Do animals experience pain and pleasure like we do?

Do animals experience pain and pleasure like we do? This is the basis of veganism, but is it true? I have done some research, but still am not quite sure. Many sources state that animals experience pain and pleasure similarly to humans, but also state that they can not conceptualize it in the same way. Is their pain and pleasure the same as ours but less intense, or is it only in terms of the actual neurons and brain chemistry? I am confused. Any body have any thoughts on this?