MONDAY, Jan. 28 (HealthDay News) -- Popular dog treats called bully or pizzle sticks may contain more calories than expected and could be contaminated by bacteria, according to a new study.

The treats are made from the uncooked, dried penis of a bull or steer.

Researchers examined 26 bully sticks made by different manufacturers and found that they contained between 9 and 22 calories per inch. That means that the average 6-inch bully stick had a total of 88 calories, which is 30 percent of the daily calorie requirement for a 10-pound dog and 9 percent of the daily calorie requirement for a 50-pound dog.

"While calorie information isn't currently required on pet treats or most pet foods, these findings reinforce that veterinarians and pet owners need to be aware of pet treats like these bully sticks as a source of calories in a dog's diet," study first author Dr. Lisa Freeman, a professor of nutrition at the Tufts University Cummings School of Veterinary Medicine, said in a university news release.

"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," she added.

The researchers also found that about one-third of the treats were contaminated with bacteria. One stick had Clostridium difficile, one stick had methicillin-resistant Staphylococcus aureus, and seven had E. coli.

All pet owners should wash their hands after touching such treats, as they would with any raw meat or raw meat diets. Very young children, elderly people, pregnant women and people with weakened immune systems should never touch or handle raw animal-product-based treats and raw meat diets, the researchers said.

The study was published in the January issue of the Canadian Veterinary Journal.

More information

The U.S. Food and Drug Administration offers safe handling tips for pet foods and treats.