Not sure how animals of the same species being affectionate qualifies as beastiality. Are all those documentaries of animal courtship rituals beastiality? Are videos of animals mating even beastiality? Not everything sexual has to be considered pornographic.
At most it'll be a small section of a wider documentary.
That footage takes time and energy to capture. Media doesn't just appear out of thin air. A few minutes in a documentary might represent weeks of effort informed by centuries of research.
It isn't quick or easy to do animal research. People spend their entire lives studying specific types of behavior, and fucking is an important type of behavior to study. Even if they only write one paper about it across a long career, that paper probably took months of time and effort.
