Neutering and spaying: pros, cons and timing

Neutering is one of the most common operations vets perform, and one of the first big decisions for a new dog owner. For a long time the advice was simple: neuter every dog at around six months. Research over the last decade has made the picture more nuanced, especially for larger breeds. This guide explains what is well established, what is still debated, and the questions to discuss with your vet.

What neutering involves

• Castration removes a male dog’s testicles.
• Spaying removes a female dog’s ovaries and womb.

Both are done under general anaesthetic, and most dogs go home the same day. Some vets offer keyhole (laparoscopic) spays, which make smaller wounds but need special equipment. For males, a hormone implant or injection can mimic the effects of castration temporarily and reversibly, which some vets suggest to see how castration might affect a dog before a permanent operation.

The benefits

Veterinary charities list several clear benefits:

• No unwanted litters. Neutering prevents pregnancies, including between related dogs, which carries a higher risk of puppies with birth defects.
• For females: no seasons, no false pregnancies, and protection against pyometra, a serious womb infection. Spaying before the first season significantly reduces the risk of mammary (breast) cancer, according to the PDSA, a veterinary charity.
• For males: no risk of testicular cancer, fewer prostate problems later in life, and usually less roaming, urine marking and mounting.
• Practical advantages: no bleeding during seasons, which can last up to three weeks, and no need to keep entire males and females apart.

The PDSA recommends neutering all dogs unless your vet advises against it, and states that there is no evidence that letting a bitch have a litter first benefits her.

The risks and open questions

Like any operation under anaesthetic, neutering carries a small risk of complications, which your vet will discuss with you. Beyond the surgery itself, research has raised three main questions.

Joint disorders in larger dogs. A team at the University of California, Davis, studied records from its veterinary hospital. In earlier work on Golden Retrievers, Labrador Retrievers and German Shepherds, neutering before one year of age was associated with two to four times the risk of hip dysplasia, cruciate ligament tears or elbow dysplasia compared with dogs left intact, particularly when dogs were neutered by six months. Extending the study to 35 breeds, they found major differences between breeds, and that small breeds showed no increased risk of joint disorders with neutering. In mixed-breed dogs, neutering before one year was linked to more joint disorders in dogs weighing 20 kg or more, commonly three times the level of intact dogs, but not in dogs under 20 kg.

Some cancers. The same researchers found that in female Golden Retrievers, neutering at any age was associated with two to four times the rate of one or more cancers, and in only two small breeds, the Boston Terrier and the Shih Tzu, was there a significant increase in cancers. In mixed breeds, they found no increase in any weight category. Other evidence points the other way: a separate study of Golden Retrievers examined after death found that being spayed or neutered did not affect the risk of dying from cancer, while age did. The PDSA notes that neutering reduces the risk of many cancers, that there is no solid evidence it causes cancer overall, and that neutered dogs tend to live longer, which may explain some higher cancer rates.

Urinary incontinence. Spaying very young bitches, under three months old, can increase the risk of a type of urinary incontinence, according to the PDSA; after three months, it reports no evidence of an increased risk.

These studies come mostly from single hospitals or specific populations, so their results are not the final word, but they explain why many vets now tailor the timing to the individual dog.

Behaviour: what neutering will and will not do

• It can help with behaviours driven by sex hormones, such as roaming, urine marking and some mounting.
• It does not cure aggression. The PDSA states that neutering does not prevent aggression and can sometimes make it worse.
• It can make fearful dogs worse. Sex hormones such as testosterone tend to boost confidence, so neutering a nervous or under-confident dog may make it more fearful, the PDSA explains. A confident, well-socialised dog is very unlikely to change personality.

The evidence is not simple. In a UK study of Rottweilers, aggression was recorded more often in neutered females than in entire females (7.5% against 3.1%), while in males it did not differ with neutering. If you are considering neutering for a behaviour problem, speak to your vet and a qualified behaviourist first.

Weight after neutering

Neutering does not make a dog fat by itself, but it changes hormones in a way that can increase appetite and slow the metabolism. The PDSA estimates that a dog needs around 30% fewer calories after neutering, so reduce portions or choose a food for neutered dogs, and keep checking body condition. Our guide to dog food basics explains how.

When to neuter

Most dogs can be neutered from about four to six months, but the PDSA advises basing the timing on:

• Size and breed. Large and giant breeds take longer to grow, and their growth plates close later, so your vet may suggest waiting. The UC Davis studies give breed-by-breed suggestions for the timing that avoids increasing the risks they studied.
• Sex. In the studies above, the effects often differed between males and females.
• Behaviour. Delay or reconsider if your dog is nervous or fearful.
• Weight. Overweight or underweight dogs face more risk during surgery, so get them into good shape first.
• Seasons. A bitch can be spayed before her first season. After a season, the PDSA advises waiting about two to three months, because spaying too soon can cause ongoing hormonal problems such as a long false pregnancy.
• Other health conditions, which may change the ideal timing.

If you keep your dog entire

Choosing not to neuter, or to wait, is a valid decision in discussion with your vet, but it brings responsibilities:

• Keep an entire female away from all entire males throughout her season, usually two to four weeks.
• After each season, watch for signs of pyometra and false pregnancy, and check her mammary glands regularly for lumps.
• Keep an entire male away from females in season, take care around other entire males, and watch for prostate or testicle problems as he ages.
• Make sure your garden and walks prevent escapes: entire dogs are more motivated to roam.

Before and after the operation

• Before: no food for 6 to 8 hours before the anaesthetic (usually dinner the night before, no breakfast), water until 2 to 3 hours before, and tell your vet if your dog has been unwell.
• After: expect sleepiness for up to a day or two. Your dog then needs 7 to 10 days of rest, on the lead and in a small space if necessary, even if it feels well. A cone or a medical body suit stops it licking the wound. Check-ups are usually at 2 to 3 days and 7 to 10 days, and any non-dissolvable stitches come out after 7 to 14 days.

Questions to ask your vet

• What is the best age to neuter my dog, given its breed, expected adult size and sex?
• Are there breed-specific risks I should weigh up?
• Is my dog’s behaviour a reason to neuter, wait or avoid it?
• Is a keyhole spay or a temporary hormone implant an option?
• How should I adjust its food afterwards?

There is no single right answer for every dog. Breed profiles such as the Golden Retriever, Labrador Retriever and Rottweiler include the breed-specific research we cite here. If you are budgeting for a new dog, our guide to the real costs of owning a dog includes neutering among the setting-up costs.