Well we're animals ourselves. A pig has pretty much the same feelings and instincts that we do, it doesn't have abstract thought like (some) humans do, but other than that we're pretty much the same thing. I don't make a life's worth depend on its intellectual prowess, or else some AI's might be worth more than humans. To me it's the feelings of pain, fear, joy, survival instinct etc. that make a life worth being protected. And in that regard there's no reason to assume a pig is any different to us.
In fact, aside from intellectual abstraction, the other thing that separates us from other animals is the sheer amount of destruction we inflict on the world. There have been some great mass extinction events in the history of Earth, the most recent being the one that brought an end to the dinosaurs 66 million years ago, most likely caused by asteroid impact. Right now we're in the middle of the next great mass extinction, caused by humans. And we're on our way to cause even more destruction through climate change. Mankind is probably the most destructive species that has ever lived.
Given our abundance and the extreme destruction we're causing, one might argue that we're worth less than other animals.