryonicstem cells; (viii) preservation of beef cattle genetic resources;and (ix) conclusions.

Introduction

Currently, embryo biotechnology has become the mostpowerful tool for animal breeders and animal scientists toimprove genetic construction of their animal herds.Embryo transfer in cattle has recently gained considerablepopularity with seedstock dairy and beef producers. Thehistory of the embryo transfer procedure goes backconsiderably farther, but the most modern applicableembryo transfer technology was developed in the 1970sand 1980s. In the last three decades, embryo biotechnol-ogy has evolved through three major changes, ‘threegenerations’ – the first with embryo derived from donors(in vivo) by superovulation, non-surgical recovery andtransfer of cattle embryos, the second with in vitro em-bryo production by ovum pick up with in vitrofertilization and the third including further in vitrotechniques, notably cloning by somatic cell transfer,embryonic stem (ES) cell development and transgenicanimal production (Betteridge 2004; Lonergan 2007). Atthe same times, commercial bovine embryo transfer hasbecome a large international business (Betteridge 2006).The use of embryo transfer in the beef industry has been

implemented largely by purebred breeders (beef anddairy) with some growing use by show calf breeders. Thebreeders who have utilized embryo transfer have beenpursuing these basic goals to improve genetic selection byincreasing the number of progeny from females that areeither proven or perceived to be superior under anynumber of criteria, or tomultiply the number of cattle in aprogramme to expand the herd or to meet marketdemands. In this presentation, we will briefly review somekey events of early embryo development, followed byfocusing on the effect of the modern embryo biotechnol-ogies on beef cattle improvement and production.

The goals of animal genetic improvement are toaccelerate genetics progress (improvement speed) as wellas to add new genetic trait to animal body (create newbreeds). The annual rate of genetic improvement in mostanimal breeding programmes are determined by fourfactors: selection intensity, selection accuracy, geneticvariability and generation interval. Besides artificialinsemination, current developed embryo biotechnolo-gies can impact one or more of these parameters toimprove the rate of animal genetic improvement. Also,many developed biotechnologies can be used to createnew animal breeds and accelerate genetic progressionduring the period from early oocyte stage (oogenesis) topre-implantation embryo stage (Fig. 1).

Beginning from Gametes

Mammalian gametes include male sperm and femaleoocyte. So far we have known that the reproductivepotential of each normal newborn calf is enormous. Thereare an estimated 14 000–250 000 potential ‘eggs’ or ova inthe female (Erickson 1966; Ireland et al. 2008) andcountless billions of sperm produced by each male. Bynatural breeding, only a fraction of the reproductivepotential of an outstanding individual in animal popula-tion can be realized. The average herd bull will sireanywhere from 15 to 50 calves per year and the averagecow will have one calf per year. The developed artificialinsemination (AI) technology has provided a possibilityto exploit the vast numbers of sperm produced by agenetically superior bull, but the reproductive potential ofthe female has been largely unutilized. A cowwill producean average of eight to 10 calves in her entire lifetime undernormal management programmes. The embryo transfertechnique can greatly increase the number of offspringthat a genetically important cow can produce. It has beenestimated that to dramatically improve the genetic base ofa given cow herd, it will take 10–20 years to accomplish

Reprod Dom Anim doi: 10.1111/j.1439-0531.2011.01945.x

ISSN 0936-6768

� 2011 Blackwell Verlag GmbH

using only natural service, by incorporating artificialinsemination, these improvements can be completed in7–8 years. Through the use of an aggressive embryotransfer programme, this change is accelerated to 4–5years.

Embryo development begins with the fertilization.Prior to fertilization, both the oocytes and the spermmust undergo a series of maturational events to acquiretheir capacity to achieve fertilization. Much research inthis area has been geared toward improving reproductiveefficiencies of farm animals and preserving endangeredspecies. As human in vitro fertilization (IVF) techniquerapidly develops in infertility treatment, not only animalIVF has offered a very valuable tool to study mammalianfertilization and early embryo development, but also itscommercial applications have being increased quickly. Atthe male gamete stage, bull sperm can be separatedsuccessfully into X- or Y-chromosome-bearing sperm inan amount suitable for AI and therefore commercializa-tion of this sexing technology (Jonhson 1992, Garner andSeidel 2008). Thus, animal breeders may obtain theirdesired sexed herds by purchasing commercial sexedsperm.However, someof concerns associatedwith the useof sexed semen include low pregnancy rates, lowersurvival of sorted sperm after cryopreservation andnumber of sperm separated per unit time (Lonergan2007). At the female gamete stage, an ultrasound-guidedoocyte retrieval (TVOR) or non-surgical ovum pick up(OPU) technique has been developed to retrieve oocytesrepeatedly from a cow or a heifer. As many as 1000oocytes have been collected from one female cattle in ayear (Taneja andYang 1998;Machado et al. 2006). Thus,the embryo in vitro production (IVP) technology has beenable to promote a cow to producemore than 100 offspringin a year and greatly accelerate herd genetic improvementspeed (Suthar and Shah 2009). Further, the combinationof sexed semen technology with in vitro embryo produc-tion technology has been a feasible production scheme forHolstein heifer embryos to beef recipients (Wheeler et al.2006; Blondin et al. 2009; Carvalho et al. 2010).

