IMPACT OF BIOTECHNOLOGY ON ANIMAL BREEDING AND GENETIC PROGRESS Animal breeding is a field related to a whole range of biotechnologies. The impact of a biotechnology can be measured by the influence it has on genetic progress. According to the type of biotechnology considered, different component of genetic progress may be affected: accuracy of prediction, generation interval, intensity of selection and genetic variance. The first type of biotechnologies affects the efficiency of male and female reproduction: artificial insemination, multiple ovulation, in-vitro-fertilization, ova pick-up, embryo-transfer, twining, sexing of semen and embryos cloning and selfing. The impact of these technologies is mainly in the enhanced distribution of superior germplasm and the selection intensity, but also in the accuracy obtained when testing animals. In the past, artificial insemination has been a very successful biotechnology, enhancing greatly the genetic progress. A secondary, negative, impact is that these biotechnologies affect indirectly genetic diversity and therefore reduce genetic variance.
A second group of biotechnologies that can improve determination of the genetic merit of animals is connected with the identification and using of quantitative or economical trait loci (QTL/ETL). Their main feature is the early availability in life, therefore allowing an earlier and more accurate selection. Two direction of research exists: detection of markers for the unknown QTL and direct use of potential candidate genes as QTL/ETL. These genes will have a major impact on animal breeding especially if they will be use in optimization of future breeding programs. A last type of biotechnologies are those with the ability to transform artificially DNA. The impact of these technologies is however still no very clear especially as gene expression and other issues remain unsolved. Biotechnology had, has and will have a major impact on animal breeding and genetic progress. To a certain extend animal breeding is a very promising field to use biotechnology as the past has already proven (Gengler N., Druet T. -2001).
HISTORY OF BIOTECHNOLOGIES USE IN LIVESTOCK ARTIFICIAL INSEMINATION biotechnology was among the first method with positive impact on genetic progress in animal populations. The first artificial insemination –scientifically mentioned - was made in 1779 by Italian monk Lazzaro Spallanzani, which inseminates a bitch with sperm, and he obtained three puppies. In England, in 1879 Heape made inseminations in mares with positive results. Other scientists like Hoffman or Ilia Ivanoff had great contributions in this field. Around 1899 and 1900, Russian scientist E.I. Ivanoff began conducting artificial insemination on cattle, horses, birds and sheep. He was first person recorded to have accomplished the first successful artificial insemination in cattle. Because Ivanoff was so successful at animal artificial insemination, by 1931, Russia bred approximately 19,800 cows. Now, artificial insemination is use all over the world in all animal species.
EMBRYO TRANSFER is another biotechnology, with the greatest influence on genetic progress in livestock populations, especially in cattle and horses, which have a low annual prolificacy and a very long distance between generations (cattle 5 years; horses 8-9 years). The first successful mammalian embryo transfer was performed in 1891 by Walter Heape in rabbits. The first bovine embryo transfer was recovered by Hartman, Lewis, Miller and Swett in 1930 at the Carnegie Laboratory of Embryology in Baltimore. In the 1950’s, embryo transfer technology in cattle expanded with the first successful transfer performed by Umbaugh and the first calf born through a joint effort by the USDA and the University of Wisconsin. Embryo transfer in food animals began in the 1930’s using sheep and goats, but it was not until the 1950’s that successful embryo transfers were reported in cattle and pigs by Jim Rowson at Cambridge, England. Until the 1970's progress was slow, with many ideas ending in failure. As non-surgical methods advanced through the efforts of Elsden, Hasler, Seidel and others, the commercial use of embryo transfer exploded. In 2002, over 25,000 (25 093) ET calves were registered in the United States.
Embryo transfer in cattle became very popular in the last years. Applicable technologies for embryo transfer have been improved especially among 1970 and 1980.
Embryo transfer is currently made in horses, but is restricted in a little number of mares, due to the low or insignificant genetic progress. Embryo transfer in horses is limited due to higher costs and lack of embryos on the market.
