AVMA Collections: Spay/Neuter

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Single-topic compilations of the information shaping our profession

June 2010

Pet overpopulation continues to be a serious problem in the United States. In 1990 it was estimated that approximately 11 to 19 million animals were euthanatized in US animal shelters. Additionally, many unwanted animals die from exposure, starvation, or trauma each year. Veterinarians play a vital role in stemming pet overpopulation by providing safe and effective neutering services, and by providing the expertise needed to advise animal owners about neutering for their pets.

This collection of articles from the AVMA scientific journals has been compiled to help veterinarians stay informed about spay/neuter issues and options. Information presented here pertains to topics such as the pros and cons of neutering at an early age versus a traditional age, comparisons of anesthesia and pain management protocols, surgical risks associated with neutering, and alternative neutering methods.

Please note that articles presented here are representative of scientific studies published in AJVR and the JAVMA since 2000 and do not constitute a comprehensive overview of the subject.

Risks and benefits of early-age gonadectomy in dogs, cats, and ferrets are presented within the first section, "Age at neutering." In the first article of this section, "Determining the optimal age for gonadectomy of dogs and cats," the author describes a number of potential advantages and disadvantages of pediatric neutering, and offers some guidelines for veterinarians. The authors of the next 2 articles studied long-term effects of pediatric gonadectomy and concluded that gonadectomy can be safely performed in cats and male dogs under 6 months of age, but advise waiting until after 3 to 4 months of age to perform the procedure in female dogs. These articles are followed by reports of 2 studies of dogs and cats neutered at over or under 24 weeks of age. The authors found no increased risk of disease or other health problems in cats neutered early, but did find more incidence of infectious disease in dogs neutered early as compared to dogs neutered at a traditional age.

Lastly, the authors of a study performed in Denmark, where ferrets are typically neutered at a later age than in the United States, examined the relationship between age at neutering in ferrets and incidence of hyperadrenocorticism. They found that pediatric neutering is related to earlier onset of hyperadrenocorticism in ferrets. The authors suggest that loss of negative gonadal feedback may be a factor.

The "Impacts on health" section begins with an exploration of the impact of neutering on development of age-related cognitive impairment in dogs. The author of this study found a positive correlation between neutering and more rapid onset of cognitive impairment. He postulates that testosterone may slow the progression of cognitive impairment in male dogs. The next 2 studies examined the relationships betweeen neutering and various factors associated with body weight and energy use in cats. In both studies, the authors found that responses to neutering differed between sexes, with female cats tending to gain more weight after neutering than males.

In the "Anesthesia" section, researchers present findings of studies comparing several anesthetic protocols. The authors of the first article discuss the use of a combination of tiletamine, zolazepam, ketamine, and xylazine for neutering feral cats, the benefits of which include ease of use and low mortality rate. A study of 3 protocols for the use of epidural anesthesia for ovariohysterectomy in dogs is presented in the next article. The authors report that, while epidural anesthesia is generally thought to provide insufficient analgesia for use in ovariohysterectomy, higher dosing provided sufficient analgesia with all 3 protocols studied.

The final 2 articles in the Anesthesia section contain findings from studies in which dogs were given medetomidine prior to undergoing ovariohysterectomy. In the first, cardiorespiratory responses and plasma cortisol concentrations were studied, and the authors concluded that pretreatment with medetomidine reduced the amount of anesthetic needed, and provided analgesia up to 1 hour after extubation. Noting that pain-induced distress with this procedure can persist for 5 hours after surgery, the authors recommend giving supplemental analgesia at the time of extubation. In the second article, researchers compared electrocardiographic effects of pretreating dogs with medetomidine and acepromizine prior to ovariohysterectomy. They found no significant difference in cardiac disturbances between groups, but did find a lower minimum heart rate among dogs pretreated with medetomidine.

In the "Pain management" section, studies of a range of analgesia considerations are presented. The first article, "Behavioral alterations and severity of pain in cats recovering at home following elective ovariohysterectomy or castration," contains findings that emphasize owner concerns about pain in their cats. The authors of the next 2 articles studied pretreatment of dogs with ketoprofen prior to undergoing ovariohysterectomy. They found that, while use of ketoprofen did not reduce the amount of anesthetic needed, it did result in improved postoperative activity levels. Additionally, they found that ketoprofen's negative effect on platelet aggregation did not increase hemorrhage or adversely affect mucosal bleeding time.

The authors of the next article compared the blood gas effects of perioperative administration of butorphaol or hydromorphone in dogs undergoing ovariohysterectomy. They found that PaCO2 increased with hydromorphone and that either drug may cause decreases in PaO2, but mean values remained within reference limits.

The final article in the Pain Management section contains findings of a study comparing preoperative administration of buprenorphine and meloxicam in cats undergoing ovariohysterectomy. The authors found no significant differences in sedation scores between use of the 2 drugs, and no difference in visual pain scores, but did find more pain on palpation in cats given buprenorphine orally.

In the first article within the "Surgical risks" section, "Ovarian remnant syndrome in dogs and cats: 21 cases (2000-2007)," researchers found 21 cases at 3 veterinary teaching hospitals in which remnants of ovarian tissue were present and causing clinical signs in dogs and cats that had undergone ovariohysterectomy previously. All ovarian tissues were found near ovarian pedicles, suggesting error in surgical technique to be the cause. Surgical removal of ovarian tissue resolved clinical signs.

Causes and treatment of major abdominal evisceration are discussed in "Major abdominal evisceration injuries in dogs and cats: 12 cases (1998-2008)." The inciting causes were found to be either postsurgical dehiscence or dehiscence secondary to trauma. In all cases of postsurgical dehiscence, ovariohysterectomy was the original surgical procedure performed, with a median interval between surgery and dehiscence of 4 days. The authors found the survival rate to be unexpectedly high, which they attributed to rapid intervention.

In the "Alternative methods" section, authors of 3 articles explore alternatives to traditional surgical ovariohysterectomy and castration. The first article, "Duration, complications, stress, and pain of open ovariohysterectomy versus a simple method of laparoscopic-assisted ovariohysterectomy in dogs," contains findings that demonstrate less pain and stress in dogs when a laparascopic-assisted procedure is used. The authors of the second article studied use of a laparascopic-assisted procedure for performing crytorchidectomy in both dogs and cats, finding the technique to be minimally invasive and allow good visibility. Finally, use of intratesticular injection of zinc gluconate in dogs was compared to traditional surgical castration by the authors of the last article in this section. They found a number of advantages to neutering with intratesticular injection, but the complication of necrotizing injection site lesions required more extensive postsurgical treatment than typical surgical complications.

These are just some of the highlights of the information to be found in the "Spay/Neuter" collection. We hope you will find this resource useful as you address spaying and neutering in your practice.