Somatic cell nuclear transfer (SCNT) involves transferring the nucleus of a differentiated somatic cell into an enucleated oocyte and artificially activating it to initiate development of the reconstructed embryo, which ultimately develops into an individual with a genetic background identical to that of the donor cell. The core principle of the technology is to use key factors in the oocyte that can reprogram the epigenetic state of the somatic cell nucleus, restoring totipotency to the differentiated nucleus and restarting the gene expression program required for embryonic development. Since the birth of “Dolly,” the world’s first somatic cell-cloned livestock animal, in 1996, research and application of somatic cell nuclear transfer in livestock have spanned 30 years. In pigs, in 2000, the British company PPL Therapeutics successfully cloned 5 female piglets for the first time, laying the foundation for the development of somatic cell cloning technology in pigs. In 2005, China Agricultural University successfully produced China’s first somatic cell-cloned pig, marking China’s entry into the international forefront in this field. Since then, China has continued to make breakthroughs in pig cloning efficiency, survival rates, and large-scale application. Several research institutions and pig farming companies have established mature technical systems for somatic cell cloning in pigs. This article focuses on analyzing the economics and adoption bottlenecks of the current application of somatic cell cloning technology in pigs, with the aim of providing pig farming businesses with a reference for choosing and applying this technology.
1. Technical Process for Somatic Cell Cloning in Pigs
The process of somatic cell cloning in pigs mainly includes: preparing donor cells; obtaining and enucleating mature recipient oocytes; reconstructing cloned embryos; activating cloned embryos and culturing them in vitro; embryo transfer; and the birth and identification of cloned piglets. Somatic cell cloning in pigs is a complex process. The type and condition of donor cells, the quality of oocytes, and technical procedures such as cloned embryo reconstruction and embryo transfer all have a significant impact on the birth rate and health of cloned pigs.
2. Application Areas of Somatic Cell Cloning Technology in the Livestock Industry
(1) Rapid Multiplication of Superior Breeding Pigs
Somatic cell cloning technology enables the rapid “replication” of superior breeding pigs, overcoming the bottleneck in traditional breeding whereby it is “difficult to reproduce superior individuals in large numbers within a short period.” Therefore, building on breeding work, breeding companies can obtain multiple superior individuals with identical genetic backgrounds in a short period by cloning top boars or sows, accelerating the spread of superior genes within the population and the pace of breed improvement. Guangdong Wens Foodstuff Group was the first in China to carry out large-scale cloning of top breeding boars, and provides high-quality breeding pig cloning services and semen products from cloned pigs to the public. Sichuan Dekang Agriculture and Animal Husbandry Food Group, Fujian Aonong Biotechnology Group, Shanghai Xiangxin Livestock and Poultry Co., Ltd., and other organizations have also conducted work on producing cloned breeding boars using somatic cells and evaluating the results. They concluded that somatic cell cloning technology can be effectively used for the rapid multiplication of elite breeding boars, enabling the efficient transmission of superior breeding pig genes.
(2) Conservation and Restoration of Local Pig Genetic Resources
China has abundant local pig breed resources. However, affected by factors such as African swine fever outbreaks and competition from commercial breeds, many excellent local breeds face the risk of becoming endangered or even extinct. Somatic cell cloning technology helps safeguard these valuable genetic resources. By cryopreserving somatic cells from local pig breeds, populations can still be restored through cloning even if live populations suffer a devastating blow. At present, somatic cell cloning technology has become a key technology for conserving excellent local pig breeds and expanding populations of endangered pig breeds. Cloned pigs have been successfully obtained using somatic cell cloning technology for local breeds including Northeast Min pigs, Eastern Guangdong Black pigs, Lantang pigs, Qingyu pigs, Jinhua pigs, and Hetao Large-Eared pigs.
( 3 ) Creation of Gene-Edited Pigs
Combining somatic cell cloning technology with gene-editing technology is the main technical approach for creating gene-edited pigs, and is also a key high-tech technology for the future of pig breeding. At present, gene-editing cloning technology has been used to create new breeding materials with excellent production traits and disease resistance (such as resistance to PRRS). Knocking out the CD163 gene gives pigs complete resistance to PRRS without affecting production performance. Several research institutions and pig farming enterprises are conducting safety evaluations of CD163 gene-knockout pigs, with applications for certificates expected in the near future.
3. Economic Analysis of the Large-Scale Application of Somatic Cell Cloning Technology in Pigs
Somatic cell cloning technology can “replicate” superior breeding boars with outstanding performance on a large scale, but producing cloned pigs with this technology involves a high technical threshold and substantial financial investment. The economics of cloned pigs need to be analyzed from different perspectives.
