Early Spaying or Neutering Often Leads to Frail Older Dogs

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New data, which is bound to fuel the controversy over the benefits versus the health costs of spaying and neutering dogs, has just come out of the Center for Exceptional Longevity Studies at the Gerald P. Murphy Cancer Foundation in West Lafayette, Indiana. The focus of this newest research is on “frailty” in older dogs. Here frailty is defined as it is in humans, namely as a broad complex of conditions that include physical weakness, reduced stamina, poorer cognitive performance, weakened hearing and vision and increased sensitivity to stressors. The results indicate that dogs who underwent sterilization procedures in their early developmental stages exhibit significant declines in their robustness later in life, when compared to intact dogs or those with late sterilization.

Why Spay or Neuter Animals?

At least 8,000 years ago, when farming came to include husbandry of cattle, horses, sheep and goats, castration of livestock became commonplace. Gonadectomized male livestock were strong enough to work and easier to control than unaltered bulls, and such oxen or gelded horses became the preferred draft animals. Spaying females did not become a popular practice until much later because of the surgical complexity and risks.

The spaying and neutering of dogs became more common in the US when there was a movement toward having dogs live inside homes where they came to be considered members of the family. While obviously preventing unwanted pregnancies, there was some evidence for a few behavioral benefits, namely a reduction of roaming, mounting and urine marking.

Particularly around the 1960s and 70s, the problem of overpopulation of dogs and cats, which resulted in mass euthanizing programs in animal shelters, became a public concern. In response to this, the American Veterinary Medical Association issued a number of publications and leaflets containing variants of the phrase, “Having your pet spayed or neutered is a part of responsible pet ownership”. These also highlighted the positive changes in behavior (specifically claiming that sterilization resulted in the reduction of aggression and overexcited behavior in dogs). They further suggested that there are various health benefits associated with these procedures. This campaign and others were clearly successful since, in the US, approximately 32 states now require that all dogs or cats adopted from shelters be sterilized, with violations punishable through civil and criminal penalties. In contrast, in Europe, particularly in some Scandinavian countries, spaying or neutering is illegal unless needed for health reasons or special circumstances.

Are There Really Benefits of Sterilizing Dogs?

Most discussions of this issue emphasize neutering as a means of making the male or female infertile by removing the source of sperm and ova. At the behavioral level, the emphasis seems to be on the fact that neutering also removes the primary source of the hormones testosterone and estrogen. What tends to be left out is that these sex hormones are part of a complex chemical loop which interacts with pituitary hormones, such as the luteinizing hormone and the follicular stimulating hormone. This chemical quartet has a complex and intricate set of interactions with the central nervous system, the gastrointestinal and urinary tracts, the pancreas and the thyroid glands. That means that these procedures can have a widespread effect on the chemical environment throughout the body.

With such a general disruption of the normal hormonal balance of the body, it should not be surprising to find that there might be physical downsides related to these procedures. For example, Michelle Kutzler of Oregon State University has pointed out that spaying and neutering are associated with an increased risk of several long-term health problems in dogs, including urinary incontinence, bladder stones, hypothyroidism, diabetes mellitus, hip dysplasia, cruciate ligament rupture, obesity, as well as several forms of cancer. Even more recent data suggests that spayed and neutered dogs show more early signs of aging.

The evidence about behavioral changes is perhaps even less encouraging. Data from two large studies suggests that spaying and neutering dogs actually increases the amount of aggression, excitability and fearfulness rather than reducing it.

Obviously, clarification from further research seems to be needed, hence this newest study.

A Databank of Special and Rare Dogs

The team of researchers headed by David Waters took advantage of the Exceptional Aging in Rottweilers Study, which is a remarkable database. Since 2003, more than 400 Rottweilers with exceptional longevity (living 30% longer than their breed average), have been enrolled in the data-gathering. These dogs represent the canine counterpart of human centenarians (individuals who have lived beyond 100 years of age) and 222 dogs had their health status assessed when they were at least 13 years of age. The dogs were divided into three groups, with the group showing the largest number of negative symptoms being designated as “frail” and the third of the sample with the fewest number of symptoms labeled as “robust”.

The research team reasoned that the most important variable that they were dealing with was the total lifetime exposure to the gonadal hormones, thus they divided the group by age of sterilization: early (less than two years), adult (from two years to 9.8 years), and late (greater than 9.8 years or still intact).

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The Shorter the Exposure to Sex Hormones, the More Fragile the Dogs

The results were quite unambiguous and also startling in terms of their magnitude. The researchers summarize their results saying, “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.”

The male dogs in the lowest gonadal hormone exposure group (neutering at less than two years of age) proved to be the most frail. The dogs with the longest exposure to sex hormones (still intact or with older adult sterilization) were 13 times more likely to have late-life robustness.

The results for the females were in the same direction with a somewhat smaller magnitude, but still remarkably strong. Female dogs in the lowest exposure to sex hormones group (spaying at less than two years of age) were the most frail as they grew older. Females with the longest lifelong exposure to sex hormones were almost three times more likely to be robust later in life.

The conclusion that one can reach from such data is that spaying and neutering are harmful to dogs in the long run. Thus, it would seem that following the common veterinary recommendation of early sterilization (often before the age of six months) would appear to be the most damaging.

At a societal level, the need to control the population of unwanted dogs is understandable. However, the practice of spaying and neutering most companion animals, especially at an early age, seems to be scientifically questionable. The majority of companion animals across North America and Europe do not roam outdoors in any uncontrolled fashion, which means that such dogs typically have no opportunity to become pregnant or to make other dogs pregnant. So, if you own an urban dog who lives in your house most of the time, especially given the evidence of the negative outcomes of such procedures, a responsible dog owner must ask, "Is sterilization of my dog really needed?"

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