> but agronomists have been doing selective breeding as a science for several centuries by now

Not of beings we knew to be sentient. People who tried that became the "eugenics" movement and got into very bad territory very quickly.

And even with animals, I believe part of why public knowledge about animal cognition is changing so slowly despite all the things we are already know is that a lot of our behavior towards animals is resting on the assumption they are not conscious. If it would turn out that many are, things will be... awkward.