Update on findings at the mid-year 2 in a study to develop a generalized understanding of the impact of early spay and neuter on disease risk in dogs. The goal of this project is to evaluate, using one consistent and uniform database at their large veterinary medical center (UC Davis). This update provides conclusions for several medium-to-large breed dogs regarding the impact of early spay/neuter on cancer and musculoskeletal risks. Additionally, several small breeds were evaluated determining negligible risk with early spay/neuter.Findings indicate risk vary from breed to breed.
The long-term goal of this project is to evaluate, using one consistent and uniform database at our large veterinary medical center with 50,000 cases per year, the breed-specific effects of neutering (referring to both neutering and spaying) at different ages on joint disorders (hip dysplasia, cranial cruciate ligament tear and elbow dysplasia) and some cancers (lymphosarcoma, hemangiosarcoma, mast cell tumor). The effects of neutering at various ages are also examined with regard to mammary cancer, urinary incontinence, and pyometra in females. Our previous studies were on the Golden Retriever and Labrador Retriever (supported by CHF), published in two papers in the open-access journal, PLOS ONE (doi: 10.1371/journal.pone.0102241 and doi: 10.1371/journal.pone.0055937). This report of unpublished research since this earlier work, will give a rough idea of the findings.
German Shepherd Dog
Using a database for this breed of 1,250 cases, we found that 7 percent of gonadally intact males and 5 percent of intact females were diagnosed with one or more joint disorders. But neutering in the first year increased the incidence of one or more joint disorders by 3-fold over that of the intact dogs. The occurrence of the cancers we followed in this breed was at a low 3 percent in the intact males and females, and was not affected in either sex by neutering. The take-home message is that delaying neutering until the dogs are at least 1 year old markedly reduces the likelihood of one or more disabling joint disorders.
Using the database for this breed of 696 cases we found that 9 percent of intact males and 16 percent of intact females had at least one joint disorder. Neutering during the first year increased the likelihood of a joint disorder in both sexes by up to 3 times. The occurrence of one or more of the cancers in the intact dogs was relatively high, 12-13 percent, but neutering at any age did not increase the rate. Delaying neutering in this breed until the dog is well past a year of age should avoid increasing the already high risk of a joint disorder.
With a database for this breed of 646 cases, we found that the occurrence of one or more joint disorders in intact males and females was just 2 percent, and there was no indication of an effect of neutering at any age. We are tentatively attributing this to the somewhat wide stance of this breed. The underlying occurrence of at least one of the cancers in intact dogs was high; 12 to 16 percent respectively in males and females, but there was no indication of an increase in this measure for any neuter period with the exception of a higher cancer occurrence in the 1-year neuter period of males. Until the statistical analyses are done, it seems like avoiding neutering males at the age of 1 to 3 years would be advised.
Small breeds: Chihuahua, Yorkshire Terrier and Shih Tzu
The complete data sets available for analyses were: Chihuahua, 831 cases; Yorkshire Terrier, 553; and Shih Tzu, 322 cases. In all three breeds there was no diagnosis of a joint disorder in intact males and females, and almost complete absence of any indication that neutering increased the incidence of joint disorders. For cancers in the small breeds, the occurrence in the intact males and females ranged from 0 to about 2 percent. For the Chihuahua and Yorkshire Terrier neutering at one time or another increased the occurrence only slightly. In the
Shih Tzu the occurrence of one or more cancers increased somewhat in females neutered at 1 year; this is still under analysis. Other than this it appears there is no disease-related issue with regard to age of neutering in these breeds.
With a database for this breed of 548 cases, we found that the occurrence of joint disorders was zero in both the intact and neutered dogs. The occurrence of cancers was also very low in intact males and females with little indication of an effect of neutering. There was a strikingly high level of occurrence of intervertebral disc disease diagnosed in intact males and females, 45 and 35 percent respectively, but this disease was not increased by neutering. It appears that there is no disease-related issue with regard to age of neutering in this breed.