When to spay or neuter your dog or cat

For cats, the answer is simple: spay or neuter by 5 months old, the age recommended by the Feline Fix by Five consensus and supported by the AVMA and feline specialists. For dogs, it depends on expected adult size. AAHA suggests about 6 months (or before the first heat) for dogs that will weigh under 45 lb (20 kg), and after growth stops, usually 9 to 15 months, for larger dogs, with your vet weighing the risks for your breed.

Dog guidance has changed in the last decade, and there is no single age that suits every dog. Here is what the current guidelines say, why, and what to ask your vet.

The short answer by species and size

These are starting points. Your vet may suggest something different for your pet’s breed, health or home.

Cats: by five months

In 2016 a veterinary task force recommended neutering cats not intended for breeding by 5 months of age, and the AVMA and the American Association of Feline Practitioners (AAFP) endorsed it. The reasons:

• Kittens mature early. Female kittens can come into heat from about 4 months, and pregnancy can follow. Waiting until 6 months, the old habit, leaves a window for an unplanned litter
• No added surgical risk. The AAFP notes that studies show no increase in major complications, and fewer minor ones, when cats are neutered younger than five months
• Lower mammary cancer risk for females spayed young
• Fewer hormone-driven behaviours: spraying, yowling in heat, roaming and fighting, which also spreads infections such as FIV

International Cat Care goes slightly earlier and recommends around 4 months. Either way, keep your kitten indoors until they are neutered and vaccinated. Your vet will still decide on the day, based on your kitten’s health.

Dogs: why size matters

For years, 6 months was the standard age for every dog. Research from UC Davis, which reviewed the hospital records of dogs across 35 breeds, found that for some breeds, especially some larger ones, neutering before about a year was linked with more joint disorders (hip dysplasia, cruciate ligament tears, elbow dysplasia) and, in a few breeds, certain cancers. In most breeds studied, and in most small breeds, the age of neutering made little difference to those risks.

The likely reason for the joint findings is that sex hormones help close the growth plates in the bones. Removing them while a large dog is still growing changes how the joints develop.

So AAHA’s 2019 guidelines split dogs by expected adult weight:

Small dogs (under 45 lb / 20 kg as adults)

• Males: neuter at about 6 months
• Females: spay before the first heat, at around 5 to 6 months

Small breeds finish growing early, and the joint and cancer concerns seen in some large breeds were mostly not found in small ones.

Large dogs (over 45 lb / 20 kg as adults)

• Males: neuter after growth stops, usually 9 to 15 months
• Females: anywhere between 5 and 15 months, which is where the trade-off is hardest

For large-breed females, the choice is between two kinds of risk:

The AVMA’s view is that there is no single recommendation that suits all dogs, and that the decision should be made case by case with your vet. For a few breeds, breed-specific research points to waiting even longer. Ask your vet what is known for yours.

Mixed breeds and unknown sizes

If you don’t know how big your puppy will get, ask your vet to estimate from their weight and growth. The puppy weight calculator gives a rough idea too.

Benefits of spaying and neutering

Both species

• No unplanned litters
• Less roaming, which means fewer road accidents, fights and lost pets
• Less urine marking and fewer hormone-driven behaviours

Females

• Lower risk of mammary tumours. In dogs, figures cited by the American College of Veterinary Surgeons put the risk at about 0.5% when spayed before the first heat, 8% after one heat and 26% after two
• No pyometra, a life-threatening infection of the womb that is common in older unspayed females
• No heat cycles: no bleeding in dogs, no repeated calling in cats

Males

• No testicular cancer
• Lower risk of some prostate problems in dogs
• In cats, much less spraying and a less pungent smell

Risks and side effects

• Surgery and anaesthesia carry a small risk, as any operation does. Your vet will examine your pet first, and many recommend pre-anaesthetic blood tests
• Weight gain. Neutered pets often need fewer calories. Weigh them regularly after surgery and adjust portions: the dog calorie calculator and cat calorie calculator can help
• Joint disorders and some cancers in some large dog breeds when neutered early, as above
• Urinary incontinence in some spayed female dogs, which is usually treatable with medication

Some vets also offer hormone-sparing options such as a vasectomy or an ovary-sparing spay. They prevent pregnancy without removing hormones, but they don’t give the same behaviour and health benefits and aren’t widely available. Ask your vet whether they make sense for your dog.

What about letting her have one litter first?

There is no health benefit to a female dog or cat having a litter, or a season, before she is spayed. In dogs, each heat before spaying increases the risk of mammary cancer.

Before and after the surgery

Before

• Your vet will usually ask you to stop food the night before. Follow their exact instructions, which may differ for young kittens and puppies
• Make sure vaccines are up to date
• Ask about pain relief, the cone or recovery suit, and when stitches come out

After

• Most pets go home the same day and are sleepy that evening
• Keep them calm and on a lead for about 10 to 14 days, or as long as your vet says: no running, jumping or rough play
• Stop licking at the wound with a cone or recovery suit
• Check the wound once or twice a day

Call your vet if the wound opens, bleeds, swells or oozes, if your pet is still very sleepy or not eating the day after surgery, keeps vomiting, or seems in pain despite their medication.

Questions to ask your vet

• What age do you recommend for my pet’s breed and expected size?
• What are the specific risks for this breed if we spay or neuter earlier or later?
• How do we prevent pregnancy if we wait? (Female dogs in heat need careful supervision for about three weeks)
• What does the surgery involve, and what pain relief will they have?
• Should we change their food afterwards?