Dr Peggy Root-Kustriz, Univ. of MN
Benefits and detriments of neutering and spaying depend on the breed and what the working needs are of that dog.
Population Benefits
Overpopulation: Note, however, that in other countries where gonadectomy is not so much the norm as it is here that they pften have less of an overpopulation problem. The problem seems to be associated with attitudes; unlike US owners, they are less inclined to drop off a nuisance dog because it is inconvenient or irritating.
Relinquishment: Intact animals more likely to be relinquished, maybe because they are more annoying, for example, because they come in heat or mark.
Surveys of pet owning households that have had litters reveal that 56% of dog litters and 68% cat litters were unplanned. This was often because of lack of knowledge about normal reproductive physiology, such as recognizing signs of heat.
Spay neuter contracts, such as those sent out with dogs from shelters, have only about 60% compliance. Because of this, it's recommended that dogs with no owners, such as those in shelters, be gonadectomized prior to placing. For dogs with owners, you must weigh pros and cons.
Health Considerations
Benefits of castration:
- Risk of testicular neoplasia is removed. Testicular neoplasia mostly occurs in older dogs, it usually stays in the testes, and has a low morbidity of about 0.09%. Reduces benign prostatic hypertrophy because that condition is testosterone related. This condition occurs in 75-80% of male dogs over the age of 6 years. Signs include blood in the semen. The condition has low morbidity and can be treated with among other things, castration.
- Some research suggest castration may increase lifespan. This could be due to increased owner investment, decrease in risky behavior, or some other unidentified reason.
Detriments of castration:
- Obesity: a cause and effect relationship has been shown in cats due to decreased metabolic rate. It has not been studied in dogs. It can be controlled by the owner.
- Increased anterior cruciate ligament rupture: Overall incidence is 1.8%. More common in large breeds. Castrated dogs at greater risk (even allowing for obesity). Morbidity and cost of repair is high.
- A very few studies have looked for or found a relationship between castration and cancer:
- Prostatic adenocarcinoma: Overall incidence 0.2-0.6%. Castrated dogs have a two to four greater risk when aged. This is a cancer with high morbidity/mortality. Findings are based on three to four studies.
- Osteosarcoma: Overall incidence 0.2%. Castrated dogs have a one to three times greater risk. This is a cancer with high mortality. It has a higher risk in large and giant breeds. This finding is based on a study in Rottweilers.
- Hemangiosarcoma: Overall incidence is 0.2%. Castrated dogs have a two time greater risk. More common in large breeds. High mortality. This finding is based on one study and one comment paper.
Recommendation: Castration should be decided on a case by case basis. It may not be the best choice for all breeds, such as those already predisposed to osteosarcoma, hemangiosarcoma, or ACL rupture. But it also depends on the individual dog and owner.
Benefits of spaying:
- Decreases mammary neoplasia: This is the most common tumor of female dogs' overall incidence is 3.4%. About half are malignant. There is a decreasing benefit of spaying the more heat cycles a bitch has.
- Removes possibility of pyometra: This affects 15.2% of bitches by age 4 years, 23-24% by age 10 years. Morbidity is high. Spay is curative, depending on timeliness (mortality post spaying is 17%). Each time a bitch goes into estrus, progesterone damages the uterine health, making the uterine lining thicker, increasing cystic hyperplasia, which in turn makes its easier for infection to set in.
Detriments of spaying:
- Increased obesity: same as in male.
- Increased ACL rupture: same as in male.
- Increased osteosarcoma: spayed females are at a one to three times greater risk.
- Increased hemangiosarcoma: spayed females are at a two to six times greater risk.
- Increased transitional cell carcinoma: These cells line the urethra and bladder. Overall incidence is <1%.) Mortality is high.
- Urinary incontinence: Occurs in 5-20% of spayed females, more common large (>20 kg) breeds. Not all are responsive to estrogen. Risk is greater if spayed before 3 months old.
Recommendations: Again, this needs to be decided on a case by case basis. Spaying decreases the incidence of some common, high morbidity disorders, but increases the risk of some less common, high mortality disorders. Overall, it is probably best to spay bitches between 3 months of age and their first heat.
Dr. Root's website: http://www.tc.umn.edu/~rootk001
