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Surgical sterilisation of dogs and cats

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Ratification Date: 14 Jul 2022

Policy

Surgical sterilisation is an important tool to reduce unwanted dogs and cats in the community, particularly when combined with relevant community education programs.

Veterinarians should make recommendations about the type of sterilisation procedure and age of sterilisation on a case-by-case basis, in consultation with the client, based on the risks and benefits to the individual animal and current scientific evidence. Relevant regulations and registration requirements should be taken into account.

Background

Surgical sterilisation

There are a range of surgical procedures that may be performed in order to render an individual companion animal incapable of reproducing (sterilisation).  They are broadly divided into two categories:

  • Procedures which involve gonadectomy, including ovariohysterectomy (“spey”) or ovariectomy in females, and orchidectomy (“castration”) in males. The terms “desex” and “neuter” are usually used to refer to these full surgical procedures.
  • “Gonad-sparing” surgical sterilisation procedures are ovary-sparing hysterectomy or salpingectomy in the female, and vasectomy in the male.  These options are sometimes used to maintain the hormonal status of a dog, either temporarily or permanently, where an owner or veterinarian has concerns about developmental, health or behavioural impacts of gonadectomy. However, these options come with a range of potential risks to both male and female dogs (see below).

All surgical sterilisation techniques are major procedures, and the skills, equipment and facilities used should be of sufficient standard to reflect the needs of the animal. The surgeon should have the necessary competence and experience to perform the procedure. Veterinarians should ensure that all appropriate precautions are taken to minimise the risks of anaesthesia, surgery, stress and infection for animals undergoing desexing procedures.

Medical sterilisation

Reversible temporary medical sterilisation of male dogs is possible using an implant of Deslorelin, a gonadotropin releasing hormone (GnRH) agonist, replaced every 6-12 months.3 This alternative can also be offered to owners with concerns about health or behavioural impacts of gonadectomy, or those who want reproductive control without surgery or control of androgen-induced diseases, such as benign prostatic hyperplasia. However, medical means of fertility control are not permanent, and require reimplantation to maintain long-term infertility.

Risks and benefits of surgical sterilisation.
Surgical sterilisation is currently the only widely available, effective and permanent method of preventing breeding, and is strongly supported by the AVA as a means of dog and cat population control.

Benefits of desexing (with gonadectomy)

Traditional desexing with gonadectomy can reduce some behavioural problems in dogs such as free-ranging and some aggressive behaviours, which can otherwise cause public nuisance. In cats, it stops calling behaviour in queens, reduces spraying in toms, reduces fighting, abscesses and transmission of infectious diseases.

It is commonly accepted that gonadectomised female dogs have a greatly reduced incidence of mammary neoplasia if the procedure is performed from pre-puberty up to when one or two seasons have occurred.22,23 However, a review of the literature in 2012 advised “due to limited evidence available and the risk of bias in published results, evidence that the age of neutering has an effect (on the risk of mammary tumours in dogs) is judged to be weak and is not a sound basis for firm recommendations”.5 More research is needed in this area.

Desexing using traditional ovariohysterectomy or “spey” in female dogs and cats eliminates diseases of the ovaries and uterus. Gonadectomy in males eliminates testicular tumours, and reduces the incidence of prostate disease, perianal tumours and perineal hernias.

Potential health consequences of desexing (with gonadectomy)

There is increasing evidence that gonadectomy may increase risks of several conditions in dogs including orthopaedic diseases and neoplasia.17 Gonadal hormones influence reproductive, skeletal, physical and behavioural development in immature animals.16 Knowledge of the benefits and detriments of gonadectomy enables veterinarians to provide appropriate advice to clients to make informed decisions and promote animal health.17

Depending on the age at which gonadectomy is performed, potential adverse effects in the dog include increased risks of:

  • Obesity19,20,21
  • Under-development of external genitalia and the genital tract16,18
  • Urinary incontinence24,25
  • Prostatic carcinoma18,26
  • Osteosarcoma and other cancers in at least some breeds18,27,29,30
  • Musculoskeletal Diseases:
    • Hip dysplasia18,25,27
    • Cranial cruciate ligament18,27,28
    • Intervertebral disc disease31

The risks of gonadectomy should be weighed against the benefits, and decisions made on a case-by-case basis.  In some cases, there may be justification for gonad-sparing sterilisation initially, with subsequent review including consideration of gonadectomy once the animal has reached skeletal maturity.

