Sterilisation in female dogs

The decision that avoids drama… and adds years of peace of mind 

In everyday language, “sterilisation” is used for almost everything, but in veterinary medicine it is important to distinguish between two different concepts.

Sterilisation strictly means that the animal can no longer reproduce, but it can keep its gonads (ovaries or testicles) and therefore continue to produce sex hormones. Fertility is blocked, but the “hormonal engine” can continue to function.

Castration means that the gonads (ovaries in females, testicles in males) are removed. When these structures disappear, not only is reproduction prevented, but the production of sex hormones also decreases or disappears, which has very important effects on reproductive health and on some behaviours linked to the cycle.

In practice, when a vet says “spay” a dog, they are very often referring to surgical castration (OVH or OVE). That is why it is so important to clarify the term during the consultation, so that we are all talking about the same thing.

Explained as if to 12-year-olds: imagine that reproduction is a two-part system. One part is the hormone factory (the ovaries), which sends signals to the body. The other part is the “pathways” through which the eggs travel. In sterilisation, a lock is placed on the pathways, but the factory can continue to operate. In castration, the factory is turned off, which is why many diseases and problems that depend on those hormones are greatly reduced or disappear.

In female dogs, when the greatest preventive effect is sought, the most common procedure is castration by ovariectomy (OVE), which removes the ovaries, or ovariohysterectomy (OVH), which removes the ovaries and uterus. When talking about sterilisation in the strict sense, without removing the gonads, tubal ligation is often mentioned, which blocks fertility but preserves much of the hormonal function.

Benefits of sterilisation and, above all, castration in companion animals

When seeking real long-term prevention, the big health leap usually comes from castration, because it markedly reduces the hormonal influence on the reproductive system. Even so, many families use “sterilisation” as a general term, and in this text it is understood in that broad sense.

Prevention of reproductive and hormone-dependent diseases

Pyometra: the silent emergency that can be avoided

Pyometra is a serious uterine infection that can quickly develop into a serious general condition. It usually appears weeks after oestrus, when progesterone promotes a uterine environment that is more susceptible to bacterial proliferation and the accumulation of secretions. It is often associated with cystic endometrial hyperplasia, which means that the inner lining of the uterus thickens and forms cystic structures; simply put, the uterus becomes more vulnerable and can act as a “container” that facilitates infection.

Most importantly, this is not an uncommon problem. Population studies have reported that around 19% of bitches develop pyometra before the age of 10, with a mean age of around 7 years, and other analyses have estimated figures of around 23–24% before that age, with significant variations depending on breed. When it occurs, it often requires stabilisation and surgery, and although survival at discharge can be around 97%, it is still an episode that usually involves emergencies, hospitalisation and considerable stress. Selected medical treatments have also been described, but with significant recurrences, reinforcing the idea that prevention is extremely valuable.

Mammary tumours in female dogs: the effect of “timing” in figures

The mammary glands respond to sex hormones, and the risk behaves as a cumulative phenomenon because each reproductive cycle is a new exposure. A classic study described very instructive figures on the impact of the timing of the intervention: the estimated relative risk of mammary tumour was approximately 0.5% when performed before the first heat, around 8% if performed after one heat, and about 26% after two or more heats. These figures help to understand why prevention has a particularly interesting time window, although it must always be individualised according to the patient.

In certain population contexts, frequencies of around 13% of mammary tumours before the age of 10 have been reported in female dogs, which reminds us that this prevention is not theoretical, but clinical.

Pseudopregnancy in bitches: when the body ‘believes’ it is pregnant

Pseudopregnancy is an endocrine phenomenon in which, after oestrus, the body behaves as if it were pregnant. Maternal behaviour, restlessness, object guarding, changes in appetite and even milk production may be observed. In bitches in which these episodes are intense or repetitive, eliminating the cycle through spaying usually provides a clear benefit in terms of well-being and stability.

Benefits for the family and for coexistence

Emotional condition and daily behaviour

Sex hormones influence behaviour, especially during periods of heat. In many bitches, the absence of cycles eliminates periods of marked changes and reduces problems associated with pseudopregnancy.

