Should I neuter my pet?

It’s always a tricky decision when it comes to deciding whether your cute bundle of fluff should be given the chance of having a litter, or whether they should be neutered. I believe we should only do surgery when absolutely necessary (and then the minimum intervention possible) so how do we decide? In this article I’ll look at the procedure and the evidence of benefit and risk. It might be heavy going in places but hopefully answers all the questions!

Cats

The suffering caused by unwanted kittens outweighs any effect in the individual, so unless you’re a breeder then neuter them! At 12 weeks old for preference 🙂 And if you don’t neuter then someone’s having kittens!

Dogs

Males (Castration)

Why do it?

  • Less likely to roam
  • Stops production of male dog pheromones so less likely to be challenged by other males when out. The result is a calmer dog
  • Reduces likelihood of cocking leg to scent mark
  • Reduces occurence of other secondary sexual behaviours such as “humping”

How is it done?

Usually through an incision in front of the scrotum. There’s a 10 day healing time, and the main operative risk is intra-scrotal bleeding (approx 1 in 100). Some vets and owners prefer to remove the scrotum too (scrotal ablation). There is an implant (Suprelorin) which causes all the effects of surgical castration and lasts 6 – 24 months depending on implant strength.

What age should it be done?

We advise castration when the dog achieves musculoskeletal maturity between 6 and 18 months old. The smaller the breed of dog, the earlier in the range, and vice versa for larger. So a Great Dane should be neutered no earlier than 18 months, but a Yorkie from 6 months. It’s all to do with bone growth plate closure; castration delays closure so can lead to problems in larger breed dogs.

Females (Spaying)

Why do it?

  • Stops bleeding during seasons
  • Stops risk of pyometra (infected uterus) in later life. Risk of pyometra in unspayed bitches over 10 years is approximately 1 in 4 and the death rate from surgery to fix a pyometra is 1 in 25, so overall risk of death from a pyometra in an unspayed bitch over 10 is 1 in 100. Overall risk of death during a spay op is less than 1 in 1,000.
  • Reduces likelihood of developing mammary cancer
  • Stops male dogs pestering your bitch when on walks, at shows, when working etc.

How is it done?

Usually through an incision in the abdomen. Either only the ovaries are taken out (ovariectomy or OVE), or the ovaries + fallopian tubes + womb is removed (ovariohysterectomy or OVH). See my video for the evidence base on OVE vs OVH. We find OVE is technically more challenging but safer (doesn’t go near large arteries near the cervix), is less painful and less likely to cause post op problems due to smaller size of wound. OVE can also be done through keyhole surgery (laparoscopic OVE) which lessens pain, post op problems and risk even further.

What age should it be done?

There is no evidence that letting your bitch have a season influences the development of urinary incontinence later in life UNLESS your bitch develops a urinary tract infection before the first season. However, neutering (spaying) before the second season significantly reduces the risk of developing mammary cancer in later life.

Effect of neutering on disease:

ConditionFemaleMale
LifespanMild increase in lifespanMild increase in lifespan
ObesityModerate increaseModerate increase
Cranial cruciate ligament diseaseModerate increaseModerate increase
Hip dysplasiaMild increaseMild increase
Mammary tumoursMarked decreaseN/A
Uterine, ovarian, vaginal tumoursPreventsN/A
Testicular tumoursN/APrevents
Perianal gland tumoursN/AMarked decrease
Prostatic carcinomaN/AMild increase
LymphomaMild increaseMild increase
Mast cell tumorsMild increaseN/A
HemangiosarcomaMild increaseMild increase
OsteosarcomaMild increaseMild increase
Transitional cell carcinomaMild increaseMild increase
Urinary sphincter mechanism incompetenceModerate increaseN/A
CystitisMild increaseN/A
Benign prostatic hyperplasiaN/AMarked decrease
Perineal herniaN/AModerate decrease

Evidence base

IMPORTANT- it is very important to understand that the risks quoted below are RELATIVE. i.e. a three times increase in the risk of developing a rare cancer still means it is RARE! You and your vets have to consider the ABSOLUTE risk numbers vs the risk of not getting your pet neutered.

Obesity

Can be an issue but usually easily controlled through diet and a reduction in overall calories.

Lefebvre SL, Yang M, Wang M, Elliott DA, Buff PR, Lund EM. Effect of age at Neutering on the probability of dogs becoming overweight. JAVMA. 2013;243(2):236-243.
McGreevy PD, Thomson PC, Pride C, Fawcett A, Grassi T, Jones B. Prevalence of obesity in dogs examined by Australian veterinary practices and the risk factors involved. Vet Rec. 2005;156(22):695-702.
Courcier EA, Thomson RM, Mellor DJ, Yam PS. An epidemiological study of environmental factors associated with canine obesity. J Small Anim Pract. 2010;51(7):362-367.

