Dogs and Neutering

Neutering your dog

Much misinformation exists about neutering dogs and bitches. I am often asked if neutering will help with behavioural problems, particularly in relation to male dogs. Most notably, people want to know if it will calm their adolescent dog down. They want to know if it will stop the dog mounting other dogs/people/furniture. Will it make them less aggressive? Stop guarding behaviour? Most people expect it will, and common wisdom states that 6 months is the appropriate age to neuter.

Last year I attended an insightful talk by veterinary behaviourist Caroline Warnes, which examined in depth the effects of neutering on canine behaviour, as well as the health implications of deciding to neuter or not to neuter. The talk was really an eye-opener for me, and I’d love to share some of what I learned, in the hope that it will help inform your decision when the time comes to decide whether or not, and if so, when to neuter your dog.

Health considerations

One reason people neuter their dogs is to avoid potential health problems in the future. According to Warnes, castrating a male dog will reduce the risk of:

  • Testicular tumours (although there is a less than 1% risk of a non-neutered dog dying from testicular cancer) or torsions;
  • Peri-anal adenomas and fistulas;
  • Benign prostatic hypertrophy (a benign increase in the size of the prostate);
  • Perineal hernias;
  • Possibly diabetes.

However, it increases the risk of :

  • Obesity;
  • Orthopaedic problems (especially if the procedure is carried out before puberty);
  • Prostate and urinary tract tumours;
  • Osteosarcoma (and this risk is doubled if the dog is neutered before he is one year old);
  • Age-related Cognitive Dysfunction (canine Alzheimers);
  • Hypothyroidism;
  • Splenic and cardiac haemangiosarcoma (a fast-growing cancer arising from the lining of blood vessels).

In female dogs, the situation is a little more complex. Spaying will reduce the risks of:

  • Mammary tumours, the most common malignant tumours in female dogs, especially if done before 2.5 year of age;
  • Pyometra (spaying almost eliminates the risk of this uterine infection, which kills 1% of non-neutered dogs, and affects around 23% of non-neutered dogs);
  • Peri-anal fistulas;
  • Uterine, cervical and ovarian tumours.

On the other hand, it increases the risk of:

  • Obesity;
  • Orthopaedic problems;
  • Osteosarcoma (the risk is doubled if she is neutered before one year of age);
  • Hypothyroidism;
  • Splenic and cardiac hemangiosarcoma and mast cell tumours (risk multiplied by 5);
  • Incontinence;
  • Urinary tract infection ( 3-4 times as common);
  • Recessed vulva, vaginal dermatitis and vaginitis, especially if spayed before puberty;
  • Urinary tract tumours (risk is doubled).

As you can see from the above, the affects of neutering on health are not as straightforward as one may have thought, and in male dogs especially, the risk of adverse affects may outweigh the perceived benefits. The other thing which is apparent from the above is that the health-related risks of early neutering are greater than the risks of neutering post-puberty.

Behavioural considerations

Warnes mentioned a 2010 study by Parvene Farhoody and M. Christine Zink in which a 101 question survey was used to collect information on 7 behavioural characteristics for over 10,000 dogs. The results showed that the behaviour of neutered dogs was significantly different to that of intact dogs, but not in the way that supports the prevailing view…

Neutered dogs were found to be more aggressive, fearful, excitable and less trainable than intact dogs. Although there is some limitations in this study, it still presents some thought-provoking findings.

One reason that neutering is not always an effective way of eliminating sexually dimorphic behaviours (i.e. behaviours that differ between the sexes, usually part of the reproductive repertoire) is that the male brain is masculinised before birth. Furthermore, testosterone is produced by the brain and adrenal glands as well as the testes, so removing the testes will not eliminate testosterone completely. And we cannot forget that behaviour is complicated and is influenced by other hormones, neurotransmitters and of course, learning.

Looking more explicitly at the effects of neutering on male dogs, Warnes referenced a study by Hart & Eckstein (1997) who summarised the findings of several other studies looking at the effect of castration on problem behaviours in dogs. They found that neutering resulted in:

  • a 90% reduction in roaming,
  • a 65% reduction in mounting,
  • a 60% reduction in fighting,
  • a 50% reduction in urine marking
  • a 30% reduction in aggression directed at the owner

However, neutering showed no marked reduction in fear aggression or territorial behaviour. The former might well be due to the fact that one of the effects of testosterone is to increase self-confidence. A dog who is showing aggressive behaviour out of fear, and whose confidence is reduced by the reduction of testosterone which results from neutering, may be likely to show an increase in that aggression.

Warnes pointed out that neutering was unlikely to be beneficial to dogs showing unruly, over-excitable adolescent behaviour or inappropriate predatory, herding or hunting behaviours. Furthermore, she highlighted the fact that neutering may be detrimental to dogs who are fearful or under confident.

In bitches, spaying can prevent behavioural problems associated with hormonal changes during the bitch’s season, including increased reactivity and arousal, urine marking, roaming in search of males, and competitive aggression towards other bitches which occurs when one or both are in season. It can also prevent pseudo-pregnancy, especially if the bitch is spayed before puberty. However, spaying can conversely also increase reactivity and aggression in some bitches.

Another particularly interesting aspect of Warnes’s talk, was her discussion of the possible androgenisation of female pups in the uterus. Some female dogs display male-typical behaviour, such as cocking their leg to urinate, urine marking, and increased aggression. Warnes discussed the possibility that these changes were a result of a female pup being subjected to increased levels of testosterone in the uterus as a result of being positioned in between two male pups. In these masculinised bitches, there is the chance that spaying will, by virtue of the fact that it will reduce the levels of female hormones, increase any aggression that was fuelled by the androgenising effects of testosterone in the womb.

In short…

Neutering plays an important role in the population control of dogs, and may be beneficial in dealing with certain behavioural issues.

But remember, neutering is not a fix-all solution for problem behaviours. In male dogs, while unlikely to have an adverse effect on behaviours (apart from in the case of dogs displaying fearful or under confident behaviour), it will not improve behaviours that are not affected by testosterone. It can potentially make some behaviours worse, such as fearful aggression, and there is some suggestion that neutering dogs before puberty may lead to the retention of adolescent behavioural characteristics, including excitability, short attention span and low attention threshold. The health-related risks of neutering may also outweigh the benefits.

In bitches, the health-related benefits of spaying generally outweigh the risks (although there are clear benefits to waiting until after puberty where possible). Apart from in the case of androgenised bitches, it is unlikely to have an adverse effect on behaviour, although it may result in the retention of adolescent behaviour if performed before puberty.

So, on the basis of what I learned at this seminar, my advice to clients now is to hold off on any decision about neutering until after puberty, at which point a decision should be made on a case-by-case basis.

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