In an interview with Birth.Movies.Death, Marvel Producer and MCU ringleader Kevin Feige was answering questions about the film, when he dropped a devastating little nugget.
When asked if Thanos eliminated 50% of all sentient life, a question was asked, concerning if it was ALL life that was culled. Feige answered “Yes. All Life.”
So that includes, plants, bugs, animals and most importantly; your pets.