Also, slaughterhouse ovaries have been widely used asin vitro embryo production. A lot of immature oocytes

could be collected from these ovaries and be in vitromatured for 20–26 h culture (Wu et al. 1997). Althoughthe detail genetic backgrounds of these slaughterhouseanimals are not known, we may use elite bull semen withthese oocytes for IVF. The obtained embryos have avery high genetic merit from elite bulls. Transferringthese embryos may greatly accelerate beef herd geneticimprovement.

Multiple Ovulation and Embryo Transfer(MOET) and its Development

With the introduction of multiple ovulation, embryorecovery and transfer technique plus embryo freeze-thaw methods in the early 1980s, the breeding industryhas the tools in hand to increase the number of calvesfrom donors of high genetic merit. MOET was usedinitially to produce more embryos from genetic elitecows in shorter time periods. Currently the MOETbreeding schemes have widely established in manycountries and their use accounts for approximately80% of cattle embryos transferred commercially (Thi-bier 2005). The fundamental difference between MOETscheme and progeny testing is that MOET scheme usesembryo transfer to create large full-sib or half-sibfamilies, while progeny testing is just to gather someinformation based on a bull’s sisters as well as hisdaughters to do male selection (Lohuis 1995). Thus,decisions on culling or semen usage can occur approx-imately 2 years before daughter information would beavailable from a progeny. MOET, by increasing thereproductive rate of females, may offer the opportunityto decrease the number of selected dams for nextgeneration while at the same time increasing the amountof information available on sibs for estimating breedingvalues. This scheme may significantly increase annualgenetic improvement as generation interval decreases.However, early farm practice had shown that donorcows had significant difference for superovulationtreatment (Kruip et al. 1991). It have been reportedthat one-third of treated donors failed to respond, one-third yielded 1–3 embryos and only remaining one-third

MOET

OPU

AI

GV oocyte MII oocyte Zygote Blastocyst

Maturation IVF/ICSI

Sexing sperm

Genomic Reconstruction

Transgenesis Cloning Nuclear transfer

Sexing embryoCloning Mosaic

Gene injection

ParthenogenesisOPU In vitro embryo production

Stem cellsAndrogenesis

Fig. 1. Schematic representation of main embryo biotechnologies which can impact on the beef genetic improvement programmes

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actually yielded a significant number of embryos(Boland et al. 1991). In particular, after one to twostimulations, many cows showed a reduced respond forsuperovulation stimulation. This reduces MOET schemeefficiency. Currently, the application of transvaginalultrasonically guided OPU technique may significantlyimprove MOET scheme efficiency because approxi-mately 1000 oocytes may be collected and 300 embryosmay be produced from a cow in a year at frequentintervals (Van Wagtendonk-de Leeuw 2006; Presicceet al. 2011). Also, oocytes may be collected fromprepubertal heifers (Presicce et al. 1997; Fry et al.1998; Su et al. 2011). Further, the use of sexed frozen-thawed sperm (‡90% X-sperm biased and 10 · 106 totalsperm) may be economically viable for commercialMOET programmes in Holstein heifers (Hayakawaet al. 2009). Thus, in combination with IVF, MOET isproviding a more efficient route to producing moreembryos from individual donor where facilities andskills permit than superovulation stimulationprogramme (Betteridge 2004). From original in vivoembryo production to in vitro embryo production, it willgreatly increase MOET breeding scheme efficiency inbeef industry.

