Ash in cat food is the inorganic mineral content left over when the organic
portion of the food has been burned off. The mineral content can be any
combination of calcium, magnesium, phosphorus, potassium, sodium, silicon,
sulfur and other trace minerals.
Ash is measured by heating a food to 550 to 600 degrees – the inorganic residue
is the “ash content”.
Confusion about ash content in pet foods developed as veterinarians and cat
guardians were looking for the cause of Feline Lower Urinary Tract Disease (FLUTD
- formerly known as FUS). In the 70’s & 80’s veterinarians thought ash was a
factor in causing crystals in the urine. There are, however, a variety of causes
and ash is no longer considered a factor in causing FLUTD. Further research has
shown that the main problem was the formulation of commercial pet foods: most
pet foods were creating a more alkaline urine (higher pH) which lead to an
increase in struvite (magnesium ammonium phosphate) crystals. Dry kibble diets
are mainly formulated with a high vegetable and grain content which creates a
more alkaline urine. An all meat diet such as a cat would eat in
nature creates a more acidic urine.
Magnesium content in foods has also been implicated in contributing to FLUTD.
Magnesium content, however, is most likely a minor contributor compared to the
influence of urine pH. Studies have shown that supplementing the diet with
magnesium chloride did not cause urinary crystals to form in the urine as long
as an acidic urine was maintained. Further studies have shown that if the urine
is at a higher pH of 7.5 or more, struvite crystals will occur even if the diet
is low in magnesium.
Magnesium is an essential mineral in the diet of cats and dogs for a variety of
functions including energy production, proper muscle function, heart health,
bone growth and dental health among others. Rather than the specific magnesium
content of a food guardians would be better served by looking for the proper
ratio of Calcium, Phosphorus and Magnesium in the diet which should be
approximately Ca-1.3:P-1:Mg-.06. A deficiency of any essential mineral in an
animal’s diet will eventually lead to mineral imbalance and disease.
Pet food manufacturers developed low ash and/or low magnesium foods in response
to the theories that ash or magnesium were the cause of struvite crystals. When
it was apparent that urine pH, and not ash or magnesium was the problem, they
began to add Ammonium Chloride to their cat foods to acidify the diet. This
practice, however, does not necessarily solve the problem since continued use of
Ammonium Choloride can lead to a condition called chronic acidosis, which leads
to mobilization of Calcium from the cat’s bones. The combination of chemically
induced acidosis, calcium loss from the bones leading to increased calcium in
the blood & urine, along with a reduced level of magnesium in the diet leads to
the formation of oxalate stones. Oxalate stones have now become an increasingly
common side effect of treatment for struvite crystals.
What to feed?
A high protein diet is the best way to maintain a low urinary pH naturally. Cats
eating canned diets have fewer problems with FLUTD than those eating primarily
dry kibble diets. This could be due both to the higher meat content of canned
diets as well as the higher moisture content. Increased hydration also prevents
crystal formation. A raw food diet is ideal for maintaining a lower urinary pH
and providing proper hydration.
Cats do not drink water naturally, in the wild the moisture they consume comes
from the moisture content of their prey. A cat eating dry kibble would need to
consume approximately 8 oz. of water per day to prevent dehydration.
Please see the article
Feline Lower Urinary Tract Disease for additional information on preventing
and treating FLUTD.