Many dog owners don't know how many calories are in a bully stick, or that it's made from a bull's penis. Tufts University

Dog owners might want to think twice about “bully sticks” or “pizzle sticks,” the hot canine treat that’s made from dried bull penis. Not because of the main ingredient, mind you, but because it turns out that these snacks can pack a lot of calories into a small stick.

In a new paper published in the Canadian Veterinary Journal, Tufts University veterinary nutrition researcher Lisa Freeman and colleagues from Guelph University in Ontario took a close look at the bully stick. They sampled 26 bully sticks for microbiological testing and sent five off for a nutritional analysis.

The bully sticks the team tested contained anywhere from nine to 22 calories per inch.

“If you give one six-inch bully stick a day to a 50-pound dog, that’s 9 percent of its daily calorie needs,” Freeman said in a phone interview. “For a 10-pound dog, that’s 30 percent of its daily calorie needs.”

Somewhere between 34 and 59 percent of dogs are estimated to be overweight or obese, Freeman says.

There are several reasons why our pets are getting fatter – like people, the modern cat or dog tends to be less active. Pet food companies are also making food that’s tastier and higher in calories, so animals are more likely to overeat. Plus, most pet foods and treats don’t have to have nutrition information on their labels. Many owners underestimate the calories in food and overestimate how many calories a pet needs.

“Fifty calories for a small dog is quite a lot,” Freeman says.

There’s a wide range of pet treats made from offal and organs these days: You can have your pick of pig’s ears, or the trachea, lungs, or heart of a cow. But dog owners might not fully realize that these treats, though dried, are still raw meat, which can harbor dangerous bacteria.

In the small group of 26 bully sticks that Freeman and her colleagues looked at, they found one tainted with Clostridium difficile, a bug that can cause serious gastrointestinal ills. Another stick had traces of methicillin-resistant Staphyloccocus aureus, or MRSA, a dangerous germ that evades antibiotics. One other had an antibiotic-resistant strain of E. coli living on it.

Dog owners should wash their hands after handling treats made from organs, as they would with any raw meat, and vulnerable people – the very young and old, pregnant, and those with compromised immune systems – should avoid contacting such treats in general, the team advises.

While Freeman says she wasn’t surprised by the high caloric content of bully sticks, she was taken aback by the results of a web survey that the team conducted. Answers came from 852 respondents, mostly female dog owners, questioned about dog food and dog treats.

The survey revealed that basic misconceptions about bully sticks are prevalent. Many people don’t actually know what the treat is made of. Sixty-two percent of veterinarians who answered the survey correctly identified bully sticks as made from a bull or steer penis, as compared to 44 percent of general respondents. Of the 180 dog owners surveyed who fed their pets bully sticks, nearly three-quarters said they avoided animal byproducts in pet food – yet the stick itself is pretty much all byproduct.

Half of the people surveyed underestimated the number of calories in a bully stick.

“There’s a lot of misperception out there,” Freeman says. “Owners really need to find out the facts and make their decisions based on those.”

SOURCE: Freeman et al. “Nutritional and microbial analysis of bully sticks and survey of opinions about pet treats.” Canadian Veterinary Journal 54: 50-54, January 2013.