A new review published in the Journal of Animal Science and Biotechnology, looks at how the application of new and developing biotechnologies could provide a strong platform from which to meet the increasing demands for high-quality pork, whilst reducing carbon footprints and waste excretion.

The researchers, Guoyao Wu and Fuller Bazer, discuss the applications of genetic modification in pigs to date: pig genomes have been edited to express bovine growth hormone, bacterial phytase, fungal carbohydrases, plant and C. elagans fatty acid desaturases, and uncoupling protein-1; and to lack myostatin, α-1,3-galactosyltransferase, or CD163 (a cellular receptor for the "blue ear disease" virus). This said, the opportunities for future application of biotechnology are far-reaching and are currently being explored.

Cloning

An advantage of cloning is the ability to conserve breeds or species, particularly rare breeds, as this allows the maintenance (or increase) in genetic diversity.

Cloning also allows castrated males with valuable traits, such as high-quality meat or high feed efficiency, to be replicated in offspring.

Recombinant DNA technology

Recombinant DNA technology is the foundation for producing transgenic animals and is highly valuable in the production of proteins, peptides, vaccines, amino acids, fatty acids, and vitamins by bacteria.

rDNA is proving to be valuable for the development of nutrient-rich feed products, such as amino acids which can significantly reduce the protein volume in pig diets, thereby reducing the total volume of nitrogen excreted into the environment.

The modification of bacterial genomes using rDNA technologies also allows more efficient generation of enzymes for feed fermentation; can be used to develop successful vaccines; and is aiding in the elimination of bacterial resistance to antibiotics.

Genetic modification of animals

Transgenic animal technology allows for the introduction of a foreign gene into the germ line of an animal to establish a desirable trait (eg high rates of lean tissue gain and feed efficiency) and a new capacity (eg synthesis of a protein with nutritional applications) in a breeding line of livestock.

Gene modification can complement the traditional breeding techniques to improve the efficiency of livestock production by enhancing: (a) the digestion, absorption and utilisation of dietary nutrients, (b) resistance to metabolic and infectious diseases; and (c) adaptation to the living environment.

Transgenic animals can also produce enzymes to eliminate anti-nutritional factors which can improve the efficiency of nutrient utilisation to reduce the number of animals on farms as well as the environmental pollution of nitrogen and phosphorus.

Gene editing through gene knock-out or knock-in

Traditional livestock breeding is beset with such problems as long breeding cycles and limitations of genetic resources. In contrast, genome editing tools can provide more precise, more specific, more predictable and more rapid solutions to solving these problems at relatively affordable costs. Gene editing techniques require fewer steps and have a higher efficiency than the previous methods of animal transgenesis.

Gene editing also increases successes in single-gene and multi-allelic modifications of the livestock genome, as well as in site-specific introductions of foreign genes during embryogenesis.

There are many examples for the genome editing-based production of transgenic pigs with important production and disease-resistance traits, including nutrient utilisation and meat production as well as resistance to viral infections and metabolic disorders. The knock-in of Uncoupling protein 1 into pig genomes has proven to increase nonshivering thermogenesis and piglet survival, and knock-out of the CD163 gene has proven to increase resistance to porcine reproductive and respiratory syndrome virus (PRRS).

Antibiotic resistance and alternatives to antibiotics

Some bacteria are resistant to one class of antibiotics, and others are resistant to multiple antibiotics, thereby posing a serious global health concern. For ensuring the optimal efficacy of antibiotics in treating bacterial infections in animals and humans, there is increasing concern worldwide over antimicrobial resistance (AMR).

Antimicrobial resistance genes in bacteria can be inherited from mother to daughter cells by division, as well as from one strain to another via plasmid transfer. The plasmids (small DNA molecules which are independent from the chromosomal DNAs) in bacteria often carry information that may benefit their own survival through resistance to antibiotics produced by themselves or by other organisms in their environment.

The antimicrobial-resistant genes produce enzymes to destroy or inactivate antibiotics, which is the mechanism upon which CRISPR-based gene editing methods act. CRISPR-Cas possesses its ability to selectively target specific DNA sequences and, therefore, easily distinguish between pathogenic or commensal bacterial species. This has been shown in a number of studies, including experiments where CRISPR-Cas9 has been successfully used to knockout AMR genes in Staphylococci aureus (Gram-positive bacteria).

A practical application of this technology would be to mitigate AMR and develop alternatives to in-feed antibiotics in swine production.

Conclusions

With continuous improvements, this biotechnology holds great promise in conserving the diverse breeds of swine, augmenting feed efficiency and pork production, and developing alternatives to antibiotics in the future.