It is important to be precise so as not to create false expectations. Sterilisation or castration does not erase personality or turn an active animal into an apathetic one. What usually decreases is the “hormonal drive” that, at certain times, amplifies behaviours of excitement, searching or stress. In practice, this translates into more predictable and often calmer coexistence.

Longevity and quality of life

Large clinical databases have observed an association between sterilisation/castration and increased longevity in female dogs. Average increases of around 23% have been reported in sterilised female dogs.

Association between sterilisation and longevity

The database of more than 70,000 animals found that neutered dogs lived longer than unneutered dogs, with sterilised dogs living 9.4 years compared to 7.9 years for intact animals. 

The responsible interpretation is to understand that longevity depends on many factors, but that reducing serious diseases and indirect risks associated with reproduction can tip the balance towards a longer and more stable life. 

Zero accidental pregnancies and an end to unwanted mating

Sterilisation/castration completely eliminates the risk of unwanted mating and suppresses the risk of unintended pregnancy, with all that this avoids in terms of stress, emergencies, expenses and difficult decisions. It also reduces the likelihood of impulsive reproductive escapes, which can decrease the risk of loss, being run over or conflicts.

In addition, when diseases such as pyometra are prevented or the risk of mammary tumours is reduced, the consequences of these diseases are avoided: emergencies, hospitalisation, more complex treatments and often intense family concern. Preventive medicine is often measured by what does not happen.

Disadvantages and points to watch out for after spaying or neutering

A serious article does not present sterilisation as a magic solution. It presents it as a decision with clear benefits and possible drawbacks that are much better managed when anticipated.

Metabolism: when the body needs less energy

After sterilisation/castration, changes in metabolism and hunger and satiety signals may occur. This means that if the diet is not adjusted, the energy balance can easily be disrupted.

Your vet advises: “The first 6 weeks are crucial”

The key time to prevent weight gain is not “when they have already gained weight”, but during the first few weeks: adjust their diet, weigh them frequently and increase their daily exercise. This is the kind of advice that owners can actually follow.

The tendency to become overweight is probably the most common problem, but also the easiest to prevent. When the diet is adjusted from the outset, treats are monitored and body condition is checked regularly, most spayed bitches maintain a healthy weight. The importance of this point is not aesthetic, but medical, because obesity increases the risk of osteoarthritis, reduces exercise tolerance and contributes to other health problems.

Urinary incontinence in some bitches: a real risk with possible management

A percentage of spayed bitches may develop urinary incontinence in the medium to long term. Approximate prevalences of 2.26% per year, close to 9.01% at 3 years and around 11.27% at 5 years after sterilisation have been reported in certain follow-ups. Data have also been published suggesting that the age of sterilisation could influence the risk of early incontinence in some contexts. The most common cause of incontinence in adult spayed bitches is urethral sphincter mechanism insufficiency (USMI), which occurs more frequently in heavier bitches. The most important thing to remember in clinical practice is that, if it does occur, there is usually effective medical management available and it can be addressed with an individualised plan.

Weight matters: practical threshold

One study (JAVMA) found an association between size/weight and incontinence rates, with more incontinence in large bitches (e.g., ≥15 kg in their analysis). This is a good hook for linking to body condition control after surgery. 

A decision that protects today and cares for the future

Spaying and, especially, neutering are preventive medicine tools with a real and measurable impact on female dogs. They drastically reduce the risk of pyometra, significantly decrease the risk of mammary tumours when performed early, provide emotional stability in many patients, and completely eliminate the possibility of accidental pregnancies. Possible drawbacks, such as weight control or incontinence in a group of female dogs, are better managed when planned from day one with nutrition, monitoring and check-ups.

Many veterinarians recommend spaying/neutering because, on balance, it prevents serious diseases that occur with considerable frequency and because it reduces indirect risks related to reproduction, escapes and accidents. The recommendation is usually based on years of clinical experience and simple preventive logic: if a potentially life-threatening emergency can be avoided and the risk of tumours reduced, it is usually worth considering, always with an individualised approach and a weight control plan.

