A dog may have blood in his urine due to:
Urinary Tract Infection
The dog's urinary tract is comprised of the kidneys, ureters, bladder, and urethra. A urinary tract bacterial infection is usually found in the bladder or the urethra. Urinary tract infections can be very painful.
Tumors
Tumors may cause blood in the urine. Tumors may be non-malignant (benign) or malignant (cancerous). In the event of a tumor, your dog’s stomach may be distended.
Kidney or Bladder Stones
Stones are a collection of minerals that form in the urinary bladder or kidneys. The stones may range from small to large. In addition to blood in the urine, your dog may show signs of straining and frequent urination.
Poisoning
Your dog may have blood in his urine because he ingested a toxic substance. Other symptoms of poisoning may include lethargy, coughing, swollen abdomen and respiratory distress.
Injury
If a canine experiences an injury such as a substantial fall, a kick or a vehicular trauma, he may be bleeding internally. Internal bleeding may cause blood to be in the urine.
Prostate Disorders
Male dogs may have an infection, cancer, cysts or abscess in his prostate. Dogs with prostate disorders may have blood in the urine, labored urination and a decrease in urination. Dogs that are not neutered are more prone to prostate issues.
Estrus
During estrus, female dogs will bleed. The menstrual blood may mix with urine, which will appear as blood in the urine.