Todd Bruce, a herd manager on a farm in Oregon City, Ore., had long resisted neutering his 5-year-old Australian cattle dog, Cody, for fear of losing the extra set (or two) of legs in the field.
“I just wanted him to maintain his working abilities,” said Bruce, 28. “I’ve had other dogs neutered that have had a lot of weight gain, and their bodies go through huge changes, and I didn’t want that to happen with my dog this time.”
Then Bruce’s sister, a veterinary student, told him about Zeuterin, a drug that sterilizes male dogs without the removal of the testicles, thus preserving some testosterone production. In June, Bruce volunteered Cody for the procedure, performed by veterinarians as part of a training program at a clinic in Portland, Ore. The next day, Cody was back at work, enthusiastically rounding up livestock.
“It was quick, painless and superuninvasive,” Bruce said. “He’s mellowed out a bit, but I haven’t had the problems I had before.”
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The 40-year movement to convince Americans that they should spay or neuter their pets has been nothing short of a triumph: 83 percent of owned dogs and 91 percent of owned cats in the United States have been spayed or neutered, compared with only about 10 percent in the 1970s. But the surgical removal of the reproductive organs of every pet is still time-consuming for veterinarians, unpopular among a subset of pet owners and ethically troubling to animal welfare advocates.
It is also an impractical solution to sterilizing stray animals, which constitute the bulk of the United States’ nuisance animal problem. “Surgery is definitely a bottleneck for humane animal control,” said Dr. Julie K. Levy, a veterinarian at the University of Florida who has researched the problem.
Now, a handful of nonsurgical sterilization treatments — led by Zeuterin, which could be commercially available in the United States by the end of this year — are emerging and could reduce or even eliminate the need for traditional neutering.“The truth is, we may have maximized what we can do with surgical spay-neuter,” said Joyce Briggs, the president of the Alliance for Contraception in Cats and Dogs, a group advocating alternative approaches. “Nonsurgical sterilants could be a game changer for animal welfare across the world.”
The problem, she added, is persuading enough veterinarians, pet owners and pharmaceutical companies to embrace the new form of treatment.
The remedy nearest to market is Zeuterin, a mix of zinc gluconate and arginine that is injected into a dog’s testicles, killing the sperm and shutting down the passageway through which it would normally travel. The results are permanent, and the process takes only a few hours, poses little risk compared with surgery and works in 99.6 percent of dogs, according to research trials.
“I think it’s an outstanding product,” said Levy, who used the drug nearly a decade ago to sterilize wild dogs in the Galápagos Islands. She is eager for Americans to see what Zeuterin can accomplish.
“There’s just a communication issue,” she added.
The drug, which must be injected precisely and delicately, has been on the market before and failed. Introduced as Neutersol in 2003, the drug was sold to veterinarians without much training or support. As a result, too many dogs had adverse reactions (inflamed testicles, mostly), and the drug earned a bad reputation. By 2005, both it and the company behind it had disappeared.
“This product isn’t a product,” said Joe Tosini, the founder and chief executive of Ark Sciences, which bought the rights to the drug and renamed it. “It’s really a procedure that has to be taught.”
The company is waiting for the Food and Drug Administration to approve Ark Sciences’ manufacturing facilities, so it can sell the drug in the United States. Approval may come as early as this month.
Tosini, a former minister who was an original investor in Neutersol, said Ark Sciences had learned from the mistakes of its predecessor. To provide Zeuterin, veterinarians will have to complete a five-hour course that includes injecting the drug into several dogs.
The idea that surgical castration causes weight gain or even behavioral changes in dogs is still a matter of debate among veterinarians. Nonetheless, the procedure remains unpopular among some pet owners who rely on their dogs for hunting, sports or protection, and fear that castration could affect their pets’ performance.
Some owners simply cannot afford the procedure, which can cost as much as $400, depending on the region (Ark Sciences plans to make Zeuterin available at clinics for as little as $15). Other owners, particularly those with male dogs, make a conscious choice not to sterilize.
“In certain cultures, and Latin cultures are among them, castration is really viewed as very emasculating, and I think people identify with their dogs,” Levy said.
Few other companies have shown much enthusiasm for walking the long, expensive regulatory path required to get approval for nonsurgical sterilization drugs — a process that takes five to seven years and can cost more than $10 million.
The perception, some researchers say, is that surgical spaying and neutering are just too deeply ingrained in veterinary practices.
“What I often hear from the big animal health company executives is, ‘Well, vets just like to spay and neuter dogs and cats, so there’s no market for this,’” said Dr. Linda Rhodes, the chief scientific officer of Aratana Therapeutics, a company that licenses the rights to use drugs developed for humans in animals.
Although most veterinarians lose money on spaying and neutering, they prefer to stick with the technique they know, rather than try something they consider experimental, said Dr. Mark Russak, immediate past president of the American Animal Hospital Association. “We wonder, ‘What’s going to happen in 10 years? Are these dogs going to get cancer?’ We’d rather let the guy up the street try it first.”
Elsewhere, nonsurgical sterilants are starting to catch on. In recent years, castration-resistant owners in Australia, New Zealand and parts of Europe have been turning to Suprelorin, an implant that sterilizes male dogs for six or 12 months by neutralizing the production of reproductive hormones.
Though an implant like Suprelorin, which must regularly be replaced, is not practical for strays, a vaccine known as GonaCon and developed by the federal Department of Agriculture to sterilize deer and wild horses may be a viable alternative, Levy said. Studies have shown that a single injection of GonaCon will sterilize most cats and dogs for up to four years — about the life span of a stray animal. And because it blocks reproductive hormones, GonaCon eliminates many of the nuisance behaviors, like fighting and spraying, associated with strays.
But GonaCon would need to be approved by the FDA for use in dogs and cats, and there is hardly enough money to be made in treating stray animals to justify that cost for a for-profit company.
“We’re kind of looking at a charity population,” Levy said. “It’s like developing drugs to treat disease that only occur in impoverished countries.”
One charitable organization, The Found Animals Foundation, is offering a $25 million award to the inventor of the first single-shot, nonsurgical sterilant that works in both dogs and cats. But no one has been able to claim the prize.
With a successful Zeuterin debut, other companies might choose to invest in similar treatments. But for now, Ark Sciences, aware of the resistance to change, is focusing its marketing efforts on early adopters, veterinarians like Levy, who already know the virtues of nonsurgical sterilants.
For many of them, the switch to a new neutering strategy will be like “giving an airplane to people who are used to traveling by covered wagon,” Tosini said.