I'm not convinced it's not for feeding animals. Wouldn't a device for that have a similar mechanism inside as a ball point pen? When flipped upside down a little ball would fall and plug the hole. Then an animal would come and push the ball a tiny bit out of the way releasing a little bit of water, or whatever. If I'm right then you are missing the little ball.
I know what you're thinking, if you turned the bottle upright wouldn't the ball fall out? Well there would be a little mesh screen inside as well that holds the ball in the tube, but allows fluid to pass. So over time the screen broke or was lost and the ball was lost.
I'm not sure this is right but it's a theory.