In Vitro Fertilization and Intracytoplasm SpermInjection (ICSI)

In animals, IVF has offered a very valuable tool to studymammalian fertilization and early embryo development.This technique has widely been used in human infertiletreatment. In the dairy and beef cattle industry, anultrasound-guided retrieval technique has been devel-oped to retrieve oocytes repeatedly from live cows andheifers. However, the eggs to pick up from live cowovaries under no drug stimulation are often immatureoocytes. Thus, in vitromaturation needs to be performedin culture dishes with maturation medium for 20–26 hand then the insemination is carried out with bull semen.Currently, the combinations of OPU and IVF haveresulted in rapid commercial application in the dairy andbeef cattle industry throughout the world. The IVFtechnique may be efficacious to solve the infertileproblem of high productive cows or elite beef heifersbecause of oviduct block or ovary disease such aspolycystic ovarian syndrome. When the semen of someelite bulls is lacking, ICSI technique has been used toobtain genetic merit embryos (Rho et al. 1998; Haraet al. 2011). The application of this technique to beef anddairy cattle industry has greatly increased merit bullspread in animal herd (Garcıa-Rosello et al. 2009; Abu2010).

Pronuclear Development and TransgenicAnimals

After fertilization, the zygote will be formed and twoobvious pronuclei could be observed at this stage. Thegenetic manipulation of the pre-nuclear stage embryohas resulted in two fundamental discoveries in repro-ductive biology (Wilmut et al. 1991). By pronuclearremoval and exchanges, the principle of genetic imprint-ing has been convincingly demonstrated. By injecting

foreign DNA into one of the two pronuclei of thezygote, the resulting offspring may contain a functionalforeign gene in the genome, known as transgenesis.Production of transgenic animals has great applicationin agriculture and medicine (Niemann and Kues 2003).In beef cattle industry, the transgenic technology may beapplied to develop lines of animals for faster growth,higher quality beef products or disease resistance (Gre-ger 2010). Transgenic practices of last decade haveproved that by inserting a single growth regulating geneinto an animal of agricultural value, animal growth rateand feed efficiency could be greatly increased and fatdeposition could be obviously reduced. This techniquehas been transforming the entire meat animal industry(Wheeler 2007). Furthermore, many other applications,including enhanced milk production with novel proper-ties, enhanced disease and parasite resistance andincreased wool production, were imagined (Wheeler2003). Significant advancements have been made inbovine transgenic technology in the past 20 years.Currently, it is possible to target genetic sequences intopredetermined sites in the host DNA, to transferindependent microchromosomes with the capacity tocarry hundreds of genes into the bovine genome and tosequentially introduce multiple genetic modificationsinto a single genome (Liu et al. 2011). However, a bigproblem is whether transgenic meat products areacceptable for consumers. American federal agenciesregulating genetically modified animals have stipulatedthat to receive commercial authorization in the USA infuture, producers must demonstrate that such animalsor their derived products present no risk to the health orsafety of humans or animals and that any derived foodproducts are as safe as conventional counterparts (FDA2011). Conceptually, many of the modifications thatmight be considered to enhance production efficiencywould not have any impact on the safety or quality ofthe food product. Thus, the most likely first geneticallymodified cattle to be commercialized will likely producehuman therapeutic proteins (Heodebine 2005).

Gender Pre-Selection

Sex selection is the attempt to control the sex of theoffspring to achieve a desired sex animal. It can beaccomplished in several ways, including sperm sexselection and pre-implantation embryo sex selection. Anumber of reviews have addressed the use of sexedsemen in cattle (Seidel and Garner 2002; Seidel 2003).The current successful method for separating semen intoX- or Y-bearing chromosome sperm is to use flowcytometry to sort sperm for artificial insemination orIVF (DeJarnette et al. 2007; Blondin et al. 2009).However, this method has one major limitation: spermare sexed one at a time, serially, rather than sexingmultiple sperm simultaneously (in parallel). Anotherconstraint is that sexing works best with fresh sperm, sosorters usually are located near the bulls and sperm arecryopreserved after the sexing process, and this frozensexed sperm may be used in IVF for embryo production(Carvalho et al. 2010). While other more practicalmethods of sexing sperm have been proposed andcontinued to be tested, none of these has been found

