Hence, blind nipples are not considered to have a genetic cause. The condition is also known as myoclonia congenita, trembles, shivers, shakers, or jumpy pig disease. The symptoms generally are present within a few hours of birth and are characterized by rhythmic twitching of the neck and legs with varying degrees of intensity. Animals with minor tremors are able to move and nurse, but those severely affected fail to function normally and are subject to starvation, chilling, and overlaying by the sow. The shaking becomes more intense with chilling and excitement.
Survivors generally show less intense tremors with advancing age.
Porcine circovirus has been isolated from a pig with congenital tremors and may be one of the causes of this condition. Tremors among pigs exhibiting morphological lesions have been classified into five types. Type AI is caused by transplacental infection by particular strains of hog cholera virus. Necropsy reveals a reduction in size of both the cerebellum and the spinal cord. Since the United States is free of hog cholera, this type should not be encountered.