Tibial dyschondroplasia (TD) is a metabolic disease of young poultry

Poultry

Poultry are domesticated birds kept by humans for the purpose of producing eggs, meat, and/or feathers. These most typically are members of the superorder Galloanserae , especially the order Galliformes and the family Anatidae , commonly known as "waterfowl"...

 that affects the growth of bone

Bone

Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

 and cartilage

Cartilage

Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

.
Often occurs in broilers (chickens raised for meat) and other poultry which have been bred for fast growth rates. The tibial cartilage does not mature enough to ossify (turn into bone). This leaves the growth plate prone to fracture, infection, and deformed bone development.
It is the leading cause of lameness, mortality, and carcass condemnations in commercial poultry.