Surrogate Sire – A Future Leap in Livestock Breeding
Dr. Ayushi Singh
MVSc Animal Genetics and Breeding, ICAR-NDRI, Karnal (132001)
Corresponding author – ayushi61404@gmail.com
Livestock farmers and researchers have selectively bred animals using artificial insemination for years to obtain superior traits such as production, disease resistance and climate resilience. However, techniques such as artificial insemination has its own technical and biological challenges. Artificial insemination is easy to implement in dairy cows but it is quite difficult in case of beef cattle as they freely graze on distant pastures causing difficulty in monitoring of heat. Similarly, the survival rate of frozen semen of pigs is very less. Moreover, artificial insemination in goat involves surgical manipulation which again makes it a tedious job. In view of these challenges, surrogate sire offers a new opportunity which can be easily exploited with the help of gene editing tool Crispr-Cas9.Surrogate sire is the sire that does not have its own germline, but have transplanted spermatogonia cells from donor superior males. This technology can optimally utilize the potential of high genetic merit male to produce large number of progenies.
Method
Identification of donor
For identification of high genetic merit sires, an initial genomic test followed by two subsequent progeny tests is found to be an effective strategy during experiment. Strategy includes generating genome followed by quantitative trait and breeding value estimation, generation of animal breeding and selection, dissemination to commercial herd by surrogate sire technology.
Creation of surrogate sires
CRISPR-Cas9 gene editing tool have been used to create animals called surrogate sires. Surrogate sires are created after knocking out NANO2 gene specific to male fertility. These sires are born sterile; but can start sperm production after transplantation of stem cells from donor animals in testes of surrogate sires. This has already been tested in mice and pigs.
Risk
Application of surrogate sire technology pose several serious threats including genetic homogeneity of commercial animals due to less diverse genes. Spread of any emerging disease could have detrimental impact on commercial production as whole herd is based on few sire genetics. Requirement of molecular biology and progeny testing infrastructure leads to costly implementation of surrogate sire technology.
Opportunities
Surrogate sires help in increasing genetic gain by 6.5 to 9.2 years as compared to conventional breeding program. It provides a shorter lag between nucleus and commercial herd as small number of parents are contributing to commercial herd. Profitability in meat market can be achieved by increased meat marbling character through this technology. Genetic conservation of extinct species across boundaries could be easily implemented with large number of progenies through surrogate sires.
Conclusion
Genetic improvement in lean meat percentage, meat marbling, high fat percentage in milk can be achieved at faster pace with help of surrogate sire technology. It will provide a leap in transfer of genetic improvements from nucleus herd to commercial herd quickly. Commercialization of surrogate sire technology in food chain is hampered by current ethical regulations. Current policy of gene edited animals will decide the future of surrogate sire technology in practise.
Reference
Gottardo, P., Gorjanc, G., Battagin, M., Gaynor, R. C., Jenko, J., Ros-Freixedes, R., Bruce A. Whitelaw, C., Mileham, A. J., Herring, W. O., & Hickey, J. M. (2019). A strategy to exploit surrogate sire technology in livestock breeding programs. G3 Genes|Genomes|Genetics, 9(1), 203–215.
