Before her first heat, around five to six months. I have to tell you honestly that the research on this breed suggests waiting until she is two — and that I disagree with it. This page is my working, so you can judge the disagreement for yourself.
Almost everywhere else on this site, when the research and I disagree, I move toward the research. On the German Shepherd I wait longer than my own default because the evidence is strong. On the Golden Retriever and the Border Collie I simply repeat what the paper concluded.
This is the page where I go the other way, and I am not going to bury that.
The study's guideline for Shih Tzu females is to delay spaying until she is two years old. It found that among females spayed around a year of age, cancers reached about 18% — against 0% in intact females — and that result was statistically significant.
I still recommend spaying before her first heat. That is a real disagreement with a peer-reviewed finding, published under my own name, and you are entitled to see exactly why before you decide anything.
— Dr. P
So let me put the finding first, fairly and in full, and then tell you what I think it can and cannot carry.
What the research actually shows
The Shih Tzu is one of the 35 breeds in the UC Davis neutering study, with 77 intact and 139 spayed females inside a total of 432 dogs.
On joints, the result is as clean as it gets: no occurrences at all, in intact or spayed dogs, of either sex, at any age. No case of urinary incontinence in any female either. On cancers, intact dogs of both sexes recorded 0%. Among spayed females, the figure was about 7% in those spayed between six and eleven months, and about 18% in those spayed at around a year — and that one-year figure was significant at p<0.01. On that basis the paper's guideline for females is to delay spaying until two years of age.
I want to be clear that I am not disputing any of that. It was measured, it was peer-reviewed, and it reached significance. Two things nonetheless give me pause, and neither is that the researchers made a mistake.
One: the comparison is against a zero. That 0% does not mean intact Shih Tzu females never develop cancer — of course some do. It means that among the 77 intact females in this dataset, none happened to during the study. With a group that size, a condition affecting a small percentage of dogs will frequently produce no cases at all purely by chance. So the true intact rate is almost certainly above zero, and the genuine gap is narrower than nought-to-eighteen makes it look. I make the same argument about a 0% baseline on the Miniature Poodle page, where it cuts in the same direction.
Two: it is a small band. The 139 spayed females divide across four spay-age groups and the paper does not publish the per-band counts. If they split anything like evenly, the one-year group holds somewhere in the mid-thirties — so 18% is roughly six dogs. That is a real finding on a small foundation.
Why I come down where I do
If waiting until two years were free, I would do it. Uncertainty about a cancer signal would be reason enough, and elsewhere on this site I act on findings weaker than this one — on the Husky page I follow a cruciate result that never even reached significance.
The difference is entirely in the price. There, waiting cost one heat cycle. Here it costs two or three, and each one takes something well-evidenced away from her.
The mammary side of the ledger. The relationship between spaying before the first heat and substantially reduced mammary tumour risk has been described consistently since the 1960s. It is one of the more durable findings in small animal medicine, mammary tumours are among the more common cancers in intact female dogs, and a meaningful share of them are malignant. That protection erodes with every cycle she goes through. There is also pyometra, which stops being possible the day she is spayed and remains possible every month we wait.
The weaker the evidence, the cheaper the precaution has to be. I use exactly the same rule on the Boxer page and on the Husky page, and it produces opposite answers there because the prices differ.
Here I am being asked to trade a well-replicated benefit I can bank for protection against a single significant result resting on roughly six dogs measured against a zero. I do not think that is the right trade for most Shih Tzus, and that judgement is mine rather than the paper's.
What would change my mind: a larger study finding the same thing, or this one replicated in a population with a non-zero intact baseline. If several hundred Shih Tzu females were examined and the one-year band still stood out, I would rewrite this page that week and say plainly that I had been wrong.
What I recommend
This one is genuinely yours to decide. On most pages here I am fairly confident and I say so. Here I am weighing a well-established benefit against an uncertain risk, and reasonable people can put those on the scale differently. If the cancer finding worries you more than the mammary trade-off does, that is a coherent position — say so and I will spay her at two without making you justify it. What I will not do is pretend the disagreement does not exist.
And whichever we choose, we hedge. I want to see her once a year while she is young and twice a year once she is older, and I want you telling me about any new lump rather than watching it yourself. That costs nothing and it covers the possibility that the researchers were right and I am wrong.
