Spay and Neuter

The decision to spay or neuter companion animals has been a subject of much debate for decades. When looking at population control alone, the answer seems simple. Humane society organizations estimate that 7.6 million animals enter the shelters in this country each year. Unfortunately, many of these animals do not find homes and are euthanized. Given this staggering number, decreasing births through spaying and neutering seems logical, yet in this article will dig a little deeper.

Research is beginning to look at specific breeds and diseases with the intent to determine if spay or neuter plays a role in these diseases. These studies are retrospective in nature; meaning the study looks back at a particular population of pets. In these studies neutered pets are compared to intact pets, however other factors like  diet, environment, medications and the like are not controlled or consistent between subjects. Clearly a limitation to the credibility of the studies, and never proving a true cause and effect relationship between neutering and disease. Perhaps the most meaningful finding of these retrospective studies is that neutered animals are associated with an increased lifespan. Despite this general statement it might play out differently with certain diseases and breeds. Let’s look at a couple specific studies.

In the case of hemangiosarcoma a malignancy of the blood vessel which often effects the spleen; there appears to be an increased incidence in the spayed female especially in the Swiss Mountain Dog and Vizsla. The real question is wether sex hormones have a protective effect on the body against cancer. This question still needs to be answered by further research.

Studies on osteosarcoma (bone cancer) and mast cell cancer were mixed; some showing a connection between the presence of sex hormones and the cancer; versus the absence of sex hormones and the same cancer. Clearly other factors are likely influencing the study and more research needs to be completed.

Relative to canine behavior it appears the the neutered male is less likely to show roaming, mounting, urine marking and aggressive behavior. However in the areas of separation anxiety, storm phobias, and fear behavior there may be a link to the animal neutered prior to 6 months. These studies involved small numbers and no firm conclusions were made.

Orthopedic conditions have been looked at as well with some preliminary retrospective studies showing that early spay neuter could be linked to the development of hip dysplasia, elbow dysplasia, and injury to the anterior crucial ligament. Again these studies are crude and and not controlled.

I admire the scientific query here, and the desire to determine new ways to limit the expression of disease. Yet, there is limited evidence to link gonadectomy to various diseases. Further there is clear evidence to support that neutered animals are associated with increased longevity.

The quest to link disease to neutered animals needs to be further studied with appropriately designed research studies. The decision to spay or neuter should be made individually with the veterinarian. At this time the evidence leading to the decision to delay neutering to attain health benefits is not founded.

It may well be that pet owners who neuter their pets also visit their veterinarian more regularly. The more regular visits lead to more and earlier diagnoses, which in turn effects the studies. This compares to the intact dog that rarely visits the veterinarian, yielding no documented diagnoses to be found in the studies. The most telling finding in these studies, is likely that neutered pets live longer.