Tibial dyschondroplasia (TD) is a common skeletal bone deformity that occurs in modern rapid growing, heavy chicken breeds (usually broilers).
In 1995, it was estimated 30-40% of male broiler birds suffered from TD. TD involves the development of an abnormal mass of cartilage at the growth plate of the long bones of the leg, usually the tibia bone. Instead of calcifying, the cartilage remains soft and will often bend backwards under pressure or heavy body weight. As a result, chickens with TD often suffer from spontaneous leg fractures, necrosis, and severe lameness. Birds with severe lameness are often unable to stand due to the pain, and often die from starvation from being unable to reach food or water, or trampled to death by other flock members. TD is thought to be similar to osteochondrosis which occurs in rapidly growing horses.
TD has been shown to have multiple possible causes, which include:
- Ingestion of commercial feed contaminated with fusarochromanone, a mycotoxin produced by Fusarium equiseti has been associated with the development of TD in chickens.
- Vascular endothelial growth factor (VEGF) deficiency in the growth plates.
- Diet with excess vitamin A have been linked with chickens developing TD, since excess vitamin A depresses absorption of vitamin D.
- An imbalanced calcium to phosphorus ratio, with too low of calcium levels and too high of phosphorus.
- Improper incubation conditions
- Limited exercise and/or restricted movement
- Poor sanitary conditionsLarge meat-type chicken breeds, such as modern day commercial broilers