Sterilising your pet Print E-mail
News - Rubrieke
Friday, 20 February 2015 00:44
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Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

The overpopulation of dogs and cats and the thousands which are euthanized each year, prompt all vets to recommend early sterilisation in non-pedigreed animals not earmarked for breeding.

Sterilisation is not without its risks and side-effects. I am going to discuss them, but to put them into perspective I will still recommend sterilisation of all bitches and most male dogs not of breeding stock, as the medical complication of not sterilising outweigh the complications that may occur because you sterilise.

Although the primary intention of a gonadectomy is to sterilize the pet, there are numerous health and other benefits. Bitches which have been sterilised do not attract males, are less likely to fight or cause fights, do not roam in search of a breeding partner and do not come on heat every six months, with all the attendant mess and inconvenience.  

The medical benefits of sterilisation in bitches include a decrease in the incidence of mammary neoplasia, with only a .05% risk if she is sterilised before her first heat cycle. Sterilisation also prevents ovarian and uterine neoplasia and infection of the uterus, which is a common and severe septic condition in intact females.

For owners of queens (intact female cats), the signs of heat can be quite bizarre and prompt veterinary advice due to strange behaviour such as calling and rolling. The period between heats in cats is only two weeks unless they are mated. The medical benefits are similar to those in dogs.

In male dogs, castration has numerous advantages in addition to sterilisation, mainly related to removal of the main source of testosterone. Castration controls urine marking in most males and reduces the tendency to roam in search of in-season bitches. A common misconception is that castration is highly effective in reducing aggressive behaviour in male dogs. Castration may reduce the aggression slightly, but other methods such as behavioural modification and training need to be explored
The medical benefits of castration are a decreased incidence of benign prostatic hyperplasia (BPH), testicular neoplasia and perianal tumours. Prostatic enlargement is the most common of these conditions and can occur in up to 75-80% of uncastrated dogs, six years and older.

Tomcats should definitely be sterilised if kept as pets due to their persistent habit of urine spraying, roaming and fighting, leading to  treatment for abscesses and an increased likelihood of contracting infectious diseases. Some people have postulated that early sterilisation of male cats increases their predisposition to developing urethral blockage from bladder stones, due to an underdeveloped urethra. This has not been proven in any medical study.

The behavioural benefits are numerous. Roaming in cats can be reduced in over 90% of cases and 70-80% of dogs have a reduction in roaming but only about 40% are completely resolved. Mounting of other animals, people or inanimate objects in dogs is reduced in 70-80% of cases but resolved in only 25%.

Castration reduces marking in about 70-80% of dogs but only about 40% are completely resolved. Marking by spraying urine is reduced in 90% of cats. Inter-male aggression can be reduced in about 60% of dogs and 90% in cats.

Aggression towards family dogs and family members may be reduced in about 30% of dogs. Aggression towards unfamiliar dogs and intruders may be reduced in 10-20% of dogs. Sterilisation will not decrease your pet’s ability as a watch dog, but will also not necessarily resolve behavioural problems which have become entrenched.

No procedure is ever 100% safe or has no side effects. There are some conditions which seem to result because of sterilisation. Surgical and post-surgical complications occur. These are reduced with the safer anaesthetics available these days, but they cannot be eliminated in a human medical system and with a patient who cannot be managed or told what not to do. Anaesthetic deaths occur, sometimes intra-operative haemorrhage can be severe, and patients will chew at their stitches.

An increased tendency towards obesity and obesity related conditions exists post-sterilisation. This is due to a reduced metabolic rate (up to 30%) which hasn’t been taken into account when feeding. This obesity can easily be managed with diet and exercise.

The next most common side effect of sterilisation is the development of urinary incontinence in bitches, especially large breeds, due to the relative lack of oestrogen, which normally acts to increase tone in the bladder neck and urethra. In some dogs this can occur within weeks of sterilisation but usually within two to three years.

There is probably also an anatomic component of bladder position within the pelvis, which also impacts on the degree of incontinence. Urinary incontinence occurs in 4-20% of spayed bitches and only 0–1% of intact  bitches. Obesity can worsen urinary incontinence.

Rupture of the knee ligaments is also slightly more likely in sterilised dogs, both male and female, as the ligaments seem slightly weaker without the effect of the sex hormones.

Thanks to Dr Feddie Hurley (Behavivet) and Dr Kurt de Cramer (Rant-en Dal vet) for use of their material


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