The Renal System of the Greyhound

by Jordan Graustark, PA

We are probably all too familiar with the product of our greyhound’s urinary tract! Telltale yellow stains on the rug, brown spots on the shrubs, and liquid “post-it notes” our dogs leave on trees and fire hydrants serve as a reminder that our greys eventually have to pass what fluids they ingest.

But our greyhound’s urinary tract has a far more complex function than the elimination of liquid waste. The kidneys are responsible for controlling fluid status, helping the body regulate itself during times of dehydration or fluid overload by either conserving or eliminating water, respectively. The kidneys also serve to filter multiple waste products that, if allowed to accumulate, are potentially toxic. Also controlled by the kidneys (or renal system, as it is referred to) is the acid-base balance of the body, as well as the excretion of electrolytes such as sodium, potassium, magnesium and calcium. The renal system does this by acting as a filter and, simultaneously, withholding or excreting various electrolytes to maintain metabolic balance.

This article discusses the anatomy and function of the kidneys and lower urinary tract. We’ll also explore why the kidneys are important indices of the overall health of the greyhound, and how your veterinarian — or even you yourself — can monitor kidney function.

The Anatomy of the Renal Sysytem

The Greyhound has two kidneys, each weighing approximately three ounces, and three to four inches long. The right kidney lies under the loin muscles and is partially covered by the last two ribs. The left kidney lies a few inches further back, and the front portion of it lies at the level of the last rib. The kidneys receive their blood supply from the renal arteries, which originate at the aorta — the largest artery in the body, running from the heart and carrying blood to each of the major organs. There are also nerves running through the kidneys that regulate blood flow as well as blood pressure within each kidney. The renal veins return blood from the kidney back to the blood vessels and to the heart.

Care of the Racing Greyhound describes the efficiency of the kidney: “In a twenty-four hour period, the kidneys will filter and decontaminate an amount of blood equal to forty times that in the normal average Greyhound, i.e., the entire volume of blood in the greyhound passes through the kidney filters forty times in every twenty four hours….”

Pretty impressive!

The filters within the kidney are called “nephrons.” Within the nephrons, a series of tubules and compartments containing capillaries (“glomeruli”) filter fluids. They excrete or absorb substances and, finally, form urine. The urine leaves the kidneys through long passages called “ureters” which carry the urine into the bladder for storage. Once the bladder fills, the Greyhound has the urge to urinate and the muscles at the exit of the bladder release. This action allows the urine to flow through the passageway called the “urethra” to the outside.

The urine contains approximately 95% water, along with various waste products and inorganic salts, such as sodium chloride. The yellow color occurs as a result of the pigment “urochrome,” which originates from bile. The waste products include creatinine, urea, and uric acid.

Evaluating your Greyhound’s urine

You may buy urine test strips without a prescription from drugstores and even from Amazon. The 10-test variety is very useful for pets and humans alike. If things look abnormal, the urine should be examined by your veterinarian.

Your greyhound’s urine may be checked for many reasons. The urine itself provides much information regarding the dog’s health status and helps formulate a diagnosis when a dog is ill. Your vet may ask for a sample of your dog’s urine for testing. The best urine to collect is the first urine the dog passes in the morning. Use a clean cup to obtain and store the specimen. If your vet suspects the dog might have an infection, he or she may ask you to wipe the dog’s external genitalia in order to clean off as much bacteria and dirt as possible before collecting the specimen. Store the urine sample in the refrigerator until you bring it to the vet for analysis.

What the test results mean

The most common test performed on urine is a “dipstick analysis.” Chemically treated dipsticks can show the presence of glucose, protein, blood, bacteria and other substances that should not normally be present. The dipstick can also indicate how concentrated the urine is, which in turn reflects kidney function as well as the dog’s hydration status. This test only takes sixty seconds to perform and is normally quite accurate. Below is a more specific account of the information a dipstick analysis provides.

