A popular dog treat could be adding more calories than pet owners realize, and possibly be contaminated by bacteria, according to a study published this month by researchers at the Cummings School of Veterinary Medicine at Tufts University and the University of Guelph. The treat in question: the "bully" or "pizzle stick." The American and Canadian researchers analyzed the caloric density and bacterial contamination of these popular items, made from the uncooked, dried penis of a bull or steer（阉牛）. They also administered a survey to pet owners to assess their knowledge of these treats.

The study, published in the January 2013 issue of the Canadian Veterinary Journal, examined 26 bully sticks purchased from retailers in the United States and Canada and made by different manufacturers.

A random subset of the 26 bully sticks was tested for caloric content. These bully sticks tested contained between nine to 22 calories per inch, meaning the average six inch stick packed 88 calories--nine percent of the daily calorie requirements for a 50-pound dog, and 30 percent of the daily calorie requirements for a 10-pound dog.

"While calorie information isn't currently required on pet treats or most pet foods, these findings reinforce that veterinarians（兽医） and pet owners need to be aware of pet treats like these bully sticks as a source of calories in a dog's diet," said Lisa M. Freeman, DVM, PhD, DACVN, professor of nutrition at TCSVM who is board-certified by the American College of Veterinary Nutrition.

Freeman was first author on the paper. Co-authors were J. Scott Weese, professor in the Department of Pathobiology at the University of Guelph, and Nicol Janecko, a research associate at the Canadian university.

"With obesity in pets on the rise, it is important for pet owners to factor in not only their dog's food, but also treats and table food," Freeman added.