Cranial cruciate ligament disease (CCL rupture)

Large breed dogs that were neutered before 6 months old had x3 risk of rupturing their CCL. In a study of 750 Golden Retrievers, none of the intact dogs had CCL disease, compared with an incidence of 5% in castrated dogs and 7.7% in spayed dogs that underwent neutering at <12 months of age. Change in confirmation, not weight, was responsible.

Duerr FM, Duncan CG, Savicky RS, Park RD, Egger EL, Palmer RH. Risk factors for excessive tibial plateau angle in large-breed dogs with cranial cruciate ligament disease. JAVMA. 2007;231(11):1688-1691.

Hip dysplasia

Males neutered at less than 12 months have a 20% increased risk of developing hip dysplasia

Witsberger TH, Villamil JA, Schultz LG, Hahn AW, Cook JL. Prevalence of and risk factors for hip dysplasia and cranial cruciate ligament deficiency in dogs. JAVMA. 2008;232(12):1818-1824.

Mammary tumours

Spaying before the second season reduces the risk of developing mammary cancer in later life from 3 in 100 to between 1 in 10,000 (before first season) and 1 in 1,000 (before second season).

Schneider R, Dorn CR, Taylor DO. Factors influencing canine mammary cancer development and postsurgical survival. J Natl Cancer Inst. 1969;43(6):1249-1261.
Sonnenschein EG, Glickman LT, Goldschmidt MH, McKee LJ. Body conformation, diet, and risk of breast cancer in pet dogs:a case-control study. Am J Epidemiol. 1991;133(7):694-703.
Beauvais W, Cardwell JM, Brodbelt DC. The effect of neutering on the risk of mammary tumours in dogs: a systematic review. J Small Anim Pract. 2012;53(6):314-322.
Egenvall A, Bonnett BN, Ohagen P, Olson P, Hedhammar A, von Euler H. Incidence of and survival after mammary tumors in a population of over 80 000 insured female dogs in Sweden from 1995 to 2002. Prev Vet Med. 2005;69(1-2):109-127.
Brønden LB, Nielsen SS, Toft N, Kristensen AT. Data from the Danish veterinary cancer registry on the occurrence and distribution of neoplasms in dogs in Denmark. Vet Rec. 2010;166(19):586-590.
Benjamin SA, Lee AC, Saunders WJ. Classification and behavior of canine mammary epithelial neoplasms based on life-span observations in beagles. Vet Pathol. 1999;36(5):423-436.

Uterine, ovarian, vaginal tumours

Spaying either stops or reduces the risk of these cancers.

Smith AN. The role of neutering in cancer development. Vet Clin North Am Small Anim Pract. 2014;44(5):965-975

Testicular, perianal and prostatic tumours

Stops testicular cancer as no testicles are present!

Benign prostatic hyperplasia is seen in half of intact males by 5 years of age. Castration prevents benign prostatic hyperplasia as well as other associated diseases (eg, prostatitis, prostatic cysts, perineal herniation). However, late castration is usually curative, as it is with most testicular cancer. Some studies suggest that castration INCREASES the risk of prostatic cancer two to eight fold (from 1 in 200 to 1 in 50!)

Teske E, Naan EC, van Dijk EM, Van Garderen E, Schalken JA. Canine prostate carcinoma: epidemiological evidence of an increased risk in castrated dogs. Mol Cell Endocrinol. 2002;197(1-2):251-255.
Bryan JN, Keeler MR, Henry CJ, Bryan ME, Hahn AW, Caldwell CW. A population study of neutering status as a risk factor for canine prostate cancer. Prostate. 2007;67(11):1174-1181.
Cornell KK, Bostwick DG, Cooley DM, et al. Clinical and pathologic aspects of spontaneous canine prostate carcinoma: a retrospective analysis of 76 cases. Prostate. 2000;45(2):173-183.

Lymphoma

Intact female dogs have a significantly lower risk for developing lymphoma as compared with neutered female or male dogs.

Villamil JA, Henry CJ, Hahn AW, et al. Hormonal and sex impact on the epidemiology of canine lymphoma. J Cancer Epidemiol. 2009:591753.

Mast cell tumours

Neutering has been associated with 2× to 4× the risk for mast cell tumoors, particularly in female dogs.

