Yeah, the horse is definitely a photoshop. They don't get fat in that way!
As for the rest... fat isn't any healthier on animals than humans. And it DOES slow them down, hurts their joints and causes cardiac stress.
Heck, our little Border Collie just had her pups on Sunday... she was working cows Saturday afternoon, and went back to work (insisted on it... we thought she'd probably take a couple weeks off!) on Monday. The difference in how she's moving, and how obviously happy she is to NOT be carrying all that extra weight (albeit "puppy weight", not "fat") is amazing, and really funny. She's SO happy... those cows aren't being allowed to dawdle or balk.
While there are animals with adrenal or thyroid issues, most of them get obese the same way humans do... way too many calories, way too little exercise.
Summerthyme