Her brother's answer is much simpler — the male findings in this breed are entirely null. That is on when to neuter a Shih Tzu.
How I do the surgery
At nine to sixteen pounds this is where the laparoscopic advantage is modest, and I would rather say so than sell it to you. The strongest case for keyhole surgery is in large dogs, where a conventional spay means a long abdominal incision. At her size the traditional incision is already small and the recovery already quick. It remains a gentler operation with less tissue disturbed, and some families choose it for that reason. It is not, however, the decision on this page that actually matters — that one is the timing, and it is above.
What the day looks like
She comes in that morning having skipped breakfast, has pre-anaesthetic bloodwork and an IV catheter, and is monitored continuously while she is under, on a warming system throughout. Shih Tzus have a shortened muzzle, so I pay particular attention to her airway while she is anaesthetised and while she wakes up — not a reason for concern, a reason for care. I do the surgery myself; I have been a solo veterinarian since 1998.
She goes home the same day with pain medication, closed with absorbable suture and surgical glue, so there is nothing to remove later. While she is asleep I will also check her mouth for retained baby teeth, which the small breeds keep more often than not. More detail on the day itself is on what to expect from your pet's surgery.
Shih Tzu spay questions
You should listen to both of us and then decide, and I would rather set out my reasoning than ask for trust. The finding is real: among Shih Tzu females spayed around a year of age, cancers reached about 18%, and that was statistically significant. I am not disputing it. What I am weighing is that it is measured against an intact rate of 0%, in a group of 77 dogs — and an observed zero in a group that size is what a low-but-real rate looks like, not proof that intact Shih Tzus never develop cancer. So the true gap is narrower than nought-to-eighteen suggests. Against that uncertainty sits a definite cost: waiting to two years means two or three heat cycles, and mammary protection falls away with each one.
Probably around six, though nobody can say precisely. The paper reports 139 spayed Shih Tzu females in total, spread across four spay-age bands, and it does not publish how many fell into each. If they divide anything like evenly, the one-year band holds somewhere in the mid-thirties, and 18% of that is roughly six dogs. Six dogs is a real finding and it cleared statistical significance, so I am not waving it away. It is also a small foundation on which to ask every Shih Tzu owner in the country to accept a known, quantified loss of mammary protection.
It is the better-established of the two, which is precisely why it wins this argument for me. The relationship between spaying before the first heat and reduced mammary tumour risk has been described consistently since the 1960s and is one of the more durable findings in small animal medicine. Mammary tumours are among the more common cancers in intact female dogs and a meaningful proportion are malignant. So on one side I have a well-replicated benefit I can bank, and on the other a single significant result resting on roughly six dogs measured against a zero. I would rather take the certain benefit.
A larger study finding the same thing, or this one being repeated in a different population with a non-zero intact baseline. If someone published data on several hundred Shih Tzu females and the one-year band still stood out, I would change this page the same week — and I would say plainly that I had been wrong. I would also shift if the cancers involved turned out to be a specific, identifiable type with a plausible hormonal mechanism, the way the mast cell finding in Cocker Spaniels at least gives you something concrete to think about. Right now it is a general cancer signal in one band, and that is thinner.
No, and I would be uncomfortable if you took that away. Two things follow from taking it seriously. First, if this worries you more than the mammary trade-off does, that is a legitimate position and I will spay her later without arguing — this is genuinely a judgement call and yours is the deciding vote, not mine. Second, whatever we decide, I want to see her properly once a year and twice a year once she is older, and I want you telling me about new lumps rather than watching them. That vigilance costs nothing and it hedges the possibility that the researchers were right and I am wrong.
No, and this is the uncomplicated part. The study recorded no joint disorders at all in Shih Tzus — none in intact dogs, none in spayed dogs, at any age, in either sex. There were also no cases of urinary incontinence in any female. So the large-breed reasoning about growth plates and joint angles has nothing to stand on here, and the entire disagreement is about one cancer figure. Her skeleton is not part of this conversation.
Keep reading
Every breed grows on its own schedule. If one of these is closer to your dog, start there.
Your Shih Tzu, the other half of the question:
Similar-size breeds:
The whole picture: read the veterinarian's breed-by-breed spay and neuter guide, or see how the laparoscopic spay works.
I've set out where I disagree with the published guidance and why. Bring her in and we'll weigh it together — on this page your view genuinely decides it.
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