Glucose: The presence of glucose in the urine usually indicates diabetes mellitus. In this case, an excess amount of glucose is in the bloodstream, not all of which can be filtered out by the kidneys. This is also referred to as “spilling glucose” into the urine.

Ketones: A positive test for ketones may indicate one of two states. The greyhound may be suffering from advanced diabetes. When there is insufficient insulin in the body to process the glucose produced by the liver, the body begins to digest fats in order to provide energy for bodily functions. Ketones are a byproduct of fat breakdown. Another reason for ketones in the urine is malnutrition or starvation, which result in the same fat breakdown.

Bilirubin: Bilirubin can be present in the urine for a few reasons. If there is liver dysfunction resulting in increased production of bilirubin, or if the bile ducts carrying the bile from the liver to the intestines are blocked, the bilirubin may be “spilled” into the urine. Often, you will also notice a dark discoloration of the urine in this case. The other cause is a destruction of red blood cells throughout the bloodstream (“hemolysis”), often referred to as “hemolytic anemia.” The kidneys filter excessive hemoglobin in the blood vessels and convert it to bilirubin.

Blood: Several factors can result in blood (hemoglobin is the blood component actually being measured) being present in the urine. A severe bladder infection can cause erosion of the bladder wall, resulting in bleeding (this may not be visible to the naked eye, but rather only seen on dipstick or in a microscopic analysis). Kidney infection or disease can be present as blood in the urine (also known as “hematuria”). Another possible cause is a bruise to the kidney, such as may occur from trauma or a fall. One of the less common, but more critical causes of blood in the urine is “azoturia,” or “rhabdomyolisis.” This is a disease state that usually occurs after exertion. As a result of muscle damage, a byproduct called “myoglobin” spills into the urine. Unfortunately, dipsticks cannot differentiate between hemoglobin and myoglobin, so additional testing must be done by the veterinarian as soon as possible. One additional cause for blood in the urine is the presence of bladder or kidney stones.

Leukocytes: These are white blood cells, and generally indicate infection in the urinary tract or kidneys.

Nitrites: The presence of nitrites usually indicates infection or the presence of bacteria.

Specific Gravity: This test indicates how dilute or concentrated the urine is. In turn, it reflects whether the dog is adequately hydrated and how well the kidneys are functioning in their capacity as “regulators” of the Greyhound’s fluid status.

pH: This will tell you how acidic or alkaline the urine is. Very alkaline urine (high pH) may represent infection. Acidic urine (low pH) may indicate a metabolic disorder.

Protein: Several factors may cause protein to appear in the urine. Infection may lead to inflammation as well as to the production of an increased number of leukocytes, both of which result in protein being passed in the urine. Of greater significance is the possibility of kidney disease. Normally, protein molecules are large enough to be filtered by the kidneys before they can be passed into the urine. Damaged kidneys are not able to filter protein molecules properly. Some disease states which result in protein in the urine (or “proteinuria”) are glomerulonephritis, nephrotic syndrome, tumors, or renal failure.

What if the tests were positive?

If any of these tests are positive, your veterinarian may elect to do a microscopic analysis of the urine, which he or she generally will perform right at the office. By looking at the urine “sediment” (which is a highly concentrated urine specimen obtained by placing a vial containing urine in a centrifuge), your vet can directly observe and quantitate red blood cells, white blood cells, crystals, mucous, “casts” (collections of red or white blood cells, protein, or other substances which may indicate renal disease) and bacteria. Observing the urine before centrifuging can also provide additional information. Cloudy or dark, discolored urine may indicate the presence of infection or blood. A change in the typical odor of urine may also point toward dehydration, diabetes or infection.

If dipstick and/or microscopic analysis reveal the presence of infection, your vet may send the urine to the lab for a “culture and sensitivity”, which will indicate what type of bacteria are causing the infection and what specific antibiotics will be effective in eradicating the infection.

Sources: (1) Care of the Racing Greyhound: Blythe, Gannon and Craig, AGC, c 1994

(2) All About the Greyhound, Rollins, Weldon Publishing, c 1982

CG SP 97

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