A white-tailed deer at a deer farm in Vernon County has tested positive for chronic wasting disease, or CWD, the Wisconsin Department of Agriculture, Trade and Consumer Protection said Wednesday.   According to the DATCP, a buck tested positive for CWD and the test results were confirmed by the National Veterinary Services Laboratories in Ames, Iowa.   The single-acre farm has been placed under quarantine, meaning no live animals or whole carcasses can leave the property. The DATCP and U.S. Department of Agriculture will conduct an investigation of the farm.