Your older dog is stretched across the kitchen floor when the young one barrels through toward the back door and clips his hip. For years that got a sigh, maybe a lazy thump of the tail. Last week it got a snap, fast and loud, and then the old dog laid his head back down as if nothing had happened.
It has happened twice more since, and the family has an explanation ready. He’s getting grumpy, they say. What nobody has lined up yet is when it happens. Each time, he was lying down, and each time, something touched his back end.
Grumpy is a word for a mood. Lying down and touched on the hip is a pattern, and a pattern is something a vet can work with.
Quick answer
Joint pain can change how a dog behaves. Long-term pain may show up as new irritability, especially around being touched or handled, or as a dog pulling away from the family, and behavior specialists suspect it in a large share of the dogs referred to them. You can’t confirm it at home, and not every change in temper is pain. What helps is noting where he was and what touched him each time it happens, and bringing that to your vet. A change that came on over a few days, or a bite that broke the skin, needs a call to your vet today.
Can pain change a dog’s behavior?
Yes, and owners are often the first to see it. The Merck Veterinary Manual points out that owners are the ones placed to catch the subtler signs of long-term pain, “such as changes in attitude or interaction with family members” (Allweiler, Merck Veterinary Manual). Those are the changes that get filed under personality.
Behavior specialists see it from the other side. Looking back at recent cases from their own referral clinics, a group of veterinary behaviorists estimated, conservatively, that pain was suspected in around a third of the dogs brought to them for behavior problems, and at some clinics in close to 80% (Mills et al., 2020).
They urge vets to lean toward treating pain whenever it might be involved, rather than waiting to see whether behavior therapy fails.
Those figures have limits. Pain was suspected in those cases, and how often it was then confirmed varied widely from clinic to clinic. The dogs had also already been referred to a specialist, so the numbers don’t tell you how common this is in dogs in general.
What does pain-related grumpiness tend to look like?
The research sketches a dog who puts up with less: handling, being approached while he’s lying down, the bumps he used to shrug off. None of the studies behind that sketch is large.
The 2020 review summarizes a clinical comparison of aggressive dogs with and without musculoskeletal pain, meaning pain in the muscles, bones and joints. The dogs in pain were often described as having a changeable temper, easy one hour and short the next. Trouble typically came when someone approached one of them, often while he was lying down, and a closer look tended to turn up a general reluctance to move (Mills et al., 2020).
Their bites were usually quick, easy to interrupt, and aimed at the ends of the limbs, a hand, a foot or a paw, more than at the face or body. The review’s authors read them as “a low level violent threat aimed at saving the animal from further interaction.” They are also clear that traits like these can help flag pain but can’t confirm it.
Handling comes up again in a small study from Barcelona. It described 12 dogs chosen because their aggression had been linked to pain, most often hip dysplasia, a malformed hip joint that tends to lead to arthritis. Dogs that had never been aggressive before the pain began were more impulsive, and more likely to be aggressive when handled, than dogs with an earlier history (Camps et al., 2012).
Because every dog in that study was picked for having pain-related aggression, it describes what that aggression looks like. It can’t say how many aggressive dogs are in pain.
Snapping is one version; pulling back is another. A 2024 study from the UK compared 46 dogs with long-term musculoskeletal pain with a group of healthy dogs. The dogs in pain scored worse for how often they showed fear, how they coped with stress, how much they engaged with toys and play, and how much good social contact they had (Malkani et al., 2024).
The healthy dogs had been chosen partly for being emotionally healthy, which likely widens the gap, while some of the dogs in pain had already been treated, which could narrow it. And every dog in pain was assessed after the diagnosis, so the study shows that these things occur together, not which one came first.
Why is “he’s getting grumpy” the easy answer?
Because it can be true. Dogs change as they age, and an old dog who shares a house with a boisterous youngster may simply have had enough of him.
The trouble is what the word leaves out. It’s the behavioral cousin of “he’s just getting old,” which we looked at in My Dog Is Slowing Down. Is He in Pain?.
Age doesn’t explain the Barcelona dogs, either. They ranged from 1 to 13 years old, and averaged about five (Camps et al., 2012).
Anxiety is also common in dogs generally. In one survey of 13,700 Finnish dogs, which didn’t look at pain, close to a third were often afraid of at least one loud noise (Salonen et al., 2020). So a new fear can’t be read as a sign of pain on its own, and some dogs have both.
If what you’re seeing looks more like new fear than new irritation, Anxiety in Older Dogs Is Rarely Just Age walks through the other causes worth checking. If fear has been part of his life all along, our guide to dog anxiety is the better place to begin.
What details help the vet most?
The moments around each episode help more than a count of them. “He snaps sometimes” leaves your vet guessing. “He snaps when he’s lying down and gets bumped on the left hip” gives them a place to start.
