In a post-apocalyptic world, three young adventurers and somewhat crazy, find that the chickens they’ve been hunted as a food will be part of a dire threat that could destroy what it remains of humanity.

"When his chickens are infected with an extraterrestrial virus, an eccentric farmer must stop the mutated beast before they infect the rest of the world."
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Here was my thought process:

When his chickens are infected with an extraterrestrial virus- inciting incident.
an eccentric farmer- lead character
must stop the mutated beasts- goal
before they infect the rest of the world- the stakes.

You logline will be different but if you see what I did there you can incorporate your story the same way.

Hope that helped, good luck with this!

Hi! They are infected by swallowing a seed that came from out of the space. They become bigger, (and ugly) to hatch all together a bigger and giant monster chicken. It's a story of my manga, Tinkers of the Wasteland, which is already published.

Are the chickens infected or they mutated into some kind of giant killer chickens?