Surgical risks

There are potential risks associated with all surgical sterilisation techniques, but vasectomies and ovary-sparing options in dogs have added risks. Vasectomy complications include development of spermatocoeles, sperm granulomas and testicular degeneration.1 Vasectomy does not change circulating hormonal (testosterone) levels, libido or other undesirable behaviours1 Ovary-sparing options  also come with a complex set of complications, including sperm peritonitis following unwanted mating when where the uterus has been retained, as well as the potential for a pyometra if uterine epithelium has been left in-situ.2

Age of sterilisation/desexing

Veterinarians must decide the appropriate age of sterilisation/desexing based on current scientific evidence, and consideration of the animal’s weight, vaccination status, health status and ability to withstand major surgery.

Cats

Prepubertal desexing (before 16 weeks) is particularly important in cats,7 which may be able to reproduce from 4 months of age. At the veterinary practitioner’s discretion, desexing of cats can be performed from as early as 8 weeks of age and at 1kg bodyweight.4 Current scientific evidence strongly supports desexing cats before puberty and finds that this does not increase the risk of short-term complications or long-term health effects. 4  A survey in 201210 identified that participating veterinarians had already reduced their age for desexing cats to on average 3.4 months for queens and 3.2 months for toms.

Dogs

Veterinarians may recommend sterilisation/desexing of dogs before puberty. Performing this sooner than the traditional age of 6 months may be recommended based on the likelihood of failure to comply by a percentage of owners at 6 months (including failure to redeem discount certificates) and /or puberty being possible prior to this age. Desexing before 6 months of age is commonly undertaken in the shelter situation. Results of a survey of Australian veterinarians in 2014 demonstrated a preference towards traditional (6 month) age desexing, but a willingness to perform desexing earlier in some situations. 

There are advantages and risks of early age desexing in dogs. Benefits include a faster surgery time, lower anaesthetic dose and faster healing.19 Recorded side effects of full desexing with gonadectomy include infantile external genitalia, delayed growth plate closure and the potential for associated orthopaedic conditions (including angular limb deformities, hip dysplasia, and cranial cruciate ligament disease). There is a statistically increased risk of urinary incontinence in the bitch if desexed (gonadectomy) before 20 weeks of age,24,25 plus evidence is emerging identifying some behavioural risks associated with age of desexing.35

There are currently two published papers assisting in the decision making on the age of desexing in dogs based on weight categories and breeds and corresponding risks of joint disorders and cancers, published by Hart et al from UC Davis.32,33 Future research will add to our understanding of the risks and benefits.   

Desexing as a population control measure
The success of sterilisation as a population control technique depends on the percentage of animals sterilised and the freedom of those remaining intact. It is unlikely to succeed as a single measure. 75% - 90% of breeding animals must be desexed to halt population increase.12,36

Problems with mandatory desexing of dogs and cats

There are inherent problems with the concept of mandatory desexing/sterilisation, and mandatory desexing of privately owned animals has not been shown to substantially reduce the unwanted dog and cat population to date. Successful enforcement of compliance would depend on universal registration and permanent identification, which have already proven difficult to enforce. Evidence suggests that, at least for cats, mandatory desexing of owned animals would have little effect on the cat population as the majority of over-supply emanates from the semi-owned and unowned populations11 

However, the desexing of unowned animals prior to rehoming is supported. Physical containment of an animal in oestrus is not recommended as an alternative to desexing.

Subsidised desexing schemes

Economic analysis suggests that low cost desexing schemes are effective at raising total community desexing rates, but previous studies show no clear impact on reducing the number of euthanasia cases.12  However, some more recent studies in cats have shown decreases in Council impoundments and euthanasias with these schemes.38,39  Although the desexing rates amongst owned cats is very high, overpopulation issues are predominantly in low socio-economic areas where cost is a barrier to desexing37 In areas with high levels of cat-related complaints, impoundments and shelter admissions, targeted, high intensity and free desexing campaigns can be effective in reducing the number of cats in target areas.38  Effects of such schemes must be assessed over a long period.34

Desexing in animal shelters
For animal shelters, desexing animals is influenced by legislative factors and the need to prevent breeding in adopted animals. Animal shelters should keep statistics on desexing status and desexing outcomes for shelter animals.

