I don't believe in feeling gratitude towards "nature". Animals aren't as far as we know some group of beings that collectively agreed to help us humans grow as a species. Dogs didn't all meet one day and decide HEY LETS HELP BLIND PEOPLE. Animals feed us and work for us because we make them do it. We use animals the same way we use wind and fire. I understand we should be glad animals are there, but they do not form some sort of collective we should feel gratitude to.
For the feelings part, yeah of course animals have "feelings". A dog that is left alone will start crying, and be visibly glad when their masters come back. Fishes that are well fed and have a clean place to live will swim around quick, and hungry fish in murky water will be almost motionless and look almost depressed. Animals very sensitive, and express their states of mind in their own way. People who claim otherwise are usually just trying to provide a convenient answer to the nagging question of "why is it okay to slaughter cattle by millions", and are ashamed to rely on meaningless cop-out answers like "WE HAVE SOULS AND THEY DON'T".
However, I don't think attributing animals "feelings" and using that as a reason to treat them equally(or whatever) makes any more sense: feelings in their POETIC sense are pretty much a human-created concept, and we project these concepts on animals when trying to understand how they feel.
For instance, looking in a dog's eyes: As you stare at the dog, you try to imagine that it is also staring back at you, and try to imagine what he is thinking, doing that from your own understanding of life and through this falsely attributing the dog human traits. Its empathy, its how we deal with other humans, its what gives you a natural inhibition from hurting another human being. Looking at them and understanding they are staring right back at you, like a mutual understanding of each others' sentience. For animals, the effect of empathy still remains, but the more different the animal is to you the weaker is its effect: you have a harder time making that connection.
Attributing them romantic and vague concepts of feelings we humans made up makes no sense however. Animals are sad, or happy, or angry. They are territorial, protective. They are hungry, thirsty, they are in heat, they are passive, they are active, they are agressive, they feel safe or threatened. It is the same for us, except that because of our intelligence and natural need of beautifying things and classifying things and placing greater meaning in things that are mostly meaningless in our search for existential answers and shit, we made up a whole panoply of different tones and contexts and combination's and half-tones and tangents to these basic emotions and then attribute them to everything around us. Dolphins laugh, birds are happy, bears are grumpy, dogs are faithful, mice are curious, hyenas are cruel, lions are proud. Ants weren't so lucky though, they're just "hard workers". Heh, suckers, must be because of the wiggly legs and beady eyes and antennas.
So basically, yeah, animals do feel things like we do, but its not all that special and is sort of an arbitrary reason to use in deciding what we should consider to have rights to be "ethically treated". As I said before, I do think torturing animals and killing or raping them is never a good thing, but it is not the animal victims I worry about, but rather the damage that such behavior could represent on mankind. As for the question of, what SHOULD we use to decide what deserves rights for ethical treatment and where to draw the line however, I have no idea. My first guess would be intelligence, creativity or capacity to communicate, but we barely know how these things even work.