But if the entire sentence is capitalised (perhaps in a title), then use ‘S (upper case).

If you choose to type a word all in caps, you may add other punctuation as if you did not use all caps. Rarely is there a situation when an added “s” should be capitalized, but a possible reason is “it looks good on signage”. Using a cap “s” may mislead readers into thinking that the apostrophe and the “s” are part of the word or name. Keeping the “s” miniscule (small) assures there is no such misunderstanding.

If an abbreviation or acronym is also a name for something like an organization, then treat it like it were a proper name and add the punctuation you want according to the usual rules.

If the abbreviation or acronym is NOT the name for something, you cannot make it into a possessive.

one of the rules of writing is to not distract the reader with unusual word format. writing “ANIMAL’s” draws the readers attention to the fact that there is a small ‘s’ and away from the point the writer is trying to make. go with “ANIMAL’S” and the reader won’t look twice.