Occurrence: Increasing more common in fasting growing meat type birds due to a metabolic disturbance and in breeder pullets due to a bacterial infection. The incidence of affected birds may reach 2% of the flock.
Species affected: Broilers and broiler breeders.
Age affected: Young fast growing broilers at 5 to 8 weeks of age and breeder pullets from 10 to 18 weeks of age.
Causes: In broilers it is a developmental disorder influenced by conformation and growth rate and in breeder pullets it is due to a bacterial infection.
Kinky Back (spondylolisthesis)
It is a disorder influenced by conformation and growth rate, resulting in a deformity of the 6th thoracic vertebra, which causes spinal cord compression and posterior paralysis. In boilers it is due to a developmental disorder influenced by fast growth rate, whereas in breeder pullets it is caused by a bacterium.
In broilers it is a noninfectious metabolic disease of broilers, which is aggravated by fast body development. In breeder pullets it is caused by a bacterium.
Severely affected birds often become laterally recumbent (lay on their sides) and may die from dehydration, if not culled. Lordosis (curving forward) and subclinical Spondylolisthesis are common in broilers and develop soon after hatching.
The posterior paralysis results from rotation of the body of the 6th vertebra along the axis of the spine with the posterior part of the body moving dorsal (backward) and anterior (forward), relative to the anterior part. The rotation causes a kyphotic (humpback) angulation of the floor of the spinal canal between the 6th and 7th thoracic vertebrae, and spinal cord compression. The deformation of the spinal column can be readily recognized by palpating the ventral surface of the spinal column during necropsy. Pus in the lesions.
Spondylolisthesis is best confirmed by removing, decalcifying and splitting the spinal column along a midline longitudinal plane. This allows visualization of the spinal cord compression. A twisted spinal column resulting in a definitive diagnosis can be seen without decalcifying in extreme cases. Isolation of bacteria from the spinal lesion.
Slowing growth rate as is done in breeders (by restriction of light or feed), and genetic selection of birds that are less susceptible is helpful.