A number of diseases can cause blood in the urine. The best diagnosis can only come from a veterinarian who can examine the animal.
Red colored urine can be because of red blood cells in the urine or hemoglobin.
Red cells in the blood come from bleeding or inflammation. The kidney or bladder may be inflamed due to an infection. Straining to urinate or dribbling urine frequently are other signs of a bladder infection or the formation of stones. Some rat poison could cause bleeding into the urine. Some BVDV infections cause a bleeding syndrome. All of these conditions should be treated by a veterinarian.
Hemoglobin sometimes gets into the urine when red blood cells are rupturing in the blood vessels. These are usually serious diseases. Sometimes when calves drink a lot of cold water red cells burst and hemoglobin shows up in the urine. Usually this condition self-corrects.
There are many other possible causes of blood in the urine but these are the most common.