Another biotechnology with great influence on genetic progress and quantitative genetics is EMBRYO BISECTION procedure. Blastomeres bisected are introduced in empty “zona pellucida”. After, is made the implantation of both zygotes, resulting monozygotic twins, "identical", almost always the same sex and their traits and physical appearances are very similar but not exactly the same; although they have nearly identical DNA.
Embryo microsurgery has created much interest both with researchers and commercial livestock producers because of the many options it offers in embryo bisection and biopsy.
In 1982, the embryo bisection procedure was developed by three independent labs, two in the USA (Colorado State University [CSU] and Louisiana State University [LSU]) and one in France. Each procedure requires specific microscopy and micromanipulators to conduct the extremely small delicate incisions needed in working with embryos.
By dissection the result is 50-60% for each half of the embryo if the transfer is made at the same receptor female, which means that the pregnancy rate rich 120% from a single embryo. EMBRYO BIOPSY techniques also offer advantages to producers in knowing the sex of a calf prior to its implantation into a recipient. The procedure begins with a small sample of two to three cells aspirated from each embryo and a three hour DNA analysis to determine the sex. Normally, embryos collected in the morning from super ovulated donors can be "sexed" before noon the same day. Embryo biopsy
MICROINJECTION of a single sperm cell (spermatozoa) into oocytes is another reproductive technology using microsurgery that has tremendous potential for livestock production. The most advance biotechnology is CLONING . The term clone is derived from the Greek word for "twig, branch", referring to the process whereby a new plant can be created from a twig (Shmaefsky B. – 2006). Molecular cloning refers to the process of making multiple copies of a defined DNA sequence. Cloning is frequently used to amplify DNA fragments containing whole genes, but it can also be used to amplify any DNA sequence such as promoters, non-coding sequences and randomly fragmented DNA. Cloning of any DNA fragment essentially involves four steps: - Fragmentation - breaking apart a strand of DNA - Ligation - gluing together pieces of DNA in a desired sequence - Transfection - inserting the newly formed pieces of DNA into cells - Screening/selection - selecting out the cells that were successfully transfected
Dolly (05-07-1996 - 14-02-2003), a Finn Dorsett ewe, was the first mammal to have been successfully cloned from an adult cell.
List of animals that have been cloned (McLaren A - 2000).
Tadpole: (1952) many scientists questioned whether cloning had actually occurred and unpublished experiments by other labs were not able to reproduce the reported results.
Carp: (1963) In China, embryologist Tong Dizhou cloned a fish. He published the findings in a Chinese science journal which was never translated into English.
Mice: (1986) a mouse was the first successfully cloned mammal. Soviet scientists Chaylakhyan, Veprencev, Sviridova, and Nikitin had the mouse "Masha" cloned. Research was published in the magazine "Biofizika" volume ХХХII, issue 5 of 1987.
Sheep: (1996) from early embryonic cells by Steen Willadsen. Megan and Morag cloned from differentiated embryonic cells in June 1995 and Dolly the sheep from a somatic cell in 1997.
3. BIOTECHNOLOGIES IMPORTANCE IN CATTLE IMPROVEMENT
Cows and heifers artificial insemination lead to rapid genetic progress. In this case, the reproductive potential of dams and sires is very great.
In the ova of heifer there are around 150 000 oocyte, while in sires can be obtained billions of spermatozoa in a single ejaculate. Using artificial inseminations makes possible maximum use of superior sires, which means an increasing of the genetic progress in the cattle population.
Embryo transfer is a biotechnology which increase the number of offspring’s with a higher genetic progress, originate in nominee couples. This biotechnology method contributes to a faster genetic progress, in higher rate.
In developed countries, around 95% from the dairy sires tested, are obtained from embryo transfer, which indicate the importance of this biotechnology in the selection programs.
Obtaining monozygotic twins by embryo bisection has implications in realising genetic progress and also for estimating some genetic parameters necessary in estimation of genetic programs (Morris D.G., Diskin M.G., Sreenan J.M.- 2001).
