First, I should specify that I'm not a utilitarian. I follow rights-based moral theory - that living things have rights, and it is wrong to violate them. What rights they have depends on what they are capable of. For example, adult humans have the right to free agency, and it's wrong to control their behavior, assuming they do not violate someone else's "stronger" right, such as right to life. So it's okay to send murderers to jail to prevent them from murdering more people, but it's not okay to enslave adults. Children and mentally handicapped people have a limited version of this right - it's still wrong to enslave them, but it's not wrong to stop them from running out into the street since they don't know any better. Please don't try to change my view on this, that's an entirely different conversation than the one I want to have.

With that out of the way, I think that the desire to live is sufficient to qualify for a right to life. It seems blatantly clear to me that many animals demonstrate the desire to live. When posed with a threat, they run away or try to defend themselves. It's certainly possible (although I personally think improbable) that in many cases, this behavior is mindless, and they run away from harm not because they don't want to die, but because of instincts, or because they grew up seeing their parents run away from danger and mindlessly copy this behavior.

However, I think it's very clear that some animals (apes, dogs, dolphins, and pigs, for example) function at a much higher level, closer to ours. I'm not saying that they're as intelligent as we are, but they are aware of their own existence, have emotions, and presumably, a will to live. Therefore, it's obviously wrong to kill them for any reason except self-defense. Killing an animal for food does not count as self defense because humans are perfectly capable of being healthy and vegetarian.