Sterilisation of male cats: nonsurgical sterilisation techniques
Various alternatives to surgery for sterilising male cats have been explored over the last few decades. Immunocontraception has been used to control feral populations, but the possibilities to date do not provide long-term sterility.
Gonadotropin-releasing hormone (GnRH) agonists delivered through implants have proven effective in suppressing fertility, but only for 6 to 12 months. Work on gene therapy to inhibit reproduction by interfering with RNA is also under way, as described in a study published in the journal Reproduction in Domestic Animals1.
Three nonsurgical alternatives for sterilising male cats
1. Contraceptive products
Sustained exposure to GnRH agonists results in pituitary cell downregulation and supresses FSH and LH release, making it a valid alternative for sterilising male cats. Due to its poor oral bioavailability, it must be administered parenterally, which is why implants have been designed for subcutaneous insertion in the cat’s neck. Among the available GnRH agonists, deslorelin has shown efficacy in sterilising male cats, as confirmed in a study conducted at Chulalongkorn University2.
GnRH antagonists are also being studied. They have an immediate effect, but require higher doses, and as controlled release systems have not yet been developed, it tends to be a more expensive treatment modality. A study conducted in 2016 by García et al.3 found that the GnRH antagonist acyline reversibly reduces spermatogenesis and sperm motility for 2 weeks.
2. Chemical castration
The first drug approved by the FDA for sterilising pets was Neutersol®, an intratesticular injection containing zinc gluconate and arginine, which cause testicular sclerosis and permanent sterility. Since then, similar products have been launched, such asZeuterin™, which has the advantage of providing permanent results after a single administration without general anaesthesia, although mild sedation is recommended.
It has been tested with good results in dogs, but its efficacy in the sterilisation of male cats has yet to be evaluated. However, a small study conducted by Fagundes et al.4 found atrophic and dilated seminiferous tubules, reduced germ cell numbers, incomplete spermatogenesis and azoospermia in 73% of cats treated with zinc gluconate.
Another promising chemical agent is calcium chloride dihydrate, either in saline solution or combined with dimethylsulfoxide, which is already used in male dogs and other mammals. Researchers at the University of West Bengal5 were the first to document its use in the sterilisation of male cats. After 60 days, there was complete testicular necrosis, which was replaced with fibrous tissue, a very low sperm count, and a reduction of at least 70% in serum testosterone. The activities of androgen enzymes and their expressions were also lower, so researchers believe that CaCl2 has huge potential in the nonsurgical sterilisation of male cats.
The main objective of immunocontraception is to develop a vaccine that promotes the formation of antibodies, so that the immune system suppresses normal reproductive function. GnRH vaccines, some of the most promising vaccines to date, should inhibit LH and FSH release, but the options developed so far are characterised by a large variability in individual responses and, therefore, have not yet reached the desired level of efficacy.
In fact, a study on a small sample conducted at the University of Florida6 concluded that, “Single-dose GnRH treatment resulted in testosterone concentrations and semen quality consistent with immunocastration in a majority of cats treated”, but it only worked in 66.67% of cases.
In summary, the products tested up to now for the sterilisation of male cats have certain limitations, so further studies into their possible side effects7 are required. However, new solutions will probably be developed in the future that achieve permanent sterilisation with a single dose.