Do yaks live at high or low altitudes?

Yaks are animals of high altitudes,as they are native to Himalayan highlands.Normal altitude for yaks is 3500 meters and above and their body is adapted for that.They got larger lungs than other dary and higher number of red blood cells to absorb oxygen.However some dude in Vermont is succesfully farming yaks at lower altitudes.He has his own website and you may google it with keyWord vermont yak company.Thanks,safriz@gmail.com