CHAPTER 75 A Review of Neutering Cats
Neutering is widely accepted as an essential component of preventive healthcare for cats and represents the best method of birth control for the species. In this chapter the authors review the importance of these procedures, describe recommended veterinary medical guidelines and techniques for neutering cats, and present various models of targeted large-scale spay-neuter programs.
Although exact estimates do not exist, it is believed that between three and four million cats enter animal shelters in the United States each year and nearly 75 per cent of them are euthanized.1 Indeed, cat impoundments and euthanasias significantly outnumber those of dogs. Of cats entering shelters with an unknown ownership status, less than 2 per cent are reunited with their owners compared with as many as 15 to 19 per cent of lost dogs.2–4 Many cats are relinquished by their owners, with “too many in house” being cited as the leading reason.5 Millions of other cats survive as free-roaming strays with their reproduction resulting in generations of unsocialized feral cats.6 In fact, as much as 50 per cent of the total cat population in a given community may be feral.7 These cats represent both an effect of feline overpopulation and a significant source of it. Free-roaming and feral queens may produce up to 80 per cent of the kittens born annually in the United States.7 The reader is referred to Chapter 71 in the fourth volume of this series for a discussion of the control of feral cat populations.
Four nonlethal strategies for reducing feline overpopulation have been described: increasing sterilization of cats, increasing owner retention of cats, increasing adoption of cats from animal shelters, and increasing educational efforts and laws designed to help owners be more responsible.8 Certainly efforts should emphasize preventing cats from entering animal shelters through proactive strategies to decrease their birthrates and keep them in their homes. Neutering cats not only prevents reproduction and decreases the number of unwanted, unowned cats, but also improves the odds that owned cats will be retained in their homes because being sexually intact has been identified as the leading risk factor for owner relinquishment of cats.9–11 Thus neutering cats represents the core strategy to reduce feline overpopulation humanely. In order to maximize their impact, sterilization efforts should target recognized sources of surplus cats in communities. Box 75-1 contains recommended target groups of cats for sterilization.8
These groups consist of those cats who otherwise would not likely be neutered, including both unowned free-roaming and feral cats and pet cats from low-income households. Ensuring the availability of affordable services for all cats regardless of ownership status is critical to success. Given that relinquished cats are likely to originate from low-income households,5 sterilization programs should strive to provide opportunities for affordable surgery for this population. Successful marketing of services is required to ensure owner acceptance and compliance with neutering of their cats. Sustainable programs that ensure a large majority of cats are neutered in a timely fashion are required for population control.
Neutering all cats prior to adoption represents another important target or goal for spay-neuter programs. Approximately 18 per cent of owned cats are acquired from animal shelters.12 These organizations generally require cats to be neutered; however, neutering is not always performed prior to adoption. Adoption agencies employ a variety of programs to encourage sterilization of pets after adoption including monetary incentives, contracts, and vouchers; however, national compliance rates for neutering after adoption average only 50 to 60 per cent.13 This is clearly an unacceptable outcome and has the potential to contribute to pet overpopulation rather than to reduce it. In its policy statement on dog and cat population control, the American Veterinary Medical Association (AVMA) concludes that “Public policies should prohibit the sale or adoption of intact dogs and cats by humane organizations and animal control agencies.”14 Published veterinary medical guidelines for spay-neuter programs state that neutering is best performed prior to adoption.15 Neutering all cats prior to adoption, including kittens as young as 6 weeks of age, ensures control of reproduction and sets an example of responsible ownership for the community.
