Spay-Neuter Considerations to Maximize Health

By  | 


Those of us responsible for the health of dogs need to continually read and evaluate new scientific studies to ensure we are taking the most appropriate care of our canine patients. This article reviews scientific evidence that, taken together, suggests that veterinarians and dog owners need to revisit the current common recommendation that all dogs not intended for breeding have their gonads removed at or before six months of age. The results of a number of studies on the effects that removing the ovary or testicles (gonadectomy) has on orthopedics, cancer, behavior and other health issues are briefly summarized.


  • Bitches spayed at seven weeks had significantly delayed closure of growth plates as compared to those spayed at seven months, and those spayed at seven months had significantly delayed closure of growth plates as compared to those left intact.1
  • In a study of 1,444 golden retrievers, bitches and dogs spayed or neutered at less than a year of age were significantly taller than those spayed or neutered after a year of age.2
  • In a study of 203 agility dogs, the author demonstrated that the tibia, radius and ulna were significantly longer than the femur and humerus, respectively, in dogs that were spayed or neutered at or prior to eight months of age as compared to intact dogs (C. Zink, unpublished data).
  • Several studies have shown that spayed and neutered dogs have a significantly higher prevalence of CCL rupture,3–6 even when controlling for body size.3
  • In a study of 759 male and female golden retrievers neutered or spayed before six months of age, the incidences of CCL rupture were 5% and 8% respectively, compared to no CCL rupture diagnosed in intact males and females.7
  • Dogs neutered at least six months prior to a diagnosis of hip dysplasia were 1.5x more likely to develop hip dysplasia than sexually intact dogs.8
  • Spayed/neutered dogs had 3.1x higher incidence of patellar luxation.9
  • In Labrador and golden retrievers, neutering before six months of age increased the incidence of one or more joint disorders by 2x and 4x to 5x, respectively.10
  • In a study of 1,170 German shepherds, followed through eight years of age, 21% of neutered males and 16% of spayed females were diagnosed with one or more joint disorders compared with 7% of intact males and 5% of intact females.11

Discussion: Dogs spayed or neutered at or before puberty can often be identified by their longer limbs, lighter bone structure, narrower chests and narrower skulls than intact dogs of the same breed. This differential growth frequently results in significant alterations in body proportions and particularly the lengths (and therefore weights) of certain bones relative to others. For example, if the femur has achieved its genetically determined normal length at eight months, prior to a dog being spayed or neutered, but the tibia (which normally stops growing at 12 to 14 months of age) continues to elongate for several months after that point because of the removal of the sex hormones (which contribute to growth plate closure), then the relationship between the femur and tibia will be different than what was genetically determined. This may result in an abnormal angle at the stifle and a longer (and therefore heavier) tibia placing increased stress on the cranial cruciate ligament (of the knee or stifle joint). It is well known that spayed and neutered dogs are more likely to be overweight or obese than sexually intact dogs,12 and this can be an additional contributing factor to orthopedic diseases. Thus, keeping spayed/neutered dogs lean can help mitigate the increased risk of orthopedic conditions.


  • Spayed females had more than 5x greater risk than intact bitches of developing cardiac hemangiosarcoma; neutered males had 1.6x higher risk than intact males of developing cardiac hemangiosarcoma.13
  • Spayed females had 2.2x increased risk for developing splenic hemangiosarcoma.14
  • Male and female Rottweilers neutered or spayed before a year of age had 3.8x and 3.1x greater risk, respectively, of developing bone cancer than intact dogs.15 In a second study, spayed/neutered dogs had a 2.2x higher risk of developing bone cancer than intact dogs.16
  • Neutered dogs had a 2.8x greater risk for developing prostate cancer than intact dogs.17 Neutered dogs had a 4.3x higher risk of developing prostate carcinoma.18,19
  • Neutered dogs had a 3.6x higher risk for developing transitional cell carcinoma of the bladder than intact dogs, and a 3x greater risk of developing any bladder tumor.17 Spayed/neutered dogs had more than 4x greater risk for developing transitional cell carcinoma of the bladder than intact dogs.20
  • Early neutered male golden retrievers were 3x more likely to be diagnosed with lymphoscarcoma than intact males, and late-spayed females were significantly more likely to develop hemangiosarcoma and mast cell tumor than intact females.7
  • In a survey of 2,505 Vizslas, dogs spayed or neutered at any age were found to have a significantly higher risk of mast cell cancer, hemangiosarcoma, lymphoma and all cancers together than intact dogs.21
  • Female Labrador retrievers spayed between two and eight years of age were shown to have a significantly increased prevalence of mast cell cancer, hemangiosarcoma, and lymphoma.10