References

  1. Urfer SR and Kaeberlein M (2019). Desexing dogs: A Review of the Current Literature, Animals, 9 (12) 1086. Doi: 10.3390/ani9121086
  2. Kutzler M (2020) Gonad-Sparing Surgical Sterilization in Dogs. Frontiers in Veterinary Science, 7:342. Doi:10.3389/fvets.2020.00342
  3. Suprelorin APVMA label, 56107 and 60359
  4. RSPCA Australia Prepubertal Desexing Research Report June 2021. https://kb.rspca.org.au/wp-content/uploads/2018/11/2021-06-Pre-Pubertal-Desexing-Report.pdf
  5. Beauvais W, Cardwell JM, Brodbelt D.C. (2012) The Effect of Neutering on the Risk of Mammary Tumours in the dog – a Systematic Review. Royal Veterinary College Journal Small Animal Practice 53, 314-322
  6. Farnworth MJ et al. (2012) Veterinary Attitudes towards pre-pubertal gonadectomy of cats: a comparison of samples from New Zealand, Australia and the United Kingdom. NZ Vet Journal (12)
  7. Mazeau Loic, Wylie Claire, Boland Larc and Beatty Julia A. (2021) A Shift Towards Early Age Desexing of Cats under Veterinary Care in Australia. Scientific Reports 11, Article number 811
  8. Frank J M and Carlisle-Frank P L.(2007) Analysis of programs to reduce overpopulation of companion animals: Do Adoption and low-cost spay/neuter programs merely cause substitution of sources? Ecol. Econ.(62)740-746
  9. Headey B. (2006) National People & Pets Survey. Published by Australian Companion Animals Council.
  10. Leung V (2014) The View of Australian Veterinarians on the Age of Desexing of Dogs and Cats. Honours Dissertation University of Sydney.
  11. Marston L et al (2006): Cat Admissions to Melbourne Shelters, Report to Bureau of Animal Welfare. Dec2006.Access at http://www.ccac.net.au/files/Cat%20Admission%20to%20Melbourne%20Shelters...
    Viewed 17 Jan 2013
  12. Nasser R, Mosier J(1991).Projections of pet populations from census demographic data. J Am Vet Med Assoc 198:1157–1159
  13. Spain CV, Scarlett JM and Houpt KA (2004). Long-tern risks and benefits of early-age gonadectomy in dogs. J Am Vet Med Assoc 224: 380-387
  14. Urfer SR and Kaeberlein M (2019). Desexing Dogs: A Review of the Current Literature. Animals, 9(12) 1086. doi: 10.3390/ani9121086
  15. Kutzler, M (2020) Gonad-Sparing Surgical Sterilization in Dogs. Frontiers in Veterinary Science, 7:342. doi: 10.3389/fvets.2020.00342
  16. Salmeri K, Bloomberg, Scruggs S, et al. Gonadectomy in immature dogs: effects on skeletal, physical, and behavioral development. Journal of the American Veterinary Medical Association 1991;198:1193–1203.
  17. Kustritz M. Determining the optimal age for gonadectomy of dogs and cats. Journal of the American Veterinary Medical Association 2007;231:1665-1675.
  18. Reichler I. Gonadectomy in Cats and Dogs: A Review of Risks and Benefits. Reproduction in Domestic Animals 2009;44:29–35.
  19. Zwida K, Kutzler M. Non-Reproductive Long-Term Health Complications of Gonad Removal in  Dogs as Well as Possible Causal Relationships with Post-Gonadectomy  Elevated Luteinizing Hormone (LH) Concentrations. Journal of Etiology and Animal Health 2016;1:1-11.
  20. O’Farrell V, Peachey E. Behavioural effects of ovariohysterectomy on bitches. J Small Anim Pract 1990;31:595–598.
  21. Jeusette I, Detilleux J, Cuvelier C, et al. Ad libitum feeding following ovariectomy in female Beagle dogs: effect on maintenance energy requirement and on blood metabolites. J Anim Physiol An N 2004;88:117–121.
