*3.4.3 Multiple ovulation and embryo transfer (MOET)*

MOET was first proposed in 1987, and it demonstrated how MOET programs may increase genetic gains by raising selection intensity and shortening generation intervals [70]. Multiple-ovulation (superovulation) is a pharmacologic procedure that increases the number of oocytes released at ovulation by 2 to 10 times, hence raising the quantity of embryos that can be produced. Embryo transfer (ET), on the other hand, refers to the techniques used to collect embryos from a female (donor) and transfer them into the uterus of another female (recipient) where they develop to term. Typically, a cow ovulates a single oocyte during each reproductive cycle, and therefore may produce only 8 to 12 calves in her reproductive lifetime. However, utilizing the technology for MOET, it is possible to obtain 30 to 40 calves from a single cow over a period of a year [71]. Through MOET, the numbers of imported highly valuable and scarce cattle breeds could be multiplied rapidly, leading to increased genetic improvement of cattle populations [72]. Highly valued cows that are injured or too old to carry normal pregnancy could also be made to continue producing calves via MOET, rather than these animals being culled or sold for slaughter. Natural twinning ranges from 1 to 2% in beef cattle, but the efficiency of beef production could also be increased in intensively managed farms by inducing twinning using MOET. This technology also offers commercial advantage to farmers via a lower cost of importation of cryopreserved embryos compared to live cattle [68].

### *3.4.4 In vitro fertilization (IVF)*

*In vitro* fertilization (IVF) is a technology via which fertilization and maturation of oocytes takes place outside of the female (in the laboratory). The method is also called *in vitro* embryo production. The resulting embryos are then transferred back to the same or different females for development. Mature oocytes can be collected by flushing the oviducts shortly after ovulation. Alternatively, immature oocytes can be obtained from abattoir ovaries or by aspiration of pre-ovulatory follicles using ovum pick up (OPU) from live cows. These oocytes must be cultured *in vitro* for 24 hours in sterile medium to allow for nuclear maturation prior to fertilization. Following *in vitro* maturation of oocytes, spermatozoa must also be capacitated using a capacitation medium (or alternatively by using ejaculated sperm) before they are capable of fertilizing the oocyte [66]. The technology offers the potential for large numbers of *in vitro* produced embryos together with exciting opportunities for other technologies in cattle reproduction such as sex determination, cloning, genetic engineering and embryo transfer.

### *3.4.5 Sex determination*

This technology is useful when calves of a particular sex are considered to be more valuable than those of the opposite sex. For instance, dairy farmers would desire that the majority of their calves be female (replacement heifers for the milking herd) whereas beef farmers would prefer bull calves for their higher body mass and beef production potential. Sex could be determined either by semen sexing or embryo sexing. The presence of Y chromosome determines male offspring in mammals. In cattle, the X-bearing sperm contain 3.8% more DNA than the Y-bearing sperm. Thus, sperm can be separated using specific dye (Hoechst 33342) that binds to DNA and a flow cytometer/cell sorter. Embryos can also be sexed using several techniques including chromosome analysis (karyotyping), immunology, DNA analysis and detection of metabolic differences [66]. Sexed semen could be applied in farms to inseminate cows in order to create necessary sex calves, or to fertilize oocytes in vitro in order to produce required sex embryos. Sexed embryos could likewise be implanted into recipient cows to create sex-matched calves [73].

### *3.4.6 Cloning and nuclear transfer*

These technologies involve cloning by embryo splitting to produce identical twins, triplets and quadruplets or the use of nuclear transfer to produce large numbers of genetically-identical or cloned cattle. In the nuclear transfer technique, the nuclei from either a blastomere (from early-stage embryos) or a somatic cell (other body cells) are fused individually to enucleated oocytes. The resulting zygotes are then cultured and transferred to recipient cows to develop till term. Interestingly, this technique has attracted much international attention since 1996 when the first mammal (the sheep, Dolly) was cloned [74] followed later by cloning in cattle [75]. With cloning technology, it is possible to exceed pregnancy rates of 100% in cattle farms. It also offers the potential for producing large numbers of genetically-superior cattle to drive increased dairy and beef production [69]. For instance, it normally requires 78 months to reach production flock status in cows, but this can be achieved within 33 months with the nuclear transfer technology [67]. The success rate for propagating animals by nuclear transfer is expected to increase along with a reduction in the cost as newer methods are developed in the technology.

*Assisted Reproductive Technologies as Veritable Tools for Improving Production Efficiencies… DOI: http://dx.doi.org/10.5772/intechopen.100066*

### *3.4.7 Genetic engineering*

Transgenic livestock (pigs and sheep) were produced for the first time in 1985 [76]. This technology involves transferring a selected gene into an embryo so that the resulting offspring carry and express that gene later in life. Animals that carry a copy of a desired foreign gene are referred to as being transgenic [69, 77]. Generally, transgenic technologies utilize embryo-mediated or cell-mediated genetic modification to generate an entire animal. In recent years, new technologies referred to as "gene editing" have also been added to the molecular tool box for genetic engineering of various organisms. Efficient and robust protocols are now available for producing sheep, goats, pigs, cattle and other species in which specific genes have been targeted for editing [78].

The technology has been applied to improve different aspects of animal production. In cattle, these include the enhancement of milk quality, muscle yield, disease resistance (mastitis, tuberculosis), or improved welfare such as the production of hornless dairy cattle [77, 79, 80]. Nevertheless, the application of genetic engineering in livestock production has been limited by several significant factors. These include the cost of large animals, long generation times, and most importantly, legal, ethical and public health concerns and considerations [78]. However, it is likely some of the newer technologies involving gene editing will become more acceptable particularly in the face of the increasing global animal protein demands and food insecurity. Already, the first genetically engineered salmon has received approval to be sold as food by regulatory agencies in the US and Canada [81]. It is likely that other international agencies will begin to reconsider regulatory gridlocks on animal products from genetic engineering. In Africa, and particularly Nigeria, genetic engineering of bovine embryos may offer opportunities for the production of cattle that retain the genetic predisposition to hardiness, adaptation to the tropical environment (e.g. heat stress) and tolerance to tropical diseases (e.g. trypanosomosis) while incorporating genetic potential for rapid growth and increased milk and beef production [82].
