Two cases of Polish/ Silkie cross chickens with neurological signs

by Solomon Bhandi, solomonb@elsenburg.com

History

Two live Polish/Silkie cross chickens around six months of age were brought to the Western Cape provincial veterinary laboratory showing neurological signs appearing like torticollis or paraplegia. The owner bought the two chicks in the Klapmuts area and kept them as pets together with other adult backyard chickens. The chicks were a cross between a Polish/Silkie cross cock and a pure-bred Silkie hen. The eggs were hatched using an incubator. The owner brought the chicks from Klapmuts to Maitland at three weeks old and separated them from the adult chickens when they were young. She only introduced them to the adult chickens at six months of age. The owner reported that she saw an element of aggression from the older chickens towards the Polish/Silkie chicks. A few days later she noticed that the chicks were showing neurological complications. The chicks were fully vaccinated but the neighbour’s chickens had died from Newcastle disease a few weeks prior to the chicks developing neurological problems.

At presentation, the chicks were obtunded (desensitised), non-ambulatory and showing torticollis (a twisted neck in which the head is tipped to one side, while the chin is turned to the other). Closer examination revealed that the skull was missing from both chicks and the brain was covered by the skin only, forming a dome-shaped head. There was no evidence of trauma. The chicks were euthanised humanely by manual cervical dislocation.

Post-mortem findings

Both chicks had a good body condition score and had no external injuries. There was no nasal congestion or nasal discharge. Upon opening into the abdomen and thoracic cavity, the respiratory and gastrointestinal tracts were not remarkable. The liver, spleen and kidneys appeared normal. What was striking was that both chicks had a vaulted calvarium (upper dome-like portion of the skull) and the brain was covered by skin only. The brain appeared as though it had prolapsed (displaced from its normal position; downward or outward), forming a dome-shaped head. The chicks tested negative for Newcastle disease and avian influenza. Organs and tissues were submitted for histopathological examination and the findings were not remarkable. Bacteriological analysis isolated no bacterial agent.

Both chicks had failed to develop a skull to house and protect the brain. The hypothesis is that because of this and it being a habit of chickens to peck the head when fighting, the neurological damage was the result of trauma caused by this aggression.

Brief literature review

The Silkie chicken, which is believed to be of East Asian descent, is one of the most unusual chicken breeds. The chicks are hatched with a vaulted skull which usually closes at four weeks old, but it is not uncommon for it not to close. If the skull stays unclosed, the brain becomes vulnerable to injury and the chickens would then present with neurological signs. Silkie chickens need a specific type of care when their skulls remain unclosed. There is not much literature about this condition. It may be of genetic origin or could happen by chance.

References:

Roberts, J. 2021. Silkie Chicken Breed Guide: Care, Background, and How-To Guide. https://www.knowyourchickens.com/silkie-chicken/

Ruthersdale, R. 2014. Silkie Chickens Silkie Chickens as Pets Silkie Chickens Owner S Manual Book. Available from https://www.itseyeris.com/book/silkie-chickens-silkiechickens-as-pets-silkie-chickens-owner-s-manual AP