In a few words: Pig and human biology are very close to each other.

Pigs have genetic and physiological traits similar to humans, which make them one of the most useful and versatile animal models. Owing to these similarities, data generated from porcine models are more likely to lead to viable human treatments than those from murine work.

https://covid19.elsevierpure.com/en/publications/antiviral-activity-of-portulaca-oleracea-l-extracts-against-porci