4. EMBRYO TRANSFER AND THE INFLUENCE ON GENETIC PROGRESS IN CATTLE
4.1. INDUCTION OF ARTIFICIAL TWINS
Embryo transfer in dairy or beef cattle, lead to the INDUCTION OF ARTIFICIAL TWINS . Obtaining artificial dizygotic twins, lead to the increasing of offspring number that is the reason why it’s use especially in beef production.
In dairy cows, twining can be induce only with sexed embryo, to prevent the born of freemartin heifers, which are sterile. It can be transfer two embryo to an an-covering recipient cow or only one embryo to a recipient at the beginning of the natural pregnancy (7-8 days).
After the non-surgical transfer of an embryo, in each uterine horn can be obtained a pregnancy rate around 60%, from which 50% are twins’ pregnancys. Transfer of an additional embryo in recipient females cover before (7-8 days) is followed by a pregnancy rate similar to that obtained by artificial insemination, but the incidence of the twinning pregnancy is lower (25-40%).
Another biotechnology for artificial twinning induction is preinplantation of splitting embryos when are obtained identical twins. From young morula and blastocysts, are obtained by embryo microsurgery half embryos, which are doubling the number of the embryos that can be transfer from a single flushing (Pacala N., Corin N, Bencsik I., Dronca D., Caraba V. – 2004).
In cow, by this method it can be obtained a pregnancy rate of 50-60% if the transfer is made in the same recipient female, finally the pregnancy rate reaching 120% starting from a single embryo. This technology for obtaining monozygotic twins has the advantage that is avoid the birth of freemartin heifers, unlike the transfer of the unsexed embryos.
With modern apparatus, flushing embryos from the donor in the morning can be „sexed” until the evening.
4.2. EMBRYO TRANSFER FACILITATE THE GENETIC STRUCTURE CHANGING, IMPORT AND THE EXPORT OF FROZEN EMBRYO
Embryo transfer offers an alternative to the traditional methods of genetic material changes. Import or export of the frozen embryo allowed the access to the most valuable animals in the world, with the lowest costs compared with the purchasing live animals.
Offspring resulted from embryo transfer are 100% the elected genotype. Embryo transfer reduces of costs with transport, quarantine and other veterinary welfare restrictions. Embryo transfer is a technology that helps to avoid the acclimatisation effects.
It was suggest that animals obtained using embryo transfer can receive immunity from the surrogate mothers for some diseases bound with a special climate, the result being a faster adaptation to the new environmental conditions (Del Campo, 1987).
4.3. EMBRYO TRANSFER REDUCE THE RISK OF CONTAGIOUS DISEASES
The possibility of diseases transmition through the embryos is much lower comparatively with the use of artificial insemination or live animals.
European and International Legislation stipulate the use of sterile technologies for embryos flushing and manipulation. Before frozen, embryos are flushed for ten times in normal saline and then examined on the microscope to establish the integrity of “zona pellucida”. For a better security, embryos can be treated with trypsin to remove pathogens attached at the “zona pellucida” ( Troxel T.R. 2007, Sing, E. -1987).
4.4. USING EMBRYO TRANSFER CAN BE OBTAINED AND TEST PRECIOUS SIRES IN A SHORTER TIME
In testing dairy sires, estimation of the improvement value is finished until four years, because of the great number of sisters and half-sisters which allow to appreciation on the basis of collateral relative.
Embryo transfer allowed the FOUNDATION BANKS OF FROZEN EMBRYOS (GENE BANKS) to can save some animal small populations, and also of some endangered breeds. Embryo banks are a novel method to preserve the complete genome and the conservation of the genetic diversity of the livestock breeds. Preserving frozen embryos is less expensive than live animals as gene reserves (Davis R. L. – 2004).
