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S. Corr1, P. Sandøe2, C. Palmer3
1University of Glasgow, School of Veterinary Medicine- College of Medical- Veterinary and Life Sciences, Glasgow, United Kingdom
2University of Copenhagen, Department of Food and Resource Economics and Department of Veterinary and Animal Sciences, Copenhagen, Denmark
3Texas A&M University, Department of Philosophy, Texas, USA
In the UK and USA, veterinary associations strongly encourage owners of dogs and cats to have their companion animal neutered, promoting it as an element of responsible pet ownership. In contrast, vets in continental Europe have traditionally been more reluctant to neuter companion animals, especially dogs. One potential area of disagreement concerns effects on the health of the animals. This paper reviews some of the medical bene ts and adverse effects of neutering, and considers confounding factors.
Techniques and Timing.
Hormonal products can be used for temporary (chemical) sterilization, but are not commonly used long-term, due to concerns over potential adverse effects, and issues of convenience, cost and effectiveness. Surgical neutering achieves permanent control of reproduction, but carries the risk of minor (e.g. in ammation at the surgical
site) or major side effects (e.g. bleeding, infection, or death). Surgical risks are greater for females, as the procedure is more invasive. Ovariohysterectomy is
most common, but has no reported advantages over ovariectomy, which is a simpler and less invasive surgery. Minimally invasive laparoscopic techniques further decrease morbidity. Male animals are typically castrated by surgical removal of the testicles, although vasectomy is also an option for dogs. Complication rates vary with the procedure: a study of 1,016 dogs and 1,459 cats undergoing elective surgery reported post-operative complications in 6.1-19.4% of dogs and 2.6-12.2% cats, most of which were minor1.
Conventional neutering is traditionally performed at around 6 months of age in cats and bitches, with male dogs castrated a few months later. However ‘early’ neutering at 6-16 weeks is increasingly promoted, particularly by charities, for population control. Initial concerns that neutering animals at such a young age would carry increased perioperative risks have proven
unfounded, and no signi cant differences in short- or long-term health issues were reported in a recent study of 800 shelter kittens, randomly assigned to be neutered at 8-12 weeks vs 6-8 months2.
Gender, species and breed-speci c concerns.
The current literature contains hundreds of studies on the effects of neutering, and the results are often con icting. This may be as a result of different methodologies, for example grouping subjects based on gender but mixing breeds; reproductive status is often inferred based on age, which may be inappropriate; and descriptors such as ‘early’ and ‘prepubertal’ are not synonymous. Despite this, the relationship between neutering and conditions such as obesity is relatively consistent, neutering being
a predisposing risk factor, but seeming to be mitigated to a degree if the neutering occurs at a younger age. In contrast, studies on the relationship between neutering and overall longevity have produced con icting results. In many cases, the interactions are complex, with gender, species, breed and the timing of neutering (with respect to the animals’ reproductive status), all having an in uence.
Female dogs (bitches): Neutering prevents complications from pregnancy and decreases the risk
of diseases of the reproductive tract, such as pyometra. In contrast, the risk of developing urinary incontinence, especially in large breeds, is increased. As an example,
a recent study reported a signi cantly higher incidence of incontinence in female German Shepherds neutered < 1 year of age (7.2%) compared to intact females (0%)3.
The relationship between neutering and the occurrence of neoplasia is more complex. Neutering was believed
to reduce the risk of mammary tumours especially if performed before the  rst season, however a systematic review by Beauvais et al4 found limited evidence to support this. More recently, Hart et al3,5 reported mammary cancer rates of 0-4.1% in entire bitches and up to 5% in bitches neutered between 2-8 years of age. However Hart et al5 highlighted the importance of breed, reporting that neutering Labrador Retrievers of either
sex at any stage had little effect on increasing cancers, while neutering a female Golden Retriever > 6 months of age increased the risk of one or more cancers to three to four times that of intact females. Similarly, female Rottweilers, neutered at < 1 year of age were three times more likely than intact females to develop osteosarcoma (OSA)6, while neutering did not increase the risk of OSA in German Shepherds3.
Similar breed- and age-speci c effects have been reported for musculoskeletal disease: Hart et al5 reported the incidence of joint disease in intact female and male Labrador Retrievers and Golden Retrievers to be around
An Urban Experience

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