Researchers explore alternatives to surgical neutering

Photo courtesy of Spay First!

The hunt for chemical alternatives to surgical neutering is heating up with a recently awarded grant.

In mid-January, Harvard bioengineer David Mooney received a $700,000, three-year grant to pursue development of a vaccine that would provide a nonsurgical method for spaying and neutering dogs and cats.

Mooney will use the grant award to adapt existing work to target and disrupt a hormone crucial to reproduction in mammals. His team’s goal is to develop a safe approach for spaying and neutering dogs and cats using a one-time, permanent contraceptive vaccine.

At a time when 83% of dogs and 91% of cats are spayed or neutered, the award of this grant signals the continuing emergence of nonsurgical sterilization options. 

The grant was awarded by The Gary Michelson Found Animals Foundation.

Calcium Chloride

Around the world, interest continues to build in using calcium chloride as a neutering agent. Calcium chloride was first tested in the 1970s with calves, colts and other animals. In the last 10 years, it has been the subject of research studies in India and Italy with dogs, cats and goats. In October 2014, Scandinavian researchers reported about its use with dogs. 

One Scandinavian study confirmed the efficacy of its use for sterilization but noted that at dosages free of adverse effects, calcium chloride in saline may not provide permanent sterilization as previously believed. Another Scandinavian study found that a single, bilateral intratesticular injection of 20% calcium chloride in 95% ethanol was a reliable method for induction of sterilization in male dogs. This method showed long-term efficacy and reduced sexual behavior.

In the United States, research has been stymied because calcium chloride is a common household chemical. It can’t be patented and marketed profitably so there is little motivation to invest the $10 million required to do clinical trials. And without those trials, and the resulting FDA approval, veterinarians and most animal welfare groups aren’t using or endorsing it despite its low cost of about $1/dog.

Spay First! is an exception. It uses calcium chloride, injected into a dog’s testicles while the dog is under a light sedation, in its free spay/neuter clinics. The clinics are offered in rural areas such as Native American reservations that don’t have easy access to veterinarian services and where wild dogs abound. (According to a CBS report in 2011, the wild dog population in the Navajo Nation alone numbered 445,000, or 4-5 dogs for every one of its 89,000 household.)  

Ruth Steinberger, founder of Spay First!, uses calcium chloride in South Dakota in her team’s work with the Rosebud Sioux Tribe (Sicangu Lakota), as reported in The Wall Street Journal. (They visit the reservation three times a year.) Steinberger and Billy Clay, DVM, DABVT and adjunct professor at Oklahoma State University, plan to document testosterone levels every 10 days from day 0 to day 28 on five dogs during their visits and publish a white paper about the results.


Zeuterin, another tool in the nonsurgical sterilization market, received FDA approval in 2014. A mix of zinc gluconate and arginine, it is used in dogs 3-10 months of age and injected directly into the testicles to kill sperm and shut down the passageway sperm normally travel.

According to the research data, the results are permanent, the process takes only a few hours, it works in 99.6% of dogs, and the cost is $15-$25/dog.

Zeuterin was originally on the market in 2003, under the product name Neutersol. However, according to The New York Times, it was sold without a lot of training or support about the procedure for the veterinarians who used it, and resulted in adverse reactions in dogs. By 2005, Neutersol and the company that sold it had vanished.

"This product isn’t a product," Joe Tosini, founder and chief executive of Ark Sciences, which bought the rights to the drug and renamed it, told The New York Times. "It’s really a procedure that has to be taught." 

Due to the need for precise and delicate injections into a dog’s testicles, Ark Sciences requires veterinarians who purchase the drug to be "Zeuterin-trained" by taking a five-hour course that includes injecting several dogs.

Evidence-based medicine requires proof that new methods work well and safely.

"We wonder, ‘What’s going to happen in 10 years? Are these dogs going to get cancer?’" Mark Russak, DVM and a past president of the American Animal Hospital Association told The New York Times.

With both formal and informal research into chemical approaches continuing, it may be only a matter of time until such questions are answered.


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