Updated: Nov 15
*This post is still being tweaked in regards to references in grammatical modification*
NOTE: Numbers in brackets denotes the reference which can be found in the reference section at the end of the article.
Neutering is a great topic of debate in our current society. For some, neutering is a no-brainer provided that you are not looking to breed from your dog; for others, it is an unnecessary procedure, which should not be done without reason. By just doing a quick google you will find a wide variety of opinions and reasonings. Traditional thinking that neutering prevents aggression in adult dogs is often at the forefront of many peoples minds, whilst others would argue that there is no true risk to neutering. With a range of conflicting and bias information, it can be difficult to determine what is fact and what is fiction. It can also be difficult to determine who to believe when even advice amongst vets can vary greatly.
To try and help you come to a conclusion of your own, I have looked into a wide range of scientific, peer reviewed research into the area of neutering. What this means is that every piece of research mentioned has been studied from a scientific standpoint, controlling many different factors to ensure that the results found are as accurate as possible. The aim of the article is to remain as objective as possible as I lay out these findings in a concise way. This will hopefully help you with your decision as to whether you want to neuter your dog or not.
The article will only focus on male neutering at this time and will not touch upon the female spay, this is because the findings in this area have significant differences which cannot be applied to both sexes. Due to this, I will be working on an article on female castration after this one.
Disclaimer: I am not a veterinary professional; therefore, I can only comment on the findings of the research to hand. Whilst I have tried to use up-to-date papers, I may also reference some older papers if I feel this is appropriate. I cannot give a conclusive statement as to whether you should neuter or not or at what age to do this but I can present the current available literature on the subject. If you are interested in the research papers, a reference list is provided at the end.
For anybody who has studied academia, you will know the pitfalls of research. Research has flaws due to methodology, samples and other variables. Throughout the article, I will attempt to pinpoint some obvious issues with particular research, but I will discuss this in general at the end.
Scientific research vs Anecdotal evidence
Scientific Research is conducted with a research question in mind. Samples of dogs are collected and controlled for a variety of differences known as variables. This helps to ensure that the results are as accurate as possible and help us to understand any trends and relationships between two things. These findings are then written and checked by a review board. These are a group of experts in the field who may have conducted other research on the same or similar topic. They look for any biases or problems with the way the study was carried out and then approve this for publications. These are then published in scientific journals for other researchers, medical & veterinary professionals and others who are interested in academia to read and understand the latest knowledge in the field. Scientific research is not always conclusive, there are often limitations such as sample size, variables that could not be controlled for or something else may have affected the results which hasn’t been accounted for.
Anecdotal evidence is that has been collected in a more casual nature. For example, this may be someone’s personal experience. This is what is often seen in regards to castration on forums, website articles and Facebook pages. This will often sound like “well my dogs have never been neutered and …..” or “well my dogs have always been neutered and….”. We need to take great care with this kind of information. Because this is more about personal experience, it is not clear whether these dogs would have experienced anything different if their castration status had been different. These samples are usually only a few dogs and it is impossible to assess what other factors were involved in these dogs lives to lead to the expressed outcome. Anecdotal evidence has its place. It can often be the basis that scientific research is based on. Enough people expressing a perceived link can often prompt a researcher to look into this in a more controlled way to see if there really is a link. The problem with anecdotal evidence is there is simply no way to know which anecdotal reports are accurate and which are not. It is not a reliable way to gain information about a medical & behavioural topic because there is no control of other potential factors when the observations were made. This means we cannot be sure what the cause of the observed outcome is.
The most obvious benefit of Neutering
One of the main (and most obvious) benefits to neutering is that by neutering your male dog, you take away the ability for them to reproduce. The risk of your male dog being the cause of an unwanted pregnancy becomes 0 after castration.
It is difficult to find exact figures on the total number of dogs who are euthanised in kennels each year due to lack of space but take a look at rescue pages and websites from around the country and you will see the number of dogs in need of new homes. For many rescues, kennels are full and there are waiting lists for dogs coming in. There are simply more dogs than there are homes for.
Many people worry that they are taking something away from their dog by not allowing them to be a parent. This isn’t how animals think. They have little concept of what could have been and for a dog who has never had a litter or been given an opportunity to tie with a bitch, they do not think that they are missing anything. Considering to breed has a huge financial consideration. Responsible breeding includes ensuring your dog will not pass on genetic conditions onto their offspring. Parents must have sound temperaments and a clean bill of health. For many breeds, this includes expensive testing. I won’t get into the many different cost factors of breeding BUT there is no denying that neutering completely eliminates the risk of any unexpected litters and therefore the financial fallout from this.
For those who do not intend to responsibly breed from their dog, the advice has always been to neuter to prevent the risk of such accidental litters. For multi-dog households which may contain an unspayed bitch, careful management may be something that owners just don’t want to deal with. On top of this, having a bitch in heat in the same house may lead to great stress and frustration for the intact male(37) which can lead to destruction and other unwanted behaviours. The reasons listed above are usually the main consideration when thinking about castration but there are also behaviour and medical effects of neutering. This is what we will be focussing on for the remainder of this article.
A note on alternatives
Something that many owners have not heard about is the canine vasectomy. This is where the testicles are kept intact and instead a small incision is made to cut the tubes. The benefits of this is that the dogs levels of testosterone remain unchanged but the dog is still unable to reproduce. This is no common procedure, however it is gaining more ground. This is something I will be looking into over the coming weeks/months and will hopefully write another article on comparing the two. For now though, I will focus only on the full castration.