To prevent pregnancy and to avoid contributing to overpopulation, neutering must be performed before puberty. Pediatric, early-age, or prepubertal sterilization refers to the neutering of patients between the ages of 6 and 16 weeks of age and is supported by the AVMA.16 Given that queens may experience estrus as early as 4 to 5 months of age,17 delaying spaying of juvenile cats is likely to result in a significant number of unintentional litters. In fact, many queens are neutered after sexual maturity and are allowed to have one or more litters prior to being spayed.18–20 Educating pet owners about the appropriate timing of surgery is a crucial task, because they are seldom aware of the precocious nature of cats and often believe that their pets are too young for surgery. One survey of pet owners indicated that 20 per cent of owned cats were allowed to have one or more litters prior to neutering,20 and another survey showed that a majority of cat owners believed that it was better to allow cats to have a litter prior to neutering.9
Most owned pet cats are neutered in private veterinary practices in the United States. Currently most practices recommend 6 to 9 months of age as the appropriate timing for surgery.21 This recommendation is not based on a scientifically defined optimal age for neutering, but on a historical clinical sentiment that this is the appropriate age for these procedures. It probably was chosen originally because anesthetic and surgical techniques were less advanced at the time and surgical success was more likely in a larger patient. Despite considerable advances in anesthetic and surgical techniques and published data that illustrate shorter surgical times and lower complication rates for younger patients,22 these recommendations have persisted. Many practitioners routinely see kittens for a series of vaccinations and preventive healthcare between 6 and 16 weeks of age, then advise owners to return a few months later for neutering. This gap in care contributes to many cats being spayed after puberty and the birth of many unintentional litters. In the authors’ opinion, owned pet cats with private veterinarians are best served by neutering at 4 to 5 months of age after standard vaccinations. This allows time for cats to develop immunity through vaccination while ensuring they are neutered prior to sexual maturity. Because there is no gap in veterinary care between the vaccine series and the surgical appointment, owner compliance may be improved because the owner establishes a routine of veterinary appointments for their cat during kittenhood visits. In 2008 the “Spay Before Five” campaign (www.fivesaveslives.org) was launched, and serves as a spay-neuter public awareness campaign to encourage owners and veterinarians to spay cats before 5 months of age in order to ensure that they do not reproduce and that they reap the health benefits associated with being spayed prior to puberty.
Whereas there are numerous indications for neutering as a treatment option for a variety of disease states, its value as a preventive healthcare measure also deserves emphasis. Most notably, when complete ovariohysterectomy or orchiectomy is performed, diseases of the uterus, ovaries, and testes are eliminated.23 These include cystic endometrial hyperplasia, pyometra, prostatitis, and various cancers of the gonads themselves. Additionally, there are reports of significant reduction in the risk of mammary carcinoma in spayed versus intact female cats—as high as 91 per cent in cats spayed before 6 months of age.24,25 Feline mammary carcinomas typically occur in middle-age to older cats and are characterized by both aggressive local invasion and metastasis. Even with treatment, median survival times usually are less than 1 year.24 Given that mammary tumors are the third most common tumor in cats and that as many as 96 per cent of them are malignant, this is a significant benefit.
Perhaps the greatest benefit of sterilization for feline welfare is that of a reduction in behaviors that are objectionable to human beings. Indeed, behavioral problems are leading reasons for relinquishment of companion animals and their subsequent euthanasia.5,9,11,26–28 Among the most commonly cited behavioral reasons for relinquishment of pet cats are inappropriate elimination and various forms of aggression. Urine spraying, one form of inappropriate elimination, is very common in sexually mature tomcats. In addition, queens may spray urine occasionally during estrus. Neutering frequently results in the disappearance of this highly objectionable behavior.29 It also reduces urine odor, fighting, and roaming significantly in tomcats. In addition, both male and female cats are reportedly less aggressive and more affectionate after neutering.30 These behavioral effects serve to enhance the human-animal bond and increase the odds that cats will be retained in their homes. It is important to recognize that only sexually dimorphic behaviors can be expected to be influenced by sterilization and the degree to which they may be altered varies among individuals.31
More than 30 years ago humane organizations began sterilizing young puppies and kittens. Understandably, many veterinarians expressed concerns and questions regarding the short- and long-term safety of sterilizing pediatric patients. In response to these concerns, numerous controlled prospective studies and retrospective cohort studies have been performed to verify the safety of early age sterilization.21,22,30,32–40 Data from these studies suggest that early age sterilization is not associated with serious health problems and is surgically and medically sound. In addition, early age sterilization offers many advantages including safe anesthetic and surgical techniques, shorter surgical and recovery times, and avoidance of the stresses and costs associated with spaying while in estrus, pregnant, or with pyometra.
