Benefits and risks of neutering pets – what is the evidence – Effect of neutering on disease risk

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Effect of neutering on disease risk

Published 27 November 2020

While the effect of neutering on the risk of certain disease conditions has been known for a long time, particularly in terms of reducing disease directly associated with the reproductive tract, recent published evidence has provided more detailed evidence regarding the size of the effect and shown that the removal of reproductive hormones can have wide ranging effects on the body.

While research papers normally report on the risks (positive and negative) of neutering in relation to a particular disease, it is important to consider the overall effect on the animal in terms of overall lifespan, which combine the risks from multiple causes. It is also important to be aware of confounding factors, such as age.

Longevity

Mammary tumours

The beneficial effect of timing of spaying on the incidence of mammary tumours has been widely taught and accepted. However, for a long time this advice appears to have been based on evidence from a single paper published in 1969. A systematic review published in 2012 concluded that “Due to the limited evidence available and the risk of bias in the published results, the evidence that neutering reduces the risk of mammary neoplasia, and the evidence that age at neutering has an effect, are judged to be weak and are not a sound basis for firm recommendations.”

  • Schneider, R., Dorn, C.R. and Taylor, D.O.N. (1969) Factors influencing canine mammary cancer development and postsurgical survival. Journal of the National Cancer Institute, 43 (6), pp. 1249-126 https://doi.org/10.1093/jnci/43.6.1249
  • Beauvais, W., Cardwell, J.M. and Brodbelt, D.C. (2012) The effect of neutering on the risk of mammary tumours in dogs—a systematic review. Journal of Small Animal Practice, 53 (6), pp. 314-322 https://doi.org/10.1111/j.1748-5827.2011.01220.x
  • Stavisky, J. and Wareham, K. (2018) Age at neutering and mammary tumours in bitches [BestBETs for Vets][online] Available from: https://bestbetsforvets.org/bet/144 [Accessed 20 November 2020]
  • Egenvall, A. et al. (2005) Incidence of and survival after mammary tumors in a population of over 80,000 insured female dogs in Sweden from 1995 to 2002. Preventive Veterinary Medicine, 69 (1-2), pp. 109-127 https://doi.org/10.1016/j.prevetmed.2005.01.014

As well as questions about the benefit of neutering on preventing mammary tumours, questions also arise about whether ovariohysterectomy at the time of mammary tumour removal is beneficial.

  • Kristiansen, V.M. et al. (2013) Effect of ovariohysterectomy at the time of tumor removal in dogs with benign mammary tumors and hyperplastic lesions: a randomized controlled clinical trial. Journal of Veterinary Internal Medicine, 27 (4), pp. 935-942 https://doi.org/10.1111/jvim.12110
  • Kristiansen, V.M. et al. (2016) Effect of ovariohysterectomy at the time of tumor removal in dogs with mammary carcinomas: a randomized controlled trial. Journal of Veterinary Internal Medicine, 30 (1), pp. 230-241 https://doi.org/10.1111/jvim.13812
  • Overley, B. et al. (2005) Association between ovarihysterectomy and feline mammary carcinoma. Journal of Veterinary Internal Medicine, 19 (4), pp. 560-563 https://doi.org/10.1111/j.1939-1676.2005.tb02727.x

Pyometra

Surgical ovariohysterectomy is considered the safest and most effective treatment, as the source of infection is removed, and recurrence prevented. Medical treatment can be an alternative in young and otherwise healthy breeding animals with open cervix and without other uterine or ovarian pathologies.

Medical treatment of pyometra

Prostatic disease

While experimental studies have demonstrated the effect of testosterone (and therefore the protective effect of castration) on the development of benign prostatic hyperplasia more recent epidemiological studies have demonstrated an increased incidence of prostatic carcinoma in castrated dogs. It may therefore be necessary to weigh the relative risks of different prostatic diseases in making recommendations for an individual dog.

Other

  • Sundburg, C.R, (2016) Gonadectomy effects on the risk of immune disorders in the dog: a retrospective study. BMC Veterinary Research, 12, 278 https://doi.org/10.1186/s12917-016-0911-5
  • Florey, J., Ewen, V. and Syme, H. (2017) Association between cystine urolithiasis and neuter status of dogs within the UK. Journal of Small Animal Practice, 58 (9), pp. 531-535. https://doi.org/10.1111/jsap.12707
  • Smith, A.N. (2014) The role of neutering in cancer development. Veterinary Clinics of North America: Small Animal Practice, 44 (5), pp. 965-975 https://doi.org/10.1016/j.cvsm.2014.06.003
  • Polton, G.A. (2006) Breed, gender and neutering status of British dogs with anal sac gland carcinomaVeterinary and Comparative Oncology, 4 (3), pp. 125-131 https://doi.org/10.1111/j.1476-5829.2006.00100.x
  • Oberbauer, A.M., Belanger, J. and Famula, T.R. (2019) A review of the impact of neuter status on expression of inherited conditions in dogs. Frontiers in veterinary science, 6, p.397 https://doi.org/10.3389/fvets.2019.00397
  • Adams, P. (2011) Influence of signalment on developing cranial cruciate rupture in dogs in the UK. Journal of Small Animal Practice, 52 (7), pp. 347-352 https://doi.org/10.1111/j.1748-5827.2011.01073.x
  • Robinson, K.L. (2020) Neutering is associated with developing hemangiosarcoma in dogs in the Veterinary Medical Database: an age and time-period matched case-control study (1964-2003). The Canadian veterinary journal, 61 (5), pp.499-504. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7155881/
  • Perry, K.L., Fordham, A. and Arthurs, G.I. (2014) Effect of neutering and breed on femoral and tibial physeal closure times in male and female domestic cats. Journal of Feline Medicine and Surgery, 16 (2), pp. 149-156. https://doi.org/10.1177%2F1098612X13502977
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