Neutering in dogs - commonly performed but not necessarily routine

BSc BVMS PhD Cert SAS DECVS

VRH, Veterinary Referral Hospital, Melbourne, Australia

Abstract:

Historical attitudes towards gonadectomy (neutering) of both male and female dogs have frequently been based on personal opinion and individual veterinary practice policy. For many veterinarians and affiliated personnel, the primary motivation for neutering is to reduce unwanted pregnancies. However, compulsory neutering of privately owned animals has not been shown to substantially reduce unwanted dog and cat populations. Additionally the medical consequences of neutering have been shown to be both beneficial and detrimental. 

 

In the USA, United Kingdom and Australia neutering is routinely advised however two questions have become increasingly asked:

1) should we neuter client owned pets and

2) if we do at what age should we perform the procedure.

 

The answer to these questions can no longer be provided by a standardised protocol and hence a holistic approach is required. 

 

Should we neuter client owned dogs? 

The decision to neuter a pet needs to be based on a comprehensive discussion that acknowledges both the medical and social benefits as well as the potential detrimental affects of the procedure.

Advantages – Female 

  • Avoids unplanned pregnancy / unwanted puppies 

  • Removes unwanted social impact of oestrus 

  • Removes sexually dimorphic aggression 

  • Nullify risk of mammary tumours (prior to first oestrus) 

  • Decreased risk of mammary tumour (older bitches) compared to intact female 

  • Increased survival if used as adjunct therapy for mammary carcinoma 

  • Eliminates risk of pyometra 

  • Prevents ovarian neoplasia 

  • Eliminates vaginal hyperplasia, vaginal prolapse, cystic endometrial hyperplasia 

Disadvantages - Female 

  • Increased risk of transitional cell carcinoma, osteosarcoma (2 – 4 X)1,2 

  • and Mast Cell Tumour (4X)3 compared to intact female 

  • Increased risk of haemangiosarcoma (2 – 4X)4,5,6 in late neutering compared to early neutering or intact females 

  • Increased risk of hypothyroidism 

  • Potential for obesity 

  • Increased risk for urinary incontinence due to urethral sphincter mechanism incompetence particularly early neutering 

  • Increased risk cruciate disease (2-3X or 7% vs 0%)6,7 particularly early neutering compared to intact or late neutering when early neutering is defined as prior to 12 months of age. 

Advantages – Male 

  • Prevents sexually dimorphic aggression 

  • Prevents benign prostatic hyperplasia and associated prostatitis 

  • Decreased risk of perineal rupture / hernia 

  • Prevents testicular neoplasia 

Disadvantages – Male 

  • Increased risk of hip dysplasia (10 – 17% neutered incidence vs 5% intact)6,7 (particularly early neutering which is greater than late neutering which is greater than intact male when early neutering is defined as prior to 12 months of age. 

  • Increased risk of cruciate disease (2-3X or 5% neutered vs 0% intact)6,7 with early neutering compared to intact or late neutering 

  • Increased risk of lymphoma (3X)6 with early neutering compared to late neutering or intact males 

  • Increased risk of prostate carcinoma (4X)8 

  • Increased risk osteosarcoma (2-4X)1,2 

 

With regards to the risk of developing (or not developing) a neoplastic disease it is important to recognise that the data is frequently represented as an odds ratio. This indicates that one population of patient is more at risk of a disease than another (e.g. neutered vs entire) as a multiple (e.g. 2 times more at risk). In many circumstances the risk is inherently low e.g 5% vs 10% (equivalent to a 2X risk) and hence the discussion must be kept within context of the risk. Additionally it does not indicate that neutering status is a cause of disease or that a specific population (e.g. entire dogs) is free of the disease. It is also important to acknowledge that the data is sourced from publications with varying sample sizes and hence has to be interpreted accordingly. 

At what age and when should we perform gonadectomy? 

Early neutering vs older 

 

Early neutering generally around 8 weeks of age is frequently suggested and performed by animal shelter / rescue groups for the purpose of accelerating the animal rehoming process and reducing the potential for unplanned pregnancy. The role of early neutering is generally restricted to shelter animals. Short term studies have demonstrated that early gonadectomy is safe and long term studies exist which suggest that there are no detrimental affects associated with early neutering. 

Within client owned pets gonadectomy from 5 ½ months to 6 months is frequently advised to avoid owners having to manage oestrus or pets developing unwanted sexually based behaviours. However, as discussed early neutering influences risks of developing orthopaedic disease, urinary incontinence and has a variable influence of the risk of specific neoplastic disease. As a result the age of gonadectomy should be based on the owners requirements and the pets inherent risks. For example, in at risk breed for urinary incontinence (German shepherd, Rottweiler, Doberman pinscher, Old English sheepdog, Boxer, English springer spaniel, Weimaraner, Irish setter) it would be ideal to delay the age of gonadectomy until after 1 - 2 oestrus cycles. Alternatively a large breed dog that is at risk of hip dysplasia or cruciate disease it would be appropriate to consider delaying or avoiding gonadectomy. 

If a decision is made to perform gonadectomy, for female dogs, gonadectomy is ideally performed during anoestrus. Gonadectomy in metoestrus can result in chronic pseudopregnancy. Typically it is advised to wait at least 5 weeks from the end of oestrus however it is ideal to wait 3 – 4 months. 

Gonadectomy is contra-indicated in bitches suffering pseudopregnancy as progesterone suppresses prolactin which causes pseudopregnacy. Removal of gonads results in a rapid clearance of progesterone.

For bitches following parturition, most recommend ovariohysterectomy when puppies weaned at 6 – 8 weeks. Traditional theory suggests ovariohysterectomy at time of ceasarian adds stress, increases anaesthesia time and can result in increased blood loss and cardiovascular compromise. This is supported by one retrospective study showing longer hospital stays and increased post operative complications. However, enbloc ovariohysterectomy as an alternative to caesarean section has been shown to have no difference in neonatal survival and did not show significant findings in the dams cardiovascular function. 

It is occasionally suggested that gonadectomy will influence milk production if performed at the time of caesarean. The principal lactogenic hormone, prolactin, is secreted by the anterior pituitary and is critical to the establishment of lactation with concentrations of circulating prolactin increasing during pregnancy. However, prolactin is prevented from exerting its effect on milk secretion by elevated levels of progesterone. Following clearance of progesterone and oestrogen at parturition, milk secretion begins. Gonadectomy results in clearance of progesterone and oestrogen and does not influence prolactin secretion. 

 

Options for neutering (male and female)

 

Ovariohysterectomy vs Ovariectomy 

Evidence suggests that ovariectomy requires smaller incisions, results in less surgical trauma and pain with no increase in complications. The onset of pyometra is dependent on the presence of progesterone and hence if complete removal of the ovary is performed and progesterone is not administered to the patient then pyometra will not develop following ovariectomy. 

Closed vs Open Castration 

Closed castration involves double ligation of the parietal tunic, cremaster muscle, ductus deferens and the spermatic vascular cord en bloc. Closed castration is typically reserved for immature and smaller dogs. 

Open castration involves an incision into the vaginal parietal tunic and then the parietal tunic, cremaster muscle, and ductus deferens and its vessels are separated from the spermatic vascular cord. The spermatic cord is separately ligated, the cremaster muscle, ductus deferens and its vessels separately ligated. Lastly the parietal tunic is ligated to close the peritoneal cavity. 

Avoiding complications associated with neutering 

Complications rates following ovariohysterectomy are surprisingly high (19% in one student of senior veterinary students) and hence is a procedure that should not be dismissed as low risk. Understanding the potential complications allows techniques to be adopted that decrease the risk of complications occurring.

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