Discussion: One study indicated a slightly increased risk of mammary cancer in female dogs after one heat cycle (8% increase), greater risk with two heats (26% increase) and increased risk with each subsequent heat.22 However, a recent systematic review of the publications that advocate neutering to reduce the risk of mammary tumors in dogs indicated that nine of 13 reports had a high risk of bias, and the remaining four had a moderate risk of bias.23 This study concluded that the evidence that neutering reduces the risk of mammary cancer is weak and does not constitute a sound basis for firm recommendations. Additionally, at the time when several of these studies were conducted (late 1960s), incidence rates for all malignant neoplasms were 453.4/100,000 female dogs. Mammary tumors accounted for half of these tumors, or 198.8/100,000. Thus, the actual overall risk at that time of any bitch getting a mammary tumor was only 0.2%.24 In any case, the figures for increased risk of mammary cancer must be compared with the 200% to 400% increased risk of other cancers in spayed females. While about 30% of mammary cancers are malignant,25 as in humans, when caught and surgically removed early, the prognosis is very good.26 This is in comparison to the other cancers listed, such as hemangiosarcoma, lymphosarcoma and bladder cancer, which are usually fatal. Given the balance of cancer risks listed above, owners of bitches should strongly consider having a hysterectomy (ovary-sparing spay) performed rather than an ovariohysterectomy, thus providing while retaining the benefits of female hormones. In addition, the veterinary field should be developing programs for regular examinations, including imaging, to facilitate early diagnosis of mammary cancer in all intact female dogs, as has been performed in women for decades.


  • Early age gonadectomy was associated with an increased incidence of noise phobias and undesirable sexual behaviors, such as mounting.27
  • Significantly more behavioral problems were seen in spayed and neutered bitches and dogs, with fearful behavior being most common in spayed bitches and aggression in neutered dogs.28, 29
  • In a prospective study, German shepherds spayed between five and ten months of age had significantly increased reactivity.30

Discussion: A number of early studies claiming to show the positive behavioral effects of spay/neuter were significantly flawed. For example, one of the most-quoted publications to support improvements in behavior, particularly aggression, after gonadectomy does not actually provide any statistical analysis. Additionally, 88% of dog owners in this study stated that their reason for castrating their dogs was to attempt to resolve an existing behavior problem. Owners were also surveyed regarding the dogs’ behavior a mean of 27 months post-castration. These factors likely introduced a significant amount of bias.31 Another study performed a statistical analysis but showed that the age when the dog was neutered was not correlated with the degree of improvement.32 Most critically, neither of these two studies included a control group of intact dogs. One of the more important undesirable behavioral effects of spay/neuter for canine athletes was a finding of significantly lowered energy levels. This was shown in a study that was well controlled and examined over 3,500 dogs.29


  • Female, and sometimes male, dogs that are spayed/neutered before puberty have an increased risk of urinary incontinence; it is more severe in bitches spayed earlier.33-36
  • Spayed female dogs displayed a significantly higher risk of hypothyroidism when compared to intact females.37 A health survey of several thousand golden retrievers showed that spayed or neutered dogs were more likely to develop hypothyroidism.2 Neutered male and spayed female dogs had higher relative risks of developing hypothyroidism than intact females.38
  • Neutered females had a 22x increased risk of developing fatal acute pancreatitis as compared to intact females.39
  • Risk of adverse reactions to vaccines is 27% to 38% greater in neutered dogs as compared to intact.40
  • In a study of female Rottweilers, there was a strong positive association between retention of the ovaries and longevity.41


I have gathered these studies to show that the veterinary practice of recommending every dog not meant for breeding have his/her gonads removed at or before the age of six months is not a black-and-white issue. Clearly, more studies need to be undertaken to evaluate the effects of spaying and neutering, and in particular to investigate non-gonadectomy alternatives to prevent procreation, such as vasectomy and hysterectomy. After examining the risks and benefits, I have significant concerns with removal of the gonads in both males and females. It is clear that the gonads are not just important for reproduction, but play a critical role in growth, development and long-term health. One study showed that spayed bitches had 30x higher levels of luteinizing hormone than intact bitches42; given that this hormone has receptors on diverse tissues throughout the body,43 it is possible that the lack of a feedback loop for this hormone might contribute to some of the negative effects of gonadectomy, at least in females.

It is important that we assess each dog and his/her living situation individually, weighing the risks and benefits of gonad removal. There is no single solution that fits every dog.

Acknowledgment: The author is grateful for excellent in-depth discussions with Samra Zelman on the literature regarding spaying and neutering, and for her careful review of this article.

1Salmeri KR, Bloomberg MS, Scruggs SL, Shille V. “Gonadectomy in immature dogs: effects on skeletal, physical, and behavioral development”. JAVMA 1991;198:1193-1203.