Beef Cattle Improvement by Embryo Biotechnologies 3


that meets two essential criteria: accuracy of sexing andretention of sperm fertility (Seidel 2007). Also, the spermare treated with a fluorescent dye that allows differen-tiation of the amount of DNA in the sperm. Thisprocess may result in sperm DNA damage (Gosalvezet al. 2011). Thus, although the sorted semen may beused for artificial insemination in cattle, it often resultsin lower pregnancy rates. Pregnancy loss often happensin heifers after artificial insemination with frozen-thawed, sex-sorted, re-frozen-thawed dairy bull sperm(Underwood et al. 2010). However, the use of sortedsperm in embryo IVP has massive potential for increas-ing efficiencies of animal production because muchfewer sperm are need for IVF or ICSI. Over past decadeor so the sorted semen has been used for the productionof embryos in vitro in cattle (Lu et al. 1999; Wilson et al.2005; Pontes et al. 2010). Because sexed sperm havebeen used to breed heifers successfully on many occa-sions, one obvious application is to breed heifers to havefemale calves. These should result in excellent replace-ments for beef and dairy herds, because the youngestcattle in any herd with a genetic improvement pro-gramme are genetically superior to the older cows. Amajor additional benefit is that on the average, femalecalves weigh approximately 2 kg less at birth than malecalves, so the incidence of dystocia in first calf heiferswill decrease with this application (Seidel 2007).

Like sperm sexing, the ability to determine the sex ofan embryo prior to transfer has been an objective ofdairy and beef cattle breeders because the commercial-ization of embryo transfer technology. Recent advancesin the fields of genetics, genetic diagnosis, embryobiopsy and pre-implantation genetic diagnosis (PGD)have opened up a new world for sex selection. Almost95% embryos may be sexed by Y-specific chromosomeprobe for polymerase chain reaction (PCR) or Fluores-cent In Situ Hybridization (FISH) methods (Lopes et al.2001). Under the normal farm condition, cattle embryosmay be sexed by complete cell biopsy and PCRtechnique in the farm field (Machaty et al. 1993; Thibierand Nibart 1995). On our clinic farm practice, a fewtrophoectoderm cells were micro-biopsied from blasto-cyst embryos by transzonal incision using a microsur-gical blade. After biopsy, the embryos were cultured infour-well dishes containing 1 ml holding medium perwell at ambient temperature (20–25�C), and the isolatedembryonic cells were placed in a mini-tube immediately.The mini-tube PCR was performed for approximately30 min, and the gel electrophoresis was run approxi-mately 20 min. The PCR product was detected byultraviolet light in agarose gel with ethidium bromide(10 mg ⁄ml in distilled water), and the embryos werescored as Y-chromosome determinant positive (male) orY-chromosome determinant negative (female), respec-tively (Fig. 2). All instruments represent a transferableunit that can be used in field conditions (AB Technol-ogy, Inc., Pullman, WA, USA). The sexing result couldbe obtained in 2–3 h. Hereafter, the sexed femaleembryos could be transferred to recipient cow on thesame day. At the same times, the extra female embryoscould be frozen for the future use. Based on our farmexperience, 98% of IVP blastocyst embryos and 100%of in vivo flushing blastocyst embryos could be sexed and

approximately 95% accuracy of sex prediction could beobtained. In the last few years, the PCR technique has agreat improvement and the loop-mediated isothermalamplification technique which is a new generation ofinnovative gene amplification technique may rapidlydetermine bovine and water buffalo pre-implantationembryos (Hirayama et al. 2004, 2006; Parida et al.2008). More recently, a multiplex polymerase chainreaction has been used for bovine embryo sex determi-nation (Rattanasuk et al. 2011) and a rapid improvedmethod for sexing embryo has been applied to bovineand water buffalo embryo sex determination, and 100%accuracy of sex prediction has been reported (Zoheirand Allam 2010, 2011). Not only can the sexed embryosbe freshly transferred to receipts, but also the extraembryos may be frozen for future use (Tominaga 2004;Lopatarova et al. 2010). These results clearly demon-strate that the microsurgical technique and subsequentPCR sex analysis allow the rapid commercial exchangeof genetic resources on the basis of fresh or frozen sex-desired embryos in embryo transfer programmes.

Further, FISH technique has also been used asembryo chromosome set (karyotype) diagnosis (Moriand Shiota 1994). In our human IVF center, oneblastomere is removed from eight-cell stage embryo ofDay 3 and is diagnosed by FISH method to examineembryo chromosome aneuploidy. At the same time,embryo sex could be known. After biopsy, the embryo iscultured to Day 5 for blastocyst embryo transfer. WhileIVF with PGD is only one of the methods for sex pre-determination, it is the only procedure where successrates are higher than 99.9%. Thus, current embryo sexdiagnosis technology has been able to completelydetermine all pre-implantation embryo sex, and thiswill be very useful for beef cattle improvement.

