There are a number of levels. Cow, obviously, is the first. Pig is at the second, with goat, lamb, and other higher mammals. Chicken, and other birds are generally at level 3. Fish occupy the fourth, and other weird aquatic animals are at the fifth level. So even the lowliest oyster is only 5 steps away from heaven.
Beefism is this religion I invented. The main idea is that animals, specifically cows, were created by God and given souls, and the end goal is for them to eat heaven. However, to ascend, they must be consumed by the angels of God, man. This means that you should eat as much meat as possible. Lesser animals, like pigs, are reincarnated up into cows, if they are consumed by humans.
Dogs are considered lesser angels, and they help man in his quest to consume meat. Cats are generally considered tools of Satan, as is Tofu. There are a number of schisms within Beefism, specifically as to whether or not the eating of horses is acceptable. Church doctrine says that horses are similar to dogs in that they aid man, but a growing group seems to think they qualify as meat animals. There is also an evil sect which believes that humans too have souls, and if they are eaten, they can ascend to heaven, but this heresy is stamped out wherever it is found.