The animals aren't necessarily sentient (sapient?) though. Magic helps bridge the gap between the caster and beast, allowing the caster to gain information from beasts' experiences, but it's usually not taken as Larian's "the beast speak in full sentences and show a human-like level of intelligence." Otherwise, the spells Comprehend Languages, Detect Thoughts, and Tongues would allow animals to communicate with you - but they don't because beasts don't actually have a language and/or high enough intelligence.
Also, irl we eat pigs and pigs are pretty smart.
And in real life there is an ongoing discussion about animal sentience too. If you add magic to the mix, even if you'd not be able to hold a conversation with livestock, you should be able to tell how sentient they are and how they feel about being fed to that baby dragon. Of course, the question becomes even more complicated if the dragons are on average as (or more) intelligent than humans. Because if it is fine to kill a dragon simply because they are evil, would then killing humans simply because they are evil (easy to tell with that detection spells) be also ok? There was a paladin like that in BG1.
