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Artificial insemination
No other technology in animal sciences has been so widely adopted globally as artificial insemination (AI), as it has revolutionized livestock productivity especially in cattle. Genetic constitution of an unknown animal can be replaced up to 50, 75 and 87.5% with elite animal in I, II and III generations, respectively. Progress in semen collection, evaluation, dilution and cryopreservation now enables use of a single bull simultaneously in several continents for breeding up to 100,000 cows in a year. This technology thus enables use of the very best bulls to serve a large cattle population. Also, each bull is able to produce a large number of daughters in a given time thus enhancing the efficiency of progeny testing of bulls. The high intensity and accuracy of selection arising from AI can lead to a four-fold increase in the rate of genetic improvement in dairy cattle as compared to that of natural service. Additionally, use of AI can reduce transmission of venereal diseases in a population and the need for farmers to maintain their own breeding males. Up to 75% or more conception rate has been reported in cattle following AI, however, success of AI depends on accurate heat detection, proper frozen semen handling and timely insemination by a trained inseminator.
In human infertile couples, if the female is fertile, AI is used to address the problem of impotentia couendi and oligozoospermia in males. In case of azoospermia in husband, sperm of donor (any other man) are used for AI.
AI is credited for providing the impetus for many other developments, which have had a profound impact on reproductive biotechnology. Studies of estrus detection and ovulation control which are essential for timely insemination, led to the development of embryo-transfer technology (ETT).
Multiple Ovulation and Embryo Transfer
ETT enables birth of multiple progeny from genetically superior (elite) females. To increase the number of embryos that can be recovered from elite females, the embryo donor is treated with gonadotropins to induce multiple ovulations or superovulation. Embryo donor is inseminated with high quality semen of a superior male. The fertilized embryos are collected from embryo donors by nonsurgical techniques. These genetically superior embryos are then transferred to genetically inferior but highly fertile females (embryo recipients) nonsurgically. Unlike AI which require about seven generations for nearly total genetic transformation, ETT enables birth of many genetically superior calves in one generation.
In cattle, generally 4-6 good quality embryos are collected after each superovlation and 50-60% recipients conceive following embryo transfer. Millions of calves have been produced using ETT and in USA and Canada about 80% breeding bulls are produced using this technology.
In Vitro Fertilization
As multiple ovulation and embryo transfer has some limitations, production of embryos in vitro (in the laboratory) is considered more efficient and economic. Immature oocytes (female eggs) are harvested from ovaries of elite embryo donors or infertile/ aged females. Ovum (egg) pick up (OPU) is a nonsurgical technique that uses ultrasound and a guided needle to aspirate immature oocytes from the ovaries. Once the immature oocytes have been removed from the ovary, they are matured, fertilized, and cultured in vitro for up to seven days until they develop to a stage that is suitable for transfer or freezing. Mostly embryos are transferred nonsurgically.
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Juan Gonzalo Angel
www.tvagro.tv
