Short answer: Viral arthritis, also called viral tenosynovitis, is caused by avian reovirus. It makes broilers, mostly from about five weeks, swell at the hock, limp, and in some birds rupture the tendon at the back of the hock so they sit down and cannot reach feed. There is no specific antiviral, so the work is to separate the lame birds from the healthy ones, keep litter dry, and ask your vet to confirm the cause before you treat anything.
Key takeaways
- A broiler that sits on its hocks and will not stand is the classic sign, and it usually means a tendon problem rather than laziness.
- The swollen hock joint and the tendon sheath are the places a vet looks at first, so check the joints on a morning round.
- Viral arthritis can look like bacterial arthritis or a growth leg problem, so the diagnosis needs a vet and often a post-mortem.
- The virus spreads through litter and eggs, so dry litter, all-in-all-out batches and the breeder vaccine history matter most.
- Birds that cannot reach feed and water need removing, and your vet can advise on humane culling if they do not recover.
A broiler that sits on its hocks is not lazy
Walk into a grower house and the birds that matter most are the ones sitting still on the litter, legs stuck out behind them. Those birds are not being lazy. It is telling you the leg cannot take its weight. When the sitters are at the back of the house and the feeder line is quieter than it was a week ago, you may be looking at viral arthritis.
The disease gets its name from the joints and the tendon sheaths, which are the thin tubes that let tendons slide smoothly at the hock. In an affected bird the sheath swells and fills with fluid, and the tendon can rupture. A bird with a ruptured tendon at the back of the hock cannot stand on that leg again, and it will not walk to the feeder unless someone carries it there.
What the reovirus does in the joint and the tendon
The virus behind the disease is an avian reovirus. Reoviruses are tough, simple viruses that can survive for a long time in dry litter and dust. In broilers they target the tendon sheaths and the joints around the hock, and the damage causes inflammation, swelling and fluid. Over several days the inflamed tendon can weaken until it snaps, most often the tendon behind the hock that pulls the toes.
The reovirus is also linked with poor growth and uneven flocks, because a bird with a sore leg eats less and walks less. A house can look like a normal flock from the feed side and still be losing weight at the joints. That is why a vet looks at the legs and the tendons, not only at the dead birds.
Where it fits among the causes of lameness
Lameness in broilers has many causes, and they can look alike from a distance. Growth problems in the bones, wet litter that burns the hocks, and bacterial infections can all leave a bird standing on one leg. Our guide on leg problems and lameness covers those causes and the daily walk that picks them up early.
This page is about the viral form only. The reason the separation matters is that the treatment and the prevention differ. Bacterial joint infections are treated with antibiotics chosen by the vet. Viral arthritis is not, and a farmer who gives an antibiotic for a virus wastes money and may not stop the spread at all.
The age and the look of a flock with viral arthritis
Viral arthritis most often shows up from about five weeks of age, and it can run through the grower phase until the birds are sold. It rarely affects the first week or two, which is why a farmer who sees lame birds in week three should look at the brooding and the feed first. The heavier, faster-growing birds in the house seem to be hit hardest.
- A hock joint that is swollen, warm to the touch and thickened compared with the other leg.
- Limping on one leg, or reluctance to walk to the feeder even when the feed is close.
- Birds sitting with the hocks flat on the litter, sometimes with the foot turned under.
- A tendon at the back of the hock that is ruptured, so the foot hangs loose when the bird is lifted.
- Uneven growth in the flock, with some birds clearly smaller than the rest by the second half of the cycle.
- Mortality that is usually low, but a steady trickle of culls that adds up over the batch.
Counting the sitters on a morning round
The best tool for this disease is a simple count, done the same way every morning. The sitters tell you more than the dead birds do, because a bird that is sitting today may be dead in a week, and the count shows the trend before the losses do.
- Walk the house at the same time each morning, before the birds are fully active.
- Count the birds that are sitting, the birds that are limping, and the birds that cannot reach the feeder.
- Lift a few of the sitters gently and check each hock for swelling and for a loose, hanging foot.
- Write the numbers down by section of the house, because a corner that is wetter than the rest often shows the first cases.
- Move any bird that cannot reach feed or water to a pen with easy access, and mark it in your book.
- Compare the count with yesterday and with last week, and call the vet if it climbs over several days.
Viral arthritis against the bacterial and growth look-alikes
Your vet will work through the look-alikes before settling on a diagnosis. The table is the set of questions that usually separates them, so you know what to tell the vet and what to look for in the house.
| Condition | What you usually see | What points away from viral arthritis |
|---|---|---|
| Viral arthritis (reovirus) | Swollen hock, tendon rupture, several birds in one area from about five weeks | This is the reference picture |
| Staphylococcal arthritis | Often one swollen joint on a bird with an earlier wound or a bruise | Pus or infected material in the joint at post-mortem, and a history of wounds |
| Mycoplasma synovitis | Swollen joints with a respiratory history, sometimes a drop in egg output in layers | Respiratory signs and a history of noisy breathing in the flock |
| Growth-related leg problems | Bent or weak legs, often in the fastest growers from early on | Bones that are soft or bent, not swollen joints and ruptured tendons |
| Litter burns on the hock | Dark, sore patches on the skin of the hock | Skin damage rather than swelling inside the joint |
The best single question for your vet is whether the birds show swelling inside the joint and a tendon that has ruptured. If they do, viral arthritis moves up the list.