2Glickman L, Glickman N, Thorpe R. The Golden Retriever Club of America National Health Survey 1998-1999.

3Slauterbeck JR, Pankratz K, Xu KT, Bozeman SC, Hardy DM. “Canine ovariohysterectomy and orchiectomy increases the prevalence of ACL injury”. Clin Orthop Relat Res. 2004;(429):301-5.

4Whitehair JG, Vasseur PB, Willits NH. “Epidemiology of cranial cruciate ligament rupture in dogs”. JAVMA 1993;203:1016-1019.

5Duerr FM, Duncan CG, Savicky RS, Park RD, Egger EL, Palmer RH. “Risk factors for excessive tibial plateau angle in large-breed dogs with cranial cruciate ligament disease”. JAVMA 2007;231:1688-91.

6Duval JM, Budsberg SC, Flo GL, Sammarco JL. “Breed, sex, and body weight as risk factors for rupture of the cranial cruciate ligament in young dogs”. JAVMA 1999;215:811-814.

7Torres de la Riva G, Hart BL, Farver TB, Oberbauer AM, Messam LL McC, Willits N, Hart LA. “Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers”. PLoS ONE 2013;8:e55937.

8van Hagen MA, Ducro BJ, van den Broek J, Knol BW. “Incidence, risk factors, and heritability estimates of hind limb lameness caused by hip dysplasia in a birth cohort of boxers”. Am J Vet Res 2005;66:3071-2.

9Vidoni B, Sommerfeld-Stur I, Eisenmenger E. “Diagnostic and genetic aspects of patellar luxation in small and miniature breed dogs in Austria”. EJCAP 2005;16:149-58.

10Hart BL, Hart LA, Thigpen AP, Willits NH. “Long-term health Eff ects of Neutering Dogs: Comparison of Labrador Retrievers with Golden Retrievers”. PLoS ONE. 2014:9:e102241.

11Hart BL, Hart LA, Thigpen AP, Willits NH. “Neutering of German Shepherd Dogs: associated joint disorders, cancers and urinary incontinence”. Veterinary Medicine and Science 2016;2:191-199.

12Lund EM, Armstrong PJ, Kirk CA, Klausner JS. “Prevalence and risk factors for obesity in adult dogs from private US veterinary practices”. Intern J Appl Res Vet med 2006;2:177-86.

13Ware WA, Hopper DL. “Cardiac tumors in dogs: 1982-1995”. J Vet Intern Med 1999 13(2):95-103.

14Prymak C, McKee LJ, Goldschmidt MH, Glickman LT. “Epidemiologic, clinical, pathologic, and prognostic characteristics of splenic hemangiosarcoma and splenic hematoma in dogs: 217 cases (1985)”. JAVMA 1988;193:706-12.

15Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters D. “Endogenous gonadal hormone exposure and bone sarcoma risk”. Cancer Epidemiol Biomarkers Prev. 2002 11(11):1434-40.

16Ru G, Terracini B, Glickman LT. “Host related risk factors for canine osteosarcoma”. Vet J. 1998 156(1):31-9.

17Bryan JN, Keeler MR, Henry CJ, Bryan ME, Hahn AW, Caldwell CW. “A population study of neutering status as a risk factor for canine prostate cancer”. Prostate 2007;67:1174-81.

18Teske E, Naan EC, van Dijk EM, Van Garderen E, Schalken JA. “Canine prostate carcinoma: epidemiological evidence of an increased risk in castrated dogs”. Mol Cell Endocrinol 2002;197:251-5.

19Sorenmo KU, Goldschmidt M, Shofer F, Ferrocone J. “Immunohistochemical characterization of canine prostatic carcinoma and correlation with castration status and castration time”. Vet Comparative Oncology. 2003 Mar; 1 (1): 48.

20Knapp DW, Glickman NW, Denicola DB, Bonney PL, Lin TL, Glickman LT. “Naturally-occurring canine transitional cell carcinoma of the urinary bladder A relevant model of human invasive bladder cancer”. Urol Oncol 2000;5:47-59.

21Zink MC, Farhoody P, Elser SE, Ruffi  ni LD, Gibbons TA, Rieger RH. “Evaluation of the risk and age of onset of cancer and behavioral disorders in gonadectomized Vizslas.” JAVMA 2014;244:309-319.

22Schneider R, Dorn CR, Taylor DO. “Factors infl uencing canine mammary cancer development and postsurgical survival”. J Natl Cancer Inst 1969;43:1249-61.

23Beauvais W, Cardwell JM, Brodbelt DC. “The eff ect of neutering on the risk of mammary tumors in dogs – a systematic review”. J Small Anim Pract 2012;53:314-322.