Sources and recommended reading

Schneider, R., Dorn, C. R., Taylor, D. O. N. (1969) – Factors influencing canine mammary cancer development and postsurgical survival. – Journal of the National Cancer Institute – Classic relative risk data for mammary tumours according to previous heat cycles (0.5% / 8% / 26%). – https://academic.oup.com/jnci/article-abstract/43/6/1249/910225

Overley, B., Shofer, F. S., Goldschmidt, M. H., Sherer, D., Sorenmo, K. U. (2005) – Association between ovariohysterectomy and feline mammary carcinoma. – Journal of Veterinary Internal Medicine – Reduction in the risk of feline mammary tumours with early sterilisation. – https://pubmed.ncbi.nlm.nih.gov/16095174/

Jitpean, S., Hagman, R., Ström Holst, B., Höglund, O., Pettersson, A., Egenvall, A. (2012) – Breed variations in the incidence of pyometra and mammary tumours in Swedish dogs. – Preventive Veterinary Medicine – Cumulative risk of pyometra (19% before 10 years) and mammary tumours (13% before 10 years) in the population. – https://pubmed.ncbi.nlm.nih.gov/23279535/

Egenvall, A., Hagman, R., Bonnett, B. N., Hedhammar, A., Olson, P., Lagerstedt, A.-S. (2001) – Breed risk of pyometra in insured dogs in Sweden. – Journal of Veterinary Internal Medicine – Estimates of pyometra risk by age (around 23–24% before 10 years) and variation by breed. – https://pubmed.ncbi.nlm.nih.gov/11817057/

Pailler, S., Faucher, M., Lamy, E., et al. (2022) – Findings and prognostic indicators of outcomes for bitches with pyometra treated with ovariohysterectomy. – Journal of the American Veterinary Medical Association – Survival data at discharge around 97% in bitches with pyometra treated surgically. – https://avmajournals.avma.org/view/journals/javma/260/S2/javma.20.12.0713.xml

Ros, L., Ström Holst, B., Hagman, R. (2014) – A retrospective study of bitches with pyometra, medically treated with aglepristone. – Theriogenology – Approximate clinical success of 75% and recurrence rates close to 48% in selected medical treatment. – https://www.sciencedirect.com/science/article/pii/S0093691X14004580

Leupolt, B., et al. (2021) – Prevalence and risk factors for urinary incontinence in bitches five years after ovariohysterectomy. – Arquivo Brasileiro de Medicina Veterinária e Zootecnia – Approximate prevalence 2.26% (1 year), 9.01% (3 years) and 11.27% (5 years). https://www.scielo.br/j/abmvz/a/qkDvZf3VqW7YK47x9dFgJnF/?format=html&lang=en

Royal Veterinary College (RVC) (2024) – New RVC research reveals later-age spaying of bitches reduces risk of urinary incontinence. – Epidemiological communication – Relative reduction of nearly 20% in the risk of early incontinence with later sterilisation in certain analyses. – https://www.rvc.ac.uk/vetcompass/news/new-rvc-research-reveals-later-age-spaying-of-bitches-reduces-risk-of-urinary-incontinence

Banfield Pet Hospital (2013) – Spaying and neutering may contribute to longer lifespans (State of Pet Health 2013). – Analysis of a large clinical database with average percentage increases in longevity in spayed/neutered animals. – https://www.banfield.com/about-banfield/newsroom/press-releases/2013/spaying-and-neutering-may-contribute-to-longer-lifespans

Bermingham, E. N., Thomas, D. G., Morris, P. J., Hawthorne, A. J. (2010) – Energy requirements of adult cats. – British Journal of Nutrition – Differences in energy requirements in neutered cats (approx. 10.4% less). https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/energy-requirements-of-adult-cats/225A91E97C8B94CAB4A5BF0646EFA2A2

Alexander, L. G., Salt, C., Thomas, G., Butterwick, R. (2011) – Effects of neutering on food intake, body weight and body composition in growing female kittens. – British Journal of Nutrition – Changes in food intake and weight differences after neutering in female kittens. – https://pubmed.ncbi.nlm.nih.gov/22005425/