Tens of thousands of cats have been dying every year from a form of heart disease caused by a nutritional deficiency in some popular pet foods, scientists at the University of California, Davis, said in a report published today in Science magazine.
Pet food companies became aware of the problem in March and have reformulated their products to correct the deficiency, according to the Pet Food Institute, a trade organization. Among them is Purina Cat Chow, the best-selling brand of dry cat food.
The deficient substance is an amino acid called taurine, which regulates the entry of a small amount of calcium into heart tissues each time the heart beats, said pharmacologist Steven Schaffer of the University of South Alabama. The calcium triggers each heartbeat.
Cats and humans are among the few mammals whose bodies do not make taurine and therefore must obtain it in their diet. In humans, taurine deficiency is extremely rare because taurine is common in meat, fish and clam juice.
The Science magazine report is not the first time that a taurine deficiency has been linked to feline illness.
In the 1970s, nutritionist Quinton R. Rogers of UC Davis and others showed that a taurine deficiency can cause degeneration of the retina in cats' eyes. Kittens born to taurine-deficient mothers are often blind and show many developmental abnormalities, such as an impaired gait.
No Taurine Guidelines
Based on these studies, the National Research Council recommended in 1981 that cat food should contain at least 500 parts per million of taurine. Before 1981, Rogers said, there were no guidelines because taurine had not been known to be an essential nutrient until 1976 and some cat foods contained as little as 250 parts per million of taurine.
Paul D. Pion, UC Davis veterinarian and assistant professor of veterinary medicine, stumbled on the link to heart disease by accident, he said in a telephone interview. He was studying blood clots in cats and had asked local veterinarians to refer cats with heart disease to him.
The first cat taken to him last December had dilated cardiomyopathy (DCM), a degenerative disease in which heart muscles turn flabby, limiting the heart's ability to pump blood. Cats with DCM typically live only a few days to a few weeks after it is diagnosed. Autopsies have shown that about 3% of the estimated 56 million cats in the United States die of DCM.
That first cat also had eye disease and had been diagnosed by an ophthalmologist as being taurine-deficient, Pion recalled. "By coincidence, I had been doing some reading about taurine deficiencies and that stimulated my curiosity enough for me to look into the eyes and measure the taurine levels of other cats."
He found that every cat that had DCM also had low taurine levels, a total of more than 50 so far. When he treated the cats with taurine supplements, "the cats began to have miraculous recoveries," he said. "Their hearts would become normal again."
Among the first 21 cats studied, 16 had been fed Hill's C/D, Hill's Science Diet Maintenance, or Hill's H/D, all made by Hill's Pet Products Inc. of Topeka, Kan.; three had been fed Purina Cat Chow, made by Ralston-Purina Co. of St. Louis, Mo.; and one was fed both. One each had been fed 9 Lives Beef and Liver, Carnation Fancy Feast Beef and Liver and Blue Mountain Kitty O's.
Hill's pet foods have been sold for 20 years through pet stores and veterinarians.
Rogers, a co-author of the Science report, called Ralston-Purina in February with the team's results. A Hill's spokeswoman said the company had heard rumors about the same time and had contacted Pion.
Representatives of both companies said Thursday that their products met the National Research Council guidelines but that in March they had increased the amount of taurine to the level of 800 parts per million recommended by Rogers.