1) Health concerns
a. Research has shown that there can be positive effects of the sex steroid hormones. The sex steroids are hormones produced by the ovaries and testes, and are only present in intact males and females. Gonadectomy at any age deprives the body of the positive health effects of these hormones. Although in most cases, the benefits of spay-neuter outweigh the benefits of exposure to the sex steroids, this is not true in all cases. Since gonadectomy prior to puberty or sexual maturity may make the risks of some diseases higher in certain breeds or individuals, the option to leave an animal intact must be available to the pet owner.
i. Advantages of remaining intact:
1. There is a decreased incidence of hemangiosarcoma in intact bitches and dogs.
2. There is a decreased incidence of osteosarcoma in intact male and female dogs.
3. There is a decreased risk of transitional cell carcinoma in intact dogs and bitches.
4. There is a decreased risk of prostatic adenocarcinoma in intact male dogs compared to gonadectomized male dogs.
5. There is a decreased incidence of obesity in intact male and female dogs and cats, which may be due at least partly to increased metabolic rate.
6. There is a decreased incidence of urinary incontinence in intact bitches (equivocal if bitches are spayed after 5 months but before their first heat).
7. There may be a reduced incidence of urinary tract infection in intact bitches.
8. There may be a reduced incidence of feline lower urinary tract disease (FLUTD) in intact male and female cats which may be partly due to decreased obesity in these animals.
9. There may be a reduced incidence of autoimmune thyroiditis and hypothyroidism in intact male and female dogs.
10. There is a decreased incidence of diabetes mellitus in intact female cats and a possibly reduced incidence in diabetes mellitus in intact male dogs.
11. There is a reduced incidence of cranial cruciate rupture in intact male and female dogs.
12. There may be a reduced incidence of hip dysplasia in male and female dogs that are not gonadectomized before 5 months of age.
13. There may be an increased incidence of capital physeal fractures in castrated male cats that may be partially due to increased weight gain in gonadectomized males.
b. Research has shown that there are a number of detrimental effects of the sex steroid hormones. Spaying and neutering will remove these hormones and thus lower the risk of these conditions.
i. Advantages of being spayed or castrated:
1. There is an increased risk of mammary, testicular, and ovarian neoplasia in intact male and female dogs and cats.
a. There is an increased risk of mammary cancer with each subsequent cycle and the benefit of spaying does not disappear until the animal reaches old age.
i. Mammary cancer is one of the most common types of neoplasia in small animals.
1. Mammary neoplasia is malignant 60% of the time in dogs and 90% of the time in cats.
b. The incidence and mortality risk for ovarian cancer are very low
c. The incidence for testicular cancer is more common but malignancy and mortality are very low.
2. There is an increased risk of pyometra in both intact female dogs and cats and this risk increases with increasing age.
3. There is an increased risk of prostatitis, benign prostatic hyperplasia, prostatic cysts and squamous metaplasia of the prostate in intact male dogs.
4. There is a decreased incidence of perineal and inguinal hernia and perineal adenoma in neutered male dogs.
c. Based on the research available, it is clear there are a number of health benefits of the sex steroid hormones and that this benefit varies with age, sex, and breed. Therefore, although spay-neuter is the responsible choice for most pets, it is in the best interest of each individual patient for its veterinarian to assess the risks and benefits of gonadectomy and to advise his/her clients on what is appropriate for each individual pet at each stage of its life.