How the virus gets from one bird to the next
Reoviruses spread mainly through faeces. A bird that is infected sheds the virus, and the next bird picks it up from litter, drinkers, feeders and the feet of the birds that walked through the mess. The virus can survive for a long time in dry, dusty litter, so a house that looks clean can still carry it into the next batch.
The egg route also matters. A breeder hen infected with reovirus may pass it to her chicks through the egg, so a flock can start its life with the virus already in it. The chick buyer cannot see that from the outside. That is why the parent flock and the litter both matter, and why the two are linked in the prevention plan below. Our cleaning guide between batches sets out the order of work for the house.
Why wet litter and fast growers make it worse
Wet litter does three things to a flock with this disease. It keeps the virus alive, it burns the hocks of birds that are already sitting in it, and it makes the birds sit more, which puts more load on the joints that are already sore. In the Ghanaian rainy season, a drinker that leaks or a roof that drips can turn one patch of litter into a source of infection for the whole section.
Our stocking density guide explains how many birds a house can carry before the litter starts to suffer. Fast growers carry more risk too. A bird that puts on weight quickly puts more strain on its tendons, and a tendon that is already inflamed will snap sooner. Keep stocking density sensible and the litter dry, and you lower the load on the legs as well as the virus. Our broiler litter management guide sets out how to keep the litter dry day to day.
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The breeder vaccine question, and what our chicks carry
The parent flock is the most important defence against viral arthritis that a chick buyer can ask about. Breeder hens are commonly vaccinated against reovirus, so the chicks start with antibodies in their blood. Whether the parent flock was vaccinated, and against which strain, depends on the supplier and the breeder's vet, so ask before you buy.
Our hatchery programme takes in Marek's, Newcastle and Gumboro (IBD), plus infectious bronchitis and coccidiosis, but reovirus is not among them. The timings are in our poultry vaccination schedule guide, and your vet can plan any extra protection for your area.
What the post-mortem can show your vet
A vet confirms viral arthritis through a combination of signs, post-mortem findings and laboratory tests. The post-mortem usually shows swollen hock joints with fluid in the joint and the tendon sheath, and the tendon at the back of the hock may be ruptured or thickened. The vet can look for inflammation in the sheath and rule out a bacterial infection in the joint.
Send two or three birds that are still fresh, with sitters that are not too far gone. Tell the vet how many birds are affected, which sections of the house they come from, and whether the birds have had a wound or a bruise. A clear history often decides the case before the lab results come back.
Culling, welfare and when a bird is beyond saving
There is no antiviral that will mend a ruptured tendon. A bird that cannot stand, cannot reach feed or water, and is losing condition should not be left in the house in the hope it will recover. Move it to a pen where it can reach food and water, and if it does not improve, ask your vet about humane culling. If you are unsure whether a bird is suffering, our guide on treating a sick chicken gives the first checks to make.
Do not sell a bird that is sick, lame to the point of distress, or that has been treated with a medicine that has a withdrawal period. The vet decides what can be used for food and what must be disposed of, and your records should show what each bird received and when.
What a tendon outbreak costs a 250-bird house
Consider a 250-bird Ross 308 house. At GH₵20 a chick, that is GH₵5,000 before feed and heat. Suppose 18 birds are culled over the grower phase because their tendons ruptured in weeks six and seven. That is 18 chicks at GH₵20, or GH₵360 in birds, plus the feed those birds ate before they were culled.
The bigger loss is the sale. Each of those 18 birds would have reached about 2.5 kg live, which is worth GH₵110 at our live broiler price, so the lost sales come to 18 times GH₵110, or GH₵1,980. The figures are a sketch, but they show why a daily sitter count pays for itself. Our broiler day-old chicks page and the prices page show what the starting birds cost today. Settle batch timing with us on WhatsApp at +233 24 915 1503. The order form holds your place once the date is clear.
Questions farmers ask
Is viral arthritis the same as bacterial arthritis?
No. Viral arthritis is caused by a reovirus that inflames the tendon sheaths and joints, often with a ruptured tendon. Bacterial arthritis is caused by bacteria such as staphylococci, which usually produce one swollen joint and can need a different treatment. A vet confirms which one it is.
Can antibiotics cure viral arthritis?
No. An antibiotic has no effect on the virus itself. A vet may still use one for a secondary bacterial infection, after diagnosis. Giving it for the virus wastes money and does not stop the spread.
Will the lame birds recover?
Some birds improve when the swelling settles, but a ruptured tendon does not heal in a way that lets the bird walk normally again. Birds that cannot reach feed and water should be removed and culled on your vet's advice.
Does the hatchery vaccinate against reovirus?
Reovirus is not part of the chick vaccines we give. Marek's, Newcastle, Gumboro, infectious bronchitis and coccidiosis are the ones on our list. Ask your supplier about the parent flock's reovirus vaccination, and ask your vet whether extra protection makes sense for your area.
How long does the virus stay in a house?
The virus can survive for a long time in dry litter and dust, so a house can carry it from one batch to the next. A full clean-out, a thorough drying and a sensible rest between batches are the best way to reduce the risk.
Can the meat of a lame bird be sold?
Do not sell birds that are sick, distressed or have been treated with a medicine that has a withdrawal period. Your vet decides what can be used for food and what must be disposed of, and your treatment records should show what each bird received.
Is this disease a problem for layers too?
It can be, especially in the flock's breeders, where the virus can pass to the chicks through the egg. Layers that show lameness or a drop in performance should be examined by a vet, and the parent flock's vaccination history should be checked.
