Most animals are sentient, from cockroaches to fish. Sapient is the word you are looking for, but even that word is extremely vague and realistically, parrots, apes, dolphins, elephants, crows and whales are also sapient to some degree and the more we come to understand them in at least some respect most animal are self-aware to some degree. Sapience is best defined as a spectrum and not a system of one notch to another. But we are not alone there.
There are no animals that want to be eaten. Livestock, working animals, and companion animals are arbitrary human constructs. There is nothing inherently worse about eating a dog than eating a chicken. Chickens feel every emotion a dog does, and even though we don't relate as well to them that hardly means they don't experience what we do. We view dogs as more relatable to us because over 13,000 years we have co-evolved to live with and understand them, and them us. But this has not made the dog inherently smarter or more human than say, the pig. Rather, it has more so opened a clearer window into their consciousness. But just because that window might not be so clear when we look at a pig, a rat, or a bird does not mean the animal experiences a lesser state of consciousness. Animals vary in their cognitive abilities, but even in this we have only one standard to go by, and that is to judge them by how well they can do human things. Dogs are very good at it. Dolphins, elephants, and some others can also do a good job. We consider them clever, and don't want to eat them. But they aren't inherently any smarter than other creatures. They just think more like we do. There is also the pig, which does them as well as the dog, but we only learned that after we established them culturally as food, not friend. Ultimately, it's equally bad to eat a pig as to eat a dog - or, depending on your view, equally valid to eat a dog if you are comfortable eating a pig.
There is absolutely no difference in eating a cow or a horse in the morality of it, though without a regulated industry horse meat in the USA is not a very healthy food source. Both animals are social and form strong bonds and don't want to die. Both make loving pets. In an ideal world we would not eat any of these animals. The plant kingdom provides all the nutrition the human body needs, especially in this day and age where many nutrients can be synthesized. If you disagree, then there is still no nutrient found in birds or mammals not found in insects, molluscs and other life with a more demonstrably primitive level of consciousness. But we consider those food sources unappealing, even though to use them would reduce global animal suffering. Why eating a bug is repulsive but killing a pig with emotions just like ours is not is foreign to me.
I am not a vegetarian, though I would like to be. I don't expect everyone to be, though I very strongly applaud those who are - they are at a higher level of morality than I, and I cannot refute their perspective that meat is murder because it is. You're killing another for your own reasons. But we are predators, and while we don't have to be, it is natural for us. If you do eat meat, you should be able to stomach killing it and processing it yourself, and to accept that is it a dirty process. If you can do that, I don't think it's worse to eat a dog than a chicken, as long as the animal lived a happy life free of harm or undue stress, and was able to exhibit its array of natural behaviors. Death should be as quick as possible, but it will never be peaceful. It may last only a few seconds, but death - except in sleep of old age - cannot be without some degree of stress.
If you are intending to eat chickens, goats or anything else that you get from an internet ad, it is your responsibility to be up front about your intentions especially if you are responding to an ad for a conventionally pet animal. I saw someone remark about picking up free llamas and suggesting they butchered them? I doubt very much anyone with llamas in the USA would expect their animals to be eaten and that is simply dishonest.
Coming back to the original post, it's distasteful. I was going to post earlier about it, because posting an ad that all chickens go to heaven, implying sanctuary, and then killing them is very dishonest, but then I saw the photo is a freezer. Hopefully, anybody who saw the ad would not really believe it a chicken sanctuary, and so I did not comment at the time.
But if you're looking for free meat, just post an honest ad for it. Don't be sneaky and try to get a hold of the animals that people have raised as pets and had to rehome.
Some of my most cherished pets have been conventionally pest animals - rats and a pigeon.