Pets are great for collecting extra experience points just for feeding them some carrots, milk, or bacon.
And don't forget to name your pets ;-)
Experience points for feeding every 6 hours:
DogsRetriever level 20 + 28 - 30 xp
Pinscher level 22 + 28 - 40 xp
Hound level 30 both - 50 xp
Puppies
Retriever level 35 + 44 - 35 xp
Pinscher level 50 both - 35 xp
Hound level 54 both - 35 xp
Cats
Tabby level 21 + 29 - 20 xp
Calico level 23 + 29 - 30 xp
Tuxedo level 31 both - 40 xp
Kittens
Tabby level 40 + 58 - 40 xp
Calico level 56 both - 40 xp
Tuxedo level 60 both - 40 xp
Horses
Bay level 27 + 37 - 60 xp
Palomino level 32 + 37 - 80 xp
Pinto level 34 + 37 - 100 xp
Andalusian level 40 both - 100 xp
Lipizzaner level 47 both - 100 xp
Bunnies
White level 31 + 41 - 30 xp
Black level 38 - 30 xp
Fluffy level 41 both - 30 xp
Donkeys (xp every hour)
Provence level 43 + 55 - 25 xp
Anatolian level 52 + 55 - 35 xp
Andalusian level 55 both - 30xp
Town Animal Sanctuary (xp every 10 hours)
Elephant town level 3 - 25 xp
Giraffe town level 3 - 25 xp
Hippopotamus town level 3 - 25 xp