Perhaps the single greatest concern expressed by veterinary practitioners regarding early age neutering of cats involves the influence of early neutering on urinary tract development and health of male kittens. Anecdotally, veterinarians have expressed concern that neutering young kittens may result in decreased urethral size increasing the risk of feline lower urinary tract disease and urethral obstruction. Numerous studies have evaluated urethral size, function, and health in neutered cats.30,32,33,35–37 Based on contrast retrograde urethrograms and urethral pressure profiles, neither urethral diameters nor dynamic urethral function differ significantly between intact tomcats and neutered cats regardless of age of neuter (7 weeks versus 7 months).30,35–37 In addition, the incidence of urethral obstruction and lower urinary tract disease has not been shown to be different regardless of age of neuter.32,33
More recently concerns have been raised regarding the relationship between prepubertal sterilization and spontaneous femoral capital physeal fractures in cats.41,42 Overweight male cats who were neutered prior to puberty and physeal closure have been shown to be at greatest risk for these fractures. Timing of physeal closure of the long bones is controlled in part by gonadal hormones; thus gonadectomy prior to physeal closure may delay the process. Studies of physeal closure in cats have not demonstrated significant differences in time to closure between cats neutered at 7 weeks of age compared with those neutered at 7 months of age.30,43
Physeal closure in normal intact cats begins at 4 to 7 months of age and is complete by 14 to 20 months of age.43 The risks associated with performing sterilization prior to puberty and physeal closure must be weighed against any theoretical orthopedic benefit of delaying surgery. Keeping in mind that many tomcats begin to exhibit urine spraying after attaining puberty at 8 to 10 months of age, delaying surgery until after physeal closure may not be feasible for most clients.
It is a common misperception that veterinarians who perform a high volume of surgical sterilizations per day or who perform surgical procedures at a reduced cost are not providing quality care for their patients.44,45 Although exceptions may exist, this is not the case in the majority of situations. Increasing the volume of procedures or lowering costs is not obtained by reducing quality. To the contrary, concentrating on a single practice area has already been used very successfully in human surgery both in the United States and abroad to improve outcomes and reduce complications while reducing costs simultaneously. The goals of dedicated spay-neuter surgeons are achieved by efficient use of support staff, equipment, and protocols to provide safe, high-quality surgical sterilization at low cost to large numbers of companion and feral cats and dogs. In fact, the mortality rates reported by high volume spay-neuter programs are lower than those published for elective surgeries in small animal private practice and teaching hospitals.46–48
State practice acts and professional organizations provide recommended guidelines for the practice of veterinary medicine.49–51 Guidelines that specifically address spay-neuter practice also have been published and serve as a valuable adjunct to state and local practice acts.15 Guidelines for medical and surgical care must take into consideration the population being served. For example, a standard recommendation is that a physical examination should be performed on every patient prior to an anesthetic event. In the case of feral cats, however, physical examination can not be performed safely or humanely prior to anesthesia. Despite this difference, it is still possible to provide quality veterinary care.
Although specific protocols and procedures necessarily will differ among programs, certain aspects should remain consistent.15 Attentive care to preoperative procedures is necessary in order to ensure patient safety and minimize client, patient, and staff stress. A veterinarian (or veterinary student under their supervision) should examine every patient, and medical records should be prepared in compliance with state practice acts. Medical records should include informed owner consent for surgery, medical history (if available), physical examination findings, body weight, dosages of all drugs administered or prescribed and routes of administration, the surgical procedure performed, any abnormalities that are identified, and any other pertinent information regarding the animal’s condition. Standardized operative reports may be used, but should allow for additions when necessary. Systems for infectious disease control should be in place to prevent or minimize transmission among patients. Vaccination is recommended prior to surgery; however, perioperative vaccination is acceptable when necessary and has been demonstrated to induce immunity effectively in cats and kittens.52,53
Balanced anesthetic protocols are required, including the provision of adequate analgesia for all patients. Protocols for general use, as well as those for high-risk patients, should be available. Care should be taken to ensure thermoregulation throughout the perioperative period, and cats should be monitored continuously by vigilant, trained hands-on observers. In addition, emergency readiness plans always should be in place.15
Regarding surgery, aseptic technique must never be compromised and separate instruments that have been sterilized via steam, gas, or plasma should be used for all patients. Veterinarians (or veterinary students under their direct supervision) must perform all surgical procedures. For female patients, ventral midline, flank, and laparoscopic approaches are acceptable for ovariohysterectomy or ovariectomy. The general surgical principles of gentle tissue-handling, meticulous hemostasis, and aseptic technique are required, and hemostasis must be ensured and verified prior to completion of any procedure. Either an interrupted or continuous suture pattern is acceptable for abdominal closure. Perioperative antibiotics should not be used routinely.15
