Alucard817

I have been playing NV since it's release and well I was running low on bighorner meat so I went hunting. I walked around the mountains for well over an hour and not one big horner. I have also noticed all the Brahmin are gone as well. Actually the Desert since....well kind of lifeless now. I have waited 2 weeks (real time) with about an hour and a half of playtime per day for things to respawn and I get nothing. Any ideas of how I can force these things to respawn?