September 14, 2017
Among the most common surgical procedures in small animal practice are those for sterilization and neutering. The goal of these procedures is both to prevent reproduction and to provide a net health benefit for the patient that may include avoiding the risks of reproduction, reducing the incidence of those disease that are more common in intact animals, and reducing behaviors associated with intact status that can lead to relinquishment.1-2
There are many variations on these procedures, and the specific techniques used by individual veterinarians seem to depend more on tradition, personal habit, and cultural preference than on explicit evaluation of the pros and cons from a scientific perspective.3 There is, however, research evidence concerning some of these procedures that we can use to make rational decisions about our choice of technique. We also can use this research to inform the recommendations we make to clients. Pet owners increasingly are aware that multiple alternatives exist, and they may come to us with strong opinions or misconceptions about the most appropriate procedure for their pets.
Most procedures are intended to prevent reproduction. Some also involve gonadectomy, which has a complex array of both beneficial and harmful effects that depend on breed, sex, age, timing of surgery, and many other factors. The long-term pros and cons of gonadectomy are controversial, and I have reviewed them in detail elsewhere.2 In brief, there appears to be a net health benefit for most female dogs and cats from neutering, though the details of the risks and benefits and the effect of the timing of neutering are variable. There is much less evidence for a net health benefit in neutering males, though there are other justifications for doing so. Here I will consider the relative advantages and disadvantages of different surgical sterilization and neutering options for females.
Ventral midline ovariohysterectomy (OVH) is considered an effective technique for sterilization and neutering of both dogs and cats with very low complication rates when performed by surgeons that are experienced with this procedure.4-6 There are many minor variations with no research evidence comparing the relative merits of most.
One exception is the flank approach to OVH, which is preferred in some countries for cats and small dogs. There are theoretical advantages and disadvantages to this approach, and research evidence comparing flank and midline approaches is mixed. Some comparisons suggest it’s faster with fewer complications,7 but other studies find no difference,8 and some indicate more discomfort associated with it.9-10 Access to both ovaries is more difficult with this approach unless bilateral flank incisions are made, which significantly complicates the procedure, and hysterectomy can be difficult by this method.11 The flank and midline methods both achieve the goal of gonadectomy and sterilization.
Traditionally, OVH has been preferred in the U.S., while ovariectomy (OVE) is the more common choice in some other countries.12 Both techniques are equally effective at achieving gonadectomy and preventing mammary carcinoma and pyometra.12-14 Some studies have suggested that OVE is less painful than OVH15; however, other studies have not identified any difference in postoperative pain or other complications.10,16
Laparoscopic OVE and OVH have been reported using a variety of equipment and techniques. Comparisons are difficult given the many different approaches, equipment, and assessments used in published studies. In general, the disadvantages of laparoscopic OVE and OVH include the cost of equipment, the need for extensive training and practice to achieve proficiency, and the longer surgical time.17-20 Laparoscopic spay may have the advantage of decreasing postoperative pain, complications, and recovery time, but the literature is inconsistent, and high-quality studies are lacking.21
With a growing awareness of the potential negative effects of neutering, there has been some increased interest among breeders and pet owners in sterilization procedures that do not involve gonadectomy. For females, two such procedures are hysterectomy (or ovary-sparing spay) and ligation of the fallopian tubes or uterine horns. Both procedures have been described in the literature,22-23 but neither have been widely adopted.
There are no controlled research studies comparing tubal ligation or hysterectomy to OVE or OVH. While ligation of the fallopian tubes or uterine horns can prevent reproduction, it is highly likely that any risks and benefits associated with the presence of ovaries2 are the same for females having a tubal ligation as for those not spayed at all. A complete hysterectomy, including removal of the cervix, likely eliminates the concern for pyometra, while the other risks and benefits of intact status remain unchanged.
OVH and OVE are equally effective methods of neutering. OVE may be slightly quicker and cause less postoperative discomfort. A flank approach can be used for OVE and OVH in cats and small dogs, though there is some evidence that it’s more painful than a ventral midline approach and may be more technically challenging for OVH or for larger patients.
Laparoscopic spay techniques also are effective, and these may cause less discomfort that open techniques. However, laparoscopy requires expensive equipment and specialized training and typically takes longer than an open spay.
Tubal ligation and hysterectomy are uncommon techniques that can prevent reproduction without neutering. However, these procedures are equivalent to not spaying at all with regard to most health effects and do not accomplish most of the goals of spaying female dogs and cats.
The most appropriate spay procedure for a specific dog or cat must be determined by individual circumstances and in consultation with the owner. The existing evidence suggests that the most common procedures, ventral midline OVH and OVE, are safe and effective in achieving the goals of spay for most pets. Other procedures can be considered in select cases and with an awareness of their relative advantages and disadvantages. A thorough understanding of the options and the risks and benefits of each can help us to effectively counsel and educate our clients.
Dr. McKenzie discovered evidence-based veterinary medicine after attending the University of Pennsylvania School of Veterinary Medicine and working as a small animal general practice veterinarian. He has served as president of the Evidence-Based Veterinary Medicine Association and reaches out to the public through his SkeptVet blog, the Science-Based Medicine blog, and more. He is certified in medical acupuncture for veterinarians.
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