At present, large-scale application of somatic cell cloning technology has only been reported for breeding boars, with few reports of its use in breeding sows. Considering the cost of breeding a single boar, producing one cloned pig requires an investment of approximately 2 ten thousand yuan, 10 times the cost of breeding a conventional pig. This is mainly due to the low efficiency of pig cloning. Currently, the average birth rate of cloned pigs is only 1%-2%, and the mortality rate of newborn cloned pigs is as high as 30%. However, given the genetic value of cloned breeding boars themselves, their economic benefits are considerable. Cloning technology is generally used to clone the top 1% of breeding boars in a population, as ranked by breeding index. To obtain a pig with equivalent genetic performance, conventional breeding methods require selecting from 100 boars, at a breeding cost of 20 ten thousand yuan. Therefore, calculated on the basis of the breeding cost per top breeding boar, applying cloning technology can save 18 ten thousand yuan in breeding costs. At present, multiple institutions in China and abroad have systematically evaluated the growth and reproductive performance of cloned pigs and found no significant differences between cloned boars and naturally bred pigs in these traits. However, the offspring of cloned breeding boars show significantly improved growth rate and feed conversion, potentially creating substantial additional economic benefits for pig farms. In particular, cloned top terminal boars can pass on 50% of important economic traits, such as rapid growth and a low feed-to-weight ratio, to commercial herds. According to reports, each 0.1 reduction in the terminal sire feed-to-weight ratio can increase economic benefits by 95.2 yuan.
4. Analysis of Bottlenecks and Countermeasures for the Large-Scale Application of Somatic Cell Cloning Technology in Pigs
(1) Low cloning efficiency and high cost
Although somatic cell nuclear transfer (SCNT) in pigs has shown great potential for application in breeding, its low cloning efficiency remains a core bottleneck restricting its large-scale industrial application. It is currently believed that incomplete epigenetic reprogramming of donor cell nuclei is the fundamental cause of low cloning efficiency in pigs. During development, the ooplasm cannot completely erase the donor cells’ “epigenetic memory” from cloned embryos. To address this issue, the quality and developmental capacity of cloned embryos can be improved by selecting cell types that are easier to reprogram (such as cumulus cells), using drug treatments to promote reprogramming in somatic cells or cloned embryos, improving oocyte cytoplasmic quality and reprogramming capacity, and refining cloning techniques and culture systems.
(2) Cloned populations have a uniform genetic structure, and genetic progress stagnates
Although somatic cell cloning can rapidly produce large numbers of copies of elite breeding pigs, cloned individuals have almost identical genetic compositions and lack variation, causing genetic progress to reach a ceiling and preventing continued improvement. In addition, a uniform genetic structure in a population can make pig herds more vulnerable to specific pathogens or extreme climates, or lead to inbreeding depression and reproductive disorders. Therefore, cloning cannot replace conventional breeding; it is better suited as an auxiliary technology within a breeding system. Somatic cell cloning can be used as a “copy machine” for elite breeding stock to mass-produce high-quality breeding boars. Their superior genes can then be disseminated through crossbreeding with natural populations, restoring population diversity and achieving heterosis.
(3) Epigenetic drift occurs, limiting the potential for serial cloning
Because somatic cell cloning is subject to incomplete epigenetic reprogramming, each round of cloning a donor cell causes “errors in genetic information” to accumulate in its genome, a process known as epigenetic drift, which leads to declining cloning efficiency in successive generations of cloned pigs. In pigs, continuous somatic cell cloning has not progressed beyond the third generation. This may be related to factors such as changes in telomere length, the accumulation of mitochondrial heteroplasmy, and the progressive loss of epigenetic imprints. The decline in the efficiency of successive rounds of cloning limits the application of porcine somatic cell cloning technology to multigenerational propagation. Epigenetic-modifying drugs can reduce the risk of epigenetic drift accumulating to some extent, but this problem has not yet been fundamentally solved.
In summary, porcine somatic cell cloning technology has broad potential for wider application. However, its large-scale commercialization still faces challenges due to factors such as operational complexity, low efficiency, and high cost. Its core commercial value lies in the precise preservation and efficient propagation of elite genetic resources, making it more suitable as a “breeding accelerator” than as a conventional breeding method. The key to future large-scale application will depend on whether epigenetic reprogramming technology can overcome the efficiency bottleneck. Article author: Wei Hengxi (College of Animal Science, South China Agricultural University)