Hmmm, You're serious eh?

Sending an animal into space as a test is much less complicated than sending an animal to another planet that is hostile to life as we know it.
Not only would there be little chance of the animal making the trip to Mars, even if it landed safely and had automated functional space suit and support systems one tear in the suit and bye-bye animal.

Animals can be trained to do many things but no animal can be trained not to do something unexpected. Except man.

Agreed, but as this is not a moon landing with a quick round trip; I'm sure NASA scientists are working out all possible scenarios: unknowns & unexpected risks and planning risk responses.

But working out the 'unknowns'; for durations like 30 day stay on Mars may not be possible from earth. So animals yes, they could be sacrificed; if they reduce these 'unknowns'.

There are challenges as MM pointed out: 'breathing'; but are they really 'impossible to learn' with suitable gear? or is it cause we are so completely disconnected from 'wild' life?

Experts who train police dogs for tracking, etc; or the Swiss with their Bernard can probably tell us whether dogs wearing some breathing implants; feeding systems; sun glasses; cameras, etc; would perform even for a few days. If these animals could live even a week; that would be a signature event bringing us closer to colonization.

Bears in substitution for dogs; appear to have more advantages: natural hibernation for one and of course their fur skin properties which have spiked up their study in some univs. recently.