Is there a ‘best’ time for neutering dogs or should we be neutering them at all?
Robert Falconer-Taylor BVetMed, DipCABT, MRCVS, Val Strong MSc and Professor Peter Neville – Centre of Applied Pet Ethology (COAPE)
Incontinence of the urinary bladder is a common complaint in spayed female dogs with a reported frequency of between 5 to 30% in smaller to larger breeds respectively. UK vets cite urinary incontinence as the second most common disadvantage of spaying, and for owners it is a condition that generally requires life-long treatment, with some dogs not responding at all well to the available medical treatments. A review of all the available evidence on spaying and urinary incontinence was published last year. The conclusions drawn from the accumulated data were that spaying does increase the incidence of urinary incontinence. There is evidence that the risk of urinary incontinence decreases as the age of spaying increases. There is no evidence that having a first season or not before spaying increases the risk of urinary incontinence. The authors caution however that overall the quality of the data is too weak to draw any strong conclusions either way and that more specific research is recommended.
A university study of recurring urinary tract infections, or cystitis, in 11,000 dogs found an increased incidence of the disease in spayed female dogs, but not in neutered male dogs. Other studies have found no such relationship with neuter status however.
Hypothyroid disease is a relatively rare disease of the thyroid gland found in around 0.25% of dogs that results in decreased levels of circulating thyroid hormone. A number of studies have found an increased incidence of the disease in neutered dogs compared with unneutered dogs, although other studies have found no such link.
A few studies have reported a higher instance of pancreatitis in neutered dogs. Although the true incidence of pancreatitis in dogs is not known, different surveys have yielded figures ranging from less than 1% to over 50%.
Tumours of the reproductive tract, including the ovaries, uterus and vagina are rare in dogs accounting for between 0.5% and 6% of all canine tumours, and clearly spaying a bitch reduces this risk to zero. Tumours of the vulva represent about 2% of all canine tumours and these occur most commonly in unspayed bitches.
The physiology of the bitch’s oestrus cycle predisposes nearly 30% of dogs to develop a pyometra, which is a post-oestrus infection of the uterus, at some time in their lives. Some breeds are more susceptible than others and of course the risk increases with age, or number of oestrus cycles experienced if you prefer. Pyometra can be effectively treated with medication in some cases, but spaying a bitch is the better option because it also prevents a recurrence of the disease. Both ovariectomy and ovariohysterectomy are equally effective.
Benign prostatic hyperplasia (BPH) is a progressive enlargement of the prostate gland with age. The incidence in intact dogs of less than 7 years of age ranges from 15% to 40%, while in older dogs the incidence climbs to 60% to 100%. Remember though that only some of these dogs will ever develop symptoms of the disease, which include abdominal pain and difficulties in urinating, sometimes with blood in the urine and possibly difficulties in defaecating as well. Prostatitis is an inflammation of the prostate gland and a much more serious disease with an occurrence of up to 28% in intact dogs. Castration is an effective prevention for both these diseases in most male dogs.
When it occurs prostate cancer in dogs is a very serious disease with an incidence rate of up to 13%, and 80% of these tumours are malignant and spread to other organs rapidly, which is usually fatal. The jury is still out as to whether castration increases, decreases, or has no influence on the predisposition for dogs to develop this disease.
In male dogs tumours of the testicles ranging from 16% to 25% of all tumours making them the second most common type of tumour. Testicles that have not descended into the scrotum are more likely to develop tumours and of course castration reduces this risk to zero.
Transitional cell carcinoma is a tumour with an incidence rate of between 1% and 2% and occurs primarily of the bladder but is sometimes found in the urethra as well. This tumour is more common in females and some studies report that spaying increases the risk of developing this cancer four-fold.
Some breeds of dogs such as Retrievers, Labradors and German Shepherd Dogs, are more likely to develop the aggressive tumour hemangiosarcoma most often in the spleen or the heart. A couple of studies have shown that spaying a bitch doubles her risk of developing the splenic form of this tumour and increases her risk by a factor of 5 for the cardiac form. Castrating male dogs has no such effect on this tumour
Mammary tumours are a common and serious disease, especially in intact bitches with the risk increasing with age, one study showing figures of 1% at 6 years rising to 6% at 8 years and to 13% at 10 years old. Just over half of all mammary tumours in dogs are malignant and in these cases surgery is generally the best treatment, sometimes alongside chemotherapy. However, up to 60% of dogs with malignant mammary tumours will die some short time later despite treatment because the tumour will have already spread to other vital organs of the body. Some studies have shown that spaying is hugely successful at reducing the risk of malignant mammary tumours and the time a bitch is spayed is a significant factor here. One study suggests that spaying before the first season reduces the risk of developing mammary tumours to 0.5%, after the first season this rises to 8% and after the second season and later the risk rises again to 26%. However, these figures are challenged by more recent studies. A review of all the available evidence looking at the effects of spaying on the risk of developing mammary tumours was published last year. The researchers concluded that there was evidence that spaying before 30 months old reduces the risk of the disease significantly. Spaying before the first season reduces the risk even more. However, the authors cautioned that the data was weak and that more research specifically investigating mammary tumours in dogs and the effects of spaying is needed. In male dogs mammary tumours are very rare.
A study looking at the case records of 40,000 dogs spanning 30 years of data from a number of veterinary schools in the USA looked for links between neutering and dog’s lifespan and what they found is rather interesting. Castrated males lived 14% longer and spayed females lived 26% longer. There was variation in causes of death as well with intact dogs more likely to have died from infections, trauma, degenerative diseases or vascular disease. Neutered dogs were found to be more likely to have died from immune system related diseases and cancer. These data need to be treated with caution of course because we no nothing about the demographics of these dogs. For example it could be that the higher death rates due to infection and trauma in intact dogs is a result of poorer supervision and veterinary care. At odds with these results are the results of another study of longevity in Rottweilers. This study investigated the impact of having litters on the length of a bitch’s life by analysing the lifetime records of Rottweilers that had lived more than 30% longer that the breed average compared with Rottweilers that lived an average lifespan. What the researchers found was that having litters did not disadvantage these dogs for a long life. In fact having a ‘moderate investment in reproduction’ seemed to be an advantage in achieving longevity in these dogs.
So what conclusions can we draw from all this information? It should come as no surprise that there is not a definitive ‘yes’ or ‘no’ answer here as to whether we should be neutering our dogs or not. Of course for individual dogs there are both risks and benefits, but for the dog population as a whole, including their relationship with us and with other dogs, and canine welfare as a whole in this country, the benefits seem far to outweigh the risks.
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