Cloning and Androgenesis

Animal cloning may involve embryo cloning and adultsomatic cell cloning. During early development beforeeight-cell stage, embryonic cells may be dis-aggregatedinto individual blastomeres. Each blastomere has atotipotency, which is able to potentially to develop intoa viable embryo following nuclear transfer and toregenerate whole new individual, that is, cloning. Also,

MM M MF F F F FN N N

Donor #1 Donor #2 Donor #3

M

Fig. 2. Embryo sex determination on the farm field. In vitro producedblastocyst stage embryos from three donor cow oocytes were analysedby mini-tube PCR with specific male DNA probe on the same day.Donor no. 1 and no. 2 had four embryos, respectively. Donor no. 3had two embryos. Each embryo sex could be determined clearly by ourPCR method. F indicates female embryos and M indicates maleembryos, N is as a negative control

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embryo division is a kind of cloning and it may produceidentical twin. Cloning in cattle has been shown doable,but the efficiency is low and a relatively large proportionof the cloned calves are abnormal (Vajta and Gjerris2006). Since the birth of cloning ‘Dolly’ from amammary tissue cell of an adult sheep, a race ofattempting to clone animal from various types isunderway worldwide, and the standard somatic cellnuclear transfer techniques have resulted in the birth oflive offspring in more than 23 species including cattleuntil August of 2011 (based on author’s internet search).However, one concerning aspect of the cloning animal bymeans of somatic cell technology is its practical effectbecause cloned animals might be physiologically abnor-mal, or cloning might lack actual utility for society.Importantly, when animal cloning may become a com-mercial venture to help improve the quality of herds,people have to be concerned with the edibility and safetyof food from cloned animals. In 2001, American Foodand Drug Administration (FDA 2001) requested live-stock producers and researchers to keep food fromanimal clones or their offspring out of the food supply.Since then, FDA has conducted an intensive evaluationthat included examining the safety of food from theseanimals and the risk to animal health. Based on a finalrisk assessment, a report written by FDA scientists andissued in January 2008, FDA has concluded that meatand milk from cow, pig and goat clones and the offspringof any animal clones are as safe as food we eat every day(FDA 2011).

The application of cloning techniques to animalbreeding is numerous because many animals of thesame genotype can be theoretically produced increasingthe accuracy of evaluation, but cloning may reducegenetic variation in cattle population. Although cloningefficiency is low, it is the hope of many scientists thatcloning technique may eventually be used to clone veryvaluable embryos such as transgenic embryos or toclone ES cells as well as to clone some endangeredspecies for their preservation.

By cell nucleus transfer technique, we may create anew animal by androgenesis. Androgenesis male par-thenogenesis is that the embryo contains only paternalchromosomes because of the failure of the egg nucleusto participate in fertilization and this is a reproductionpattern from two male parents. We are using an oocytewhose nucleus has been removed to induce a malediploid cell going through meiosis to become a haploidMII oocyte. Then, a male sperm is injected into thisoocyte to form a paternal embryo. The embryo istransferred into receipt cow to produce a new individualbull with two male parents (Fig. 3).

Blastocyst Development and Mosaic and StemCells

At the blastocyst stage, two distinct cell lines in theembryos may be observed, the inner cell mass (ICM)and the trophectoderm cells. ICM cells are totipotentstem cells which will give rise to all different tissues inthe foetus. By in vitro culturing bovine ICM cells, thelines of ES cells have been developed (Wang et al. 2005).ES cells have the ability to remain undifferentiated and

proliferate indefinitely in vitro while maintaining thepotential to differentiate into derivatives of all threeembryonic germ layers. In spite of much difficulty inlivestock species (Munoz et al. 2008), researchers atUniversity of Connecticut have generated a stable line ofES cells from cloned cattle embryos that can makeunlimited copies of themselves and can morph into cellsfor nearly all bovine body tissues and organs (Bauman2005). The research may offer a breakthrough tool forscientists studying the use of such cells to treat disease,because it also suggests that cattle stem cell lines mayserve as a better model than those from other species forinsight into human cell-based therapies.

