Passionate feline enthusiasts know all too well that cats are very prone to urinary tract disease. However, the predisposition to urinary tract disease is so significant, that most novice feline owner and even some non-feline owners are aware of the high potential for this health condition. In comparison to dogs, my general observation in small animal practice is that I see four cats to every one dog presenting with urinary tract disease signs. So what is the reason for all this urinary tract disease in cats?
To really understand cats, we need to take a look at their evolutionary history. What we know today as the domestic cat, descended from what were essentially desert creatures. These more primitive felines were adapted to life in the desert where there tends to be little water, and where little grows. In this water lacking environment, cats evolved the ability to create high urine concentration consisting of more solids than liquid in comparison to other mammalian species. The tendency to carry high urine concentration enables the feline to exist with comparatively low amounts of water intake, creating a comparatively static urinary tract. Any M.D. would advise human patients prone to urinary tract disease, to promote urinary tract health by consuming more water, thus creating a more dynamic urinary tract (think of a stagnant pond versus a swiftly flowing stream, and which is cleaner, less riddled with pollutants and debris). Thus, the very mechanisms that provided feline evolutionary ancestors the ability to survive in the dry, desert environment, also makes them prone to urinary tract disease.
These same ancestral felines also ate a diet very differently from the manner in which we commonly feed our household cats. They survived essentially on high protein, low carbohydrate frequent fresh kills: a mouse here, a bird there. Because these meals were small, they were constantly on the hunt and more active, giving them leaner body condition, more lean muscle mass and more efficient metabolisms. These meals were also free of ash, the inorganic mineral content left over after food has been heated.
Comparatively, our cats of today retain much of the same physiological features as their desert ancestors, yet we tend to feed them very differently. Rather than have to hunt for their food, we feed them, so they are less active. All too often, we over feed them, through some misguided notion that this is a form of showing them love. The food itself has ash in it, and in lesser quality diets that do not attempt to properly balance mineral content, this leads to aberrations in urinary pH, which predisposes to the precipitation of crystals, formation of bladder stones, and predisposition to infection. Lastly, too many feline diets are too canine like, laden with carbohydrate content that is just not in line with feline physiology. The resultant fluctuations in blood glucose metabolism lead to obesity and stress on the kidneys, which turn leads to stress on the lower urinary tract.
The last point I will detail in explaining the disproportionately high incidence of urinary tract disease is that cats are stress driven animals, that is, their existence is very much dictated by the fight or flight response. Being by their nature solitary creatures in the wild, unable to rely on a herd or pack for alert of danger and protection, cats evolved a hair trigger fight or flight response for survival. While this constant state of stress makes them well adapted for solitary survival in the wild in comparison to a more social type animal, it does come with a physiological price. Stress suppresses the immune system, taxes the organ systems of the body, and as such, is believed to play a role in a urinary tract disease unique to cats call idiopathic cystitis (painful episodes of inflammation of the urinary bladder with no identifiable cause). What supports this postulate, is the fact that the majority of idiopathic cystitis cats I see in practice tend to be cats with a higher than typical stress levels; and that many of these cats respond to anti-anxiety therapy with medications like amitriptylline and Prozac.
Now that we have established why cats have such a high incidence of urinary tract disease, in my next post, I will discuss strategies to prevent urinary tract disease in your feline companions.