Whether something is funny really depends on how it's written, I suppose. Douglas Adams managed to find humor in the birth (via the improbability drive), very short life in free fall, and death, of an innocent sperm whale.
With the trying farm animals as if they were humans thing, I'd probably find it more amusing if it were approached from the perspective of how absurd it is to do something like this, maybe even from the perspective of the people doing it. But it's all in the writing. I can get an occasional wry chuckle out of readers, but the thought of having to write an entire book where every scene is playing for laughs? I don't think it's where my talent lies.
And yes, I've heard of the "rule of threes" with humor. That two repetitions of a joke creates maximum amusement, then the returns start to drop off. But that doesn't really get at why a joke is funny in the first place.
Humor in the abuse and death of animals is a touchy subject in any case. Yes, cultures differ here, but in the US and western Europe, many, possibly mos, people regard animals as, if not quite equal to people, at lease deserving of humane treatment and protection. When animals appear in stories, they tend to elicit the same kind of protective instincts we feel towards children. This doesn't mean we don't have our everyday hypocrisies, like meat eating, here. But there's a difference between being "ok" with something happening out of sight and something in a story that's aiming for laughs.
So know who your audience is and consider it.