Over the next week or two, keep track of those moments. Where was he: lying down, getting up, on the stairs? What had just happened: a touch, a lift, a step over him, a bump from the other dog, a request to move? Which part of him was involved, if any? And what has he stopped choosing to do, like jumping on the bed or joining a game?
Bring all of it to the appointment, whatever it seems to point to. Sorting pain from behavior is your vet’s job.
Note any physical changes alongside those moments. Why Dogs Hide Pain, and What You Can See Instead is about the quieter physical signs, and a dog can have arthritis without a limp anyone at home has noticed.
What can my vet do about it?
Your vet will examine him, joints and back included, and can compare what you’ve noticed with what the exam finds.
If pain seems likely, your vet can suggest treating it and watching what happens next. According to the Merck Veterinary Manual, a response to treatment, such as a dog becoming more active on a prescribed anti-inflammatory pain reliever (an NSAID), may tell a vet something important about the role pain plays in a change in behavior (Allweiler, Merck Veterinary Manual).
The 2020 review goes further for dogs whose problem looks behavioral. Pain relief is worth trying “even if a specific physical lesion has not been identified,” and, in the authors’ experience, one medication that fails to help doesn’t rule pain out, because some dogs need a different drug or a combination (Mills et al., 2020).
So a normal exam isn’t the last word on pain. Whether to try pain relief is your vet’s call, and a referral to a veterinary behaviorist is something you can raise.
Whatever your vet tries will be a drug they prescribe, at a dose they set. Don’t give him pain relievers meant for people. Aspirin can ulcerate his stomach, acetaminophen can injure his liver, and in large amounts ibuprofen can kill, but small daily doses of naproxen or ibuprofen have been enough to make dogs sick (Hovda, Merck Veterinary Manual).
How can I keep things calmer at home before the vet visit?
Mostly, give him room, starting with where he lies. In those clinical descriptions, trouble tended to start when the dog was approached, often while lying down.
Move his bed out of the traffic path, somewhere he won’t be stepped over or bumped. If there’s a younger dog in the house, keep their rough play short and separate them when it gets loud.
If he has snapped near a child, keep the two apart until the vet visit, and supervise any contact after that. If he hasn’t, ask the kids to call him over instead of going to him, and to leave him be when he’s lying down.
Watch for the small warnings, too. The 2020 review suggests that when quieter signals, such as a head turn or a hard stare, go ignored or unnoticed, a dog may stop offering them, and the next bite can seem to come out of nowhere (Mills et al., 2020).
All of this cuts down how many times a day he has to defend himself while you find out what’s going on. It doesn’t treat anything.
What do I do if he snaps again?
Book the appointment first. Before it, keep the young dog’s route to the back door clear of the old one, and if it happens again, notice where he was lying and what touched him. That goes to the vet along with everything else.
Common questions
He only snaps at our other dog, never at us. Does that still count?
Yes. In the clinical descriptions of dogs with musculoskeletal pain, the targets often included other dogs as well as people, familiar and unfamiliar alike. It can also be about the other dog himself, which is one more thing for your vet to weigh. Tell them about it the same way: where he was, and what the other dog did just before.
If the pain is treated, will his temper improve?
In some dogs it does. The 2020 review describes cases in which problem behavior eased once pain was treated, sometimes without any specific behavior work. Those are individual cases, so they can’t show how often it happens, and some dogs need help on the behavior side as well.
Could the pain be coming from somewhere other than his joints?
Yes. In the behavior cases the 2020 review looked at, painful gut and skin conditions came up alongside muscle and joint problems. In the Barcelona series, two of the 12 dogs had long-running ear inflammation and one had a skin injury. That’s one more reason to let the exam look at all of him.
Sources
- Allweiler S. Recognition and Assessment of Pain in Animals. Merck Veterinary Manual, last updated Sept 2024. Link
- Camps T, Amat M, Mariotti VM, Le Brech S, Manteca X. Pain-related aggression in dogs: 12 clinical cases. Journal of Veterinary Behavior. 2012;7(2):99-102. Link
- Hovda T. Toxicoses From Human Analgesics in Animals. Merck Veterinary Manual, full review Jul 2024, last updated May 2025. Link
- Malkani R, Paramasivam S, Wolfensohn S. How does chronic pain impact the lives of dogs: an investigation of factors that are associated with pain using the Animal Welfare Assessment Grid. Frontiers in Veterinary Science. 2024;11:1374858. Link
- Mills DS, et al. Pain and problem behavior in cats and dogs. Animals. 2020;10(2):318. Link
- Salonen M, et al. Prevalence, comorbidity, and breed differences in canine anxiety in 13,700 Finnish pet dogs. Scientific Reports. 2020;10:2962. Link