24Dorn CR, Taylor DO, Schneider R, Hibbard HH, Klauber MR. “Survey of animal neoplasms in Alameda and Contra Costa Counties, California. II. Cancer morbidity in dogs and cats from Alameda County”. J Natl Cancer Inst. 1968 Feb;40:307-18.

25Misdorp W. “Tumors of the Mammary Gland” in: Meuten DJ. Tumors in Domestic Animals. 4th Edn. Iowa State Press, Blackwell Publishing Company, Ames, Iowa, p. 575.

26Lena L, De Andres PJ, Clemente M, Cuesta P, Perez-Alenza MD. “Prognostic value of histological grading in noninfl ammatory canine mammary carcinomas in a prospective study with two-year follow-up: Relationship with clinical and histological characteristics”. Vet Pathol 2012; June 11. [Epub ahead of print.]

27Spain CV, Scarlett JM, Houpt KA. “Long-term risks and benefi ts of early-age gonadectomy in dogs”. JAVMA 2004;224:380-387.

28Serpell JA. “Measuring behavior and temperament in dogs”. American Kennel Club Canine Health Foundation Biennial National Parent Club Canine Health Conference. 2005. St. Louis, MO. p. 46-8.

29Duff y DL, Serpell JA. “Non-reproductive eff ects of spaying and neutering on behavior in dogs”. Proceedings of the Third International Symposium on Non-surgical Contraceptive Methods for Pet Population Control. 2006. Symposium%20Docs/Session%20I.pdf.

30Kim HH, Yeon SC, Houpt KA, Lee HC, Chang HH, Lee HJ. “Eff ects of ovariohysterectomy on reactivity in German Shepherd dogs”. Vet J 2006;172:154-9.

31Hopkins SG, Schubert TA, Hart BL. “Castration of adult male dogs: eff ects on roaming, aggression, urine marking, and mounting”. JAVMA 1976;168:1108-10.

32Neilson JC, Eckstein RA, Hart BL. “Effects of castration on problem behaviors in male dogs with references to age and duration of behaviors”. JAVMA 1997;211:180-2.

33Stocklin-Gautschi NM, Hassig M, Reichler IM, Hubler M, Arnold S. “The relationship of urinary incontinence to early spaying in bitches”. J. Reprod. Fertil. Suppl. 57:233-6, 2001.

34Aaron A, Eggleton K, Power C, Holt PE. “Urethral sphincter mechanism incompetence in male dogs: a retrospective analysis of 54 cases”. Vet Rec 1996;139:542-6.

35Thursfi eld MV. “Association between urinary incontinence and spaying in bitches”. Vet Rec. 1985;116:695.

36Thrusfi eld MV, Hold PE, Muirhead RH. “Acquired urinary incontinence in bitches: its incidence and relationship to neutering practices”. J Small Anim Pract 1998;39:559-66.

37Milne KL, Hayes HM Jr. “Epidemiologic features of canine hypothyroidism”. Cornell Vet. 1981;71:3-14.

38Panciera DL. “Hypothyroidism in dogs: 66 cases (1987-1992)”. JAVMA 1994;204:761-7.

39Hess RS, Kass PH, Shofer FS, Can Winkle TJ, Washabau RJ. “Evaluation of risk factors for fatal acute pancreatitis in dogs”. JAVMA. 1999;214:46-51.

40Moore GE, Guptill LF, Ward MP, Glickman NW, Faunt KK, Lewis HB, Glickman LT. “Adverse events diagnosed within three days of vaccine administration in dogs”. JAVMA 2005;227:1102-8.

41Waters DJ, Kengeri SS, Clever B, Booth JA, Maras AH, Schlittler DL, Hayek MG. “Exploring mechanisms of sex differences in longevity: lifetime ovary exposure and exceptional longevity in dogs”. Aging Cell 2009;8:752-5.

42Beijerink NJ, Buijtels JJ, Okkens AC, Kooistra HS, Dieleman SJ. “Basal and GnRH-induced secretion of FSH and LH in anestrous versus ovariectomized bitches”. Theriogenology 2007;67:1039-45.

43Zwida K, Kutzler MA. “Non-reproductive long-term health complications of gonad removal in dogs as well as possible causal relationships with post-gonadectomy elevated luteinizing hormone (LH) concentrations”. J. etiology An Health 2016;11-11.

44Reif JS, Maquire TG, Kenny RM, Brodey RS. “A cohort study of canine testicular neoplasia”. JAVMA 1979;175:719-23.

45Nieto JM, Pizarro M, Balaguer LM, Romano J. “Canine testicular tumors in descended and cryptorchid testes”. Dtsch Tierarztl Wochenschr. 1989;96:186-9.