By Carien Kruger
The success achieved with gene editing to make pigs resistant to the disease porcine respiratory and reproductive syndrome (PRRS) also holds great promise for South African farmers’ fight against African swine fever.
The US Food and Drug Administration (FDA) recently approved global animal genetics company Genus’ use of CRISPR technology in pigs to make them resistant to PRRS. Genus is the parent company of pig genetics company PIC.
Genus says this approval is an important step towards the commercial use of PRRS gene editing.
Marguerite Schwarzer, marketing manager and member of PIC South Africa’s technical services team, says the research and development was in collaboration with the University of Missouri was done on two breeding farms in the US. In order to export these gene-edited pigs from the US, the relevant authorities of each importing country must separately approve the use of the technology.
Brazil, Colombia and the Dominican Republic have already approved it, while approval is awaited from the Chinese, Japanese and Canadian authorities.
“PRRS is one of the most devastating global pig diseases, causing suffering and premature mortality in pigs. Recent research indicates that PRRS also increases the need for antibiotics by more than 200%,” says Genus.
The disease causes fever, respiratory challenges, impeded growth, poor feed conversion rate and increased post-weaning mortality in growing pigs. In breeding pigs, it also causes fever and increased post-weaning mortality, as well as a decrease in conception, an increase in sow mortality and premature birthing.
PRRS is estimated to have cost the US pork industry $664 million annually from 2005 to 2010 (about R11.8 billion at current exchange rates). It has a devastating impact on farms.
Piece of DNA removed
Schwarzer says in layman’s terms, gene editing involves removing the part of a pig’s DNA that the PRRS virus binds to. In the trials, gene-edited pigs were exposed to various PRRS strains, but none bound to the pigs’ DNA.
In scientific terms, it is specifically the CD 163 protein in pigs which the PRRS virus binds to. Through gene editing, the connection point is removed from the CD 163 protein.
The gene editing was done in the following PIC lines: PIC Landrace (L02), PIC Grootwit (L03), PIC337 and PIC800 (Duroc).
The trials proved that the pigs still have the same production and reproductive characteristics and that their meat quality is exactly the same as that of comparable pigs without gene editing.
Schwarzer says it’s important to know the difference between gene editing and genetically modified organisms (GMOs).
“Gene editing involves taking out a piece of DNA. No other foreign DNA is inserted.”
Gene editing is also done in cattle, which are referred to as “SLICK1” cattle.
Gene therapy is used in human health to treat sickle cell anemia, hereditary hearing loss and hereditary blindness.
The success achieved with gene editing to make pigs resistant to PRRS followed after ten years’ work, Schwarzer says.
After the recent FDA approval, it could take some time to breed enough gene-edited pigs for export, which would first go to countries most affected by PRRS.
Hope for the fight against African swine fever
South Africa is one of the few countries that are free from PRRS, a status the industry is protecting and which is the reason why there are restrictions on specific pork imports from certain countries.
Schwarzer says the technology does though hold promise in terms of the losses the local industry is suffering due to African swine fever (ASF). Genus is already conducting research into using gene editing to make pigs resistant to ASF.
