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Ovary Sparing Spay - OSS

Updated: Feb 20

Read this very detailed research article on OSS (link below).

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(Credit given to Murrayville Animal Hospital for the Article below)

Is an Ovary Sparing Spay Right For My Dog?

Your decision to spay your pet must be made on a case-by-case basis.  This decision should be made between you and your veterinarian, taking into consideration your pet’s age, breed, sex, health status, intended use, household environment, and temperament. While there are health benefits to spaying, the benefits must be weighed against the health benefits of retaining the sex hormones achieved by leaving your pet intact (not spayed). Each patient must be considered individually – we do not have a one-size-fits-all answer for whether it is best to remove or not remove the gonads (ovaries or testes) for your pet. If you have determined you do not plan to breed your dog, you are now faced with other decisions. What is the difference between a spay and an ovary sparing spay? What are the advantages and disadvantages? When is the best time to perform the surgery?

What Spay Options Are Available?

Both a spay (ovariohysterectomy) and an ovary sparing spay render the dog incapable of breeding. The ovariohysterectomy removes the uterus, cervix and both ovaries. An ovary sparing spay is where one or both ovaries are left in the abdomen, near the kidneys, but the uterus and cervix are removed. Because the uterus is removed, the female will not be able to become pregnant, even if a mating occurs. The female will still have heat cycles and be attractive to male dogs. She will have little to no bloody vaginal discharge during her heat cycles.

Ovary Sparing Spay (OSS):

  • Removes the Uterus and some part of Cervix 

  • Leaves at least 1 Ovary if not both Ovaries

  • Hormones are maintained

  • Has a heat cycle and may have a very small amount of bloody discharge, will be attractive to male dogs

  • Not fertile

Ovariohysterectomy (Traditional):

  • Removes Ovaries and some of the Uterus

  • Leaves Part of the Uterus and Cervix

  •  Hormones are NOT maintained

  • Does not have a heat cycle

  • Not fertile

What Are The Advantages Of Retaining The Ovaries

Health Advantages:

  • Lower incidence of hemangiosarcoma (cancer usually found in the spleen or heart)

  • Lower incidence of osteosarcoma (bone cancer)

  • Lower risk of transitional cell carcinoma (bladder cancer)

  • Lower incidence of obesity, which may be due at least partly to increased metabolic rate

  • Lower incidence of urinary incontinence (equivocal if females are spayed after 5 months but before their first heat)

  • Lower incidence of urinary tract infection

  • Lower incidence of autoimmune thyroiditis and hypothyroidism

  • A reduced incidence of cranial cruciate rupture

  • A reduced incidence of hip dysplasia in female dogs that are not spayed before 5 months of age

  • Anesthesia and surgery are not appropriate for some patients with high-risk medical conditions

  • Lower incidence of adverse reactions to vaccines

  • Evidence of increased lifespan in females left intact past puberty. David J. Waters, associate director of Purdue University's Center on Aging and the Life Course and a professor in the Department of Clinical Sciences says: "Taking away ovaries during the first 4 years of life completely erased the female survival advantage. We found that female Rottweilers that kept their ovaries for at least 6 years were 4 times more likely to reach exceptional longevity compared to females who had the shortest lifetime ovary exposure."

Behavioral Advantages:

  • Less aggression towards people and animals

  • A decreased incidence of cognitive dysfunction

  • Less fearfulness, noise phobias, and undesirable sexual behaviors

The sex hormones, by communicating with a number of other growth-related hormones, promote the closure of the growth plates at puberty, so the bones of those dogs spayed before puberty continue to grow. Dogs that have been spayed well before puberty can frequently be identified by their longer limbs, lighter bone structure, narrow chests, and narrow skulls. This abnormal growth frequently results in significant alterations in body proportions and particularly the lengths (and therefore weights) of certain bones relative to others. This is related to increased orthopedic conditions in dogs spayed prior to puberty. In addition, sex hormones are critical for achieving peak bone density.

What Are The Disadvantages Of Retaining The Ovaries

Health Disadvantages:

  • Increased risk of mammary (breast) cancer. This increased risk of mammary (breast) cancer occurs with each subsequent cycle and the benefit of spaying does not disappear until the animal reaches old age. Mammary cancer is one of the most common types of cancer in small animals. Mammary neoplasia is malignant under 50% of the time in dogs, but few dogs die from breast cancer due to low metastatic rates and early detection and treatment.

  • Increased risk of ovarian cancer. The incidence and mortality risk for ovarian cancer is very low

  • In very rare cases, a pyometra can develop with OSS or traditional spay


Behavioral Disadvantages:

  • Inter-dog aggression may be due to competition for available territory or availability of cycling animals

  • Ongoing sexual behaviors, including heat cycles in females who have had an ovary sparing spay

Dr. Villalobos, a well-respected veterinary oncologist states, "It is earth-shattering to consider that some of the cancers we have been battling may have been enhanced by early neutering instead of the reverse." Based on the research available, it is clear there are a number of health benefits of the sex steroid hormones. This benefit varies with age, sex, and breed. Therefore, although surgically altering your dog to be unable to breed is the responsible choice for most dogs, it is in the best interest of each individual patient for its veterinarian to assess the risks and benefits of removing the ovaries versus the options like a ovary sparing spay and to have your veterinarian advise you on what is appropriate for each individual pet at each stage of its life.

When Should You Spay A Dog?

If you opt for a traditional spay, the age at which this is done is important. Removing the ovaries interrupt the hormonal axis of the sex hormones with the pituitary and other organs. There are age-related conditions to consider when making this decision. 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 your pet intact should be available to you. If you opt to leave the ovaries this can be done at any age. If you opt to remove the gonads, ovaries or testes, the age should be decided in a conversation with you and your veterinarian. We recommend waiting until at least 6 months of age, or older, usually, after they have gone through their first heat cycle, due to health and behavioral advantages.

If you opt for a non-traditional approach, the ovary sparing spay, when you leave the ovaries but interrupt the reproductive tract to prevent fertility, you may consider doing this at any age. Because the ovaries are left to function, your dog will still have her hormones. Research has shown that there can be positive effects of the sex steroid hormones. The sex steroids are hormones produced by the ovaries and are only present in intact females. For canine athletes, Dr. Christine Zink recommends waiting until after 14 months of age (the age at which the growth plates have closed) for females to be spayed.

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