Health Considerations of Early Spay and Neutering

Veterinary Medical Abstracts researched and compiled by
Melody Farquhar Chang

Presentation Summary & Powerpoint

Risks and Benefits of Neutering and Early-Age Neutering in Dogs and Cats: Effects on Development, Obesity, and Select Orthopedic and Neoplastic Conditions

C. Victor Spain, Philadelphia, Pennsylvania

Neutering of dogs and cats confers a mix of benefits and adverse risks. The objective of this presentation is to highlight recent research findings on the associations between neutering (whether early-age or at a traditional age) and select medical conditions. In this abstract, the term neutering is used in the broadest sense to include both castration of male dogs and cats or ovariohysterectomy (or ovariectomy) of female dogs and cats. The data on early-age neutering is from a retrospective cohort study of 1,579 cats and 1,659 dogs adopted from a large animal shelter between 1989 and 1998 (Spain, 2004). Obesity. Several studies have indicated an increased prevalence of obesity in neutered dogs and cats. Energy consumption appears to decrease after neutering in dogs and cats, although the degree and timing varied between studies. Some researchers attribute neutering-related obesity in cats to increased food consumption and not to altered metabolic rate, suggesting that the weight gain can be prevented with a lower fat diet (German, 2006, Nguyen, 2004, Kanchuck, 2002). Obesity does not appear to be affected by age of neutering in cats, but among dogs, early-age neutering is associated with a lower incidence of obesity than neutering after 6 months of age (Spain, 2004). Canine Hip Dysplasia (CHD) and Cranial Cruciate Ligament (CCL) Injury. One study found an increased incidence of CHD after neutering in boxers (van Hagen, 2005), and among dogs seen in an orthopedic surgical clinic, the prevalence of CCL injury among neutered dogs (4.7%) was more than twice that of intact dogs (2.3%) (Slauterbeck, 2004). These findings regarding CCL injury incidence are consistent with findings that the level of sex hormones affects the incidence of anterior cruciate ligament (ACL) rupture in humans. Hip dysplasia is increased among early-neutered dogs compared to those neutered after 6 months of age (Spain, 2004). Mammary Cancer and Prostatic Cancer. Spaying before 1 year of age reduces the risk of mammary carcinoma approximately 90% in cats, and spaying before second estrus in dogs similarly reduces the risk by about 90% (Overley, 2005). The incidence of mammary cancers does not vary between ovariohysterectomy (traditional spay with removal of the uterus and ovaries) and ovarioectomy (removal of just the ovaries) (van Goethem, 2006). Traditional thought is that neutering reduces the risk of prostatic cancer among male dogs. Recent research suggests that after neutering, however, changes in endothelin, a cell protein involved in cell growth, may eventually reverse the benefits of neutering on prostatic cancer risk (Padley, 2002) and the incidence of prostatic cancer may actually be higher in castrated dogs than intact dogs (Teske, 2002).

Select References

Early-age Neutering

CV Spain, JM Scarlett, KA Houpt, 2004. Long-term risks and benefits of pediatric gonadectomy in cats. Journal of the American Veterinary Medical Association. 224(3):372-379. CV Spain, JM Scarlett, KA Houpt, 2004. Long-term risks and benefits of pediatric gonadectomy in dogs. Journal of the American Veterinary Medical Association . 224(3):380-387. CV Spain, JM Scarlett, SM Cully, 2002. When to neuter dogs and cats: a survey of New York state veterinarians' practices and beliefs. Journal of the American Animal Hospital Association, 38(4): 482-488.

Physical Development and Obesity

M Hoenig, DC Ferguson, 2002. Effects of neutering on hormonal concentrations and energy requirements in male and female cats. American Journal of Veterinary Research. 63(5): 634-639. AJ German. 2006. The growing problem of obesity in dogs and cats. Journal of Nutrition.136: 1940S-1946S. PG Nguyen, HJ Dumon, BS Siliart, et al. 2004. Effects of dietary fat and energy on body weight and composition after gonadectomy in cats. American Journal of Veterinary Research. 65(12):1708-1713. ML Kanchuck, RC Backus, CC Calvert, et al., 2002. Neutering induces changes in food intake, body weight, plasma insulin and leptin concentrations in normal and lipoprotein lipase-deficient male cats. Journal of Nutrition. 132:1730S-1732S. PD McGreevy, PC Thompson, C Pride, et al., 2005. Prevalence of obesity in dogs examined by Australian veterinary practices and the risk factors involved. The Veterinary Record. 156:695-702.

Orthopedic Disorders

JR Slaughterbeck, K Pankratz, KT Xu, et al. 2004. Canine ovariohysterectomy and orchiectomy increases the prevalence of ACL injury. Clinical Orthopedics and Related Research. 429: 301-305. MAE van Hagen, BJ Ducro, J van den Broek, et al., 2005. Incidence, risk factors, and heritability estimates of hind limb lameness caused by hip dysplasia in a birth cohort of Boxers. American Journal of Veterinary Research. 66(2):307-312.

