If you're looking for manga similar to Butareba: The Story of a Man Turned into a Pig (Light Novel), you might like these titles.
A thirty-year-old Japanese male is teleported to Japan's warring-era. But instead of being reincarnated as a samurai or ninja, he is now a pony! Cute and spry, he is enjoying is carefree new life but all that changes when he runs into a human who is fighting off a bear attack! The pony dashes and rescues the man, and thus begins his new life...as a warhorse!
Three sisters go on a journey to aid a cursed prince, who has been transformed into a pig.
When Shu Tang, a sickly young woman, fell ill and passed away in the 21st century, she thought she would finally be able to drink a bowl of Meng Po’s soup, take a trip across the Neihe bridge, and not be such a sickly person in her next life. But, after her soul left her body, forget about Meng Po’s soup, she didn’t even see soup dregs before being transmigrated into the body of a pig! After being adopted by Fuyu Shangxian, one of the three great immortals and heaven’s peerless beauty, hilarity ensues.
42 year old "shachiku" (company slave) Matsuda Takeshi gets worked to death, as is customary in Japan. His one dying wish is to work for a decent enterprise, not the black company he had been working for. His wish is heard by a god who, for his own amusement, has him reincarnate as a young elf male in another world, with increased affinity for earth magic and ability to command golems. The new golem master sets out on a quest to acquire the Seven Treasures left behind by a legendary mage from 1000 years ago.
When a 30-year-old salaryman and games enthusiast is suddenly killed in a car accident, he finds himself reborn into a fantasy world…but in the form of a sword! Now he’s in search of a beautiful woman to wield him, and a cat girl named Fran might be the exact adventuring partner he needs.
Karin Kokubu is late for school one day when she comes across an apparently injured yellow pig. It turns out the pig wasn't injured, just hungry, and he gets back his health when he eats Karin's apple. Later she meets the pig again, who explains that he is actually Prince Tonrariāno III of the planet Buuringo. He tells her how she can transform: by saying "BA BI BU BE BOorin!" and she transforms into a superpowered pink piglet called Buurin. This is not something Karin is happy about at all, as she'd rather transform into a heroine like her idol "Cutey Chao". Tonrariano tells her if she can collect 108 pearls by doing good deeds as Buurin, she can do so.