Zink MC, Farhoody P, Elser SE, et al. Evaluation of the risk and age of onset of cancer and behavioral disorders in gonadectomized Vizslas. JAVMA. 2014;244(3):309-319.
White CR, Hohenhaus AE, Kelsey J, Procter-Gray E. Cutaneous MCTs: associations with spay/neuter status, breed, body size, and phylogenetic cluster. JAAHA. 2011;47:210-216.

Haemangiosarcoma

Golden retrievers that underwent OHE after 1 year of age had 4× the incidence of haemangiosarcoma as compared with intact females or females that underwent OHE before 1 year of age. No significant differences in incidence of haemangiosarcoma were found in male Golden Retrievers.

Torres de la Riva G, Hart BL, Farver TB, et al. Neutering dogs: effects on joint disorders and cancers in golden retrievers. PLoS One. 2013;8(2):e55937.

Osteosarcoma

Historic studies have reported a 1.3× to 1.9× increased risk for osteosarcoma in animals that underwent neutering at a non-specified age.

Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters DJ. Endogenous gonadal hormone exposure and bone sarcoma risk. Cancer Epidemiol Biomarkers Prev. 2002;11(11):1434-1440.
Priester WA, McKay FW. The occurrence of tumors in domestic animals. Natl Cancer Inst Monogr. 1980;(54):1-210.

Transitional cell carcinoma

Female dogs are predisposed to bladder transitional cell carcinoma compared to male dogs. Neutering (at a non-specified age) increases the risk up to 3× in both male and female dogs.

Norris AM, Laing EJ, Valli VE, et al. Canine bladder and urethral tumors: a retrospective study of 115 cases (1980-1985). JVIM. 1992;6(3):145-153.
Mutsaers AJ, Widmer WR, Knapp DW. Canine transitional cell carcinoma. JVIM. 2003;17(2):136-144.

Incontinence – Urinary sphincter mechanism incompetence (USMI)

Studies have a variety of outcomes, but the key paper is “The effect of neutering on the risk of urinary incontinence in bitches – a systematic review”.

Of 1,853 records screened, seven studies were identified that examined the effect of neutering or age at neutering on the risk of urinary incontinence but four were judged to be at high risk of bias. Of the remaining three studies, which were at moderate risk of bias, there was some weak evidence that neutering, particularly before the age of three months, increases the risk of urinary incontinence. However, overall the evidence is not consistent nor strong enough to make firm recommendations on the effect of neutering or age at neutering on the risk of urinary incontinence.

The evidence for a relationship between neutering and urinary incontinence is weak, although there is some evidence of an association. There is some weak evidence that the risk of urinary incontinence decreases as the age at spay increases, up to 12 months of age, after which there is no evidence of an effect of age at spay. There was no direct evidence found in this review that the occurrence or absence of oestrous [season] before neutering plays a role in the cause of urinary incontinence.

Beauvais W, Cardwell JM, Brodbelt DC.The effect of neutering on the risk of urinary incontinence in bitches – a systematic review.J Small Anim Pract. 2012 Apr;53(4):198-204.
Forsee KM, Davis GJ, Mouat EE, Salmeri KR, Bastian RP. Evaluation of the prevalence of urinary incontinence in spayed female dogs: 566 cases (2003-2008). JAVMA. 2013;242(7):959-962.
Stöcklin-Gautschi NM, Hässig M, Reichler IM, Hubler M, Arnold S. The relationship of urinary incontinence to early spaying in bitches. J Reprod Fertil Suppl. 2001;57:233-236.
Beauvais W, Cardwell JM, Brodbelt DC. The effect of neutering on the risk of urinary incontinence in bitches: a systematic review. J Small Anim Pract. 2012;53(4):198-204.
de Bleser B, Brodbelt DC, Gregory NG, Martinez TA. The association between acquired urinary sphincter mechanism incompetence in bitches and early spaying: a case-control study. Vet J. 2011;187(1):42-47.

Cystitis

There is a greater risk of cystitis in bitches undergoing OHE before 5 months old.

Spain CV, Scarlett JM, Houpt KA. Long-term risks and benefits of early-age Neutering in dogs. JAVMA. 2004;224(3):380-387.

Perineal hernia

Castration significantly decreases the risk of perineal hernia

Mann FA, Nonneman DJ, Pope ER, Boothe HW, Welshons WV, Ganjam VK. Androgen receptors in the pelvic diaphragm muscles of dogs with and without perineal hernia. Am J Vet Res. 1995;56(1):134-139.
12Snell WL, Orsher RJ, Larenza-Menzies MP, Popovitch CA. Comparison of caudal and pre-scrotal castration for management of perineal hernia in dogs between 2004 and 2014. N Z Vet J. 2015;63(5):272-275.