I think this is a first for this site so lets just get in there and explore our very first Horsestronaut in the form of Mister Ed, season 2, episode 2.
So, according to Wikipedia the episode synopsis is;
"In order to appease Mr. Mencken, a potential new client, Wilbur takes an office downtown. Ed now feels unwanted and attempts to become the first horse astronaut into space. Ed goes to the space center and passes the intelligence test. The day of the flight, Wilbur rushes to the space center, but the rocket is just taking off. Mr. Ed shows up and tells Wilbur they picked another horse at the last minute because Ed was too heavy."
Which is all very informative but what you really want to see is this rather splendid Destination Moon style spacesuit on that there horse
Its a cracking job isn't it and its fun to note that they've left a little grill in the horse shaped fishbowl (?) helmet so that the 'actor' can still breath with out steaming it up and obscuring his talent.
If we never see another horse shaped spacesuit again, I still think we've already seen the best.
Big thanks to Bill for this find. You are a good friend to the blog and its greatly appreciated.