Mammary and Prostate Cancer

RJ Padley, DB Dixon, JR Wu-Wong, 2002. Effects of castration on endothelin receptors. Clinical Science. 103(suppl. 48):442S-445S. B Overley, FS Shofer, MH Goldschmidt, et al., 2005. Association between
ovariohysterectomy and feline mammary cancer. Journal of Veterinary Internal Medicine. 19:560-563. B van Goethem, A Schaefers-Okkens, J Kirpensteijn, 2006. Making a rational choice between ovariectomy and overiohysterectomy in the dog: A discussion of the benefits of either technique. Veterinary Surgery. 35:136-143. E Teske, EC Naan, EM van Dijk, et al., 2002. Canine prostate carcinoma: epidemiologic evidence of an increased risk in castrated dogs. Molecular and Cellular Endocrinology.197:251-255

Journal of the American Veterinary Medical Association 224(3):
380-387. ISSN: 0003-1488. Spain, C., J. Scarlett, and K. Houpt (2004).

Long-term risks and benefits of early-age gonadectomy in dogs.
NAL Call Number: 41.8 Am3

OBJECTIVE: To evaluate the long-term risks and benefits of
early-age gonadectomy, compared with traditional-age gonadectomy,
among dogs adopted from a large animal shelter. DESIGN: Retrospective
cohort study. ANIMALS: 1,842 dogs.

PROCEDURE: Dogs underwent gonadectomy and were adopted from an animal shelter before 1 year of age; follow-up was available for as long as 11 years after surgery. Adopters completed a questionnaire about their dogs' behavior and medical history. When possible, the dogs' veterinary records were reviewed. Associations between the occurrence of 56 medical and behavioral conditions and dogs' age at gonadectomy were evaluated.

RESULTS: Among female dogs, early-age gonadectomy was associated with increased rate of cystitis and decreasing age at gonadectomy was associated with increased rate of urinary incontinence. Among male and female dogs with early-age gonadectomy, hip dysplasia, noise phobias, and sexual behaviors were increased, whereas obesity, separation anxiety, escaping behaviors, inappropriate elimination when frightened, and relinquishment for any reason were decreased.

CONCLUSIONS AND CLINICAL RELEVANCE: Because early-age gonadectomy appears to offer more benefits than risks for male dogs, animal shelters can safely gonadectomize male dogs at a young age and veterinary practitioners should consider recommending routine gonadectomy for client-owned male dogs before the traditional age of 6 to 8 months. For female dogs, however, increased urinary incontinence suggests that delaying gonadectomy until at least 3 months of age may be beneficial.

J Anim Physiol Anim Nutr (Berl). 2001 Aug;85(7-8):195-9.
Leptin, body fat content and energy expenditure in intact and gonadectomized adult cats: a preliminary study.

Martin L, Siliart B, Dumon H, Backus R, Biourge V, Nguyen P. Laboratory of Nutrition and Endocrinology, National Veterinary School of Nantes, Nantes France.

The present study was conducted to assess the body composition, leptin, and energy expenditure changes following gonadectomy in cats. Twenty-one females (12 intact and nine spayed) and 21 males (11 intact and 10 castrated) were used. Body weight was recorded. Serum plasma leptin was measured by radioimmunoassay and body composition and energy expenditure were assessed after injection of doubly labelled water. These results confirmed the gain in body weight and body fat following neutering and demonstrated a strong linear relationship between body fat and serum level of leptin. Energy expenditure decreased in castrated cats in comparison with intact ones. This study underlined the effect of gonadectomy as a major factor of obesity in cats and showed that the increase in circulating leptin reflected the amount of body fat. The present results provide further evidence that the regimen of gonadectomized cats should be carefully controlled to avoid excessive weight gain.

PMID: 11686788 [PubMed - indexed for MEDLINE]

Am J Vet Res. 1996 Mar;57(3):371-4.
Effect of prepuberal and postpuberal gonadectomy on heat production measured by indirect calorimetry in male and female domestic cats.
Root MV, Johnston SD, Olson PN. Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul 55108, USA.

OBJECTIVE: To use indirect calorimetry to compare heat production between gonadectomized and sexually intact male and female cats. DESIGN--Male (n = 6) and female (n = 6) kittens were gonadectomized at 7 weeks or 7 months of age, or left sexually intact. Body heat production was measured by indirect calorimetry in all cats at 12, 18, and 24 months of age.

ANIMALS: 18 male and 18 female clinically normal domestic shorthair cats.

PROCEDURE: Heat production was measured, using an open-circuit, respiratory, indirect calorimeter. All cats underwent calorimetry at 12, 18, and 24 months of age. The heat coefficient, a measure of resting metabolic rate, was calculated for each cat at each test; heat coefficient is defined as logarithm of heat (kcal/h) divided by logarithm of body weight (kg).

RESULTS: Heat production did not vary with age in male or female cats. Heat coefficient was higher in sexually intact male and female cats than in gonadectomized male and female cats at 12, 18, and 24 months of age (12 months, females, P < 0.01, males, P = 0.04; 18 months, females, P < 0.01, males, P = 0.02; and 24 months, females and males, P < 0.01).

CONCLUSIONS: These data suggest that resting metabolic rate in cats decreases after gonadectomy.

CLINICAL RELEVANCE: A decrease in metabolic rate is synonymous with a decrease in caloric requirements. Gonadectomized animals fed in a manner similar to sexually intact animals may be predisposed to obesity and its sequelae.

PMID: 8669771 [PubMed - indexed for MEDLINE]