As the most publicized advance in cloning Dolly sheep,recent achievement showed that completely differentiatedcells (both foetal and adult) may be reprogrammed toreturn to multipotential embryonic cells. The two sepa-rate reports in 2006 and 2007 revealed that mouse andhuman fibroblasts could be reprogrammed to generateinduced pluripotent stem cells (iPSCs) with qualitiesremarkably similar to ES cells like state by being forced toexpress genes and factors important for maintaining thedefining properties of ES cells (Takahashi andYamanaka2006; Yu et al. 2007). This discovery has created avaluable new source of pluripotent cells for drug discov-ery, cell therapy and basic research. Technically, iPSCsmay be carried out by inducing a quiescent state (G0 phaseof the cell cycle) in the somatic cell and then fusing it withthe enucleated cytoplasm of a mature egg. This methodwould be even more efficient to genetically manipulatesomatic cells of sheep or cattle in culture and to use thesecells for cloning (Hodges andStice 2003).Offspringwouldprobably always have the desired transgene. This couldcode for a human protein used to treat or prevent disease(such as factor VIII and interferon), and large quantitiesof the protein could be produced in the animal’s milkunder the control of specific promoters. As proteins canbe isolated from milk relatively simply, this might be anextremely cheap and efficient way to produce largequantities of human or animal pharmaceuticals (Cooper2009). It might also be very competitive with presentmethods of producing recombinant proteins (e.g. frombacterial, yeast and mammalian cell lines). When oneconsiders the cost and problems of producing antiviraldrugs as well as proteins for immunization and therapy(e.g. for haemophilia, HIV infection and multiple sclero-sis), the potential for pharmaceutical production in cattlebecomes economically attractive.

GV

Inject male diploid cell GVBD MII

Paternal embryo

Meiosis

Male haploid

ICSI

Remove Nucleus

oocyte

Fig. 3. Male parthenogenesis. A new individual bull can be created byandrogenesis



Successful establishment of ES cell lines will havenumerous applications. ES cells may be the ideal sourceof donor cells for embryo cloning. Various geneticmanipulations such as homologous recombination maybe performed on ES cells. In beef industry, the stem cellsfrom different breeds may be embedded together to forma mosaic embryo. Also, the gene-transferred ES cellsmay lead to the development of a transgenic animalthrough the production of chimeras or cloning. Re-cently, scientists in Holland said that they are a yearaway from creating ground beef from stem cells, and theburger will be grown from 10 000 stem cells extractedfrom cattle (Watercooler 2011).

Preservation of Genetic Resources

China has vast animal genetic resources with a widevariety of indigenous farm animals including cattle.Particularly, many local yellow cattle breeds have a longhistory of evolution. The most important five nativeyellow cattle breeds are Qinchun, Luxi, Jinnan, Nanyangand Yanbian cattle breeds and each breed has its richgenetic resources. These cattle breeds have evolved overgenerations to adapt to the agro-climatic and socio-economic needs of the people. However, a number ofthese breeds are now subjected to fast genetic degradationand dilution because of unplanned breeding and intro-duction of exotic germplasm. Long since, these cattlebreeds have widely been used farm cattle and strongdraught animals. In recent years, as developing mecha-nization in agriculture, these cattle have been transformedinto beef and meat use by introducing foreign beef cattlebreed crossbred, but these native yellow cattle have manygenetic merits which needs to be preserved. AlthoughChinese local cattle breeds produce lower amount meat,

many studies have showed that these cattle have a highquality of meat. Based on the developed embryo technol-ogies, both elite bull semen and cow egg as well embryosmay be frozen in the liquid nitrogen for permanentcryopreservation. Also, as somatic cell cloning techniquesdevelops, the somatic cells, such as skin, hair and othercells from these cattle breeds, may be collected andcrypreserved so that they will be used in the future.

Conclusions

Embryo biotechnologies have already become an inte-gral part of the beef and dairy industries and anincreasingly important component of beef breedimprovement. The combination of IVP with OPUtechnique has promoted MOET schemes availablepractice in beef and dairy industries. This techniquehas greatly accelerated cattle herd genetic improvement.Successful sex determination from sperm and embryoshas achieved better economic results for farmers. Newlydeveloped technologies such as embryo cloning, nucleartransfer, transgenic animals and stem cells havedemonstrated great promises for application in agricul-tural and biomedical sciences. In the next decade, thesetechnologies will greatly promote beef cattle improve-ment and create new beef cattle breeds.

Conflict of interest

None of the authors have any conflict of interest to declare.

Author contributions

Dr. Bin Wu designed and wrote full paper and Dr. Linsen Zanprovided information and discussed paper construct and revised paper.

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Submitted: 20 Jun 2011; Accepted: 26 Oct

2011

Author’s address (for correspondence): BinWu, Arizona Center for Reproductive Endo-crinology and Infertility, 5190 E Farness Dr.#114, Tucson, AZ 85712, USA. E-mail:[email protected]



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