In the postoperative period care should be taken to provide patients with a smooth transition from the anesthetized state to wakeful comfort for return to their home environments. Patients should be evaluated immediately prior to release. Cat owners, caregivers, or their agents should be provided with clear instructions (written and verbal) for postoperative care. Finally, regular policies for managing complications and emergencies that occur within the 48-hour period after surgery must be in place.15
Naturally possessing heightened fight or flight responses, feline patients are particularly prone to experiencing acute stress and fear in novel environments. Both acute stress and fear are accompanied by catecholamine release, which can induce tachycardia and increase the risk of serious cardiac arrhythmias during anesthetic induction.54 Behaviorally, fearful cats may be overtly aggressive or may be “teetering on the edge” of defensive aggression. Such responses can not only compromise cat welfare, but staff safety as well. For these reasons spay-neuter programs should have protocols in place to minimize stress for feline patients beginning prior to their arrival at the clinic and continuing until their discharge. Caregivers should be required to present cats for surgery in individual carriers or traps. From the time they arrive at the clinic, care should be taken not to place cats within spatial, visual, or auditory range of other species, especially dogs. Tractable juvenile and adult cats should be housed individually throughout their stays in the facility. Pediatric littermates or house mates generally benefit from being housed together to prevent stress induced by separation. Cats instinctively feel more secure when they can perch at a high point and studies indicate that feline stress responses are significantly reduced when cats are housed in elevated cages compared with floor-level cages.55 For these reasons, carriers containing cats should never be placed on the floor, and cats preferentially should be transferred to the highest available holding cage. When possible, and in a manner that does not interfere with perianesthetic monitoring, the provision of a hiding box or towel to cover the cage can reduce the stress of a feline patient substantially. Indeed, the ability to control aversive stimuli through hiding decreases stress hormones profoundly in cats.56 If cats are to be held for more than 12 hours, a litterbox should be provided once the patient is ambulatory.
Intractable or feral cats should be housed in traps or other enclosures that allow for administration of anesthetics without extensive handling in order to minimize stress and safety for both cats and personnel. They should only be removed from their trap or enclosure after heavy sedation and should be returned to the holding enclosure when adequately recovered. During holding, traps should be elevated to allow urine and feces to fall through the wire bottoms away from the patient. Feral cats should be returned to their environments as soon as they are fully recovered from anesthesia (e.g., when their mental status and motor coordination have returned to normal).15
In the context of spay-neuter programs, handling and restraint of cats of varying ages, personality types, social experiences, and stress levels require skill, knowledge of normal feline behavior and signaling, finesse, and proper equipment. Minimal, gentle restraint should be used to handle tractable cats, because research indicates that gentle human contact can attenuate the adverse effects of unpleasant stimuli, eliminate fear responses, and alleviate signs of pain in animals.57 Providing time for cats to acclimate to new surroundings prior to handling, avoiding escapes and the need to recapture, and using transport carriers also are helpful methods of reducing stress when handling cats in the spay-neuter clinic. In some cases, chemical restraint should be administered with the use of humane restraint equipment such as nets or squeeze devices. Control poles should never be used to restrain cats. Finally, the use of commercially available diffusers containing synthetic analogues of naturally occurring feline facial pheromones (Feliway, Veterinary Product Laboratories, Phoenix, AZ) also may aid in reducing patient stress.58
The induction of a balanced state of anesthesia is required for all patients undergoing any surgical sterilization procedure. The specific protocol used may vary, but it must provide rapid, reversible loss of consciousness, immobility with muscle relaxation, anxiolysis, and analgesia. By definition, surgical sterilization induces tissue damage, which can result in pain; therefore administration of analgesics is not optional.59,60 Anesthetic protocols that combine multiple analgesic agents in a single protocol (multimodal analgesia) are preferred.15,61 Numerous balanced anesthetic protocols have been utilized successfully for neutering cats.62–68 Sample protocols are presented in Table 75-1 and Box 75-2. When selecting an anesthetic protocol for a spay-neuter program, consideration should be given to a number of factors, including the type and number of patients, an individual animal’s physical examination findings and risk assessment, the procedure to be performed, the duration of anesthesia and analgesia desired, whether or not a reversible protocol is desired, the organization’s physical and economic resources, the technical skill of clinic staff, and the efficiency of the surgeon.15
IM, Intramuscularly; IV, intravenously; SQ, subcutaneously.