The new research has the “frailty” of elderly dogs at its centre. This term is defined in the same way as in humans: a complex condition that includes physical weakness, reduced endurance, weaker cognitive performance, the deterioration of hearing and sight, and an increased sensitivity to stress.

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The results show that those dogs that were neutered already at a young age showed a much more significant degree of physical decline in their old age than the intact or later-neutered dogs.

Why Do We Neuter Our Animals?

At least 8000 years ago, when agriculture already included the breeding of cattle, horses, sheep and goats, the castration of male livestock became a general practice. Neutered males were strong enough for work but easier to handle than intact bulls, therefore the ox and the gelding became the preferred draught animals. The neutering of females, however, only spread much later, since the procedure was more complex and riskier from a surgical point of view.

The neutering of our pets became general when dogs entered households and people regarded them as family members. The obvious advantage of neutering was the prevention of unwanted pregnancies, and some behavioural advantages were also experienced in these four-legged ones, since as a result of the procedures the production of the sex hormones (testosterone, progesterone, oestrogen) also ceases.

These hormones are part of a complex chemical feedback loop, into which the hormones of the pituitary gland are also included. These hormones are in close interaction with the central nervous system, the digestive system, the urinary tract, the pancreas and the thyroid. And this means that neutering influences the chemical balance of the whole organism.

Such a degree of disruption to hormonal balance is expected to have physical consequences as well. Michelle Kutzler, researcher at Oregon State University, pointed out that neutering may be associated with several long-term health issues, for example:

• urinary incontinence;
• bladder stones;
• hypothyroidism;
• diabetes;
• hip dysplasia;
• cruciate ligament rupture;
• obesity;
• as well as certain tumour types.

According to newer data, the signs of ageing also appear earlier in neutered dogs.

The data regarding behavioural changes are even less encouraging: according to two large-sample studies, neutering does not reduce but increases aggression, excitability and fear. Therefore it became necessary to investigate the question more precisely – the newest study originates from here.

It Seems that Early-Life Neutering May Lead to Problems

David Waters and his research group used the data of the programme Exceptional Longevity in Rottweilers, which has monitored more than 400 exceptionally long-lived rottweilers since 2003 – ones who lived at least 30% longer than the average lifespan of their breed. (These dogs are the equivalents of human centenarians.) They examined 222 dogs after the age of 13. The dogs were sorted into three groups: those showing the most negative symptoms were called “frail”, the ones with the fewest symptoms “vigorous”.

The researchers argued that the most important factor is the cumulative lifetime exposure to gonadal (sex-gland) hormones, therefore the dogs were divided according to the time of sterilisation: early (before 2 years of age), adult (between 2–9.8 years), late or intact (after 9.8 years, or not neutered).

The results were clear and surprising. “This research in companion dogs supports the notion that gonadal hormones exert an important impact on the retention of late-life robustness in both males and females.” Among the males, those neutered before 2 years of age proved to be the frailest. Those dogs that retained their sex hormones for the longest (meaning stayed intact or only had the surgery at an older age) were 13 times more likely to remain vigorous in their old age. In the case of females, they found a similar, though smaller but still strong, connection: those who were neutered before 2 years of age were much more fragile in their later years, while those who preserved their hormonal function for longer were three times more likely to remain healthy and active.

On the basis of the data, the early neutering widespread in general veterinary practice (often before 6 months of age) may carry a high risk. (However, we consider it important to note that the research was conducted exclusively on rottweilers, which may have influenced the results.) On a societal level, the aim is understandable, yet it may be worth reconsidering exactly when we neuter the pet – as long as a dog lives in an enclosed environment, under controlled circumstances, breeding can be prevented with good chance until the appropriate age for neutering is reached.

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