Surgical spaying and neutering in dogs and cats: a review of its risks and benefits

Gonadectomy or surgical castration is a very common surgery used for the reproductive control of dogs and cats, which is included in responsible pet ownership. However, the need and timing of spaying and neutering remains controversial due to the advantages and disadvantages depending on the age, sex, species and breed of the animal.

In this article, we review the long-term benefits and drawbacks of gonadectomy at different ages in dogs and cats using data describing the effects of castration on the urogenital tract and on other medical conditions, such as the development of mammary tumors.

Effect of sterilization on the reproductive tract

In some countries, ovariohysterectomy (OVH) is the preferred technique for spaying female dogs based on the assumption that removal of the uterus prevents future uterine pathology.

However, historical reviews of short- and long-term complications after HVO and oophorectomy (OVE) lead to the conclusion that there is no benefit and therefore no indication to remove the uterus during routine sterilization.

With the removal of the gonads, diseases such as ovarian tumors and ovarian cysts no longer occur. In addition, spayed female dogs and cats are no longer susceptible to ovarian hormone-mediated disorders such as vaginal hyperplasia or pyometra.

Effect of gonadectomy on the development of mammary tumors (MT)

MTs are the most common tumors in female dogs, with an estimated risk ranging from 2% to over 20%. In female cats, although the incidence is lower, these tumors can represent 17% of neoplasms.

There is evidence to support a breed-associated predisposition: Siamese cats, breeds such as the Spaniel, Poodle or Dachshund seem to be predisposed.

Apart from genetic predisposition, gonadal hormones seem to mainly influence the pathogenesis of MTs. Neutered dogs and cats are less affected by MTs than unneutered ones, although the timing of neutering also plays a critical role.

The risk of developing malignant MTs in female dogs spayed before the first estrus is reduced by 99.5% compared to those that are not. Female dogs spayed after the first and before the second estrus have a 92% reduction in the risk of developing malignant MTs compared to others that haven’t undergone that surgery.

Similar effects were observed in female cats: those that were spayed before 6 months of age had a 91% reduction in the risk of developing malignant MTs compared to others. Those spayed before 1 year of age had an 86% risk reduction.

Reichler, I. M (2009) Gonadectomy in cats and dogs: a review of risks and benefits” Lugar: University of Zurich.
DOI:19754532