Hitting any animal with short legs and large body is bad news with a tractor trailer, A bear or hog is dangerous. As a wildlife office I have investigated a lot of incidents with wild and domestic animals, A hog going under a tractor trailer is dangerous. If any large animal hit on the end of some t/t bumpers, The bumper end collapses against the front tire, Bumper cuts the tire. Then its Oh S!!l( where is this rig landing.
One night I got called on a wreck with a Deer and Mack dump truck. The deer looked like hairy hamburger, The new truck with less than 100 miles being driven home from the dealership was a mess. The bumper folded, Tire blew, the truck went into the ditch with a cliff of rocks jutting out of the hill. The right side of the truck cab and bed took the lick. The truck left the scene on a Wrecker.
In the area several of the truckers would remove the bumper, Replace the bumper with a piece of channel beam With a pull ring to protect the radiator, On logging and coal trucks. The wheel would run over an animals with no tire damage and driver still had control of the tractor.