Veterinarians recommend spaying cats to live with them (heat can be very annoying) and to prevent them from suffering from certain pathologies that occur when they do not reproduce. It is also the plan envisaged in the Animal Welfare Act that speaks of the CER method (Capture, Sterilization and Return) to control cat colonies and prevent them from becoming overcrowded. This Tuesday, Nature magazine published an article with the first results of an injection developed in the USA to sterilize cats. Researchers used a virus to deliver a hormone called antimüllerian (HAM) into these animals’ bodies to inhibit ovulation and prevent pregnancy.
The study was conducted with nine cats, six treated and three as controls. The first data prove the effectiveness of this method and open up an alternative route to surgery. None of the treated cats became pregnant and no side effects were observed four years after the test, which did not surprise the researchers, as the study’s lead author William Swansson explains: “It’s a natural protein that the females already produce.” The level of the hormone that is above normal stops ovulation.
A possible protective effect has even been observed against pathologies such as cystic endometrial hyperplasia (a change in the lining of the uterus) and pyometra (an infection of the uterus). Swansson of the Cincinnati Zoo and Botanical Garden (USA) attributes this to the suppression of ovulation and the resulting lower production of progesterone, which is closely linked to the development of these diseases. Four years later, the cats continue to have higher-than-normal MAH levels, which the researcher sees as a good sign.
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The currently available methods of neutering cats are medical and surgical. The first group includes hormonal treatments, which inhibit reproduction for a period of time but can have long-term side effects, explains study co-author Raquel González. Some, such as progesterone drugs, can only be used on specific occasions. There are also Deslorelin implants, a substance that regulates the hypothalamus over the long term to reduce the production of hormones that affect egg maturation and production, the vet adds.
González, who specializes in reproduction, explains that the only permanent option is surgery and consists of an ovariohysterectomy (removal of the uterus and ovaries) or an oophorectomy (removal of the ovaries only). But like any surgical procedure, it comes with risks and cures. You can even change his behavior. If done at a very young age, it can make them more anxious and elusive, adds Joaquín Cerdeira, a specialist in small animal reproduction and professor at the Complutense University of Madrid (UCM), who did not take part in the project.
There is no specific number [de gatos] that you can sterilize it and say it’s done. There are many cats that cannot be seen
Miguel Clavero, researcher at Doñana Biological Station (EBD-CSIC)
The researchers’ goal is for injection to be an alternative to surgery to permanently castrate cats with a single dose. However, they recognize that much work remains to be done. Laura Abril, a postdoctoral researcher at the University of Murcia’s Faculty of Veterinary Medicine who did not collaborate on the Nature study, argues that a larger sample is needed. “It would be interesting to know if I use this method on my cat in 10 years, for example, it can cause ovarian cancer,” he adds.
The UCM professor also considers the sample to be insufficient, but admits that it is a “very innovative and promising” project. For his part, Swansson clarifies that the goal of this experiment was to work with a small number of animals to ensure it could work before starting with larger numbers.
Although none of the cats became pregnant, two of them showed reproductive behavior in the two breeding tests conducted eight and 20 months after injection. The author is not concerned about this and attributes it to individual variability. Each female can vary in the amount of hormones that enter and are produced by the body, and it’s even possible that there are some immune responses in the cats that could have an impact [al resultado]’ says the scientist.
Cerdeira believes the key now is to find out if it’s reversible or not and from what age it would be advisable to start using it, with which Swansson agrees. In order for it to work, the HAM expression must remain elevated, and it remains so now, three years later. The author rates this as a “very good” find, but care must be taken to ensure that it can be kept for at least five to ten years. “If protein levels drop too low, they may become fertile again,” he concludes. To ensure this and to check for side effects, the cats continue to be observed and routinely examined.
control of the colonies
There are 600 million cats in the world and 80% of them are ownerless, according to the Nature article. Wild cats or domestic cats with access to nature pose a real problem for the biodiversity of the environment in which they live, says Miguel Clavero, a researcher at the Doñana Biological Station (EBD-CSIC), who is also independent of the research. In areas like the Canary Islands or the Balearic Islands, where there are no natural predators, they pose a threat to birds and reptiles and have even led to the extinction of some native species, says Clavero. In addition, they can also pose a threat to human health because they can transmit diseases such as toxoplasmosis, which are only transmitted through the feces.
For these reasons, it is so important to control cats that live in colonies and the remaining cats that live freely, says the ecologist. One of the goals of the US project is to help control animals, but Clavero believes it will have little impact on the impact these cats have on their environments. He claims that capturing all reproductive cats is very difficult: “There isn’t a certain number that you can sterilize and say, ‘It’s done.’ There are a lot of cats that don’t show up.”
However, the EBD-CSIC researcher acknowledges that this may be a step forward for the welfare of domestic cats and for colony cats that allow themselves to be trapped. “An injection is always better than open-wound surgery and then release midway through,” he summarizes.
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