Studies on spondylolisthesis ("kinky back") in broiler chickens

Spondylolisthesis was diagnosed in paralyzed commercial broiler chickens using radiology. Six affected birds when held in a favourable environment recovered sufficiently to be used for breeding. Spinal deformation was still present in these birds when they were necropsied at one year of age. One hundred and sixty pedigreed chicks produced from these birds were raised intermingled with 151 commercial broilers. Six of the experimental chicks were clinically affected with spondylolisthesis while none of the control chicks were affected. In continued studies the experimental chicks were inbred and the control chicks randomly bred for a further two generations. In the second generation 13% of the experimental chicks were clinically affected with spondylolisthesis while in the third generation 9% were affected. Less than half a per cent of the control chicks from both second and third generations were affected. No consistent relationship between incidence of spondylolisthesis, hatch, brooding environment or ration was noted. A higher incidence of scoliosis was encountered in the experimental birds than in the control birds. No relationship between deformed legs and spondylolisthesis was apparent. The incidence of leg deformities was higher in the control than in the experimental birds.