Urinary tract infection is most common reason of cloudy or milky urine in dogs. Culprit pathogens are usually bacteria. Some conditions can increase the chances of infections like stones in the kidneys, and bladder. Tumors in the bladder and cancer of bladder can also cause urinary tract infections. If your dog is having cloudy urine along with other symptoms like painful urination, lethargy, loss of appetite, fever, and excessive urination then get advice from the doctor.