Why do animals have to suffer?

I don't understand this... why do animals have to suffer?

They bought happiness to a human's life, yet, they also suffer the sickness men do. Its not their fault!

Last night when i was going to sleep, i was listening to the radio (988). The program is hosted by "Chan Fong" where people with problems all call him and talk to him, and he tries to solve it with advices etc, and this guy called. I was heartbroken when i listen to his story!

He own a dog of, should be around 10 years dee if i didn't heard wrongly... And the dog is dying of blood cancer (Or some cancer)...
He (The dog) was suffering. He won't eat, won't drink, won't sleep. When they try to feed him water, he'll just spit out blood. And... oh my god! I cried when i just heard him said that his dog was sick (Note: I'm a crazy animal-lover! Dead-crazy! Dead dramatic! And dead-emotional when it comes to animals!)... Than i wondered... why do animals have to suffer? Its just unfair! Its not like they did anything wrong - humans did more wrongs - but... they have to suffer sickness like us humans do! Its so unfair!

I hope the dog, no matter how he is now - or where he is -, i hope his happy and if he's still here, i pray he'll get well soon!

I can't have a dog, due to some stuffs, so i never got to chance to experience what dog-owners do... but i do hope all you dog/ pet-owners out there will

treat your pets as good as you can, and never make empty promises ("I'll bring you out tomorrow"... but it ends up the next tomorrow, or next next tomorrow...)... who knows... they might just leave you when you least expect it... That is why treasure every moment together, do everything you can for him, so you won't regret if anything happens...