  22. Schneider R, Dorn C, Taylor D. Factors influencing canine mammary cancer development and postsurgical survival. Journal of the National Cancer Institute 1969;43:1249–1261.
  23. Overley B, Shofer FS, Goldschmidt MH, et al. Association between ovarihysterectomy and feline mammary carcinoma. Journal of veterinary internal medicine / American College of Veterinary Internal Medicine 2005;19:560–563.
  24. Reichler I, Hubler M. Urinary Incontinence in the Bitch: An Update. Reprod Domest Anim 2014;49:75–80.
  25. Spain VC, arlett J, Houpt KA. Long-term risks and benefits of early-age gonadectomy in dogs. Journal of the American Veterinary Medical Association 2004;224:380–387.
  26. Bryan JN, Keeler MR, Henry CJ, et al. A population study of neutering status as a risk factor for canine prostate cancer. The Prostate 2007;67:1174–1181.
  27. Belanger JM, Bellumori TP, Bannasch DL, et al. Correlation of neuter status and expression of heritable disorders. 2017;4:6.
  28. Slauterbeck J, Pankratz K, Xu K, et al. Canine Ovariohysterectomy and Orchiectomy Increases the Prevalence of ACL Injury. Clinical orthopaedics and related research 2004;429:301–305.
  29. Ru G, Terracini B, Glickman L. Host related risk factors for canine osteosarcoma. The Veterinary Journal 1998;156:31–39.
  30. Cooley DM, Beranek BC, Schlittler DL, et al. Endogenous gonadal hormone exposure and bone sarcoma risk. Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology 2002;11:1434–1440.
  31. Dorn, M. & Seath, I. J. Neuter status as a risk factor for canine intervertebral disc herniation (IVDH) in dachshunds: a retrospective cohort study. Canine Genetics and Epidemiology 5, 11 (2018).
  32. Hart, B. L., Hart, L. A., Thigpen, A. P. & Willits, N. H. Assisting Decision-Making on Age of Neutering for Mixed Breed Dogs of Five Weight Categories: Associated Joint Disorders and Cancers. Frontiers Vet Sci 7, 472 (2020).
  33. Hart, B. L., Hart, L. A., Thigpen, A. P. & Willits, N. H. Assisting Decision-Making on Age of Neutering for 35 Breeds of Dogs: Associated Joint Disorders, Cancers, and Urinary Incontinence. Frontiers Vet Sci 7, 388 (2020).
  34. Frank JM (2002) The Actual and Potential Contribution of Economics to Animal Welfare Issues. Society I Animals 10:4 http://society.org/assets/library/482_s10414.pdf
  35. McGreevy Paul D, Wilson Bethany, Starling Melissa J and Serpell James A. Behavioural Risks in Male Dogs with Minimal Lifetime Exposure to Gonadal Hormones May Complicate Population Control Benefits of Desexing. PLOS One 13 (5): e0196284 (May 2 2018)
  36. Boone JD, Miller PS, Briggs JR, Benka VAW, Lawler DF, Slater M, Levy JK and Zawistowski S. (2019) A Long-term Lens: Cumulative Impacts of Free Roaming Cat management Strategy and Intensity on Preventable Cat Mortalities. Front.Vet.Sci.6:238. Doi:10.3389/fvets.2019.00238
  37. Australian Pet Welfare League (APWF) 2021 End-year progress report Community Cat Program. https://petwelfare.org.au/wp-content/uploads/2022/02/Aust-Community-Cat-Program-Dec-2021.pdf
  38. 38. Cotterell J, Rand J and Ahmadabadi Z (2021) Outcomes associated with a community cat program based on high-intensity sterilisation of owned and semi-owned cats in target areas. WSAVA Global Community Congress November 2021.
  39. Banyule City Council. Submission No 141 to House Standing Committee on the Environment and Energy, Parliament of Australia, Inquiry into the problem of feral and domestic cats in Australia (2020)

Date of ratification by AVA Board 15 July 2022