Behavioural Benefits of Neutering
As mentioned above, one of the behavioural benefits of neutering can be seen if the dog lives in a multi-dog household with an uncastrated female. For a male dog, this can cause high levels of stress and frustration, leading to undesirable behaviours. Neutering may solve these urges to mate with any household bitches and ensure that unexpected tie does not occur.
Another possible benefit of neutering is to avoid the unwanted attention of neutered males. Whilst the research in this area is scarce, some studies have shown that intact males draw the unwanted attention of neutered males. Neutered males also appear more likley to respond negatively to a neutered male(38). This means that, for those concerned about unwanted attention from other dogs, castration may help with this. In addition, this may prevent your dog experiencing a negative encounter from a neutered male. It must be noted here that this is something that has been highly understudied. It is not yet understood why this would occur between a neutered and intact male. This is one of those topics which has a far greater amount of anecdotal information over any scientific fact. In the training world, this phenomenon is greatly discussed and pondered, yet there are still very little hard facts about this kind of behaviour.
Another behavioural change which is often a factored in to a decision to castrate Is trainability. This is something that has been investigated to assess whether there is any difference between the neutered and unneutered male. Owners were asked to complete a set of questionnaires to assess how “trainable” they found their dogs to be. Those who were neutered scored higher for trainability compared to those who remained intact(1).
This was also found to be the case when researchers studied a group of Shetland sheepdogs and Rottweilers however when this was extrapolated onto other breeds, the same results could not be found(4). Instead, no difference was found between the neutered and intact males. Because of this, it is possible that trainability may be affected through castration, however this may be specific to certain breeds and not others. This is something which would benefit from greater research in the area.
Sexually driven behaviours such as mounting, marking and roaming have all been traditional reasons for neutering. In regard to marking behaviours, older research found that marking, mounting and roaming behaviours could all be reduced through the neutering of the male dog. This is because a reduction in the sex hormone, testosterone, can lead to a desire to continue these sexually driven behaviours(2). When looking at marking behaviours specifically, more recent research has suggested that intact males were more persistent when wanting to mark over a female scent. This suggests that this is a sexually driven behaviour which neutering help reduce. It must be noted, however, that when looking at marking behaviours of intact dogs on the whole, they did not mark any more than those who were neutered. It was simply that they would mark more over a female scent(3). In regards to roaming, it has been suggested that neutering may reduce these behaviours in 90% of cases(3).
For dogs who display aggression prior to neutering, castration may decrease aggression(2). The limitation of this is that this was found in less than 20% of the cases studied by and other research has suggested an opposite effect (more on this later). However, according to questionnaires which were given to owners, marking, mounting and aggressive behaviours were all reduced in around 50-60% of cases when these behaviours were present prior to neutering(6).
We must take care when we are looking at owner questionnaires as there is no standard for these behaviours to be compared to. What I mean by this is that one owners perception of aggressive behaviour may have been very different to another which may have shown a very different effect. This may be the same with marking behaviours with one owner referring to only outdoor marking and another referring to indoor marking. This can lead to results which are difficult to group together and compare.
Castration was found to be effective in decreasing dog aggression that was already present in some dogs, however this was estimated to only result in improvement in less than one third of cases. In addition to this, this had little effect when aggression was due to fear of inanimate objects or unfamiliar people(2). What this means is that whilst it was not found to prevent a dog becoming aggressive in the first place, neutering may help reduce aggression which is already present. The key point to note here is that it did not in 2/3 cases and in some of these cases, the aggression became worse (more on this later).
When looking at 636 dog bites which were reported to animal control, risk factors association with biting were having a purebred status and being an intact male. Other significant factors were having an income lower than in $41,000(26). You may be wondering why income is included here. This is noted as it is a perfect example of how other factors can statistically lead to an increased risk of an aggressive display. A low income does not guarantee a dog bite because they are not directly cause one another but instead, owners who are on a lower income may not pay for formal training or behaviour modification before a bite occurs, may be less likley to seek medical intervention and help or may not be able to afford costly day-care and dog walkers whilst out at work leading to under socialisation. When reading through the research, this is something to keep in mind. Just because there is a link found between neutering and “xyz”, it does not mean that these were directly caused or cured by neutering. This is why its so important to look at all the other factors at play before we come to a final conclusion.
Behavioural Drawbacks of Neutering
A piece of research published last year found that when studying a group of neutered and unneutered dogs, neutered dogs were seen as more “emotionally unstable” in stressful situations. It was suggested that they had a greater inability to cope with stress compared to their intact counterparts. This lead to an increased chance in fear fuelled aggressive behaviours and a reduced display of social behaviours(1). In addition to this, intact males were found to be more sociable and confident compared with their neutered male counterparts.
Whilst we mentioned previously about intact males drawing the attention of neutered males, neutered males may also draw more social attention from intact males(1). The issue that was found with this was that the neutered males were less comfortable with this added attention than their intact counterparts with aggression seen more frequently among the castrated dogs. In addition to this, 15 out of 17 neutered males displayed some level of anxiety whilst out on a walk compared to only 5 Intact males. The traditional view was that intact males were more likley to display aggression but a trend in both research(38) and anecdotal accounts find that this may not be the case. In a large sample study, it was found that aggression & anxiety was seen