Perosis (Slipped Tendon) in Chickens

Perosis is a developmental leg problem in young chickens where the hock joint becomes enlarged and misshapen, the lower leg may twist, and the Achilles tendon can slip out of its normal groove. Pet parents often notice a chick that is crouching, walking awkwardly, or unable to bear weight normally.

Even though people call it "slipped tendon," perosis is usually a sign of an underlying nutrition problem, not a primary tendon injury. In poultry medicine, it is classically associated with deficiencies of manganese or choline, but similar changes can also occur with low biotin, folic acid, niacin, or pyridoxine. Because the bones and connective tissues are still developing, growing birds are affected most often.

Perosis can range from mild to severe. In early cases, correcting the diet may help prevent progression. In advanced cases, the leg deformity may become permanent, and some birds will have lasting mobility problems even after the feed issue is fixed. That is why early evaluation by your vet matters.

The most common cause of perosis is an imbalanced diet during growth. Poultry references classically link perosis with low manganese and choline, and similar lesions may also be seen with deficiencies involving biotin, folic acid, niacin, and pyridoxine. Homemade rations, incorrectly mixed feed, old or poorly stored feed, and feeding a diet meant for a different species or life stage can all raise risk.

Feed formulation matters because chicks need the right nutrient balance, not only enough calories. Merck Veterinary Manual notes that perosis is not specific to one single deficiency, which is why your vet may look at the entire ration, supplements, treats, and how feed is stored. If multiple birds are affected, the feed itself becomes an important clue.

Genetics, rapid growth, and management can also contribute. Fast-growing birds may show leg problems sooner if nutrition is marginal. Slippery flooring, crowding, or concurrent illness can make a weak leg look worse, but these factors usually do not cause classic perosis by themselves.

Not every lame chicken has perosis. Fractures, sprains, infections, developmental bone disease, and other nutritional disorders can look similar, so a hands-on exam is important before assuming the cause.

Your vet diagnoses perosis by combining the bird's age, diet history, flock history, and physical exam findings. The classic pattern is hock enlargement with leg rotation and, in more advanced cases, displacement of the Achilles tendon from its condyles. Your vet will also ask what feed the chicken is eating, whether it is a complete ration, and whether other birds are affected.

Because several problems can mimic slipped tendon, your vet may recommend additional testing. Radiographs can help rule out fractures or other bone disorders. In flock cases, a feed review is often one of the most valuable steps. Merck notes that diagnosing poultry nutritional deficiencies may require complete diet and management information, clinical signs, necropsy findings, and sometimes tissue or feed analysis.

If a bird dies or is euthanized, necropsy can be very helpful for confirming the pattern of disease and checking for other causes of lameness. For backyard flocks, poultry diagnostic programs such as Cornell's Avian Health service can assist with consultation, necropsy, and flock-level investigation through your vet or diagnostic lab.

Prevention starts with feeding a complete, correctly formulated poultry ration for the bird's species and life stage. Chicks should not be raised on scratch grains, random kitchen scraps, or homemade diets unless a poultry nutritionist has balanced them carefully. Merck's poultry nutrition references list manganese, choline, niacin, biotin, and pyridoxine among important nutrients for normal growth, and deficiencies can contribute to leg problems.

Store feed properly and replace stale or damaged bags. Heat, moisture, and long storage times can reduce feed quality. If you mix your own ration or buy from a small mill, ask for the nutrient profile and intended age group. A feed error can affect many birds at once.

Good management also helps. Provide secure footing, avoid overcrowding, and watch fast-growing young birds closely for early gait changes. If one chick develops hock swelling or a twisted leg, separate it from bullying flockmates and contact your vet early. Catching a nutrition problem before the tendon slips gives the best chance of limiting long-term damage.

If more than one bird is affected, think flock-wide rather than individual. Your vet may recommend reviewing the ration, supplements, and feeding routine for every bird in the group so the problem does not continue in younger flockmates.