Tibial dyschondroplasia (TD) is a skeletal abnormality in fast-growing poultry, mainly broiler chickens and turkeys. It is a metabolic disease where cartilage in the tibia’s growth plate fails to become bone. This leads to a plug of weak cartilage that can cause pain, lameness, and animal welfare issues. The condition also results in economic losses from decreased growth and carcass downgrades.
Causes and Risk Factors
The development of tibial dyschondroplasia is influenced by several interrelated factors. Genetic selection for extremely rapid growth in commercial poultry is a primary contributor. This intense selection has made modern broiler strains more susceptible to skeletal problems as their body weight can outpace their skeleton’s structural development. The condition is more frequently observed in male birds, which grow faster and heavier than females.
Nutritional imbalances play a substantial role. The ratio of calcium to available phosphorus in the diet is important for bone development, and an improper balance can disrupt bone formation. Adequate levels of Vitamin D are also necessary for calcium absorption, and feed should be free from mycotoxins from molds like Fusarium. Ingesting fungicides containing tetramethyl thiuram disulfide (thiram) is another known cause.
Husbandry practices that encourage maximum growth rates also increase the risk of TD. Lighting programs and high-energy diets can push birds to grow at a pace that strains their skeletal system. This accelerated growth increases the likelihood that the cartilage-to-bone conversion process will be disrupted. The condition appears in young birds, often between three and eight weeks of age.
Identifying Tibial Dyschondroplasia
Observing bird behavior is the first step in identifying potential cases. Affected birds often display a reluctance to move, a stiff or waddling gait, and may sit for prolonged periods. This lameness can be severe enough to prevent them from accessing feed and water. In some instances, a visible swelling or bowing may be noticed in the hock or knee joint area.
While clinical signs are suggestive, a definitive diagnosis is confirmed through post-mortem examination (necropsy). Upon examining the tibia, or drumstick bone, a characteristic lesion will be present. This lesion is a distinct, white, avascular plug of cartilage located in the growth plate at the upper end of the bone, which can cause the bone to bend.
For non-invasive diagnosis, such as with valuable breeding stock, radiography can be used. X-rays allow for the visualization of the internal bone structure, clearly showing the cartilage plug without harming the bird. A specialized low-intensity X-ray device, the Lixiscope, can also screen live birds for TD. This tool is used by primary breeding companies to help select against the condition.
Prevention and Management Approaches
The primary strategy for preventing TD involves careful nutritional management. Providing a diet with a properly balanced ratio of calcium to available phosphorus is fundamental. The feed must also contain sufficient levels of Vitamin D3 and be free from mycotoxins, particularly from Fusarium molds.
Genetic selection offers a long-term solution to reducing TD incidence. Poultry breeding companies work to improve skeletal health by screening their genetic lines for susceptibility. Using tools like the Lixiscope allows breeders to identify and remove affected individuals from their programs, leading to hardier commercial populations.
Modifying flock management to control early growth rates is an effective preventative measure. Producers might implement controlled feeding programs or use specific lighting schedules to moderate activity and growth. By slightly slowing the initial growth spurt, these techniques reduce pressure on the developing skeleton, giving growth plates more time to mature properly.