The rubber tires and lack of apron point to an M8 variant designed for air drop and mechanized transport. http://www.ww2airborne.net/463pfa/index.html?http://www.ww2airborne.net/463pfa/packhowitzer75mm.html
That a pack animal has it under tow does point to an environmentally conscious commander.
I would worry though that PETA might get wind of how we are overworking those poor horse by making them tow that heavy weaponry.
Yes. The commander's explanation that he ordered his men to use horses and mules would not work with PETA. PETA would demand that his men dismount and pull the gun themselves.
Now that's darn funny.....and sadly probably true.