Bestiality does not fall into the realm of BDSM, in my opinion, neither do latex, scat, water sports, etc. These are fetishes that can be incorporated into the lifestyle, but are not a given part of the lifestyle like bondage is for example.

My problem with bestiality more than anything else is the animal's part. I like animals and the thought of using them in ways that would frighten them does not sit well with me (female animals being used). I suppose if a trained male animal is used and it is able to participate, it must be enjoying the experience? If that is the case, I don't have a problem with others participating in bestiality.
For me, personally, I have no interest in trying it.