The case here is why DL thinks they can chose what they carry.
DL does carry other prepared animal hides and artifacts like antlers, etc. from Alaska, so where's the logical argument in banning a subset of species?
If they can pick & choose within a commodity code (and from what I've seen in cargo acceptance documents, there's no distinction in the commodity code used for a large mounted trophy for a deer or moose than there'd be for a rhino or elephant), it's willful discrimination.
If they can pick and choose on what someone can or can't ship based on context, then what's to say that they won't allow shipments of, say, Bibles? Or, to give equal treatment, legal pornography?
Could DL decide that in order to gain business from the New York Times, they won't allow shipments of NY Newsday to be sent as freight?
That's the slippery slope that DL just went down.
For livestock and hazardous materials, DL is indeed free to pick and choose what they carry for liability or safety reasons, but it's not like this is commodity that could place the flight or handlers at risk (i.e. venomous snakes, or cases of muriatic acid), or be at risk itself (certain types of livestock unable to survive transport).
Taken a step further, it's like DL deciding they won't carry athiests or Hindus.
Common carriers simply don't get to project their ethics onto what they accept. That's the whole notion of having a common carrier standing -- anyone can tender a non-hazardous/non-perishable shipment without fear of discrimination.