Before I became involved with holistic medicine, I would have said that all pets should be spayed or neutered at six months of age.Dr. Judy Morgan
The single biggest reason to spay or neuter is population control. Thousands and thousands of animals are euthanized at shelters every year due to unwanted production of puppies and kittens. However, if we could all be responsible pet owners and keep our young pets from being accidentally bred, I currently feel our pets would be healthier by allowing them to reach full maturity before considering spay or neuter.
Many shelters are spaying and neutering by eight weeks of age. There have been many studies showing long term health problems related to early spay/neuter. Obesity, some cancers, hypothyroidism and other endocrine diseases, musculoskeletal disorders like hip dysplasia, incontinence, and urinary tract infections may occur more frequently in pets undergoing early spay or neuter.
Recent retrospective studies have shown higher incidence of some cancers in dogs that have undergone spay or neuter prior to maturation. In particular, hemangiosarcoma of the spleen or heart, osteosarcoma of the bones, prostate cancer, and lower urinary tract cancers may have a higher incidence of occurrence in animals spayed or neutered early. The estrogen and testosterone hormones seem to have some protective effects.
THE OTHER SIDE
On the other hand, mammary cancer dramatically increases in intact older females. Current studies show that spaying between twenty four and thirty months of age will allow females to reach maturity and may have some beneficial protective effects against certain cancers, while still having a low incidence of mammary cancer. The incidence of uterine infection, which is life threatening, also increases with age. Currently, I think allowing our pets to undergo two or three heat cycles and develop to maturity is probably the best answer. Sterilization without removal of the gonads (ovaries and testes) may be a good solution, however these techniques in animals are not commonly used. Ovary sparing spay is gaining in popularity. Again, being a responsible pet owner and not allowing a pet to be accidentally bred is paramount.
Studies of intact males, particularly large breed dogs, have shown there may be beneficial protection against cancers like prostate cancer, hemangiosarcoma, and osteosarcoma. Testicular cancers can occur, but have a low mortality rate. Benign prostatic enlargement is common in older unneutered males, but is usually treatable. Perineal hernias occur much more commonly in unneutered males than neutered males and these can be life threatening if the bladder becomes entrapped in the hernia. Neutering males can help decrease unwanted behaviors such as aggression, urine marking, and desire to roam. Prostate cancer occurrence is much higher in neutered males and is difficult to treat.
The number of health problems associated with neutering may outweigh the benefits of leaving males intact, as long as owners are responsible and do not allow their intact males to wander and produce unwanted litters. The one contradiction is the case of a retained testicle which has not descended into the scrotum. Retained testicles have a very high rate of developing into cancerous tumors, as the temperature inside the body is higher than the temperature in the scrotum. Retained testicles should always be removed if they have not descended into the scrotum by one year of age. Some acupuncturists have had success in getting the testicles to descend using herbals and acupuncture.