It is required for one of the theriogenology clinicians to speak with all clients wishing to schedule an ovary-sparing spay or vasectomy with the theriogenology service.

All gonad-sparing procedures (i.e. ovary-sparing spay and vasectomy) must be scheduled no later than 9 a.m. on the Tuesday morning of every month. Pre-operative bloodwork (complete blood count and chemistry) with the patient’s regular veterinarian needs to be performed late in the week immediately preceding the procedure; bloodwork should be sent to the OSU Lois Bates Acheson Veterinary Teaching Hospital (OSU VTH) prior to the day of surgery along with a current, accurate weight of the patient. If not possible to obtain bloodwork prior to the procedure, the patient needs to arrive NO LATER than 8 a.m. the day of the procedure. Clients who arrive more than 15 minutes late without prior notice to the hospital's small animal reception staff will be subject to late fees or be rescheduled if the service schedule will be significantly impacted by tardiness.


These procedures involve complete removal of reproductive organs, meaning testicles and epididymis for males (castration) and ovaries and uterus for females (spay or ovariohysterectomy). An all-encompassing term referring to gonadectomy of either a male or female is “neuter.” Castrations and spays are routine procedures performed by most general practitioners of veterinary medicine. The timing of a castration or spay is based on the job of the animal (competition vs bite work vs pet), lifestyle of the animal, lifestyle of the owners and possible health disorders associated with neuter may be taken into consideration.

Neutering has advantages and disadvantages that should be considered by both owners and their veterinarians; there should also be a discussion regarding timing of the procedure with the veterinarian who is familiar with both the client and the patient.

A common reason for performing a neutering procedure is to lower or completely prevent the patient from developing diseases associated with the sex organs (ovaries, uterus, testicles) compared to if they were left intact, including, but not limited to: pyometra (life-threatening infection of the uterus), prostate disease, ovarian/testicular cancers and mammary tumors. Additionally, the patient is no longer able to become pregnant, maintain a pregnancy, or impregnate a female (i.e., population control) after neutering. Some clients cannot and/or do not want to bear the responsibility of owning an intact animal, involving management of a bitch in heat, possible pseudopregnancy after heats, possible aggressive behavior in males and management of an intact male around females, not including possible patient health concerns.

It should be noted that neutering increases the likelihood of the patient gaining weight due to metabolism changes; after a spay or castration, metabolism decreases by approximately 20-30%. Obesity, urinary incontinence, various cancers, musculoskeletal disorders, and cognitive or behavior problems have been reported to occur more commonly in neutered animals compared to intact animals. For example, spayed females are more predisposed to obesity compared to intact females, but this is multi-factorial — lifestyle, breed, feed intake, and exercise habits are also contributing factors.

The above-listed disorders are also breed- and age-specific, which is why gonad-sparing procedures have become more commonplace among certain breeds. Veterinary medicine is evolving to encompass research that has previously been neglected due to traditional theories and set standards. Preservation of hormones can be as important in our canine patients’ quality of life and health as much as other aspects, such as regular vaccination and physical exams. It is important to note, however, that not all clients and pets are well suited for sterilization procedures other than standard ovariohysterectomy or castration, and that selection of patients for any gonad-sparing procedure should be done on an individual basis. The goals of the client, health concerns for the individual patient, the breed of the patient and the job of the patient should be taken into consideration.

An ovary-sparing spay (OSS) is also referred to as a “hysterectomy,” involving removal of only the uterus and possibly one of the two ovaries. OSU VTH veterinarians who perform this procedure typically also remove the cervix; however, not all veterinarians who perform an OSS will remove the cervix as there is conflicting evidence as to whether leaving the cervix intact will influence the development of a stump pyometra (potentially life-threatening infection of remaining reproductive tissue).

OSS eliminates the risk of a pyometra and pregnancy while maintaining ovarian-produced hormones, such as estrogen and progesterone. The patients that have been shown to benefit most from an OSS are large and giant breed dogs, dogs at risk for orthopedic complications, dogs at risk for certain types of cancers or neoplasms, and performance animals. An OSS has similar surgical time as a routine spay and has the potential to be prolonged if complications arise intraoperatively, and the abdominal incision is usually larger than a traditional spay. Additionally, the patient is required to be marked in a way that allows the general public and other veterinarians to know the patient is intact, but sterile. There is currently no consensus on how patients should be marked; patients undergoing an OSS at OSU VTH will be tattooed next to the incision with an “H” for “hysterectomy.”

Females who undergo an OSS with still be at an increased risk of mammary gland tumors, 50% of which are malignant, and the other half are benign. There will be an increased risk of ovarian tumors, though incidence is relatively low, and removal of the ovary is curative in most cases. Cycles will still occur with a shorter period between each cycle by 1.5-2 months compared to if they were kept fully intact, and OSS females will display the same behaviors as a fully intact female. Additionally — arguably the most important consideration — due to cycling, OSS females will attract males and if the male mounts and penetrates the bitch, there is a risk of vaginal rupture, subsequent sepsis and possible death secondary to infection.

A vasectomy is the occlusion or removal of a section of both ductus deferens (“vas deferens” in humans). This procedure prevents the ejaculation of sperm; however, the sperm are still able to be produced as the testicles are left intact. Intact testicles also produce testosterone, the male hormone associated with the development of secondary sex characteristics, such as heavy muscling, aggression, and interest in in-heat females. Additionally, vasectomy does not reduce the incidence of testosterone-dependent conditions, such as prostate disease (e.g. infection, cysts, inflammation). The most common reasons for pursuing a vasectomy are for population control and sparing of testosterone in breeds where research has shown testosterone is beneficial long-term or due to the lifestyle/job (such as bite work) of the patient. 

Vasectomy is a relatively quick procedure and less invasive than a routine castration unless complications occur. Possible long-term effects include an increased risk for: testicular torsion, loss of blood supply to the testicle, prostate disease, testicular cancer, perianal gland tumors. These conditions are typically treated with castration, should they occur. Vasectomized males will still be interested in females that are in heat and are able to mount and penetrate bitches. However, they will no longer be able to impregnate females. Vasectomy will not alter male behavior; vasectomized males may display more aggression towards other males, urine marking, mounting and roaming.

Some breeds, particularly deep-chested dogs, are prone to gastric dilation and torsion (GDV); OSU VTH has the ability to perform a vasectomy and prophylactic gastropexy laparoscopically within the same surgery.

Additionally, the patient is required to be marked in a way that allows the general public and other veterinarians to know the patient is intact, but sterile. There is currently no consensus on how patients should be marked; patients undergoing a vasectomy at OSU VTH will be tattooed next to the incision with a “V” for “vasectomy.”