Justin Bieber: Shirtless Horseback Riding -- Putin On His Best Urban Cowboy

Justin Bieber had his young guns blazing ... losing his shirt for a horseback ride/homage to Russia's most famous topless equestrian.

Bieber traded his skateboard for a proper steed at a ranch just outside L.A. yesterday.

While Justin's cowboy hat was more Sinatra than Rogers -- his shirtless pose was totally reminiscent of Vladimir Putin's pose.

Don't worry ... we've got plenty of video of JB's ride with his posse (yeah, Lil Za rode too) for your viewing pleasure.