In all fairness, with illness, injury and such also affecting animals, I would have a hard time believing many batteries were ever at that strength for long.
We have also very rarely seen full strength infantry companies portrayed by living historians, let alone full battalions. It's a big ask to get that many people together (or in this case, animals) for a situation that didn't happen often.
Edit/Add: My understanding is that groups like 1st Section and the Liberty Rifles choose their specific portrayals partially based on what they can reasonably expect from the hobby. i.e., if you can only expect to get 200 folks together who will be able to meet your authenticity standards, then you choose an impression for that weekend that encompasses 200 or fewer men. So when they say "full scale", what they mean is "to scale for the unit being portrayed at that particular time." At the reenactments i have attended where 1st Section was present, they portrayed an artillery regiment "to scale".
Now, whether they researched down to exactly how many animals were present in the section at the time? I don't know, but they do have a very good record with regard to how they perform and apply their research as far as living history goes.