>Detailed information about how to tune a car would not belong in the Ford dealership category, even if such information was sponsored and maintained by Ford, especially if it was the only such information available on the net or in print.
True. The Ford site would be listed in Business, but the detailed information on car tuning could also be listed in another category if it were really unique content and not something available in many places.
Likewise, if the alpaca site contains unique content of particular interest it is possible that that section of the site could be submitted to another part of the directory.
If it contains much information on breeding then possibly that section could be submitted to http://dmoz.org/Science/Agriculture/Animals/Mammals/Breeding_and_Biotechnology for consideration.
I say possibly. I don't know the site in question. I am merely agreeing with what you say about Ford and controlling hoof rot in horses. These pages could be submitted to other categories and the editors there would decide whether or not it was unique content which would add value to that part of the directory.
Choosing the correct category to submit to is very important here, for if a site is not listed at all we will try and forward the site to the right category for listing when we find it submitted in the wrong place. However, if it is already listed, the additional pages are not as likely to be forwarded to another category.
Likewise submitting to multiple categories, can get a site labeled as spam, so it pays to choose wisely and not get greedy.