4.5. EMBRYO TRANSFER ALLOWED THE APPLICATION OF SOME EMBRYO BIOTECHNOLOGIES AS THE FOLLOWING:
in vitro fecundation, obtaining animals of certain sex (embryo sexing), obtaining transgenic animals, embryo microsurgery (splitting) and cloning by nuclear transfer (as Dolly sheep).
5. METHOD FOR ESTIMATION OF GENETIC PROGRESS AS A RESULT OF EMBRYO TRANSFER
Embryo transfer is a method that can be used to increase the valuable female contribution to the genetic progress.
The rate of improvement in monotocous (giving birth to one offspring) is realised very slow and at low values because the little number of offspring obtained from a female in the entire reproductive life and also due the long generation interval (5 - 6 years in cattle).
Embryo transfer gives the opportunity to transcend these obstacles, by inducing super ovulation followed by flushing and embryo transfer in the recipient female. The result is more offspring.
Genetic gain per generations (Δg) or genetic gain per year depends of the number of offspring obtained from a cow in a reproductive cycle. These animals (group of selection) will be use for replacement in the herd:
The rate of keeping in the selection group is calculated using the formula:
R% = E / F (the number of females obtained per year from a cow);
R% = selection intensity;
for example R% = E/F = 20 / 0.4
R % = 50% heifers kept in the selection group
A population with a mean of 4500 kg milk ± s = 900 kg milk
(where s is standard deviation)
If embryo transfer is not use, from a cow it can be obtained only 0.4 calf/heifer in a year. In this case „R” with will be equal with 20/ 0.4 = 50%, which means that only 50% from the selection group will be retain from replacement.
In this case, the mean of the selection group “xs” = xp + i * s
Where: “i” is the standardized selection difference depending of “R”.
xs = 4500 + 0,798 *900
xs ( Pm) = 5218 kg .
If are used for A.I. sires tested by their daughters, with a phenotypic potential of 7000 kg of milk (PT), the total difference of selection (ST) will have the following relation:
If the embryo transfer is use, from the same cow at each 60 days will be flushing 8-10 embryos - from which at least half are good for transfer – in a year can be obtained 30 embryos for transfer. From those embryos with fertility rate of 60-65% will result around 20 offspring /year, from which 10-15 attain the maturity. In this case, R = 50 / 10 = 5% which represent the rate of retaining for the selection group.
In this case,
Comparing these two examples, we found that by using embryo transfer, the genetic progress is three times higher. The conclusion is that the embryo transfer lead to the increasing of the selection difference (S), and finally to a higher genetic progress (Δg).
The cost of an embryo transfer program is fairly variable, influenced by location, apparatus, scientists, etc. Minimum costs of 170 E per pregnancy have been reported by embryo transfer technicians. These costs do no include drug costs for super ovulation and certainly do not include semen, registration, embryo transfer certificates, or blood typing of donor cows and ancestors. Most importantly, the cost of owning and maintaining recipient cows until the calves are weaned must be considered. Some embryo transfer centres may also provide recipients and charge 800E to 1200E per pregnancy. Three to five straws of valuable semen will often be used for each breeding and cost 30 E to 300 E. Proper nutrition, health care, and synchronization of the donor and the recipients can add another 250E to 300 E expenses to each successful pregnancy. Consequently, many purebred operations conducting embryo transfer on a regular basis consider that each “ET” calf must have a market value of 1000E to 1200E greater than other naturally conceived and reared calves in the herd before embryo transfer is considered.
Embryo Transfer is now accepted as the quickest and most cost efficient method of increasing the rate of genetic improvement within a herd. For beef and dairy operations, it can be a valuable addition to any breeding program, leading to greater efficiency and profitability.
Biotechnologies used in livestock breeding lead to the achievement of some high productive performances and to a quick and invariable genetic progress.
Embryo transfer contribute to the annual genetic progress improvement for milk production cu 20-30%, more than the progress obtained by present programmes for dairy cow selection.
Using embryo transfer can be obtained easier animals related by mother line, which open opportunities for introduction new technologies for hierarchy similar to those used in poultry and pigs improvement.